x-ray background blazars: Topics by Science.gov

Sample records for x-ray background blazars

Blazars in Hard X-rays

NASA Astrophysics Data System (ADS)

Ghisellini, Gabriele

2009-05-01

Although blazars are thought to emit most of their luminosity in the γ-ray band, there are subclasses of them very prominent in hard X-rays. These are the best candidates to be studied by Simbol-X. They are at the extremes of the blazar sequence, having very small or very high jet powers. The former are the class of TeV emitting BL Lacs, whose synchrotron emission often peaks at tens of keV or more. The latter are the blazars with the most powerful jets, have high black hole masses accreting at high (i.e. close to Eddington) rates. These sources are predicted to have their high energy peak even below the MeV band, and therefore are very promising candidates to be studied with Simbol-X.
Blazar Gamma-Rays, Shock Acceleration, and the Extragalactic Background Light

NASA Technical Reports Server (NTRS)

Stecker, Floyd W.; Baring, Matthew G.; Summerlin, Errol J.

2007-01-01

The observed spectra of blazars, their intrinsic emission, and the underlying populations of radiating particles are intimately related. The use of these sources as probes of the extragalactic infrared background, a prospect propelled by recent advances in TeV-band telescopes, soon to be augmented by observations by NASA's upcoming Gamma-Ray Large Area Space Telescope (GLAST), has been a topic of great recent interest. Here, it is demonstrated that if particles in blazar jets are accelerated at relativistic shocks, then GAMMA-ray spectra with indices less than 1.5 can be produced. This, in turn, loosens the upper limits on the near infrared extragalactic background radiation previously proposed. We also show evidence hinting that TeV blazars with flatter spectra have higher intrinsic TeV GAMMA-ray luminosities and we indicate that there may be a correlation of flatness and luminosity with redshift.
The Effect of Blazar Spectral Breaks on the Blazar Contribution to the Extragalactic Gamma-Ray Background

NASA Technical Reports Server (NTRS)

Venters, Tonia M.; Pavlidou, Vasiliki

2011-01-01

The spectral shapes of the contributions of different classes of unresolved gamma-ray emitters can provide insight into their relative contributions to the extragalactic gamma-ray background (EGB) and the natures of their spectra at GeV energies, We calculate the spectral shapes of the contributions to the EGB arising from BL Lacertae type objects (BL Lacs) and flat-spectrum radio quasars (FSRQs) assuming blazar spectra can be described as broken power laws, We fit the resulting total blazar spectral shape to the Fermi Large Area Telescope measurements of the EGB, finding that the best-fit shape reproduces well the shape of the Fermi EGB for various break scenarios. We conclude that a scenario in which the contribution of blazars is dominant cannot be excluded on spectral grounds alone, even if spectral breaks are shown to be common among Fermi blazars. We also find that while the observation of a featureless (within uncertainties) power-law EGB spectrum by Fermi does not necessarily imply a single class of contributing unresolved sources with featureless individual spectra, such an observation and the collective spectra of the separate contributing populations determine the ratios of their contributions. As such, a comparison with studies including blazar gamma-ray luminosity functions could have profound implications for the blazar contribution to the EGB, blazar evolution, and blazar gamma-ray spectra and emission.
THE BLAZAR EMISSION ENVIRONMENT: INSIGHT FROM SOFT X-RAY ABSORPTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furniss, A.; Williams, D. A.; Fumagalli, M.

Collecting experimental insight into the relativistic particle populations and emission mechanisms at work within TeV-emitting blazar jets, which are spatially unresolvable in most bands and have strong beaming factors, is a daunting task. New observational information has the potential to lead to major strides in understanding the acceleration site parameters. Detection of molecular carbon monoxide (CO) in TeV emitting blazars, however, implies the existence of intrinsic gas, a connection often found in photo-dissociated region models and numerical simulations. The existence of intrinsic gas within a blazar could provide a target photon field for Compton up-scattering of photons to TeV energiesmore » by relativistic particles. We investigate the possible existence of intrinsic gas within the three TeV emitting blazars RGB J0710+591, W Comae, and 1ES 1959+650 which have measurements or upper limits on molecular CO line luminosity using an independent technique that is based on the spectral analysis of soft X-rays. Evidence for X-ray absorption by additional gas beyond that measured within the Milky Way is searched for in Swift X-ray Telescope (XRT) data between 0.3 and 10 keV. Without complementary information from another measurement, additional absorption could be misinterpreted as an intrinsically curved X-ray spectrum since both models can frequently fit the soft X-ray data. After breaking this degeneracy, we do not find evidence for intrinsically curved spectra for any of the three blazars. Moreover, no evidence for intrinsic gas is evident for RGB J0710+591 and W Comae, while the 1ES 1959+650 XRT data support the existence of intrinsic gas with a column density of {approx}1 Multiplication-Sign 10{sup 21} cm{sup -2}.« less
Simultaneous Planck , Swift , and Fermi observations of X-ray and γ -ray selected blazars

DOE PAGES

Giommi, P.; Polenta, G.; Lähteenmäki, A.; ...

2012-05-22

We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and γ-ray bands, with additional 5GHz flux-density limits to ensure a good probability of a Planck detection. We compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set allows us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored. Almost all themore » BL Lac objects have been detected by the Fermi Large AreaTelescope (LAT), whereas 30% to 40% of the flat-spectrum radio quasars (FSRQs) in the radio, soft X-ray, and hard X-ray selected samples are still below the γ-ray detection limit even after integrating 27 months of Fermi-LAT data. The radio to sub-millimetre spectral slope of blazars is quite flat, with >α> ~ 0 up to about 70GHz, above which it steepens to ~ -0.65. The BL Lacs have significantly flatter spectra than FSRQs at higher frequencies. The distribution of the rest-frame synchrotron peak frequency (ν peak S) in the spectral energy distribution (SED) of FSRQs is the same in all the blazar samples with peak S> = 10 13.1 ± 0.1 Hz, while the mean inverse Compton peak frequency, >ν peak IC>, ranges from 1021 to 1022 Hz. The distributions of ν peak S and ν peak IC of BL Lacs are much broader and are shifted to higher energies than those of FSRQs; their shapes strongly depend on the selection method. The Compton dominance of blazars, defined as the ratio of the inverse Compton to synchrotron peak luminosities, ranges from less than 0.2 to nearly 100, with only FSRQs reaching values larger than about 3. Its distribution is broad and depends strongly on the selection method, with γ-ray selected blazars peaking at ~7 or more, and radio
Simultaneous Planck, Swift, and Fermi Observations of X-ray and Gamma-ray Selected Blazars

NASA Technical Reports Server (NTRS)

Giommi, P.; Polenta, G.; Laehteenmaeki, A.; Thompson, D. J.; Capalbi, M.; Cutini, S.; Gasparrini, D.; Gonzalez, Nuevo, J.; Leon-Tavares, J.; Lopez-Caniego, M.;

2012-01-01

We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and gamma-ray bands, with additional 5 GHz flux-density limits to ensure a good probability of a Planck detection. We compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set allows us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored. Almost all the BL Lac objects have been detected by the Fermi Large Area Telescope (LAT), whereas 30% to 40% of the flat-spectrum radio quasars (FSRQs) in the radio, soft X-ray, and hard X-ray selected samples are still below the gamma-ray detection limit even after integrating 27 months of Fermi-LAT data. The radio to sub-millimetre spectral slope of blazars is quite flat, with (alpha) approx 0 up to about 70GHz, above which it steepens to (alpha) approx -0.65. The BL Lacs have significantly flatter spectra than FSRQs at higher frequencies. The distribution of the rest-frame synchrotron peak frequency (nu(sup s)(sub peak)) in the spectral energy distribution (SED) of FSRQs is the same in all the blazar samples with (nu(sup s)(sub peak)) = 10(exp 13.1 +/- 0.1) Hz, while the mean inverse Compton peak frequency, (nu(sup IC)(sub peak)), ranges from 10(exp 21) to 10(exp 22) Hz. The distributions of nu(sup s)(sub peak) and nu(sup IC)(sub peak) of BL Lacs are much broader and are shifted to higher energies than those of FSRQs; their shapes strongly depend on the selection method. The Compton dominance of blazars. defined as the ratio of the inverse Compton to synchrotron peak luminosities, ranges from less than 0.2 to nearly 100, with only FSRQs reaching values larger than about 3. Its distribution is broad and depends

Simultaneous Planck, Swift, and Fermi Observations of X-Ray and gamma-Ray Selected Blazars

NASA Technical Reports Server (NTRS)

Giommi, P.; Polenta, G.; Laehteenmaeki, A.; Thompson, D. J.; Capalbi, M.; Cutini, S.; Gasparrini, D.; Gonzalez-Nuevo, J.; Leon-Tavares, J.; Lopez-Caniego, M.;

2011-01-01

We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and -ray bands, and we compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set has allowed us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored. Almost all the BL Lac objects have been detected by Fermi Large Area Telescope (LAT), whereas 30 to 40% of the flat-spectrum radio quasars (FSRQs) in the radio, soft X-ray, and hard X-ray selected samples are still below the gamma ray detection limit even after integrating 27 months of Fermi-LAT data. The radio to sub-millimetre spectral slope of blazars is quite flat, with [alpha] approximately 0 up to about 70 GHz, above which it steepens to [alpha] approximately -0.65. BL Lacs have significantly flatter spectra than FSRQs at higher frequencies. The distribution of the rest-frame synchrotron peak frequency (v(sup IC) (sub (PEAK)), ranges from 10(sup 21) to 10(sup 22) HZ. The distribution of the rest-frame synchrotron peak frequency (v(sup s)(sub peak)) in the spectral energy distribution (SED) of FSRQs is the same in all the blazar samples with (v(sup s)(sub peak) = 10(sup 13:1 plus or minus 0.1) Hz, while the mean inverse-Compton peak frequency,(v(sup IC)(sub peak) ranges from 10(sup 21) to 10(sup 22) Hz. The distributions of v(sup S)(sub peak) and of v(sup IC)(sub peak) of BL Lacs are much broader and are shifted to higher energies than those of FSRQs; their shapes strongly depend on the selection method. The Compton dominance of blazars ranges from less than 0.2 to nearly 100, with only FSRQs reaching values larger than about 3. Its distribution is broad and depends strongly on the selection method

Detecting the Attenuation of Blazar Gamma-ray Emission by Extragalactic Background Light with GLAST

NASA Technical Reports Server (NTRS)

Chen, Andrew; Ritz, Steven

1999-01-01

Gamma rays with energy above 10 GeV interact with optical-UV photons resulting in pair production. Therefore, a large sample of high redshift sources of these gamma rays can be used to probe the extragalactic background starlight (EBL) by examining the redshift dependence of the attenuation of the flux above 10 GeV. GLAST, the next generation high-energy gamma-ray telescope, will for the first time have the unique capability to detect thousands of gamma-ray blazars up to redshifts of at least z = 4, with enough angular resolution to allow identification of a large fraction of their optical counterparts. By combining recent determinations of the gamma-ray blazar luminosity function, recent calculations of the high energy gamma-ray opacity due to EBL absorption, and the expected GLAST instrument performance to produce simulated samples of blazars that GLAST would detect, including their redshifts and fluxes, we demonstrate that these blazars have the potential to be a highly effective probe of the EBL.
On the origin of X-ray spectra in luminous blazars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sikora, Marek; Janiak, Mateusz; Nalewajko, Krzysztof

2013-11-26

Gamma-ray luminosities of some quasar-associated blazars imply jet powers reaching values comparable to the accretion power even if assuming very strong Doppler boosting and very high efficiency of gamma-ray production. With much lower radiative efficiencies of protons than of electrons, and the recent reports of very strong coupling of electrons with shock-heated protons indicated by particle-in-cell simulations, the leptonic models seem to be strongly favored over the hadronic ones. However, the electron-proton coupling combined with the external-radiation-Compton (ERC) models of gamma-ray production in leptonic models predict extremely hard X-ray spectra, with energy indices α x ~ 0. This is inconsistentmore » with the observed 2-10 keV slopes of blazars, which cluster around α x ~ 0.6. This problem can be resolved by assuming that electrons can be efficiently cooled down radiatively to non-relativistic energies, or that blazar spectra are entirely dominated by the synchrotron self-Compton (SSC) component up to at least 10 keV. Here, we show that the required cooling can be sufficiently efficient only at distances r < 0.03 pc. SSC spectra, on the other hand, can be produced roughly co-spatially with the observed synchrotron and ERC components, which are most likely located roughly at a parsec scale. We show that the dominant SSC component can also be produced much further than the dominant synchrotron and ERC components, at distances of gsim 10 pc. Hence, depending on the spatial distribution of the energy dissipation along the jet, one may expect to see γ-ray/optical events with either correlated or uncorrelated X-rays. In all cases the number of e +e – pairs per proton is predicted to be very low. The direct verification of the proposed SSC scenario, and particularly the question of the co-spatiality of the SSC component with other spectral components, requires sensitive observations in the hard X-ray band. Lastly, this is now possible with the
Searching for New γ-Ray Blazar Candidates in the Third Palermo BAT Hard X-Ray Catalog with WISE

NASA Astrophysics Data System (ADS)

Maselli, A.; Massaro, F.; Cusumano, G.; D'Abrusco, R.; La Parola, V.; Paggi, A.; Segreto, A.; Smith, Howard A.; Tosti, G.

2013-06-01

We searched for γ-ray blazar candidates among the 382 unidentified hard X-ray sources of the third Palermo BAT Catalog (3PBC) obtained from the analysis of 66 months of Swift Burst Alert Telescope (BAT) survey data and listing 1586 sources. We adopted a recently developed association method based on the peculiar infrared colors that characterize the γ-ray blazars included in the second catalog of active galactic nuclei detected by the Fermi Large Area Telescope. We used this method exploiting the data of the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) to establish correspondences between unidentified 3PBC sources and WISE γ-ray blazar candidates located within the BAT positional uncertainty region at a 99% confidence level. We obtained a preliminary list of candidates for which we analyzed all the available data in the Swift archive to complement the information in the literature and in the radio, infrared, and optical catalogs with the information on their optical-UV and soft X-ray emission. Requiring the presence of radio and soft X-ray counterparts consistent with the infrared positions of the selected WISE sources, as well as a blazar-like radio morphology, we finally obtained a list of 24 γ-ray blazar candidates.
SEARCHING FOR NEW {gamma}-RAY BLAZAR CANDIDATES IN THE THIRD PALERMO BAT HARD X-RAY CATALOG WITH WISE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maselli, A.; Cusumano, G.; La Parola, V.

We searched for {gamma}-ray blazar candidates among the 382 unidentified hard X-ray sources of the third Palermo BAT Catalog (3PBC) obtained from the analysis of 66 months of Swift Burst Alert Telescope (BAT) survey data and listing 1586 sources. We adopted a recently developed association method based on the peculiar infrared colors that characterize the {gamma}-ray blazars included in the second catalog of active galactic nuclei detected by the Fermi Large Area Telescope. We used this method exploiting the data of the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) to establish correspondences between unidentified 3PBC sources andmore » WISE {gamma}-ray blazar candidates located within the BAT positional uncertainty region at a 99% confidence level. We obtained a preliminary list of candidates for which we analyzed all the available data in the Swift archive to complement the information in the literature and in the radio, infrared, and optical catalogs with the information on their optical-UV and soft X-ray emission. Requiring the presence of radio and soft X-ray counterparts consistent with the infrared positions of the selected WISE sources, as well as a blazar-like radio morphology, we finally obtained a list of 24 {gamma}-ray blazar candidates.« less
Complete Hard X-Ray Surveys, AGN Luminosity Functions and the X-Ray Background

NASA Technical Reports Server (NTRS)

Tueller, Jack

2011-01-01

AGN are believed to make up most of the Cosmic X-Ray Background (CXB) above a few keV, but this background cannot be fully resolved at energies less than 10 keV due to absorption. The Swift/BAT and INTEGRAL missions are performing the first complete hard x-ray surveys with minimal bias due to absorption. The most recent results for both missions will be presented. Although the fraction of the CXB resolved by these surveys is small, it is possible to derive unbiased number counts and luminosity functions for AGN in the local universe. The survey energy range from 15-150 keV contains the important reflection and cutoff spectral features dominate the shape of the AGN contribution to the CXB. Average spectral characteristics of survey detected AGN will be presented and compared with model distributions. The numbers of hard x-ray blazars detected in these surveys are finally sufficient to estimate this important component's contribution the cosmic background. Constraints on CXB models and their significance will be discussed.
A Hard X-ray View on Two Distant VHE Blazars: 1ES 1101-232 and 1ES 1553+113

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reimer, A.; Costamente, L.; /Stanford U., HEPL /KIPAC, Menlo Park

2008-05-02

TeV-blazars are known as prominent non-thermal emitters across the entire electromagnetic spectrum with their photon power peaking in the X-ray and TeV-band. If distant, absorption of -ray photons by the extragalactic background light (EBL) alters the intrinsic TeV spectral shape, thereby affecting the overall interpretation. Suzaku observations for two of the more distant TeV-blazars known to date, 1ES 1101-232 and 1ES 1553+113, were carried out in May and July 2006, respectively, including a quasi-simultaneous coverage with the state of the art Cherenkov telescope facilities. We report on the resulting data sets with emphasis on the X-ray band, and set intomore » context to their historical behavior. During our campaign, we did not detect any significant X-ray or {gamma}-ray variability. 1ES 1101-232 was found in a quiescent state with the lowest X-ray flux ever measured. The combined XIS and HXD PIN data for 1ES 1101-232 and 1ES 1553+113 clearly indicate spectral curvature up to the highest hard X-ray data point ({approx} 30 keV), manifesting as softening with increasing energy. We describe this spectral shape by either a broken power law or a log-parabolic fit with equal statistical goodness of fits. The combined 1ES 1553+113 very high energy spectrum (90-500 GeV) did not show any significant changes with respect to earlier observations. The resulting contemporaneous broadband spectral energy distributions of both TeV-blazars are discussed in view of implications for intrinsic blazar parameter values, taking into account the {gamma}-ray absorption in the EBL.« less
The Evolution of Swift/BAT blazars and the origin of the MeV background

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ajello, M.; /SLAC /KIPAC, Menlo Park; Costamante, L.

2009-10-17

We use 3 years of data from the Swift/BAT survey to select a complete sample of X-ray blazars above 15 keV. This sample comprises 26 Flat-Spectrum Radio Quasars (FSRQs) and 12 BL Lac objects detected over a redshift range of 0.03 < z < 4.0. We use this sample to determine, for the first time in the 15-55 keV band, the evolution of blazars. We find that, contrary to the Seyfert-like AGNs detected by BAT, the population of blazars shows strong positive evolution. This evolution is comparable to the evolution of luminous optical QSOs and luminous X-ray selected AGNs. Wemore » also find evidence for an epoch-dependence of the evolution as determined previously for radio-quiet AGNs. We interpret both these findings as a strong link between accretion and jet activity. In our sample, the FSRQs evolve strongly, while our best-fit shows that BL Lacs might not evolve at all. The blazar population accounts for 10-20% (depending on the evolution of the BL Lacs) of the Cosmic X-ray background (CXB) in the 15-55 keV band. We find that FSRQs can explain the entire CXB emission for energies above 500 keV solving the mystery of the generation of the MeV background. The evolution of luminous FSRQs shows a peak in redshift (z{sub c} = 4.3 {+-} 0.5) which is larger than the one observed in QSOs and X-ray selected AGNs. We argue that FSRQs can be used as tracers of massive elliptical galaxies in the early Universe.« less
Blazar Duty-Cycle at Gamma-Ray Frequecies: Constraints From Extragalactic Background Radiation And Prospects for AGILE And GLAST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pittori, Carlotta; Cavazzuti, Elisabetta; Colafrancesco, Sergio

2011-11-29

We take into account the constraints from the observed extragalactic {gamma}-ray background to estimate the maximum duty cycle allowed for a selected sample of WMAP Blazars, in order to be detectable by AGILE and GLAST {gamma}-ray experiments. For the nominal sensitivity values of both instruments, we identify a subset of sources which can in principle be detectable also in a steady state without over-predicting the extragalactic background. This work is based on the results of a recently derived Blazar radio LogN-LogS obtained by combining several multi-frequency surveys.
Constraining the particle spectrum in blazar jets: importance of the hard X-ray spectrum

NASA Astrophysics Data System (ADS)

Sinha, Atreyee; Sahayanathan, Sunder; Chitnis, Varsha

2016-07-01

Measurement of the spectral curvature in blazar jets can throw light on the underlying particle spectral distribution, and hence, the acceleration and diffusion processes at play. With the advent of NuSTAR and ASTROSAT, and the upcoming ASTRO-H, this curvature can now be measured accurately across the broadband X-ray energies. We will discuss results from our recent works on two HBLs, Mkn421 (Sinha et al, A&A 2015) and 1ES1011+496 (Sinha et al, ApJ submitted), and show how simultaneous measurement at hard and soft X-ray energies can be crucial in understanding the underlying particle spectrum. Detection of lognormality in blazars is beginning to hint at strong disk-jet connections. India's recently launched multiwavelength satellite, the ASTROSAT will provide simultaneous time resolved data between 0.2-80keV, along with measurements at Optical-UV energies. We will discuss prospects from ASTROSAT for studying jet triggering mechanisms in blazars.
Gamma-ray blazars within the first 2 billion years

DOE PAGES

Ackermann, M.; Ajello, M.; Baldini, L.; ...

2017-02-27

Here, the detection of high-redshift (more » $$z\\,\\gt 3$$) blazars enables the study of the evolution of the most luminous relativistic jets over cosmic time. More importantly, high-redshift blazars tend to host massive black holes and can be used to constrain the space density of heavy black holes in the early universe. Here, we report the first detection with the Fermi-Large Area Telescope of five γ-ray-emitting blazars beyond z = 3.1, more distant than any blazars previously detected in γ-rays. Among these five objects, NVSS J151002+570243 is now the most distant known γ-ray-emitting blazar at z = 4.31. These objects have steeply falling γ-ray spectral energy distributions (SEDs), and those that have been observed in X-rays have a very hard X-ray spectrum, both typical of powerful blazars. Their Compton dominance (ratio of the inverse Compton to synchrotron peak luminosities) is also very large ($$\\gt 20$$). All of these properties place these objects among the most extreme members of the blazar population. Their optical spectra and the modeling of their optical-UV SEDs confirm that these objects harbor massive black holes ($${M}_{\\mathrm{BH}}\\sim {10}^{8-10}\\,{M}_{\\odot }$$). We find that, at $$z\\approx 4$$, the space density of $$\\gt {10}^{9}\\,{M}_{\\odot }$$ black holes hosted in radio-loud and radio-quiet active galactic nuclei are similar, implying that radio-loudness may play a key role in rapid black hole growth in the early universe.« less
Comparison Of Optical, UV, X-ray, And Gamma-ray Variations Of Selected Blazars In 2011

NASA Astrophysics Data System (ADS)

Consiglio, Santina; Marscher, A. P.; Jorstad, S. G.; Walker, G.

2012-01-01

We present multi-wavelength observations of several gamma-ray bright blazars. We combine optical data obtained at Maria Mitchell Observatory on Nantucket Island with space- and ground-based observations carried out with a variety of instruments. These include a number of other optical telescopes, the Fermi Gamma-ray Space Telescope at photon energies of 0.1-200 GeV, the Rossi X-Ray Timing Explorer at 2.4-10 keV, and the Swift satellite at 0.3-10 keV plus optical and UV wavelengths. Three of the observed blazars proved to be particularly active - BL Lac, 3C 279, and PKS 1510-089. BL Lac was of special interest, varying greatly in optical brightness from night to night. In addition, as reported by the VERITAS group, it exhibited a remarkable, short-lived flare at TeV gamma-ray energies on one of the nights. We cross-correlate the variations in the different wavebands in an effort to guide theoretical interpretations of the optical and high-energy emission from blazars. This project was supported by NSF/REU grant AST-0851892 and by the Nantucket Maria Mitchell Association. The research at Boston University was supported in part by NSF grants AST-0907893, and by NASA through Fermi grants NNX08AV65G and NNX11AQ03G.
Time-dependent Electron Acceleration in Blazar Transients: X-Ray Time Lags and Spectral Formation

NASA Astrophysics Data System (ADS)

Lewis, Tiffany R.; Becker, Peter A.; Finke, Justin D.

2016-06-01

Electromagnetic radiation from blazar jets often displays strong variability, extending from radio to γ-ray frequencies. In a few cases, this variability has been characterized using Fourier time lags, such as those detected in the X-rays from Mrk 421 using BeppoSAX. The lack of a theoretical framework to interpret the data has motivated us to develop a new model for the formation of the X-ray spectrum and the time lags in blazar jets based on a transport equation including terms describing stochastic Fermi acceleration, synchrotron losses, shock acceleration, adiabatic expansion, and spatial diffusion. We derive the exact solution for the Fourier transform of the electron distribution and use it to compute the Fourier transform of the synchrotron radiation spectrum and the associated X-ray time lags. The same theoretical framework is also used to compute the peak flare X-ray spectrum, assuming that a steady-state electron distribution is achieved during the peak of the flare. The model parameters are constrained by comparing the theoretical predictions with the observational data for Mrk 421. The resulting integrated model yields, for the first time, a complete first-principles physical explanation for both the formation of the observed time lags and the shape of the peak flare X-ray spectrum. It also yields direct estimates of the strength of the shock and the stochastic magnetohydrodynamical wave acceleration components in the Mrk 421 jet.
TIME-DEPENDENT ELECTRON ACCELERATION IN BLAZAR TRANSIENTS: X-RAY TIME LAGS AND SPECTRAL FORMATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lewis, Tiffany R.; Becker, Peter A.; Finke, Justin D., E-mail: pbecker@gmu.edu, E-mail: tlewis13@gmu.edu, E-mail: justin.finke@nrl.navy.mil

2016-06-20

Electromagnetic radiation from blazar jets often displays strong variability, extending from radio to γ -ray frequencies. In a few cases, this variability has been characterized using Fourier time lags, such as those detected in the X-rays from Mrk 421 using Beppo SAX. The lack of a theoretical framework to interpret the data has motivated us to develop a new model for the formation of the X-ray spectrum and the time lags in blazar jets based on a transport equation including terms describing stochastic Fermi acceleration, synchrotron losses, shock acceleration, adiabatic expansion, and spatial diffusion. We derive the exact solution formore » the Fourier transform of the electron distribution and use it to compute the Fourier transform of the synchrotron radiation spectrum and the associated X-ray time lags. The same theoretical framework is also used to compute the peak flare X-ray spectrum, assuming that a steady-state electron distribution is achieved during the peak of the flare. The model parameters are constrained by comparing the theoretical predictions with the observational data for Mrk 421. The resulting integrated model yields, for the first time, a complete first-principles physical explanation for both the formation of the observed time lags and the shape of the peak flare X-ray spectrum. It also yields direct estimates of the strength of the shock and the stochastic magnetohydrodynamical wave acceleration components in the Mrk 421 jet.« less

VizieR Online Data Catalog: Blazars in the Swift-BAT hard X-ray sky (Maselli+, 2010)

NASA Astrophysics Data System (ADS)

Maselli, A.; Cusumano, G.; Massaro, E.; La Parola, V.; Segreto, A.; Sbarufatti, B.

2010-06-01

We reported the list of hard X-ray blazars obtained adopting sigma=3 as detection threshold: with this choice a number of three spurious sources over a total of 121 blazars is expected. Each blazar is identified by a three-letter code, where the first two are BZ for blazar and the third one specifies the type, followed by the truncated equatorial coordinates (J2000). The codes are defined in the "Note (1)" below. We obtained 69 FSRQs, 24 BL Lac objects and 28 blazars of uncertain classification, representing 4.4%, 2.4% and 11.0% of the corresponding populations classified in the BZCAT, respectively. This sample has been compared with other lists and catalogues found in literature (Tueller et al., 2010, Cat. J/ApJS/186/378, Ajello et al. 2009ApJ...699..603A, Cusumano et al., 2010, Cat. J/A+A/510/A48). (1 data file).
Unidentified Gamma-Ray Sources: Hunting Gamma-Ray Blazars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Massaro, F.; D'Abrusco, R.; Tosti, G.

2012-04-02

One of the main scientific objectives of the ongoing Fermi mission is unveiling the nature of the unidentified {gamma}-ray sources (UGSs). Despite the large improvements of Fermi in the localization of {gamma}-ray sources with respect to the past {gamma}-ray missions, about one third of the Fermi-detected objects are still not associated to low energy counterparts. Recently, using the Wide-field Infrared Survey Explorer (WISE) survey, we discovered that blazars, the rarest class of Active Galactic Nuclei and the largest population of {gamma}-ray sources, can be recognized and separated from other extragalactic sources on the basis of their infrared (IR) colors. Basedmore » on this result, we designed an association method for the {gamma}-ray sources to recognize if there is a blazar candidate within the positional uncertainty region of a generic {gamma}-ray source. With this new IR diagnostic tool, we searched for {gamma}-ray blazar candidates associated to the UGS sample of the second Fermi {gamma}-ray catalog (2FGL). We found that our method associates at least one {gamma}-ray blazar candidate as a counterpart each of 156 out of 313 UGSs analyzed. These new low-energy candidates have the same IR properties as the blazars associated to {gamma}-ray sources in the 2FGL catalog.« less
UNIDENTIFIED {gamma}-RAY SOURCES: HUNTING {gamma}-RAY BLAZARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Massaro, F.; Ajello, M.; D'Abrusco, R.

2012-06-10

One of the main scientific objectives of the ongoing Fermi mission is unveiling the nature of unidentified {gamma}-ray sources (UGSs). Despite the major improvements of Fermi in the localization of {gamma}-ray sources with respect to the past {gamma}-ray missions, about one-third of the Fermi-detected objects are still not associated with low-energy counterparts. Recently, using the Wide-field Infrared Survey Explorer survey, we discovered that blazars, the rarest class of active galactic nuclei and the largest population of {gamma}-ray sources, can be recognized and separated from other extragalactic sources on the basis of their infrared (IR) colors. Based on this result, wemore » designed an association method for the {gamma}-ray sources to recognize if there is a blazar candidate within the positional uncertainty region of a generic {gamma}-ray source. With this new IR diagnostic tool, we searched for {gamma}-ray blazar candidates associated with the UGS sample of the second Fermi {gamma}-ray LAT catalog (2FGL). We found that our method associates at least one {gamma}-ray blazar candidate as a counterpart to each of 156 out of 313 UGSs analyzed. These new low-energy candidates have the same IR properties as the blazars associated with {gamma}-ray sources in the 2FGL catalog.« less
Extremely Rapid X-Ray Flares of TeV Blazars in the RXTE Era

NASA Astrophysics Data System (ADS)

Zhu, S. F.; Xue, Y. Q.; Brandt, W. N.; Cui, W.; Wang, Y. J.

2018-01-01

Rapid flares from blazars in very high-energy (VHE) γ-rays challenge the common understanding of jets of active galactic nuclei (AGNs). The same population of ultra-relativistic electrons is often thought to be responsible for both X-ray and VHE emission. We thus systematically searched for X-ray flares at sub-hour timescales of TeV blazars in the entire Rossi X-ray Timing Explorer archival database. We found rapid flares from PKS 2005‑489 and S5 0716+714, and a candidate rapid flare from 1ES 1101‑232. In particular, the characteristic rise timescale of PKS 2005‑489 is less than half a minute, which, to our knowledge, is the shortest among known AGN flares at any wavelengths. The timescales of these rapid flares indicate that the size of the central supermassive black hole is not a hard lower limit on the physical size of the emission region of the flare. PKS 2005‑489 shows possible hard lags in its flare, which could be attributed to particle acceleration (injection); its flaring component has the hardest spectrum when it first appears. For all flares, the flaring components show similar hard spectra with {{Γ }}=1.7{--}1.9, and we estimate the magnetic field strength B ∼ 0.1–1.0 G by assuming synchrotron cooling. These flares could be caused by inhomogeneity of the jets. Models that can only produce rapid γ-ray flares but little synchrotron activity are less favorable.
Observations of blazars with ASCA

NASA Technical Reports Server (NTRS)

Makino, F.; Edelson, R.; Fujimoto, R.; Kii, T.; Idesawa, E.; Makishima, K.; Takahashi, T.; Sasaki, K.; Kamae, T.; Kubo, H.;

1996-01-01

The Advanced Satellite for Cosmology and Astrophysics (ASCA) observations of 3C 279, Mkn 421, PKS 2155-304, BL Lac 0716+714 and OJ 287 blazars are presented. Blazars are a class of active galactic nuclei characterized by high variability, high polarization, flat radio spectrum and featureless spectrum. The X-ray spectra and flux variations of blazars are discussed. The inverse correlation between X-ray flux and index, soft lag, the convex curvature of the spectrum, flat gamma-ray and/or X-ray spectra, fast variability and featureless spectrum are common characteristics of blazars.

The Imprint of the Extragalactic Background Light in the Gamma-Ray Spectra of Blazars

NASA Technical Reports Server (NTRS)

Ackermann, M.; Ajello, M.; Allafort, A.; Schady, P.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R; Blandford, R. D.;

2012-01-01

The light emitted by stars and accreting compact objects through the history of the universe is encoded in the intensity of the extragalactic background light (EBL). Knowledge of the EBL isimportant to understand the nature of star formation and galaxy evolution, but direct measurements of the EBL are limited by galactic and other foreground emissions. Here, we report an absorption feature seen in the combined spectra of a sample of gamma-ray blazars out to a redshift of z approx. 1.6. This feature is caused by attenuation of gamma rays by the EBL at optical to ultraviolet frequencies and allowed us to measure the EBL flux density in this frequency band.

Gamma-ray luminosity and photon index evolution of FSRQ blazars and contribution to the gamma-ray background

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singal, J.; Ko, A.; Petrosian, V., E-mail: jsingal@richmond.edu

We present the redshift evolutions and distributions of the gamma-ray luminosity and photon spectral index of flat spectrum radio quasar (FSRQ) type blazars, using non-parametric methods to obtain the evolutions and distributions directly from the data. The sample we use for analysis consists of almost all FSRQs observed with a greater than approximately 7σ detection threshold in the first-year catalog of the Fermi Gamma-ray Space Telescope's Large Area Telescope, with redshifts as determined from optical spectroscopy by Shaw et al. We find that FSQRs undergo rapid gamma-ray luminosity evolution, but negligible photon index evolution, with redshift. With these evolutions accountedmore » for we determine the density evolution and luminosity function of FSRQs and calculate their total contribution to the extragalactic gamma-ray background radiation, resolved and unresolved, which is found to be 16(+10/–4)%, in agreement with previous studies.« less
VizieR Online Data Catalog: New gamma-ray blazar candidates in the 3PBC (Maselli+, 2013)

NASA Astrophysics Data System (ADS)

Maselli, A.; Massaro, F.; Cusumano, G.; D'Abrusco, R.; La Parola, V.; Paggi, A.; Segreto, A.; Smith, H. A.; Tosti, G.

2013-06-01

We searched for γ-ray blazar candidates among the 382 unidentified hard X-ray sources of the third Palermo BAT Catalog (3PBC) obtained from the analysis of 66 months of Swift Burst Alert Telescope (BAT) survey data and listing 1586 sources. We adopted a recently developed association method based on the peculiar infrared colors that characterize the γ-ray blazars included in the second catalog of active galactic nuclei detected by the Fermi Large Area Telescope. We used this method exploiting the data of the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) to establish correspondences between unidentified 3PBC sources and WISE γ-ray blazar candidates located within the BAT positional uncertainty region at a 99% confidence level. We obtained a preliminary list of candidates for which we analyzed all the available data in the Swift archive to complement the information in the literature and in the radio, infrared, and optical catalogs with the information on their optical-UV and soft X-ray emission. Requiring the presence of radio and soft X-ray counterparts consistent with the infrared positions of the selected WISE sources, as well as a blazar-like radio morphology, we finally obtained a list of 24 γ-ray blazar candidates. (2 data files).
The Imprint of the Extragalactic Background Light in the Gamma-Ray Spectra of Blazars

DOE PAGES

Ackermann, M.; Ajello, M.; Allafort, A.; ...

2012-11-30

The light emitted by stars and accreting compact objects through the history of the universe is encoded in the intensity of the extragalactic background light (EBL). Knowledge of the EBL is important to understand the nature of star formation and galaxy evolution, but direct measurements of the EBL are limited by galactic and other foreground emissions. In this paper, we report an absorption feature seen in the combined spectra of a sample of gamma-ray blazars out to a redshift of z ~ 1.6. Finally, this feature is caused by attenuation of gamma rays by the EBL at optical to ultravioletmore » frequencies and allowed us to measure the EBL flux density in this frequency band.« less
A low level of extragalactic background light as revealed by gamma-rays from blazars.

PubMed

Aharonian, F; Akhperjanian, A G; Bazer-Bachi, A R; Beilicke, M; Benbow, W; Berge, D; Bernlöhr, K; Boisson, C; Bolz, O; Borrel, V; Braun, I; Breitling, F; Brown, A M; Chadwick, P M; Chounet, L-M; Cornils, R; Costamante, L; Degrange, B; Dickinson, H J; Djannati-Ataï, A; Drury, L O'C; Dubus, G; Emmanoulopoulos, D; Espigat, P; Feinstein, F; Fontaine, G; Fuchs, Y; Funk, S; Gallant, Y A; Giebels, B; Gillessen, S; Glicenstein, J F; Goret, P; Hadjichristidis, C; Hauser, D; Hauser, M; Heinzelmann, G; Henri, G; Hermann, G; Hinton, J A; Hofmann, W; Holleran, M; Horns, D; Jacholkowska, A; de Jager, O C; Khélifi, B; Klages, S; Komin, Nu; Konopelko, A; Latham, I J; Le Gallou, R; Lemière, A; Lemoine-Goumard, M; Leroy, N; Lohse, T; Martin, J M; Martineau-Huynh, O; Marcowith, A; Masterson, C; McComb, T J L; de Naurois, M; Nolan, S J; Noutsos, A; Orford, K J; Osborne, J L; Ouchrif, M; Panter, M; Pelletier, G; Pita, S; Pühlhofer, G; Punch, M; Raubenheimer, B C; Raue, M; Raux, J; Rayner, S M; Reimer, A; Reimer, O; Ripken, J; Rob, L; Rolland, L; Rowell, G; Sahakian, V; Saugé, L; Schlenker, S; Schlickeiser, R; Schuster, C; Schwanke, U; Siewert, M; Sol, H; Spangler, D; Steenkamp, R; Stegmann, C; Tavernet, J-P; Terrier, R; Théoret, C G; Tluczykont, M; van Eldik, C; Vasileiadis, G; Venter, C; Vincent, P; Völk, H J; Wagner, S J

2006-04-20

The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the 'first stars', which may have formed before galaxy formation began. Direct measurements are difficult and not yet conclusive, owing to the large uncertainties caused by the bright foreground emission associated with zodiacal light. An alternative approach is to study the absorption features imprinted on the gamma-ray spectra of distant extragalactic objects by interactions of those photons with the background light photons. Here we report the discovery of gamma-ray emission from the blazars H 2356 - 309 and 1ES 1101 - 232, at redshifts z = 0.165 and z = 0.186, respectively. Their unexpectedly hard spectra provide an upper limit on the background light at optical/near-infrared wavelengths that appears to be very close to the lower limit given by the integrated light of resolved galaxies. The background flux at these wavelengths accordingly seems to be strongly dominated by the direct starlight from galaxies, thus excluding a large contribution from other sources-in particular from the first stars formed. This result also indicates that intergalactic space is more transparent to gamma-rays than previously thought.
A New Determination of the Extragalactic Diffuse X-Ray Background from EGRET Data

NASA Technical Reports Server (NTRS)

Strong, Andrew W.; Moskalenko, Igor V.; Reimer, Olaf

2004-01-01

We use the GALPROP model for cosmic-ray propagation to obtain a new estimate of the Galactic component of gamma rays, and show that away from the Galactic plane it gives an accurate prediction of the observed EGRET intensities in the energy range 30 MeV - 50 GeV. On this basis we re-evaluate the extragalactic gamma-ray background. We find that for some energies previous work underestimated the Galactic contribution at high latitudes and hence overestimated the background. Our new background spectrum shows a positive curvature similar to that expected for models of the extragalactic emission based on the blazar population.
The X-Ray Spectra of Blazars: Analysis of the Complete EXOSAT Archive: Erratum

NASA Astrophysics Data System (ADS)

Sambruna, Rita M.; Barr, Paul; Giommi, Paolo; Maraschi, Laura; Tagliaferri, Gianpiero; Treves, Aldo

1995-07-01

In the paper "The X-Ray Spectra of Blazars: Analysis of the Complete EXOSAT Archive" by Rita M. Sambruna, Paul Barr, Paolo Giommi, Laura Maraschi, Gianpiero Tagliaferri, and Aldo Treves (ApJS, 95,371 [1994]), the section regarding the object PKS 1510-08 (Section 4.4.14) contains an erroneous quotation. K. P. Singh, A.R. Rao, and M.N. Vahia (ApJ, 365,455 [1990]) in fact detected: emission line only in the 1984 data, and not in the 1985 spectrum, as stated.
DISCOVERY OF A WANDERING RADIO JET BASE AFTER A LARGE X-RAY FLARE IN THE BLAZAR MARKARIAN 421

DOE Office of Scientific and Technical Information (OSTI.GOV)

Niinuma, K.; Kino, M.; Doi, A.

2015-07-01

We investigate the location of the radio jet bases (“radio cores”) of blazars in radio images and their stationarity by means of dense very long baseline interferometry (VLBI) observations. In order to measure the position of a radio core, we conducted a 12 epoch astrometric observation of the blazar Markarian 421 with the VLBI Exploration of Radio Astrometry at 22 GHz immediately after a large X-ray flare, which occurred in the middle of 2011 September. For the first time,we find that the radio core is not stationary but rather changes its location toward 0.5 mas downstream. This angular scale correspondsmore » to the de-projected length of a scale of 10{sup 5} Schwarzschild radii (R{sub s}) at the distance of Markarian 421. This radio-core wandering may be a new type of manifestation associated with the phenomena of large X-ray flares.« less
A hard X-ray view on two distant TeV-blazars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reimer, A.; Costamante, L.; Reimer, O.

2008-12-24

We present a data set derived from {approx}50 ksec continuous Suzaku observations and covered with quasi-simultaneous TeV-observations (HESS, MAGIC) of two of the more distant TeV-blazars detected to date: 1ES 1101-232 and 1ES 1553+113. Both sources are found in a non-variable state with combined XIS-PIN spectra indicating downward curvature up to several tens of keV. 1ES 101-232 was found in a quiet state with the lowest X-ray flux ever measured. We discuss the contemporaneous broadband spectral energy distribution (SED) of both sources and implications from absorption in the EBL for the redshift of 1ES 1553+113.
Constraints on cosmic ray and PeV neutrino production in blazars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, B. Theodore; Li, Zhuo, E-mail: zhangbing91@pku.edu.cn, E-mail: zhuo.li@pku.edu.cn

2017-03-01

IceCube has detected a cumulative flux of PeV neutrinos, which origin is unknown. Blazars, active galactic nuclei with relativistic jets pointing to us, are long and widely expected to be one of the strong candidates of high energy neutrino sources. The neutrino production depends strongly on the cosmic ray power of blazar jets, which is largely unknown. The recent null results in stacking searches of neutrinos for several blazar samples by IceCube put upper limits on the neutrino fluxes from these blazars. Here we compute the cosmic ray power and PeV neutrino flux of Fermi-LAT blazars, and find that themore » upper limits for known blazar sources give stringent constraint on the cosmic ray loading factor of blazar jets (i.e., the ratio of the cosmic ray to bolometric radiation luminosity of blazar jets), ξ{sub cr} ∼< (2–10)ζ{sup −1} (with ζ ∼< 1 the remained fraction of cosmic ray energy when propagate into the blazar broad line region) for flat cosmic ray spectrum, and that the cumulative PeV neutrino flux contributed by all-sky blazars is a fraction ∼< (10–50)% of the IceCube detected flux.« less
2WHSP: A multi-frequency selected catalogue of high energy and very high energy γ-ray blazars and blazar candidates

NASA Astrophysics Data System (ADS)

Chang, Y.-L.; Arsioli, B.; Giommi, P.; Padovani, P.

2017-02-01

Aims: High synchrotron peaked blazars (HSPs) dominate the γ-ray sky at energies higher than a few GeV; however, only a few hundred blazars of this type have been cataloged so far. In this paper we present the 2WHSP sample, the largest and most complete list of HSP blazars available to date, which is an expansion of the 1WHSP catalogue of γ-ray source candidates off the Galactic plane. Methods: We cross-matched a number of multi-wavelength surveys (in the radio, infrared and X-ray bands) and applied selection criteria based on the radio to IR and IR to X-ray spectral slopes. To ensure the selection of genuine HSPs, we examined the SED of each candidate and estimated the peak frequency of its synchrotron emission (νpeak) using the ASDC SED tool, including only sources with νpeak > 1015 Hz (equivalent to νpeak > 4 eV). Results: We have assembled the largest and most complete catalogue of HSP blazars to date, which includes 1691 sources. A number of population properties, such as infrared colours, synchrotron peak, redshift distributions, and γ-ray spectral properties have been used to characterise the sample and maximize completeness. We also derived the radio log N-log S distribution. This catalogue has already been used to provide seeds to discover new very high energy objects within Fermi-LAT data and to look for the counterparts of neutrino and ultra high energy cosmic ray sources, showing its potential for the identification of promising high-energy γ-ray sources and multi-messenger targets. Table 4 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A17
1WHSP: An IR-based sample of ~1000 VHE γ -ray blazar candidates

DOE PAGES

Arsioli, B.; Fraga, B.; Giommi, P.; ...

2015-06-23

Context. Blazars are the dominant type of extragalactic sources at microwave and at γ-ray energies. In the most energetic part of the electromagnetic spectrum (E > ≳ 100 GeV) a large fraction of high Galactic latitude sources are blazars of the High Synchrotron Peaked (HSP) type, that is BL Lac objects with synchrotron power peaking in the UV or in the X-ray band. Building new large samples of HSP blazars is key to understand the properties of jets under extreme conditions, and to study the demographics and the peculiar cosmological evolution of these sources. Aims. HSP blazars are remarkably rare,more » with only a few hundreds of them expected to be above the sensitivity limits of currently available surveys, some of which include hundreds of millions of sources. To find these very uncommon objects, we have devised a method that combines ALLWISE survey data with multi-frequency selection criteria. Methods. The sample was defined starting from a primary list of infrared colour-colour selected sources from the ALLWISE all sky survey database, and applying further restrictions on IR-radio and IR-X-ray flux ratios. Using a polynomial fit to the multi-frequency data (radio to X-ray) we estimated synchrotron peak frequencies and fluxes of each object. Results. We assembled a sample including 992 sources, which is currently the largest existing list of confirmed and candidates HSP blazars. All objects are expected to radiate up to the highest γ-ray photon energies. In fact, 299 of these are confirmed emitters of GeV γ-ray photons (based on Fermi-LAT catalogues), and 36 have already been detected in the TeV band. The majority of sources in the sample are within reach of the upcoming Cherenkov Telescope Array (CTA), and many may be detectable even by the current generation of Cherenkov telescopes during flaring episodes. The sample includes 425 previously known blazars, 151 new identifications, and 416 HSP candidates (mostly faint sources) for which no optical
X-Ray Background from Early Binaries

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-11-01

What impact did X-rays from the first binary star systems have on the universe around them? A new study suggests this radiation may have played an important role during the reionization of our universe.Ionizing the UniverseDuring the period of reionization, the universe reverted from being neutral (as it was during recombination, the previous period)to once again being ionized plasma a state it has remained in since then. This transition, which occurred between 150 million and one billion years after the Big Bang (redshift of 6 z 20), was caused by the formation of the first objects energetic enough to reionize the universes neutral hydrogen.ROSAT image of the soft X-ray background throughout the universe. The different colors represent different energy bands: 0.25 keV (red), 0.75 keV (green), 1.5 keV (blue). [NASA/ROSAT Project]Understanding this time period in particular, determining what sources caused the reionization, and what the properties were of the gas strewn throughout the universe during this time is necessary for us to be able to correctly interpret cosmological observations.Conveniently, the universe has provided us with an interesting clue: the large-scale, diffuse X-ray background we observe all around us. What produced these X-rays, and what impact did this radiation have on the intergalactic medium long ago?The First BinariesA team of scientists led by Hao Xu (UC San Diego) has suggested that the very first generation of stars might be an important contributor to these X-rays.This hypothetical first generation, Population III stars, are thought to have formed before and during reionization from large clouds of gas containing virtually no metals. Studies suggest that a large fraction of Pop III stars formed in binaries and when those stars ended their lives as black holes, ensuing accretion from their companions could produceX-ray radiation.The evolution with redshift of the mean X-ray background intensities. Each curve represents a different
The cosmic X-ray background. [heao observations

NASA Technical Reports Server (NTRS)

Boldt, E. A.

1980-01-01

The cosmic X-ray experiment carried out with the A2 Instrument on HEAO-1 made systematics-free measurements of the extra-galactic X-ray sky and yielded the broadband spectral characteristics for two extreme aspects of this radiation. For the apparently isotropic radiation of cosmological origin that dominates the extragalactic X-ray flux ( 3 keV), the spectrum over the energy band of maximum intensity is remarkably well described by a thermal model with a temperature of a half-billion degrees. At the other extreme, broadband observations of individual extragalactic X-ray sources with HEAO-1 are restricted to objects within the present epoch. While the non-thermal hard spectral components associated with unevolved X-ray emitting active galaxies could account for most of the gamma-ray background, the contribution of such sources to the X-ray background must be relatively small. In contrast, the 'deep-space' sources detected in soft X-rays with the HEAO-2 telescope probably represent a major portion of the extragalactic soft X-ray ( 3 keV) background.
IR observations in gamma-ray blazars

NASA Technical Reports Server (NTRS)

Mahoney, W. A.; Gautier, T. N.; Ressler, M. E.; Wallyn, P.; Durouchoux, P.; Higdon, J. C.

1997-01-01

The infrared photometric and spectral observation of five gamma ray blazars in coordination with the energetic gamma ray experiment telescope (EGRET) onboard the Compton Gamma Ray Observatory is reported. The infrared measurements were made with a Cassegrain infrared camera and the mid-infrared large well imager at the Mt. Palomar 5 m telescope. The emphasis is on the three blazars observed simultaneously by EGRET and the ground-based telescope during viewing period 519. In addition to the acquisition of broadband spectral measurements for direct correlation with the 100 MeV EGRET observations, near infrared images were obtained, enabling a search for intra-day variability to be carried out.

X-Ray Background Survey Spectrometer (XBSS)

NASA Technical Reports Server (NTRS)

Sanders, W. T. (Principal Investigator); Paulos, R. J.

1996-01-01

The objective of this investigation was to perform a spectral survey of the low energy diffuse X-ray background using the X-ray Background Survey Spectrometer (XBSS) on board the Space Station Freedom (SSF). XBSS obtains spectra of the X-ray diffuse background in the 11-24 A and 44-84 A wavelength intervals over the entire sky with 15 deg spatial resolution. These X-rays are almost certainly from a very hot (10(exp 6) K) component of the interstellar medium that is contained in regions occupying a large fraction of the interstellar volume near the Sun. Astrophysical plasmas near 10(exp 6) K are rich in emission lines, and the relative strengths of these lines, besides providing information about the physical conditions of the emitting gas, also provide information about its history and heating mechanisms.
TANAMI blazars in the IceCube PeV-neutrino fields

DOE PAGES

Krauß, F.

2014-06-01

The IceCube Collaboration has announced the discovery of a neutrino flux in excess of the atmospheric background. Owing to the steeply falling atmospheric background spectrum, events at PeV energies most likely have an extraterrestrial origin. We present the multiwavelength properties of the six radio-brightest blazars that are positionally coincident with these events using contemporaneous data of the TANAMI blazar sample, including high-resolution images and spectral energy distributions. Assuming the X-ray to γ-ray emission originates in the photoproduction of pions by accelerated protons, the integrated predicted neutrino luminosity of these sources is high enough to explain the two detected PeV events.
Probing the diffuse optical-IR background with TeV blazars detected with the MAGIC Telescopes

NASA Astrophysics Data System (ADS)

Prandini, Elisa; Domínguez, Alberto; Fallah Ramazani, Vandad; Hassan, Tarek; Mazin, Daniel; Moralejo, Abelardo; Nievas Rosillo, Mireia; Vanzo, Gaia; Vazquez Acosta, Monica

2017-11-01

Blazars are radio loud quasars whose jet points toward the observer. The observed emission is mostly non-thermal, dominated by the jet emission, and in some cases extends up to the very high energy gamma rays (VHE; E > 100 GeV). To date, more than 60 blazars have been detected at VHE mainly with ground-based imaging atmospheric Cherenkov telescopes (IACTs) such as MAGIC, H.E.S.S. and VERITAS. Energetic photons from a blazar may interact with the diffuse optical and IR background (the extragalactic background light, EBL) leaving an imprint on the blazar energy spectrum. This effect can be used to constrain the EBL, with basic assumptions on the intrinsic energy spectrum. Current generation of IACTs is providing valuable measurements of the EBL density and energy spectrum from optical to infrared frequencies. In this contribution, we present the latest results obtained with the data taken with the MAGIC telescopes: using 32 spectra from 12 blazars, the scale factor of the optical density predicted by the EBL model from Domínguez et al. (2011) is constrained to be 0.95 (+0.11, -0.12)_{stat} (+0.16, -0.07)_{sys}, where a value of 1 means the perfect match with the model.
SYSTEMATIC STUDY OF GAMMA-RAY-BRIGHT BLAZARS WITH OPTICAL POLARIZATION AND GAMMA-RAY VARIABILITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Itoh, Ryosuke; Fukazawa, Yasushi; Kanda, Yuka

Blazars are highly variable active galactic nuclei that emit radiation at all wavelengths from radio to gamma rays. Polarized radiation from blazars is one key piece of evidence for synchrotron radiation at low energies, and it also varies dramatically. The polarization of blazars is of interest for understanding the origin, confinement, and propagation of jets. However, even though numerous measurements have been performed, the mechanisms behind jet creation, composition, and variability are still debated. We performed simultaneous gamma-ray and optical photopolarimetry observations of 45 blazars between 2008 July and 2014 December to investigate the mechanisms of variability and search formore » a basic relation between the several subclasses of blazars. We identify a correlation between the maximum degree of optical linear polarization and the gamma-ray luminosity or the ratio of gamma-ray to optical fluxes. Since the maximum polarization degree depends on the condition of the magnetic field (chaotic or ordered), this result implies a systematic difference in the intrinsic alignment of magnetic fields in parsec-scale relativistic jets between different types of blazars (flat-spectrum radio quasars vs. BL Lacs) and consequently between different types of radio galaxies (FR I versus FR II).« less
X-ray radiative transfer in protoplanetary disks. The role of dust and X-ray background fields

NASA Astrophysics Data System (ADS)

Rab, Ch.; Güdel, M.; Woitke, P.; Kamp, I.; Thi, W.-F.; Min, M.; Aresu, G.; Meijerink, R.

2018-01-01

Context. The X-ray luminosities of T Tauri stars are about two to four orders of magnitude higher than the luminosity of the contemporary Sun. As these stars are born in clusters, their disks are not only irradiated by their parent star but also by an X-ray background field produced by the cluster members. Aims: We aim to quantify the impact of X-ray background fields produced by young embedded clusters on the chemical structure of disks. Further, we want to investigate the importance of the dust for X-ray radiative transfer in disks. Methods: We present a new X-ray radiative transfer module for the radiation thermo-chemical disk code PRODIMO (PROtoplanetary DIsk MOdel), which includes X-ray scattering and absorption by both the gas and dust component. The X-ray dust opacities can be calculated for various dust compositions and dust-size distributions. For the X-ray radiative transfer we consider irradiation by the star and by X-ray background fields. To study the impact of X-rays on the chemical structure of disks we use the well established disk ionization tracers N2H+ and HCO+. Results: For evolved dust populations (e.g. grain growth), X-ray opacities are mostly dominated by the gas; only for photon energies E ≳ 5-10 keV do dust opacities become relevant. Consequently the local disk X-ray radiation field is only affected in dense regions close to the disk midplane. X-ray background fields can dominate the local X-ray disk ionization rate for disk radii r ≳ 20 au. However, the N2H+ and HCO+ column densities are only significantly affected in cases of low cosmic-ray ionization rates (≲10-19 s-1), or if the background flux is at least a factor of ten higher than the flux level of ≈10-5 erg cm-2 s-1 expected for clusters typical for the solar vicinity. Conclusions: Observable signatures of X-ray background fields in low-mass star-formation regions, like Taurus, are only expected for cluster members experiencing a strong X-ray background field (e.g. due to
The Hadronic Origin of the Hard Gamma-Ray Spectrum from Blazar 1ES 1101-232

NASA Astrophysics Data System (ADS)

Cao, Gang; Wang, Jiancheng

2014-03-01

The very hard γ-ray spectrum from distant blazars challenges the traditional synchrotron self-Compton (SSC) model, which may indicate that there is a contribution from an additional high-energy component beyond the SSC emission. In this paper, we study the possible origin of the hard γ-ray spectrum from distant blazars. We develop a model to explain the hard γ-ray spectrum from blazar 1ES 1101-232. In the model, the optical and X-ray radiation would come from the synchrotron radiation of primary electrons and secondary pairs and the GeV emission would be produced by the SSC process, however, the hard γ-ray spectrum would originate from the decay of neutral pion produced through proton-photon interactions with the synchrotron radiation photons within the jet. Our model can explain the observed spectral energy distribution of 1ES 1101-232 well, especially the very hard γ-ray spectrum. However, our model requires a very large proton power to efficiently produce the γ-ray through proton-photon interactions.
Exploring the multiband emission of TXS 0536+145: the most distant -γray flaring blazar

DOE PAGES

Orienti, M.; D'Ammando, F.; Giroletti, M.; ...

2014-09-15

We report results of a multi-band monitoring campaign of the flat spectrum radio quasar TXS 0536+145 at redshift 2.69. This source was detected during a very high γ-ray activity state in 2012 March by the Large Area Telescope on board Fermi, becoming the γ-ray flaring blazar at the highest redshift detected so far. At the peak of the flare the source reached an apparent isotropic γ-ray luminosity of 6.6×1049 erg s-1 which is comparable to the values achieved by the most luminous blazars. This activity triggered radio-to-X-rays monitoring observations by Swift, Very Long Baseline Array, European VLBI Network, and Medicinamore » single-dish telescope. Significant variability was observed from radio to X-rays supporting the identification of the γ-ray source with TXS 0536+145. Both the radio and γ-ray light curves show a similar behaviour, with the γ-rays leading the radio variability with a time lag of about 4-6 months. The luminosity increase is associated with a flattening of the radio spectrum. No new superluminal component associated with the flare was detected in high resolution parsec-scale radio images. During the flare the γ-ray spectrum seems to deviate from a power law, showing a curvature that was not present during the average activity state. The γ-ray properties of TXS 0536+145 are consistent with those shown by the high-redshift γ-ray blazar population.« less
Exploring the multiband emission of TXS 0536+145: the most distant γ-ray flaring blazar

NASA Astrophysics Data System (ADS)

Orienti, M.; D'Ammando, F.; Giroletti, M.; Finke, J.; Ajello, M.; Dallacasa, D.; Venturi, T.

2014-11-01

We report results of a multiband monitoring campaign of the flat spectrum radio quasar TXS 0536+145 at redshift 2.69. This source was detected during a very high γ-ray activity state in 2012 March by the Large Area Telescope on board Fermi, becoming the γ-ray flaring blazar at the highest redshift detected so far. At the peak of the flare the source reached an apparent isotropic γ-ray luminosity of 6.6 × 1049 erg s-1 which is comparable to the values achieved by the most luminous blazars. This activity triggered radio-to-X-rays monitoring observations by Swift, Very Long Baseline Array, European VLBI Network, and Medicina single-dish telescope. Significant variability was observed from radio to X-rays supporting the identification of the γ-ray source with TXS 0536+145. Both the radio and γ-ray light curves show a similar behaviour, with the γ-rays leading the radio variability with a time lag of about 4-6 months. The luminosity increase is associated with a flattening of the radio spectrum. No new superluminal component associated with the flare was detected in high-resolution parsec-scale radio images. During the flare the γ-ray spectrum seems to deviate from a power law, showing a curvature that was not present during the average activity state. The γ-ray properties of TXS 0536+145 are consistent with those shown by the high-redshift γ-ray blazar population.
On the intrinsic shape of the gamma-ray spectrum for Fermi blazars

NASA Astrophysics Data System (ADS)

Kang, Shi-Ju; Wu, Qingwen; Zheng, Yong-Gang; Yin, Yue; Song, Jia-Li; Zou, Hang; Feng, Jian-Chao; Dong, Ai-Jun; Wu, Zhong-Zu; Zhang, Zhi-Bin; Wu, Lin-Hui

2018-05-01

The curvature of the γ-ray spectrumin blazarsmay reflect the intrinsic distribution of emitting electrons, which will further give some information on the possible acceleration and cooling processes in the emitting region. The γ-ray spectra of Fermi blazars are normally fitted either by a single power-law (PL) or a log-normal (call Logarithmic Parabola, LP) form. The possible reason for this difference is not clear. We statistically explore this issue based on the different observational properties of 1419 Fermi blazars in the 3LAC Clean Sample.We find that the γ-ray flux (100MeV–100GeV) and variability index follow bimodal distributions for PL and LP blazars, where the γ-ray flux and variability index show a positive correlation. However, the distributions of γ-ray luminosity and redshift follow a unimodal distribution. Our results suggest that the bimodal distribution of γ-ray fluxes for LP and PL blazars may not be intrinsic and all blazars may have an intrinsically curved γ-ray spectrum, and the PL spectrum is just caused by the fitting effect due to less photons.
TIME STRUCTURE OF GAMMA-RAY SIGNALS GENERATED IN LINE-OF-SIGHT INTERACTIONS OF COSMIC RAYS FROM DISTANT BLAZARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prosekin, Anton; Aharonian, Felix; Essey, Warren

2012-10-01

Blazars are expected to produce both gamma rays and cosmic rays. Therefore, observed high-energy gamma rays from distant blazars may contain a significant contribution from secondary gamma rays produced along the line of sight by the interactions of cosmic-ray protons with background photons. Unlike the standard models of blazars that consider only the primary photons emitted at the source, models that include the cosmic-ray contribution predict that even {approx}10 TeV photons should be detectable from distant objects with redshifts as high as z {>=} 0.1. Secondary photons contribute to signals of point sources only if the intergalactic magnetic fields aremore » very small, B {approx}< 10{sup -14} G, and their detection can be used to set upper bounds on magnetic fields along the line of sight. Secondary gamma rays have distinct spectral and temporal features. We explore the temporal properties of such signals using a semi-analytical formalism and detailed numerical simulations, which account for all the relevant processes, including magnetic deflections. In particular, we elucidate the interplay of time delays coming from the proton deflections and from the electromagnetic cascade, and we find that, at multi-TeV energies, secondary gamma rays can show variability on timescales of years for B {approx} 10{sup -15} G.« less
General Physical Properties of CGRaBS Blazars

NASA Astrophysics Data System (ADS)

Paliya, Vaidehi S.; Marcotulli, L.; Ajello, M.; Joshi, M.; Sahayanathan, S.; Rao, A. R.; Hartmann, D.

2017-12-01

We present the results of a multi-frequency, time-averaged analysis of blazars included in the Candidate Gamma-ray Blazar Survey catalog. Our sample consists of 324 γ-ray detected (γ-ray loud) and 191 γ-ray undetected (γ-ray quiet) blazars; we consider all the data up to 2016 April 1. We find that both the γ-ray loud and γ-ray quiet blazar populations occupy similar regions in the WISE color-color diagram, and γ-ray loud sources are brighter in the radio and X-ray bands. A simple one-zone synchrotron inverse-Compton emission model is applied to derive the physical properties of both populations. We find that the central black hole mass and accretion disk luminosity ({L}{disk}) computed from the modeling of the optical-UV emission with a Shakura-Sunyaev disk reasonably matches that estimated from the optical spectroscopic emission-line information. A significantly larger Doppler boosting in the γ-ray loud blazars is noted, and their jets are more radiatively efficient. On the other hand, the γ-ray quiet objects are more MeV-peaked and thus could be potential targets for next-generation MeV missions. Our results confirm earlier findings about the accretion-jet connection in blazars; however, many of the γ-ray quiet blazars tend to deviate from the recent claim that the jet power exceeds {L}{disk} in blazars. A broadband study, considering a larger set of γ-ray quiet objects and also including BL Lacs, will be needed to confirm/reject this hypothesis as well as to verify the evolution of the powerful high-redshift blazars into their low-power nearby counterparts.
Discovery of very high energy γ-ray emission from the blazar 1ES 0033+595 by the MAGIC telescopes

DOE PAGES

Aleksi , J.; Ansoldi, S.; Antonelli, L. A.; ...

2014-11-11

The number of known very high energy (VHE) blazars is ~50, which is very small in comparison to the number of blazars detected in other frequencies. This situation is a handicap for population studies of blazars, which emit about half of their luminosity in the γ-ray domain. Moreover, VHE blazars, if distant, allow for the study of the environment that the high-energy γ-rays traverse in their path towards the Earth, like the extragalactic background light (EBL) and the intergalactic magnetic field (IGMF), and hence they have a special interest for the astrophysics community. In this papaer, we present the firstmore » VHE detection of 1ES 0033+595 with a statistical significance of 5.5σ. The VHE emission of this object is constant throughout the MAGIC observations (2009 August and October), and can be parametrized with a power law with an integral flux above 150 GeV of (7.1 ± 1.3) × 10 -12 photons cm -2 s -1 and a photon index of (3.8 ± 0.7). We model its spectral energy distribution (SED) as the result of inverse Compton scattering of synchrotron photons. For the study of the SED, we used simultaneous optical R-band data from the KVA telescope, archival X-ray data by Swift as well as INTEGRAL, and simultaneous high-energy (HE, 300 MeV–10 GeV) γ-ray data from the Fermi Large Area Telescope (LAT) observatory. Using the empirical approach of Prandini et al. (2010) and the Fermi LAT and MAGIC spectra for this object, we estimate the redshift of this source to be 0.34 ± 0.08 ± 0.05. Also, this is a relevant result because this source is possibly one of the 10 most distant VHE blazars known to date, and with further (simultaneous) observations could play an important role in blazar population studies, as well as future constraints on the EBL and IGMF.« less
Discovery of very high energy γ-ray emission from the blazar 1ES 0033+595 by the MAGIC telescopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aleksi , J.; Ansoldi, S.; Antonelli, L. A.

The number of known very high energy (VHE) blazars is ~50, which is very small in comparison to the number of blazars detected in other frequencies. This situation is a handicap for population studies of blazars, which emit about half of their luminosity in the γ-ray domain. Moreover, VHE blazars, if distant, allow for the study of the environment that the high-energy γ-rays traverse in their path towards the Earth, like the extragalactic background light (EBL) and the intergalactic magnetic field (IGMF), and hence they have a special interest for the astrophysics community. In this papaer, we present the firstmore » VHE detection of 1ES 0033+595 with a statistical significance of 5.5σ. The VHE emission of this object is constant throughout the MAGIC observations (2009 August and October), and can be parametrized with a power law with an integral flux above 150 GeV of (7.1 ± 1.3) × 10 -12 photons cm -2 s -1 and a photon index of (3.8 ± 0.7). We model its spectral energy distribution (SED) as the result of inverse Compton scattering of synchrotron photons. For the study of the SED, we used simultaneous optical R-band data from the KVA telescope, archival X-ray data by Swift as well as INTEGRAL, and simultaneous high-energy (HE, 300 MeV–10 GeV) γ-ray data from the Fermi Large Area Telescope (LAT) observatory. Using the empirical approach of Prandini et al. (2010) and the Fermi LAT and MAGIC spectra for this object, we estimate the redshift of this source to be 0.34 ± 0.08 ± 0.05. Also, this is a relevant result because this source is possibly one of the 10 most distant VHE blazars known to date, and with further (simultaneous) observations could play an important role in blazar population studies, as well as future constraints on the EBL and IGMF.« less
Discovery of very high energy γ-ray emission from the blazar 1ES 0033+595 by the MAGIC telescopes

NASA Astrophysics Data System (ADS)

Aleksić, J.; Ansoldi, S.; Antonelli, L. A.; Antoranz, P.; Babic, A.; Bangale, P.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; Carreto Fidalgo, D.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; da Vela, P.; Dazzi, F.; de Angelis, A.; de Caneva, G.; de Lotto, B.; Delgado Mendez, C.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher, D.; Elsaesser, D.; Farina, E.; Ferenc, D.; Fonseca, M. V.; Font, L.; Frantzen, K.; Fruck, C.; García López, R. J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Godinović, N.; González Muñoz, A.; Gozzini, S. R.; Hadasch, D.; Hayashida, M.; Herrera, J.; Herrero, A.; Hildebrand, D.; Hose, J.; Hrupec, D.; Idec, W.; Kadenius, V.; Kellermann, H.; Kodani, K.; Konno, Y.; Krause, J.; Kubo, H.; Kushida, J.; La Barbera, A.; Lelas, D.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Lozano, I.; Makariev, M.; Mallot, K.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Meucci, M.; Miranda, J. M.; Mirzoyan, R.; Moralejo, A.; Munar-Adrover, P.; Nakajima, D.; Niedzwiecki, A.; Nilsson, K.; Nishijima, K.; Noda, K.; Nowak, N.; Orito, R.; Overkemping, A.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Paredes-Fortuny, X.; Partini, S.; Persic, M.; Prada, F.; Moroni, P. G. Prada; Prandini, E.; Preziuso, S.; Puljak, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rodriguez Garcia, J.; Rügamer, S.; Saggion, A.; Saito, T.; Saito, K.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shore, S. N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Spanier, F.; Stamatescu, V.; Stamerra, A.; Steinbring, T.; Storz, J.; Sun, S.; Surić, T.; Takalo, L.; Takami, H.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Thaele, J.; Tibolla, O.; Torres, D. F.; Toyama, T.; Treves, A.; Uellenbeck, M.; Vogler, P.; Wagner, R. M.; Zandanel, F.; Zanin, R.; MAGIC Collaboration; Tronconi, V.; Buson, S.; Borghese, A.

2015-01-01

The number of known very high energy (VHE) blazars is ˜50, which is very small in comparison to the number of blazars detected in other frequencies. This situation is a handicap for population studies of blazars, which emit about half of their luminosity in the γ-ray domain. Moreover, VHE blazars, if distant, allow for the study of the environment that the high-energy γ-rays traverse in their path towards the Earth, like the extragalactic background light (EBL) and the intergalactic magnetic field (IGMF), and hence they have a special interest for the astrophysics community. We present the first VHE detection of 1ES 0033+595 with a statistical significance of 5.5σ. The VHE emission of this object is constant throughout the MAGIC observations (2009 August and October), and can be parametrized with a power law with an integral flux above 150 GeV of (7.1 ± 1.3) × 10-12 photons cm-2 s-1 and a photon index of (3.8 ± 0.7). We model its spectral energy distribution (SED) as the result of inverse Compton scattering of synchrotron photons. For the study of the SED, we used simultaneous optical R-band data from the KVA telescope, archival X-ray data by Swift as well as INTEGRAL, and simultaneous high-energy (HE, 300 MeV-10 GeV) γ-ray data from the Fermi Large Area Telescope (LAT) observatory. Using the empirical approach of Prandini et al. (2010) and the Fermi LAT and MAGIC spectra for this object, we estimate the redshift of this source to be 0.34 ± 0.08 ± 0.05. This is a relevant result because this source is possibly one of the 10 most distant VHE blazars known to date, and with further (simultaneous) observations could play an important role in blazar population studies, as well as future constraints on the EBL and IGMF.
TEMPORAL CORRELATIONS BETWEEN OPTICAL AND GAMMA-RAY ACTIVITY IN BLAZARS

DOE PAGES

Cohen, Daniel P.; Romani, Roger W.; Filippenko, Alexei V.; ...

2014-12-08

For this research, we have been using the 0.76 m Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory to optically monitor a sample of 157 blazars that are bright in gamma-rays being detected with high significance (≥10σ) in one year by the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. We attempt to observe each source on a three-day cadence with KAIT, subject to weather and seasonal visibility. The gamma-ray coverage is essentially continuous. KAIT observations extend over much of the five-year Fermi mission for several objects, and most have >100 optical measurements spanning the last three years.more » These blazars (flat-spectrum radio quasars and BL Lac objects) exhibit a wide range of flaring behavior. Using the discrete correlation function (DCF), here we search for temporal relationships between optical and gamma-ray light curves in the 40 brightest sources in hopes of placing constraints on blazar acceleration and emission zones. We find strong optical-gamma-ray correlation in many of these sources at time delays of ~1 to ~10 days, ranging between –40 and +30 days. A stacked average DCF of the 40 sources verifies this correlation trend, with a peak above 99% significance indicating a characteristic time delay consistent with 0 days. These findings strongly support the widely accepted leptonic models of blazar emission. However, we also find examples of apparently uncorrelated flares (optical flares with no gamma-ray counterpart and gamma-ray flares with no optical counterpart) that challenge simple, one-zone models of blazar emission. Moreover, we find that flat-spectrum radio quasars tend to have gamma-rays leading the optical, while intermediate- and high-synchrotron peak blazars with the most significant peaks have smaller lags/leads. In conclusion, it is clear that long-term monitoring at high cadence is necessary to reveal the underlying physical correlation.« less
Fast γ-Ray Variability in Blazars beyond Redshift 3

NASA Astrophysics Data System (ADS)

Li, Shang; Xia, Zi-Qing; Liang, Yun-Feng; Liao, Neng-Hui; Fan, Yi-Zhong

2018-02-01

High-redshift blazars are one of the most powerful sources in the universe and γ-ray variability carries crucial information about their relativistic jets. In this work we present results of the first systematical temporal analysis of Fermi-LAT data of all known seven γ-ray blazars beyond redshift 3. Significant long-term γ-ray variability is found from five sources in monthly γ-ray light curves, in which three of them are reported for the first time. Furthermore, intraday γ-ray variations are detected from NVSS J053954‑283956 and NVSS J080518+614423. The doubling variability timescale of the former source is limited as short as ≲1 hr (at the source frame). Together with variability amplitude over one order of magnitude, NVSS J053954‑283956 is the most distant γ-ray flaring blazar so far. Meanwhile, intraday optical variability of NVSS J163547+362930 is found based on an archival PTF/iPTF light curve. Benefiting from the multi-wavelength activity of these sources, constraints on their Doppler factors, as well as the locations of the γ-ray radiation region and indications for the SDSS high redshift jetted active galactic nuclei deficit are discussed.
The X-Ray Background and the AGN Luminosity Function

NASA Astrophysics Data System (ADS)

Hasinger, G.

The deepest X-ray surveys performed with ROSAT were able to resolve as much as 70-80% of the 1-2 keV X-ray background into resolved sources. Optical follow-up observations were able to identify the majority of faint X-ray sources as active galactic nuclei (AGN) out to redshifts of 4.5 as well as a sizeable fraction as groups of galaxies out to redshifts of 0.7. A new population of X-ray luminous, optically innocent narrow emission line galaxies (NELGs) at the faintest X-ray fluxes is still a matter of debate, most likely many of them are also connected to AGN. First deep surveys with the Japanese ASCA satellite give us a glimpse of the harder X-ray background where the bulk of the energy density resides. Future X-ray observatories (XMM and AXAF) will be able to resolve the harder X-ray background. For the first time we are now in a position to study the cosmological evolution of the X-ray luminosity function of AGN, groups of galaxies and galaxies and simultaneously constrain their total luminosity output over cosmic time.
“Orphan” γ-Ray Flares and Stationary Sheaths of Blazar Jets

NASA Astrophysics Data System (ADS)

MacDonald, Nicholas R.; Jorstad, Svetlana G.; Marscher, Alan P.

2017-11-01

Blazars exhibit flares across the entire electromagnetic spectrum. Many γ-ray flares are highly correlated with flares detected at longer wavelengths; however, a small subset appears to occur in isolation, with little or no correlated variability at longer wavelengths. These “orphan” γ-ray flares challenge current models of blazar variability, most of which are unable to reproduce this type of behavior. MacDonald et al. have developed the Ring of Fire model to explain the origin of orphan γ-ray flares from within blazar jets. In this model, electrons contained within a blob of plasma moving relativistically along the spine of the jet inverse-Compton scatter synchrotron photons emanating off of a ring of shocked sheath plasma that enshrouds the jet spine. As the blob propagates through the ring, the scattering of the ring photons by the blob electrons creates an orphan γ-ray flare. This model was successfully applied to modeling a prominent orphan γ-ray flare observed in the blazar PKS 1510-089. To further support the plausibility of this model, MacDonald et al. presented a stacked radio map of PKS 1510-089 containing the polarimetric signature of a sheath of plasma surrounding the spine of the jet. In this paper, we extend our modeling and stacking techniques to a larger sample of blazars: 3C 273, 4C 71.01, 3C 279, 1055+018, CTA 102, and 3C 345, the majority of which have exhibited orphan γ-ray flares. We find that the model can successfully reproduce these flares, while our stacked maps reveal the existence of jet sheaths within these blazars.
VERITAS Observations of Six Bright, Hard-Spectrum Fermi-LAT Blazars

DOE PAGES

Aliu, E.; Archambault, S.; Arlen, T.; ...

2012-10-25

In this paper, we report on VERITAS very high energy (VHE; E ≥ 100 GeV) observations of six blazars selected from the Fermi Large Area Telescope First Source Catalog (1FGL). The gamma-ray emission from 1FGL sources was extrapolated up to the VHE band, taking gamma-ray absorption by the extragalactic background light into account. This allowed the selection of six bright, hard-spectrum blazars that were good candidate TeV emitters. Spectroscopic redshift measurements were attempted with the Keck Telescope for the targets without Sloan Digital Sky Survey spectroscopic data. No VHE emission is detected during the observations of the six sources describedmore » here. Corresponding TeV upper limits are presented, along with contemporaneous Fermi observations and non-concurrent Swift UVOT and X-Ray Telescope data. The blazar broadband spectral energy distributions (SEDs) are assembled and modeled with a single-zone synchrotron self-Compton model. Finally, the SED built for each of the six blazars shows a synchrotron peak bordering between the intermediate- and high-spectrum-peak classifications, with four of the six resulting in particle-dominated emission regions.« less
Components of the Extragalactic Gamma-Ray Background

NASA Technical Reports Server (NTRS)

Stecker, Floyd W.; Venters, Tonia M.

2011-01-01

We present new theoretical estimates of the relative contributions of unresolved blazars and star-forming galaxies to the extragalactic gamma-ray background (EGB) and discuss constraints on the contributions from alternative mechanisms such as dark matter annihilation and truly diffuse gamma-ray production. We find that the Fermi source count data do not rule out a scenario in which the EGB is dominated by emission from unresolved blazars, though unresolved star-forming galaxies may also contribute significantly to the background, within order-of-magnitude uncertainties. In addition, we find that the spectrum of the unresolved star-forming galaxy contribution cannot explain the EGB spectrum found by EGRET at energies between 50 and 200 MeV, whereas the spectrum of unresolved flat spectrum radio quasars, when accounting for the energy-dependent effects of source confusion, could be consistent with the combined spectrum of the low-energy EGRET EGB measurements and the Fermi-Large Area Telescope EGB measurements.

Long-Term Multiwavelength Studies of High-Redshift Blazar 0836+710

NASA Technical Reports Server (NTRS)

Thompson, D. J.; Akyuz, A.; Donato, D.; Perkins, J. S.; Larsson, S.; Sokolovsky, K.; Fuhrmann, L.; Kurtanidze, O.

2012-01-01

Following gamma-ray flaring activity of high-redshift (z=2.218) blazar 0836+710 in 2011, we have assembled a long-term multiwavelength study of this object. Although this source is monitored regularly by radio telescopes and the Fermi Large Area Telescope, its coverage at other wavelengths is limited. The optical flux appears generally correlated with the gamma-ray flux, while little variability has been seen at X-ray energies. The gamma-ray/radio correlation is complex compared to some other blazars. As for many blazars, the largest variability is seen at gamma-ray wavelengths.
Implications of Gamma-Ray Transparency Constraints in Blazars: Minimum Distances and Gamma-Ray Collimation

NASA Technical Reports Server (NTRS)

Becker, Peter A.; Kafatos, Menas

1995-01-01

We develop a general expression for the gamma - gamma absorption coefficient, alpha(sub gamma(gamma)) for gamma-rays propagating in an arbitrary direction at an arbitrary point in space above an X-ray-emitting accretion disk. The X-ray intensity is assumed to vary as a power law in energy and radius between the outer disk radius, R(sub 0), and the inner radius, R(sub ms) which is the radius of marginal stability for a Schwarzschild black hole. We use our result for alpha(sub gamma(gamma)) to calculate the gamma - gamma optical depth, tau(sub gamma(gamma)) for gamma - rays created at height z and propagating at angle Phi relative to the disk axis, and we show that for Phi = 0 and z greater than or approx equal to R(sub 0), tau(sub gamma(gamma)) proportional to Epsilon(sup alpha)z(sup -2(alpha) - 3), where alpha is the X-ray spectral index and Epsilon is the gamma - ray energy. As an application, we use our formalism to compute the minimum distance between the central black hole and the site of production of the gamma-rays detected by EGRET during the 1991 June flare of 3C 279. In order to obtain an upper limit, we assume that all of the X-rays observed contemporaneously by Ginga were emitted by the disk. Our results suggest that the observed gamma - rays may have originated within less than or approx equal to 45 GM/sq c from a black hole of mass greater than or approx equal to 10(exp 9) solar mass, perhaps in active plasma located above the central funnel of the accretion disk. This raises the possibility of establishing a direct connection between the production of the observed gamma - rays and the accretion of material onto the black hole. We also consider the variation of the optical depth as a function of the angle of propagation Phi. Our results indicate that the "focusing" of the gamma - rays along the disk axis due to pair production is strong enough to explain the observed degree of alignment in blazar sources. If the gamma - rays are produced isotropically
Very low luminosity active galaxies and the X-ray background

NASA Technical Reports Server (NTRS)

Elvis, M.; Soltan, A.; Keel, W. C.

1984-01-01

The properties of very low luminosity active galactic nuclei are not well studied, and, in particular, their possible contribution to the diffuse X-ray background is not known. In the present investigation, an X-ray luminosity function for the range from 10 to the 39th to 10 to the 42.5th ergs/s is constructed. The obtained X-ray luminosity function is integrated to estimate the contribution of these very low luminosity active galaxies to the diffuse X-ray background. The construction of the X-ray luminosity function is based on data obtained by Keel (1983) and some simple assumptions about optical and X-ray properties.
Astrophysical interpretation of the anisotropies in the unresolved gamma-ray background

NASA Astrophysics Data System (ADS)

Ando, Shin'ichiro; Fornasa, Mattia; Fornengo, Nicolao; Regis, Marco; Zechlin, Hannes-S.

2017-06-01

Recently, a new measurement of the auto- and cross-correlation angular power spectrum (APS) of the isotropic gamma-ray background was performed, based on 81 months of data of the Fermi Large-Area Telescope (LAT). Here, we fit, for the first time, the new APS data with a model describing the emission of unresolved blazars. These sources are expected to dominate the anisotropy signal. The model we employ in our analysis reproduces well the blazars resolved by Fermi LAT. When considering the APS obtained by masking the sources listed in the 3FGL catalog, we find that unresolved blazars underproduce the measured APS below ˜1 GeV . Contrary to past results, this suggests the presence of a new contribution to the low-energy APS, with a significance of, at least, 5 σ . The excess can be ascribed to a new class of faint gamma-ray emitters. If we consider the APS obtained by masking the sources in the 2FGL catalog, there is no underproduction of the APS below 1 GeV, but the new source class is still preferred over the blazars-only scenario (with a significance larger than 10 σ ). The properties of the new source class and the level of anisotropies induced in the isotropic gamma-ray background are the same, independent of the APS data used. In particular, the new gamma-ray emitters must have a soft energy spectrum, with a spectral index ranging, approximately, from 2.7 to 3.2. This complicates their interpretation in terms of known sources, since, normally, star-forming and radio galaxies are observed with a harder spectrum. The new source class identified here is also expected to contribute significantly to the intensity of the isotropic gamma-ray background.
The Extragalactic Background Light and the Gamma-ray Opacity of the Universe

NASA Technical Reports Server (NTRS)

Dwek, Eli; Krennrich, Frank

2012-01-01

The extragalactic background light (EBL) is one of the fundamental observational quantities in cosmology. All energy releases from resolved and unresolved extragalactic sources, and the light from any truly diffuse background, excluding the cosmic microwave background (CMB), contribute to its intensity and spectral energy distribution. It therefore plays a crucial role in cosmological tests for the formation and evolution of stellar objects and galaxies, and for setting limits on exotic energy releases in the universe. The EBL also plays an important role in the propagation of very high energy gamma-rays which are attenuated en route to Earth by pair producing gamma-gamma interactions with the EBL and CMB. The EBL affects the spectrum of the sources, predominantly blazars, in the approx 10 GeV to 10 TeV energy regime. Knowledge of the EBL intensity and spectrum will allow the determination of the intrinsic blazar spectrum in a crucial energy regime that can be used to test particle acceleration mechanisms and VHE gamma-ray production models. Conversely, knowledge of the intrinsic gamma-ray spectrum and the detection of blazars at increasingly higher redshifts will set strong limits on the EBL and its evolution. This paper reviews the latest developments in the determination of the EBL and its impact on the current understanding of the origin and production mechanisms of gamma-rays in blazars, and on energy releases in the universe. The review concludes with a summary and future directions in Cherenkov Telescope Array techniques and in infrared ground-based and space observatories that will greatly improve our knowledge of the EBL and the origin and production of very high energy gamma-rays.
Investigation of the hard x-ray background in backlit pinhole imagers.

PubMed

Fein, J R; Peebles, J L; Keiter, P A; Holloway, J P; Klein, S R; Kuranz, C C; Manuel, M J-E; Drake, R P

2014-11-01

Hard x-rays from laser-produced hot electrons (>10 keV) in backlit pinhole imagers can give rise to a background signal that decreases signal dynamic range in radiographs. Consequently, significant uncertainties are introduced to the measured optical depth of imaged plasmas. Past experiments have demonstrated that hard x-rays are produced when hot electrons interact with the high-Z pinhole substrate used to collimate the softer He-α x-ray source. Results are presented from recent experiments performed on the OMEGA-60 laser to further study the production of hard x-rays in the pinhole substrate and how these x-rays contribute to the background signal in radiographs. Radiographic image plates measured hard x-rays from pinhole imagers with Mo, Sn, and Ta pinhole substrates. The variation in background signal between pinhole substrates provides evidence that much of this background comes from x-rays produced in the pinhole substrate itself. A Monte Carlo electron transport code was used to model x-ray production from hot electrons interacting in the pinhole substrate, as well as to model measurements of x-rays from the irradiated side of the targets, recorded by a bremsstrahlung x-ray spectrometer. Inconsistencies in inferred hot electron distributions between the different pinhole substrate materials demonstrate that additional sources of hot electrons beyond those modeled may produce hard x-rays in the pinhole substrate.
Investigation of the hard x-ray background in backlit pinhole imagers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fein, J. R., E-mail: jrfein@umich.edu; Holloway, J. P.; Peebles, J. L.

Hard x-rays from laser-produced hot electrons (>10 keV) in backlit pinhole imagers can give rise to a background signal that decreases signal dynamic range in radiographs. Consequently, significant uncertainties are introduced to the measured optical depth of imaged plasmas. Past experiments have demonstrated that hard x-rays are produced when hot electrons interact with the high-Z pinhole substrate used to collimate the softer He-α x-ray source. Results are presented from recent experiments performed on the OMEGA-60 laser to further study the production of hard x-rays in the pinhole substrate and how these x-rays contribute to the background signal in radiographs. Radiographicmore » image plates measured hard x-rays from pinhole imagers with Mo, Sn, and Ta pinhole substrates. The variation in background signal between pinhole substrates provides evidence that much of this background comes from x-rays produced in the pinhole substrate itself. A Monte Carlo electron transport code was used to model x-ray production from hot electrons interacting in the pinhole substrate, as well as to model measurements of x-rays from the irradiated side of the targets, recorded by a bremsstrahlung x-ray spectrometer. Inconsistencies in inferred hot electron distributions between the different pinhole substrate materials demonstrate that additional sources of hot electrons beyond those modeled may produce hard x-rays in the pinhole substrate.« less
Modelling the flaring activity of the high-z, hard X-ray-selected blazar IGR J22517+2217: Flaring activity of IGR J22517+2217

DOE PAGES

Lanzuisi, G.; De Rosa, A.; Ghisellini, G.; ...

2012-03-21

We present new Suzaku and Fermi data and re-analysed archival hard X-ray data from the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) and Swift–Burst Alert Telescope (BAT) surveys to investigate the physical properties of the luminous, high-redshift, hard X-ray-selected blazar IGR J22517+2217, through the modelling of its broad-band spectral energy distribution (SED) in two different activity states. Through analysis of new Suzaku data and flux-selected data from archival hard X-ray observations, we build the source SED in two different states, one for the newly discovered flare that occurred in 2005 and one for the following quiescent period. Both SEDs are strongly dominatedmore » by the high-energy hump peaked at 10 20–10 22 Hz, which is at least two orders of magnitude higher than the low-energy (synchrotron) one at 10 11–10 14 Hz and varies by a factor of 10 between the two states. In both states the high-energy hump is modelled as inverse Compton emission between relativistic electrons and seed photons produced externally to the jet, while the synchrotron self-Compton component is found to be negligible. In our model the observed variability can be accounted for by a variation of the total number of emitting electrons and by a dissipation region radius changing from inside to outside the broad-line region as the luminosity increases. In its flaring activity, IGR J22517+2217 is revealed as one of the most powerful jets among the population of extreme, hard X-ray-selected, high-redshift blazars observed so far.« less
DERIVATION OF A RELATION FOR THE STEEPENING OF TeV-SELECTED BLAZAR {gamma}-RAY SPECTRA WITH ENERGY AND REDSHIFT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stecker, Floyd William; Scully, Sean T.

2010-02-01

We derive a relation for the steepening of blazar {gamma}-ray spectra between the multi-GeV Fermi energy range and the TeV energy range observed by atmospheric Cerenkov telescopes. The change in spectral index is produced by two effects: (1) an intrinsic steepening, independent of redshift, owing to the properties of emission and absorption in the source and (2) a redshift-dependent steepening produced by intergalactic pair production interactions of blazar {gamma}-rays with low-energy photons of the 'intergalactic background light' (IBL). Given this relation, with good enough data on the mean {gamma}-ray spectral energy distribution of TeV-selected BL Lac objects, the redshift evolutionmore » of the IBL can, in principle, be determined independently of stellar evolution models. We apply our relation to the results of new Fermi observations of TeV-selected blazars.« less
Effective spectral index properties for Fermi blazars

NASA Astrophysics Data System (ADS)

Yang, JiangHe; Fan, JunHui; Liu, Yi; Zhang, YueLian; Tuo, ManXian; Nie, JianJun; Yuan, YuHai

2018-05-01

Blazars are a special subclass of active galactic nuclei with extreme observation properties. This subclass can be divided into two further subclasses of flat spectrum radio quasars (FSRQs) and BL Lacertae objects (BL Lacs) according to their emission line features. To compare the spectral properties of FSRQs and BL Lacs, the 1.4 GHz radio, optical R-band, 1 keV X-ray, and 1 GeV γ-ray flux densities for 1108 Fermi blazars are calculated to discuss the properties of the six effective spectral indices of radio to optical ( α RO), radio to X-ray ( α RX), radio to γ ray ( α Rγ), optical to X-ray ( α OX), optical to γ ray ( α Oγ), and X-ray to γ ray ( α Xγ). The main results are as follows: For the averaged effective spectral indices, \\overline {{α _{OX}}} > \\overline {{α _{Oγ }}} > \\overline {{α _{Xγ }}} > \\overline {{α _{Rγ }}} > \\overline {{α _{RX}}} > \\overline {{α _{RO}}} for samples of whole blazars and BL Lacs; \\overline {{α _{Xγ }}} ≈ \\overline {{α _{Rγ }}} ≈ \\overline {{α _{RX}}} for FSRQs and low-frequency-peaked BL Lacs (LBLs); and \\overline {{α _{OX}}} ≈ \\overline {{α _{Oγ }}} ≈ \\overline {{α _{Xγ }}} for high-synchrotron-frequency-peaked BL Lacs (HBLs). The distributions of the effective spectral indices involving optical emission ( α RO, α OX, and α Oγ) for LBLs are different from those for FSRQs, but if the effective spectral index does not involve optical emission ( α RX, α Rγ, and α Xγ), the distributions for LBLs and FSRQs almost come from the same parent population. X-ray emissions from blazars include both synchrotron and inverse Compton (IC) components; the IC component for FSRQs and LBLs accounts for a larger proportion than that for HBLs; and the radiation mechanism for LBLs is similar to that for FSRQs, but the radiation mechanism for HBLs is different from that for both FSRQs and LBLs in X-ray bands. The tendency of α Rγ decreasing from LBLs to HBLs suggests that the synchrotron self
Gamma-ray blazars: the combined AGILE and MAGIC views

NASA Astrophysics Data System (ADS)

Persic, M.; De Angelis, A.; Longo, F.; Tavani, M.

The large FOV of the AGILE Gamma-Ray Imaging Detector (GRID), 2.5 sr, will allow the whole sky to be surveyed once every 10 days in the 30 MeV - 50 GeV energy band down to 0.05 Crab Units. This fact gives the opportunity of performing the first flux-limited, high-energy g-ray all-sky survey. The high Galactic latitude point-source population is expected to be largely dominated by blazars. Several tens of blazars are expected to be detected by AGILE (e.g., Costamante & Ghisellini 2002), about half of which accessible to the ground-based MAGIC Cherenkov telescope. The latter can then carry out pointed observations of this subset of AGILE sources in the 50GeV - 10TeV band. Given the comparable sensitivities of AGILE/GRID and MAGIC in adjacent energy bands where the emitted radiation is produced by the same (e.g., SSC) mechanism, we expect that most of these sources can be detected by MAGIC. We expect this broadband g-ray strategy to enable discovery by MAGIC of 10-15 previously unknown TeV blazars.
The cosmic X-ray background-IRAS galaxy correlation and the local X-ray volume emissivity

NASA Technical Reports Server (NTRS)

Miyaji, Takamitsu; Lahav, Ofer; Jahoda, Keith; Boldt, Elihu

1994-01-01

We have cross-correlated the galaxies from the IRAS 2 Jy redshift survey sample and the 0.7 Jy projected sample with the all-sky cosmic X-ray background (CXB) map obtained from the High Energy Astronomy Observatory (HEAO) 1 A-2 experiment. We have detected a significant correlation signal between surface density of IRAS galaxies and the X-ray background intensity, with W(sub xg) = (mean value of ((delta I)(delta N)))/(mean value of I)(mean value of N)) of several times 10(exp -3). While this correlation signal has a significant implication for the contribution of the local universe to the hard (E greater than 2 keV) X-ray background, its interpretation is model-dependent. We have developed a formulation to model the cross-correlation between CXB surface brightness and galaxy counts. This includes the effects of source clustering and the X-ray-far-infrared luminosity correlation. Using an X-ray flux-limited sample of active galactic nuclei (AGNs), which has IRAS 60 micrometer measurements, we have estimated the contribution of the AGN component to the observed CXB-IRAS galaxy count correlations in order to see whether there is an excess component, i.e., contribution from low X-ray luminosity sources. We have applied both the analytical approach and Monte Carlo simulations for the estimations. Our estimate of the local X-ray volume emissivity in the 2-10 keV band is rho(sub x) approximately = (4.3 +/- 1.2) x 10(exp 38) h(sub 50) ergs/s/cu Mpc, consistent with the value expected from the luminosity function of AGNs alone. This sets a limit to the local volume emissivity from lower luminosity sources (e.g., star-forming galaxies, low-ionization nuclear emission-line regions (LINERs)) to rho(sub x) less than or approximately = 2 x 10(exp 38) h(sub 50) ergs/s/cu Mpc.
Time-Resolved SEDs of Blazars Flares

NASA Astrophysics Data System (ADS)

Kreikenbohm, A.; Dorner, D.; Kadler, M.; Beuchert, T.; Kreter, M.; Kreykenbohm, I.; Langejahn, M.; Leiter, K.; Mannheim, K.; Wilms, J.

2017-10-01

The origin of very-high-energy gamma rays in active galactic nuclei is still under debate. While snapshots of spectral energy distributions (SEDs) can usually be explained with simple competing models, the true emission mechanisms may be revealed from dynamic SED studies during exceptional source states. Based on the FACT monitoring program, we have set up a multiwavelength target-of-opportunity program which allows us to measure time-resolved SEDs during blazar flares. While the FACT and Fermi measurements cover the high energy peak continuously, X-ray observations with INTEGRAL and XMM-Newton are triggered in case of a bright flare. To distinguish orphan flares from time lags between the energy bands, this is combined with an X-ray monitoring with the Swift satellite. In December 2015, observations of the X-ray telescopes Swift and INTEGRAL were triggered during a moderately-high flux state of the TeV blazar Mrk 421. Pre- and post observations in X-rays are available from Swift-XRT. In this presentation, the results from the Mrk 421 ToO observations will be summarized.
High-redshift Blazars through NuSTAR eyes

DOE PAGES

Marcotulli, L.; Paliya, V. S.; Ajello, M.; ...

2017-04-20

The most powerful sources among the blazar family are MeV blazars. Often detected at z > 2, they usually display high X- and γ-ray luminosities, larger-than-average jet powers, and black hole masses ≳10 9 M ⊙. In the present work, we perform a multiwavelength study of three high-redshift blazars: 3FGL J0325.5+2223 (z = 2.06), 3FGL J0449.0+1121 (z = 2.15), and 3FGL J0453.2–2808 (z = 2.56), analyzing quasi-simultaneous data from GROND, Swift-UVOT and XRT, Nuclear Spectroscopic Telescope Array (NuSTAR), and Fermi-LAT. Our main focus is on the hard X-ray band recently unveiled by NuSTAR (3–79 keV) where these objects show amore » hard spectrum that enables us to constrain the inverse Compton (IC) peak and the jet power. We found that all three targets resemble the most powerful blazars, with the synchrotron peak located in the submillimeter range and the IC peak in the MeV range, and therefore belong to the MeV blazar class. Using a simple one-zone leptonic emission model to reproduce the spectral energy distributions, we conclude that a simple combination of synchrotron and accretion disk emission reproduces the infrared–optical spectra, while the X-ray to γ-ray part is well reproduced by the IC scattering of low-energy photons supplied by the broad-line region. The black hole masses for each of the three sources are calculated to be ≳4 × 10 8 M ⊙. Finally, the three studied sources have jet power at the level of, or beyond, the accretion luminosity.« less
Mitigation of hard x-ray background in backlit pinhole imagers

DOE PAGES

Fein, J. R.; Keiter, P. A.; Holloway, J. P.; ...

2016-09-16

Experiments were performed to mitigate the hard x-ray background commonly observed in backlit pinhole imagers. The material of the scaffold holding the primary backlighter foil was varied to reduce the laser-plasma instabilities responsible for hot electrons and resulting hard x-ray background. Radiographic measurements with image plates showed a factor of >25 decrease in x-rays between 30 and 67 keV when going from a plastic to Al or V scaffold. Here, a potential design using V scaffold offers a signal-to-background ratio of 6:1, a factor of 2 greater than using the bare plastic scaffold.
In-flight calibration of Hitomi Soft X-ray Spectrometer. (1) Background

NASA Astrophysics Data System (ADS)

Kilbourne, Caroline A.; Sawada, Makoto; Tsujimoto, Masahiro; Angellini, Lorella; Boyce, Kevin R.; Eckart, Megan E.; Fujimoto, Ryuichi; Ishisaki, Yoshitaka; Kelley, Richard L.; Koyama, Shu; Leutenegger, Maurice A.; Loewenstein, Michael; McCammon, Dan; Mitsuda, Kazuhisa; Nakashima, Shinya; Porter, Frederick S.; Seta, Hiromi; Takei, Yoh; Tashiro, Makoto S.; Terada, Yukikatsu; Yamada, Shinya; Yamasaki, Noriko Y.

2018-03-01

The X-Ray Spectrometer (XRS) instrument of Suzaku provided the first measurement of the non-X-ray background (NXB) of an X-ray calorimeter spectrometer, but the data set was limited. The Soft X-ray Spectrometer (SXS) instrument of Hitomi was able to provide a more detailed picture of X-ray calorimeter background, with more than 360 ks of data while pointed at the Earth, and a comparable amount of blank-sky data. These data are important not only for analyzing SXS science data, but also for categorizing the contributions to the NXB in X-ray calorimeters as a class. In this paper, we present the contributions to the SXS NXB, the types and effectiveness of the screening, the interaction of the screening with the broad-band redistribution, and the residual background spectrum as a function of magnetic cut-off rigidity. The orbit-averaged SXS NXB in the range 0.3-12 keV was 4 × 10-2 counts s-1 cm-2. This very low background in combination with groundbreaking spectral resolution gave SXS unprecedented sensitivity to weak spectral lines.
A NEW RESULT ON THE ORIGIN OF THE EXTRAGALACTIC GAMMA-RAY BACKGROUND

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou Ming; Wang Jiancheng, E-mail: mzhou@ynao.ac.cn

2013-06-01

In this paper, we repeatedly use the method of image stacking to study the origin of the extragalactic gamma-ray background (EGB) at GeV bands, and find that the Faint Images of the Radio Sky at Twenty centimeters (FIRST) sources undetected by the Large Area Telescope on the Fermi Gamma-ray Space Telescope can contribute about (56 {+-} 6)% of the EGB. Because FIRST is a flux-limited sample of radio sources with incompleteness at the faint limit, we consider that point sources, including blazars, non-blazar active galactic nuclei, and starburst galaxies, could produce a much larger fraction of the EGB.
RoboPol: the optical polarization of gamma-ray-loud and gamma-ray-quiet blazars

NASA Astrophysics Data System (ADS)

Angelakis, E.; Hovatta, T.; Blinov, D.; Pavlidou, V.; Kiehlmann, S.; Myserlis, I.; Böttcher, M.; Mao, P.; Panopoulou, G. V.; Liodakis, I.; King, O. G.; Baloković, M.; Kus, A.; Kylafis, N.; Mahabal, A.; Marecki, A.; Paleologou, E.; Papadakis, I.; Papamastorakis, I.; Pazderski, E.; Pearson, T. J.; Prabhudesai, S.; Ramaprakash, A. N.; Readhead, A. C. S.; Reig, P.; Tassis, K.; Urry, M.; Zensus, J. A.

2016-12-01

We present average R-band optopolarimetric data, as well as variability parameters, from the first and second RoboPol observing season. We investigate whether gamma-ray-loud and gamma-ray-quiet blazars exhibit systematic differences in their optical polarization properties. We find that gamma-ray-loud blazars have a systematically higher polarization fraction (0.092) than gamma-ray-quiet blazars (0.031), with the hypothesis of the two samples being drawn from the same distribution of polarization fractions being rejected at the 3σ level. We have not found any evidence that this discrepancy is related to differences in the redshift distribution, rest-frame R-band luminosity density, or the source classification. The median polarization fraction versus synchrotron-peak-frequency plot shows an envelope implying that high-synchrotron-peaked sources have a smaller range of median polarization fractions concentrated around lower values. Our gamma-ray-quiet sources show similar median polarization fractions although they are all low-synchrotron-peaked. We also find that the randomness of the polarization angle depends on the synchrotron peak frequency. For high-synchrotron-peaked sources, it tends to concentrate around preferred directions while for low-synchrotron-peaked sources, it is more variable and less likely to have a preferred direction. We propose a scenario which mediates efficient particle acceleration in shocks and increases the helical B-field component immediately downstream of the shock.
AGILE detection of enhanced gamma-ray emission from the blazar 3C 279

NASA Astrophysics Data System (ADS)

Cardillo, M.; Verrecchia, F.; Pittori, C.; Lucarelli, F.; Ursi, A.; Piano, G.; Minervini, G.; Bulgarelli, A.; Fioretti, V.; Parmiggiani, N.; Tavani, M.; Munar-Adrover, P.; Donnarumma, I.; Vercellone, S.; Striani, E.; Cardillo, M.; Gianotti, F.; Trifoglio, M.; Giuliani, A.; Mereghetti, S.; Caraveo, P.; Perotti, F.; Chen, A.; Argan, A.; Costa, E.; Del Monte, E.; Evangelista, Y.; Feroci, M.; Lazzarotto, F.; Lapshov, I.; Pacciani, L.; Soffitta, P.; Sabatini, S.; Vittorini, V.; Pucella, G.; Rapisarda, M.; Di Cocco, G.; Fuschino, F.; Galli, M.; Labanti, C.; Marisaldi, M.; Pellizzoni, A.; Pilia, M.; Trois, A.; Barbiellini, G.; Vallazza, E.; Longo, F.; Morselli, A.; Picozza, P.; Prest, M.; Lipari, P.; Zanello, D.; Cattaneo, P. W.; Rappoldi, A.; Colafrancesco, S.; Ferrari, A.; Paoletti, F.; Antonelli, A.; Giommi, P.; Salotti, L.; Valentini, G.; D'Amico, F.

2018-06-01

AGILE is detecting enhanced gamma-ray emission above 100 MeV from the blazar 3C 279. Integrating from 2018-06-03 07:56:19 UT to 2018-06-05 07:56:19 UT, a preliminary maximum likelihood analysis yields a detection at a flux F(E > 100 MeV)=(7.0 +/- 1.5) x 10^-6 ph cm^-2 s^-1 and a significance greater than 7 sigma.
Blazar 3C 66A: Another extragalactic source of ultra-high-energy gamma-ray photons

NASA Astrophysics Data System (ADS)

Neshpor, Yu. I.; Stepanyan, A. A.; Kalekin, O. P.; Fomin, V. P.; Chalenko, N. N.; Shitov, V. G.

1998-03-01

he observations of the object 3C 66A which were carried out with the GT-48 gamma-ray telescope at the Crimean Astrophysical Observatory in November-December 1996 revealed a flux of ultra-high-energy (>10^12 eV) gamma-ray photons from this blazar. According to preliminary estimates, the photon flux is (31) 10^11 photons cm^-2 s^-1. The blazar 3C 66A is the third extragalactic object from which a flux of ultra- high-energy gamma-ray photons was detected. Fluxes of gamma-ray photons were previously detected from the galaxies Mk 421 and Mk 501 at the Whipple observatory. This result provides further evidence that active processes proceed in blazars which are accompanied by the generation of cosmic rays responsible for the emission of gamma-ray photons.

Modeling the emission processes in blazars

NASA Astrophysics Data System (ADS)

Böttcher, Markus

2007-06-01

Blazars are the most violent steady/recurrent sources of high-energy gamma-ray emission in the known Universe. They are prominent emitters of electromagnetic radiation throughout the entire electromagnetic spectrum. The observable radiation most likely originates in a relativistic jet oriented at a small angle with respect to the line of sight. This review starts out with a general overview of the phenomenology of blazars, including results from a recent multiwavelength observing campaign on 3C279. Subsequently, issues of modeling broadband spectra will be discussed. Spectral information alone is not sufficient to distinguish between competing models and to constrain essential parameters, in particular related to the primary particle acceleration and radiation mechanisms in the jet. Short-term spectral variability information may help to break such model degeneracies, which will require snap-shot spectral information on intraday time scales, which may soon be achievable for many blazars even in the gamma-ray regime with the upcoming GLAST mission and current advances in Atmospheric Cherenkov Telescope technology. In addition to pure leptonic and hadronic models of gamma-ray emission from blazars, leptonic/hadronic hybrid models are reviewed, and the recently developed hadronic synchrotron mirror model for TeV γ-ray flares which are not accompanied by simultaneous X-ray flares (“orphan TeV flares”) is revisited.
Extreme Blazars Studied with Fermi-LAT and Suzaku: 1ES 0347-121 and Blazar Candidate HESS J1943+213

NASA Astrophysics Data System (ADS)

Tanaka, Y. T.; Stawarz, Ł.; Finke, J.; Cheung, C. C.; Dermer, C. D.; Kataoka, J.; Bamba, A.; Dubus, G.; De Naurois, M.; Wagner, S. J.; Fukazawa, Y.; Thompson, D. J.

2014-06-01

We report on our study of high-energy properties of two peculiar TeV emitters: the "extreme blazar" 1ES 0347-121 and the "extreme blazar candidate" HESS J1943+213 located near the Galactic plane. Both objects are characterized by quiescent synchrotron emission with flat spectra extending up to the hard X-ray range, and both were reported to be missing GeV counterparts in the Fermi Large Area Telescope (LAT) two-year Source Catalog. We analyze a 4.5 yr accumulation of the Fermi-LAT data, resulting in the detection of 1ES 0347-121 in the GeV band, as well as in improved upper limits for HESS J1943+213. We also present the analysis results of newly acquired Suzaku data for HESS J1943+213. The X-ray spectrum is well represented by a single power law extending up to 25 keV with photon index 2.00 ± 0.02 and a moderate absorption in excess of the Galactic value, which is in agreement with previous X-ray observations. No short-term X-ray variability was found over the 80 ks duration of the Suzaku exposure. Under the blazar hypothesis, we modeled the spectral energy distributions of 1ES 0347-121 and HESS J1943+213, and we derived constraints on the intergalactic magnetic field strength and source energetics. We conclude that although the classification of HESS J1943+213 has not yet been determined, the blazar hypothesis remains the most plausible option since, in particular, the broadband spectra of the two analyzed sources along with the source model parameters closely resemble each other, and the newly available Wide-field Infrared Survey Explorer and UKIRT Infrared Deep Sky Survey data for HESS J1943+213 are consistent with the presence of an elliptical host at the distance of approximately ~600 Mpc.
Roma-BZCAT: a multifrequency catalogue of blazars

NASA Astrophysics Data System (ADS)

Massaro, E.; Giommi, P.; Leto, C.; Marchegiani, P.; Maselli, A.; Perri, M.; Piranomonte, S.; Sclavi, S.

2009-02-01

We present a new catalogue of blazars based on multifrequency surveys and on an extensive review of the literature. Blazars are classified as BL Lacertae objects, as flat spectrum radio quasars or as blazars of uncertain/transitional type. Each object is identified by a root name, coded as BZB, BZQ and BZU for these three subclasses respectively, and by its coordinates. This catalogue is being built as a tool useful for the identification of the extragalactic sources that will be detected by present and future experiments for X and gamma-ray astronomy, like Swift, AGILE, Fermi-GLAST and Simbol-X. An electronic version is available from the ASI Science Data Center web site at http://www.asdc.asi.it/bzcat.
Cross-correlation of the X-ray background with nearby galaxies

NASA Technical Reports Server (NTRS)

Jahoda, Keith; Mushotzky, Richard F.; Boldt, Elihu; Lahav, Ofer

1991-01-01

The detection of a signal in the cross-correlation of the diffuse 2-10 keV HEAO 1 A-2 X-ray surface brightness with the galaxy surface density derived from diameter-limited samples from the Uppsala General Catalogue is reported. An ad hoc relationship between the X-ray flux and the galaxy counts is used to estimate the local X-ray volume emissivity at 2.8 + or - 1.0 x 10 to the 38th ergs/s/cu Mpc. This result implies that unevolved populations of X-ray sources correlated with present-epoch galaxies can contribute only 13 + or - 5 percent of the cosmic X-ray background.
RoboPol: connection between optical polarization plane rotations and gamma-ray flares in blazars

NASA Astrophysics Data System (ADS)

Blinov, D.; Pavlidou, V.; Papadakis, I.; Kiehlmann, S.; Liodakis, I.; Panopoulou, G. V.; Angelakis, E.; Baloković, M.; Hovatta, T.; King, O. G.; Kus, A.; Kylafis, N.; Mahabal, A.; Maharana, S.; Myserlis, I.; Paleologou, E.; Papamastorakis, I.; Pazderski, E.; Pearson, T. J.; Ramaprakash, A.; Readhead, A. C. S.; Reig, P.; Tassis, K.; Zensus, J. A.

2018-02-01

We use results of our 3 yr polarimetric monitoring programme to investigate the previously suggested connection between rotations of the polarization plane in the optical emission of blazars and their gamma-ray flares in the GeV band. The homogeneous set of 40 rotation events in 24 sources detected by RoboPol is analysed together with the gamma-ray data provided by Fermi-LAT. We confirm that polarization plane rotations are indeed related to the closest gamma-ray flares in blazars and the time lags between these events are consistent with zero. Amplitudes of the rotations are anticorrelated with amplitudes of the gamma-ray flares. This is presumably caused by higher relativistic boosting (higher Doppler factors) in blazars that exhibit smaller amplitude polarization plane rotations. Moreover, the time-scales of rotations and flares are marginally correlated.
Multiwavelength Study of Gamma-Ray Bright Blazars

NASA Astrophysics Data System (ADS)

Morozova, Daria; Larionov, V. M.; Hagen-Thorn, V. A.; Jorstad, S. G.; Marscher, A. P.; Troitskii, I. S.

2011-01-01

We investigate total intensity radio images of 6 gamma-ray bright blazars (BL Lac, 3C 279, 3C 273, W Com, PKS 1510-089, and 3C 66A) and their optical and gamma-ray light curves to study connections between gamma-ray and optical brightness variations and changes in the parsec-scale radio structure. We use high-resolution maps obtained by the BU group at 43 GHz with the VLBA, optical light curves constructed by the St.Petersburg State U. (Russia) team using measurements with the 0.4 m telescope of St.Petersburg State U. (LX200) and the 0.7 m telescope of the Crimean Astrophysical Observatory (AZT-8), and gamma-ray light curves, which we have constructed with data provided by the Fermi Large Area Telescope. Over the period from August 2008 to November 2009, superluminal motion is found in all 6 objects with apparent speed ranging from 2c to 40c. The blazars with faster apparent speeds, 3C 273, 3C 279, PKS 1510-089, and 3C 66A, exhibit stronger variability of the gamma-ray emission. There is a tendency for sources with sharply peaked gamma-ray flares to have faster jet speed than sources with gamma-ray light curves with no sharp peaks. Gamma-ray light curves with sharply peaked gamma-ray flares possess a stronger gamma-ray/optical correlations. The research at St.Petersburg State U. was funded by the Minister of Education and Science of the Russian Federation (state contract N#P123). The research at BU was funded in part by NASA Fermi Guest Investigator grant NNX08AV65G and by NSF grant AST-0907893. The VLBA is an instrument of the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Spectrum of Very High Energy Gamma-Rays from the blazar 1ES 1959+650 during Flaring Activity in 2002

NASA Astrophysics Data System (ADS)

Daniel, M. K.; Badran, H. M.; Bond, I. H.; Boyle, P. J.; Bradbury, S. M.; Buckley, J. H.; Carter-Lewis, D. A.; Catanese, M.; Celik, O.; Cogan, P.; Cui, W.; D'Vali, M.; de la Calle Perez, I.; Duke, C.; Falcone, A.; Fegan, D. J.; Fegan, S. J.; Finley, J. P.; Fortson, L. F.; Gaidos, J. A.; Gammell, S.; Gibbs, K.; Gillanders, G. H.; Grube, J.; Hall, J.; Hall, T. A.; Hanna, D.; Hillas, A. M.; Holder, J.; Horan, D.; Humensky, T. B.; Jarvis, A.; Jordan, M.; Kenny, G. E.; Kertzman, M.; Kieda, D.; Kildea, J.; Knapp, J.; Kosack, K.; Krawczynski, H.; Krennrich, F.; Lang, M. J.; Le Bohec, S.; Linton, E.; Lloyd-Evans, J.; Milovanovic, A.; Moriarty, P.; Müller, D.; Nagai, T.; Nolan, S.; Ong, R. A.; Pallassini, R.; Petry, D.; Power-Mooney, B.; Quinn, J.; Quinn, M.; Ragan, K.; Rebillot, P.; Reynolds, P. T.; Rose, H. J.; Schroedter, M.; Sembroski, G. H.; Swordy, S. P.; Syson, A.; Vassiliev, V. V.; Wakely, S. P.; Walker, G.; Weekes, T. C.; Zweerink, J.

2005-03-01

The blazar 1ES 1959+650 was observed in a flaring state with the Whipple 10 m Imaging Atmospheric Cerenkov Telescope in 2002 May. A spectral analysis has been carried out on the data from that time period, and the resulting very high energy gamma-ray spectrum (E>=316 GeV) can be well fitted by a power law of differential spectral index α=2.78+/-0.12stat+/-0.21sys. On 2002 June 4, the source flared dramatically in the gamma-ray range without any coincident increase in the X-ray emission, providing the first unambiguous example of an ``orphan'' gamma-ray flare from a blazar. The gamma-ray spectrum for these data can also be described by a simple power-law fit with α=2.82+/-0.15stat+/-0.30sys. There is no compelling evidence for spectral variability or for any cutoff to the spectrum.
Preliminary assessment of the ATHENA/WFI non-X-ray background

NASA Astrophysics Data System (ADS)

Perinati, Emanuele; Barbera, Marco; Diebold, Sebastian; Guzman, Alejandro; Santangelo, Andrea; Tenzer, Chris

2017-12-01

We present a preliminary assessment of the non-X-ray background for the WFI on board ATHENA conducted at IAAT in the context of the collaborative background and radiation damage working group activities. Our main result is that in the baseline configuration originally assumed for the camera the requirement on the level of non-X-ray background could not be met. In light of the results of Geant4 simulations we propose and discuss a possible optimization of the camera design and pinpoint some open issues to be addressed in the next phase of investigation. One of these concerns the possible contribution to the non-X-ray background from soft protons and ions funneled to the focal plane through the optics. This is not quantified at this stage, here we just briefly report on our ongoing activities aimed at validating the mechanisms of proton scattering at grazing incidence.
The Spectral Energy Distribution of Fermi Bright Blazars

NASA Technical Reports Server (NTRS)

Abdo, A. A.; Ackermann, M.; Agudo, I.; Ajello, M.; Aller, H. D.; Aller, M. F.; Angelakis, E.; Arkharov, A. A.; Axelsson, M.; Bach, U.;

2010-01-01

We have conducted a detailed investigation of the broadband spectral properties of the gamma-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi gamma-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray /gamma-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these gamma-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log v-log v Fv representation, the typical broadband spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SED to characterize the peak intensity of both the low- and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, alpha(sub ro) , and optical to X-ray, alpha(sub ox), spectral slopes) and from the gamma-ray spectral index. Our data show that the synchrotron peak frequency (v(sup S) (sub peak)) is positioned between 10(exp 12.5) and 10(exp 14) Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 10(exp 13) and 10(exp 17) Hz in featureless BL Lacertae objects. We find that the gamma-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron-inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than

The Spectral Energy Distribution of Fermi bright blazars

DOE PAGES

Abdo, A. A.; Ackermann, M.; Agudo, I.; ...

2010-05-13

We have conducted a detailed investigation of the broadband spectral properties of the γ-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi γ-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray/γ-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these γ-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log ν-log ν F ν representation, the typical broadband spectral signaturesmore » normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. Here, we have used these SED to characterize the peak intensity of both the low- and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, α ro, and optical to X-ray, α ox, spectral slopes) and from the γ-ray spectral index. Our data show that the synchrotron peak frequency (ν S peak) is positioned between 10 12.5 and 10 14.5 Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 10 13 and 10 17 Hz in featureless BL Lacertae objects. We find that the γ-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron-inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than 50% of known radio bright high energy peaked
Extreme Blazars Studied With Fermi -Lat And Suzaku : 1es 0347–121 And Blazar Candidate Hess J1943+213

DOE PAGES

Tanaka, Y. T.; Stawarz, Ł.; Finke, J.; ...

2014-05-14

We report on our study of high-energy properties of two peculiar TeV emitters: the “extreme blazar" 1ES 0347-121 and the “extreme blazar candidate" HESS J1943+213 located near the Galactic Plane. Both objects are characterized by quiescent synchrotron emission with flat spectra extending up to the hard X-ray range, and both were reported to be missing GeV counterparts in the Fermi-LAT 2–year Source Catalog. We analyze a 4.5 year accumulation of the Fermi-LAT data, resulting in the detection of 1ES 0347-121 in the GeV band, as well as in improved upper limits for HESS J1943+213. We also present the analysis resultsmore » of newly acquired Suzaku data for HESS J1943+213. The X-ray spectrum is well represented by a single power law extending up to 25 keV with photon index 2.00±0.02 and a moderate absorption in excess of the Galactic value, in agreementwith previous X-ray observations. No short-term X-ray variability was found over the 80 ks duration of the Suzaku exposure. Under the blazar hypothesis, we modeled the spectral energy distributions of 1ES 0347-121 and HESS J1943+213, and derived constraints on the intergalactic magnetic field strength and source energetics. We conclude that although the classification of HESS J1943+213 has not yet been determined, the blazar hypothesis remains the most plausible option, since in particular the broad-band spectra of the two analyzed sources along with the source model parameters closely resemble each other, and the newly available WISE and UKIDSS data for HESS J1943+213 are consistent with the presence of an elliptical host at the distance of approximatel ~ 600Mpc.« less
VLBI Monitoring of the Bright Gamma-Ray Blazar PKS 0537-441

DTIC Science & Technology

2010-06-01

active state by Fermi. It is one of the brightest ,),-ray blazars detected in the southern sky so far. The TANAMI (Tracking Active Galactic Nuclei...Active Galactic Nuclei with Austral Milliarcsecond Interferometry (TAN AMI) program (Ojha et a1. (2010» has been monitoring south- ern sky blazars such...Telescope. Studying Active Galactic Nuclei (AGN) at different wavelengths is crucial in order to understand AGN-jets and differentiate between
The Diffuse Soft X-ray Background: Trials and Tribulations

NASA Astrophysics Data System (ADS)

Ulmer, Melville P.

2013-01-01

I joined the University of Wisconsin-Madison sounding rocket group at its inception. It was an exciting time, as nobody knew what the X-ray sky looked like. Our group focused on the soft X-ray background, and built proportional counters with super thin (2 micron thick) windows. As the inter gas pressure of the counters was about 1 atmosphere, it was no mean feat to get payload to launch without the window bursting. On top of that we built all our own software from space solutions to unfolding the spectral data. For we did it then as now: Our computer code modeled the detector response and then folded various spectral shapes through the response and compared the results with the raw data. As far as interpretation goes, here are examples of how one can get things wrong: The Berkeley group published a paper of the soft X-ray background that disagreed with ours. Why? It turned out they had **assumed** the galactic plane was completely opaque to soft X-ray and hence corrected for detector background that way. It turns out that the ISM emits in soft X-rays! Another example was the faux pas of the Calgary group. They didn’t properly shield their detector from the sounding rocket telemetry. Thus they got an enormous signal, which to our amusement some (ambulance chaser) theoreticians tried to explain! So back then as now, mistakes were made, but at least we all knew how our X-ray systems worked from soup (the detectors) to nuts (the data analysis code) where as toady “anybody” with a good idea but only a vague inkling of how detectors, mirrors and software work, can be an X-ray astronomer. On the one hand, this has made the field accessible to all, and on the other, errors in interpretation can be made as the X-ray telescope user can fall prey to running black box software. Furthermore with so much funding going into supporting observers, there is little left to make the necessary technology advances or keep the core expertise in place to even to stay even with
Extremes of the jet–accretion power relation of blazars, as explored by NuSTAR

DOE PAGES

Sbarrato, T.; Ghisellini, G.; Tagliaferri, G.; ...

2016-07-18

Hard X-ray observations are crucial to study the non-thermal jet emission from high-redshift, powerful blazars. We observed two bright z > 2 flat spectrum radio quasars (FSRQs) in hard X-rays to explore the details of their relativistic jets and their possible variability. S5 0014+81 (at z = 3.366) and B0222+185 (at z=2.690) have been observed twice by the Nuclear Spectroscopic Telescope Array (NuSTAR) simultaneously with Swift/XRT, showing different variability behaviors. We found that NuSTAR is instrumental to explore the variability of powerful high-redshift blazars, even when no gamma-ray emission is detected. The two sources have proven to have respectively themore » most luminous accretion disk and the most powerful jet among known blazars. Furthermore, thanks to these properties, they are located at the extreme end of the jet-accretion disk relation previously found for gamma-ray detected blazars, to which they are consistent.« less
Extremes of the jet–accretion power relation of blazars, as explored by NuSTAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sbarrato, T.; Ghisellini, G.; Tagliaferri, G.

Hard X-ray observations are crucial to study the non-thermal jet emission from high-redshift, powerful blazars. We observed two bright z > 2 flat spectrum radio quasars (FSRQs) in hard X-rays to explore the details of their relativistic jets and their possible variability. S5 0014+81 (at z = 3.366) and B0222+185 (at z=2.690) have been observed twice by the Nuclear Spectroscopic Telescope Array (NuSTAR) simultaneously with Swift/XRT, showing different variability behaviors. We found that NuSTAR is instrumental to explore the variability of powerful high-redshift blazars, even when no gamma-ray emission is detected. The two sources have proven to have respectively themore » most luminous accretion disk and the most powerful jet among known blazars. Furthermore, thanks to these properties, they are located at the extreme end of the jet-accretion disk relation previously found for gamma-ray detected blazars, to which they are consistent.« less
On the origin of gamma-rays in Fermi blazars: beyondthe broad-line region

NASA Astrophysics Data System (ADS)

Costamante, L.; Cutini, S.; Tosti, G.; Antolini, E.; Tramacere, A.

2018-07-01

The gamma-ray emission in broad-line blazars is generally explained as inverse Compton (IC) radiation of relativistic electrons in the jet scattering optical-UV photons from the broad-line region (BLR), the so-called BLR external Compton (EC) scenario. We test this scenario on the Fermi gamma-ray spectra of 106 broad-line blazars detected with the highest significance or largest BLR, by looking for cut-off signatures at high energies compatible with γ-γ interactions with BLR photons. We do not find evidence for the expected BLR absorption. For 2/3 of the sources, we can exclude any significant absorption (τmax < 1), while for the remaining 1/3 the possible absorption is constrained to be 1.5-2 orders of magnitude lower than expected. This result holds also dividing the spectra in high- and low-flux states, and for powerful blazars with large BLR. Only 1 object out of 10 seems compatible with substantial attenuation (τmax > 5). We conclude that for 9 out of 10 objects, the jet does not interact with BLR photons. Gamma-rays seem either produced outside the BLR most of the time, or the BLR is ˜100 × larger than given by reverberation mapping. This means that (i) EC on BLR photons is disfavoured as the main gamma-ray mechanism, versus IC on IR photons from the torus or synchrotron self-Compton; (ii) the Fermi gamma-ray spectrum is mostly intrinsic, determined by the interaction of the particle distribution with the seed-photon spectrum; and (iii) without suppression by the BLR, broad-line blazars can become copious emitters above 100 GeV, as demonstrated by 3C 454.3. We expect the CTA sky to be much richer of broad-line blazars than previously thought.
The soft X-ray diffuse background

NASA Technical Reports Server (NTRS)

Mccammon, D.; Burrows, D. N.; Sanders, W. T.; Kraushaar, W. L.

1982-01-01

Maps of the diffuse X-ray background intensity covering essentially the entire sky with approx. 7 deg spatial resolution are presented for seven energy bands. The data were obtained on a series of ten sounding rocket flights conducted over a seven-year period. The different nature of the spatial distributions in different bands implies at least three distinct origins for the diffuse X-rays, none of which is well-understood. At energies or approx. 2000 eV, an isotropic and presumably extraglalactic 500 and 1000 eV, an origin which is at least partially galactic seems called for. At energies 284 eV, the observed intensity is anticorrelated with neutral hydrogen column density, but we find it unlikely that this anticorrelation is simply due to absorption of an extragalactic or halo source.
Radiation Backgrounds at Cosmic Dawn: X-Rays from Compact Binaries

NASA Astrophysics Data System (ADS)

Madau, Piero; Fragos, Tassos

2017-05-01

We compute the expected X-ray diffuse background and radiative feedback on the intergalactic medium (IGM) from X-ray binaries prior to and during the epoch of reionization. The cosmic evolution of compact binaries is followed using a population synthesis technique that treats separately neutron stars and black hole binaries in different spectral states and is calibrated to reproduce the observed X-ray properties of galaxies at z ≲ 4. Together with an updated empirical determination of the cosmic history of star formation, recent modeling of the stellar mass-metallicity relation, and a scheme for absorption by the IGM that accounts for the presence of ionized H II bubbles during the epoch of reionization, our detailed calculations provide refined predictions of the X-ray volume emissivity and filtered radiation background from “normal” galaxies at z ≳ 6. Radiative transfer effects modulate the background spectrum, which shows a characteristic peak between 1 and 2 keV. Because of the energy dependence of photoabsorption, soft X-ray photons are produced by local sources, while more energetic radiation arrives unattenuated from larger cosmological volumes. While the filtering of X-ray radiation through the IGM slightly increases the mean excess energy per photoionization, it also weakens the radiation intensity below 1 keV, lowering the mean photoionization and heating rates. Numerical integration of the rate and energy equations shows that the contribution of X-ray binaries to the ionization of the bulk IGM is negligible, with the electron fraction never exceeding 1%. Direct He I photoionizations are the main source of IGM heating, and the temperature of the largely neutral medium in between H II cavities increases above the temperature of the cosmic microwave background (CMB) only at z ≲ 10, when the volume filling factor of H II bubbles is already ≳0.1. Therefore, in this scenario, it is only at relatively late epochs that neutral intergalactic hydrogen
Radiation Backgrounds at Cosmic Dawn: X-Rays from Compact Binaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Madau, Piero; Fragos, Tassos

We compute the expected X-ray diffuse background and radiative feedback on the intergalactic medium (IGM) from X-ray binaries prior to and during the epoch of reionization. The cosmic evolution of compact binaries is followed using a population synthesis technique that treats separately neutron stars and black hole binaries in different spectral states and is calibrated to reproduce the observed X-ray properties of galaxies at z ≲ 4. Together with an updated empirical determination of the cosmic history of star formation, recent modeling of the stellar mass–metallicity relation, and a scheme for absorption by the IGM that accounts for the presencemore » of ionized H ii bubbles during the epoch of reionization, our detailed calculations provide refined predictions of the X-ray volume emissivity and filtered radiation background from “normal” galaxies at z ≳ 6. Radiative transfer effects modulate the background spectrum, which shows a characteristic peak between 1 and 2 keV. Because of the energy dependence of photoabsorption, soft X-ray photons are produced by local sources, while more energetic radiation arrives unattenuated from larger cosmological volumes. While the filtering of X-ray radiation through the IGM slightly increases the mean excess energy per photoionization, it also weakens the radiation intensity below 1 keV, lowering the mean photoionization and heating rates. Numerical integration of the rate and energy equations shows that the contribution of X-ray binaries to the ionization of the bulk IGM is negligible, with the electron fraction never exceeding 1%. Direct He i photoionizations are the main source of IGM heating, and the temperature of the largely neutral medium in between H ii cavities increases above the temperature of the cosmic microwave background (CMB) only at z ≲ 10, when the volume filling factor of H ii bubbles is already ≳0.1. Therefore, in this scenario, it is only at relatively late epochs that neutral intergalactic
Studying The Spectral Shape And The X-ray/uv Variability Of Active Galactic Nuclei With Data From Swift And Xmm Archives

NASA Astrophysics Data System (ADS)

Turriziani, Sara

2011-01-01

Many efforts have been made in understanding the underlying origin of variability in Active Galactic Nuclei (AGN), but at present they could give still no conclusive answers. Since a deeper knowledge of variability will enable to understand better the accretion process onto supermassive black holes, I built the first ensemble struction function analysis of the X-ray variability of samples of quasars with data from Swift and XMM-Newton archives in order to study the average properties of their variability. Moreover, it is known that UV and X-ray luminosities of quasars are correlated and recent studies quantified this relation across 5 orders of magnitude. In this context, I presents results on the X-ray/UV ratio from simultaneous observations in UV and X-ray bands of a sample of quasars with data from XMM-Newton archive. Lastly, I will present a complete sample of Swift/SDSS faint blazars and other non-thermal dominated AGNs. I used this sample to calculate the general statistical properties of faint blazars and radio galaxies and in particular their Radio LogN-LogS with fluxes down to 10 mJy, in order to gain knowledge on the contribution to Cosmic Microwave Background (CMB) and gamma-ray background radiation from the faint tail of the radio population. I acknowledge financial support through Grant ASI I/088/06/0.

Background-reducing X-ray multilayer mirror

DOEpatents

Bloch, Jeffrey J.; Roussel-Dupre', Diane; Smith, Barham W.

1992-01-01

Background-reducing x-ray multilayer mirror. A multiple-layer "wavetrap" deposited over the surface of a layered, synthetic-microstructure soft x-ray mirror optimized for reflectivity at chosen wavelengths is disclosed for reducing the reflectivity of undesired, longer wavelength incident radiation incident thereon. In three separate mirror designs employing an alternating molybdenum and silicon layered, mirrored structure overlaid by two layers of a molybdenum/silicon pair anti-reflection coating, reflectivities of near normal incidence 133, 171, and 186 .ANG. wavelengths have been optimized, while that at 304 .ANG. has been minimized. The optimization process involves the choice of materials, the composition of the layer/pairs as well as the number thereof, and the distance therebetween for the mirror, and the simultaneous choice of materials, the composition of the layer/pairs, and their number and distance for the "wavetrap."
Evidence for Secondary Emission as the Origin of Hard Spectra in TeV Blazars

NASA Astrophysics Data System (ADS)

Zheng, Y. G.; Kang, T.

2013-02-01

We develop a model for the possible origin of hard, very high energy (VHE) spectra from a distant blazar. In the model, both the primary photons produced in the source and secondary photons produced outside it contribute to the observed high-energy γ-ray emission. That is, the primary photons are produced through the synchrotron self-Compton process, and the secondary photons are produced through high-energy proton interactions with background photons along the line of sight. We apply the model to a characteristic case of VHE γ-ray emission in the distant blazar 1ES 1101-232. Assuming suitable electron and proton spectra, we obtain excellent fits to the observed spectra of this blazar. This indicated that the surprisingly low attenuation of the high-energy γ-rays, especially the shape of the VHE γ-ray tail of the observed spectra, can be explained by secondary γ-rays produced in interactions of cosmic-ray protons with background photons in intergalactic space.
Resolving the Origin of the Diffuse Soft X-ray Background

NASA Technical Reports Server (NTRS)

Smith, Randall K.; Foster, Adam R.; Edgar, Ricard J.; Brickhouse, Nancy S.; Sanders, Wilton T.

2012-01-01

In January 1993, the Diffuse X-ray Spectrometer (DXS) measured the first high-resolution spectrum of the diffuse soft X-ray background between 44-80A. A line-dominated spectrum characteristic of a 10(exp 6)K collisionally ionized plasma' was expected but while the observed spectrum was clearly line-dominated, no model would fit. Then in 2003 the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) launched and observed the diffuse extreme-ultraviolet (EUV) spectrum between 90- 265A. Although many emission lines were again expected; only Fe IX at 171.1A was detected. The discovery of X-rays from comets led to the realization that heavy ions (Z=6-28) in the solar wind will emit soft X-rays as the ions interact via charge exchange with neutral atoms in the heliosphere and geocorona. Using a new model for solar wind charge exchange (SWCX) emission, we show that the diffuse soft X-ray background can be understood as a combination of emission from charge exchange onto the slow and fast solar wind together with a more distant and diffuse hot (10(exp 6)K) plasma.
High-Redshift Blazars Through NuSTAR Eyes

NASA Astrophysics Data System (ADS)

Marcotulli, Lea

MeV blazars are the most powerful sources among the blazar class. With bolometric luminosities exceeding 1048 erg s-1 and powerful relativistic jets, they are usually detected at high-redshifts (z > 2) and they generally harbor extremely massive black holes (MBH 109Msun). Being able to derive their physical properties such as jet power, accretion disk luminosity, bulk Lorentz factor of the jet (Gamma) and black hole mass, enables us to put constraints in the understanding of this not well sampled class of objects and use them for example to probe the formation of massive black holes in the early universe. In this thesis we have analyzed the broadband emission of three high redshift blazars, focusing on the high energy part of their spectral energy distribution. In fact, being able to obtain hard X-ray data from the recently launched NuSTAR and having gamma-ray detections from the Fermi-LAT, we were able to constrain more accurately the high energy peak of their distribution and therefore more precisely infer their jet power, underlying electron distribution, Gamma and viewing angle (theta v). Gathering optical and UV data allowed us to determine the black hole mass of such powerful objects as well as their accretion disk luminosity. This work has recently been published in ApJ (Marcotulli et al., 2017). In Section 1, the broad family of active galactic nuclei (ANGs) and their main physical characteristics are introduced, with a focus on the subclass of blazars and specifically MeV blazars. In Section 2, the main instruments used in our research to gather and analyze data are described, with a particular interest on imaging in the hard X-ray regime. Section 3 contains the data analysis description, the results obtained combining the observations with a one-zone leptonic emission model and the discussion on our findings. In Section 4 we report our conclusions and present an outlook on future MeV blazars studies possibilities. Appendix A, B and C contain an overlook
INVERSE COMPTON X-RAY EMISSION FROM TeV BLAZAR MRK 421 DURING A HISTORICAL LOW-FLUX STATE OBSERVED WITH NuSTAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kataoka, Jun; Stawarz, Łukasz, E-mail: kataoka.jun@waseda.jp

2016-08-10

We report on the detection of excess hard X-ray emission from the TeV BL Lac object Mrk 421 during the historical low-flux state of the source in 2013 January. Nuclear Spectroscopic Telescope Array observations were conducted four times between MJD 56294 and MJD 56312 with a total exposure of 80.9 ks. The source flux in the 3–40 keV range was nearly constant, except for MJD 56307 when the average flux level increased by a factor of three. Throughout the exposure, the X-ray spectra of Mrk 421 were well represented by a steep power-law model with a photon index of Γmore » ≃ 3.1, although a significant excess was noted above 20 keV in the MJD 56302 data when the source was in its faintest state. Moreover, Mrk 421 was detected at more than the 4 σ level in the 40–79 keV count maps for both MJD 56307 and MJD 56302 but not during the remaining two observations. The detected excess hard X-ray emission connects smoothly with the extrapolation of the high-energy γ -ray continuum of the blazar constrained by Fermi -LAT during source quiescence. These findings indicate that while the overall X-ray spectrum of Mrk 421 is dominated by the highest-energy tail of the synchrotron continuum, the variable excess hard X-ray emission above 20 keV (on the timescale of a week) is related to the inverse Compton emission component. We discuss the resulting constraints on the variability and spectral properties of the low-energy segment of the electron energy distribution in the source.« less
On the origin of gamma rays in Fermi blazars: beyond the broad line region.

NASA Astrophysics Data System (ADS)

Costamante, L.; Cutini, S.; Tosti, G.; Antolini, E.; Tramacere, A.

2018-05-01

The gamma-ray emission in broad-line blazars is generally explained as inverse Compton (IC) radiation of relativistic electrons in the jet scattering optical-UV photons from the Broad Line Region (BLR), the so-called BLR External Compton scenario. We test this scenario on the Fermi gamma-ray spectra of 106 broad-line blazars detected with the highest significance or largest BLR, by looking for cut-off signatures at high energies compatible with γ-γ interactions with BLR photons. We do not find evidence for the expected BLR absorption. For 2/3 of the sources, we can exclude any significant absorption (τmax < 1), while for the remaining 1/3 the possible absorption is constrained to be 1.5-2 orders of magnitude lower than expected. This result holds also dividing the spectra in high and low-flux states, and for powerful blazars with large BLR. Only 1 object out of 10 seems compatible with substantial attenuation (τmax > 5). We conclude that for 9 out of 10 objects, the jet does not interact with BLR photons. Gamma-rays seem either produced outside the BLR most of the time, or the BLR is ˜100 × larger than given by reverberation mapping. This means that i) External Compton on BLR photons is disfavoured as the main gamma-ray mechanism, vs IC on IR photons from the torus or synchrotron self-Compton; ii) the Fermi gamma-ray spectrum is mostly intrinsic, determined by the interaction of the particle distribution with the seed-photons spectrum; iii) without suppression by the BLR, broad-line blazars can become copious emitters above 100 GeV, as demonstrated by 3C 454.3. We expect the CTA sky to be much richer of broad-line blazars than previously thought.
OPTICAL SPECTROSCOPIC OBSERVATIONS OF GAMMA-RAY BLAZAR CANDIDATES. V. TNG, KPNO, AND OAN OBSERVATIONS OF BLAZAR CANDIDATES OF UNCERTAIN TYPE IN THE NORTHERN HEMISPHERE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Álvarez Crespo, N.; Massaro, F.; Masetti, N.

The extragalactic γ-ray sky is dominated by emission from blazars, a peculiar class of active galactic nuclei. Many of the γ-ray sources included in the Fermi-Large Area Telescope Third Source catalog (3FGL) are classified as blazar candidates of uncertain type (BCUs) because there are no optical spectra available in the literature to confirm their nature. In 2013, we started a spectroscopic campaign to look for the optical counterparts of the BCUs and of the unidentified γ-ray sources to confirm their blazar nature. Whenever possible we also determine their redshifts. Here, we present the results of the observations carried out inmore » the northern hemisphere in 2013 and 2014 at the Telescopio Nazionale Galileo, Kitt Peak National Observatory, and Observatorio Astronómico Nacional in San Pedro Mártir. In this paper, we describe the optical spectra of 25 sources. We confirmed that all of the 15 BCUs observed in our campaign and included in our sample are blazars and we estimated the redshifts for three of them. In addition, we present the spectra for three sources classified as BL Lacs in the literature but with no optical spectra available to date. We found that one of them is a quasar (QSO) at a redshift of z = 0.208 and the other two are BL Lacs. Moreover, we also present seven new spectra for known blazars listed in the Roma-BZCAT that have an uncertain redshift or are classified as BL Lac candidates. We found that one of them, 5BZB J0724+2621, is a “changing look” blazar. According to the spectrum available in the literature, it was classified as a BL Lac, but in our observation we clearly detected a broad emission line that led us to classify this source as a QSO at z = 1.17.« less
Multi-TeV flaring from blazars: Markarian 421 as a case study

DOE PAGES

Sahu, Sarira; Miranda, Luis Salvador; Rajpoot, Subhash

2016-03-07

The TeV blazar Markarian 421 underwent multi-TeV flaring during April 2004 and simultaneously observations in the X-ray and TeV energies were made. It was observed that the TeV outbursts had no counterparts in the lower energy range. One implication of this is that it might be an orphan flare. We show that Fermi-accelerated protons of energy ≤168 TeV can interact with the low energy tail of the background synchrotron self-Compton photons in the inner region of the blazar to produce the multi-TeV flare and our results fit very well with the observed spectrum. Based on our study, we predict thatmore » the blazars with a deep valley in between the end of the synchrotron spectrum and the beginning of the SSC spectrum are possible candidates for orphan flaring. Future possible candidates for this scenario are the HBLs Mrk 501 and PG 1553 + 113 objects.« less
Constraining the location of gamma-ray flares in luminous blazars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nalewajko, Krzysztof; Begelman, Mitchell C.; Sikora, Marek, E-mail: knalew@jila.colorado.edu

2014-07-10

Locating the gamma-ray emission sites in blazar jets is a long standing and highly controversial issue. We jointly investigate several constraints on the distance scale r and Lorentz factor Γ of the gamma-ray emitting regions in luminous blazars (primarily flat spectrum radio quasars). Working in the framework of one-zone external radiation Comptonization models, we perform a parameter space study for several representative cases of actual gamma-ray flares in their multiwavelength context. We find a particularly useful combination of three constraints: from an upper limit on the collimation parameter Γθ ≲ 1, from an upper limit on the synchrotron self-Compton (SSC)more » luminosity L{sub SSC} ≲ L{sub X}, and from an upper limit on the efficient cooling photon energy E{sub cool,obs} ≲ 100 MeV. These three constraints are particularly strong for sources with low accretion disk luminosity L{sub d}. The commonly used intrinsic pair-production opacity constraint on Γ is usually much weaker than the SSC constraint. The SSC and cooling constraints provide a robust lower limit on the collimation parameter Γθ ≳ 0.1-0.7. Typical values of r corresponding to moderate values of Γ ∼ 20 are in the range 0.1-1 pc, and are determined primarily by the observed variability timescale t{sub var,obs}. Alternative scenarios motivated by the observed gamma-ray/millimeter connection, in which gamma-ray flares of t{sub var,obs} ∼ a few days are located at r ∼ 10 pc, are in conflict with both the SSC and cooling constraints. Moreover, we use a simple light travel time argument to point out that the gamma-ray/millimeter connection does not provide a significant constraint on the location of gamma-ray flares. We argue that spine-sheath models of the jet structure do not offer a plausible alternative to external radiation fields at large distances; however, an extended broad-line region is an idea worth exploring. We propose that the most definite additional constraint
Probing cluster potentials through gravitational lensing of background X-ray sources

NASA Technical Reports Server (NTRS)

Refregier, A.; Loeb, A.

1996-01-01

The gravitational lensing effect of a foreground galaxy cluster, on the number count statistics of background X-ray sources, was examined. The lensing produces a deficit in the number of resolved sources in a ring close to the critical radius of the cluster. The cluster lens can be used as a natural telescope to study the faint end of the (log N)-(log S) relation for the sources which account for the X-ray background.
Wide-Range Multiwavelength Observations of Northern TeV Blazars With MAGIC / HESS, Suzaku And KVA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hayashida, M.; /Munich, Max Planck Inst.; Rugamer, S.

2007-11-14

We have conducted multiwavelength observations of several northern TeV blazars employing the ground-based {gamma}-ray observatories MAGIC and HESS, the optical KVA telescope, and the Suzaku X-ray satellite. The data taken in 2006 establish measurements of the contemporaneous spectral energy distributions of the rapidly variable blazar emission over a wide range of frequencies. Results allow us to test leptonic and hadronic emission and particle acceleration models which predict different correlations between the optical, X-ray, and very high energy {gamma}-ray emissions. In this presentation, we report on the highlights of the results of these observations.
The X-ray background contributed by QSOs ejected from galaxies

NASA Technical Reports Server (NTRS)

Burbidge, G.; Hoyle, F.

1996-01-01

The X-ray background can be explained as coming from the integrated effect of X-ray emitting quasi-stellar objects (QSOs) ejected from spiral galaxies. The model developed to interpret the observations is summarized. The redshift of the QSOs consisted of an intrinsic component and of a cosmological component. The QSOs have a spatial density proportional to that of normal galaxies.
Polarization and photometric observations of the gamma-ray blazar PG 1553+113

NASA Astrophysics Data System (ADS)

Andruchow, I.; Combi, J. A.; Muñoz-Arjonilla, A. J.; Romero, G. E.; Cellone, S. A.; Martí, J.

2011-07-01

We present the results of an observational photo-polarimetry campaign of the blazar PG 1553+113 at optical wavelengths. The blazar was recently detected at very high energies (>100 GeV) by the HESS and MAGIC γ-ray Cherenkov telescopes. Our high-temporal resolution data show significant variations in the linear polarization percentage and position angle at inter-night time-scales, while at shorter (intra-night) time-scales both parameters varied less significantly, if at all. Changes in the polarization angle seem to be common in γ-ray emitting blazars. Simultaneous differential photometry (through the B and R bands) shows no significant variability in the total optical flux. We provide B and R magnitudes, along with a finding chart, for a set of field stars suitable for differential photometry. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).
Blazar Jet Physics in the Age of Fermi

DTIC Science & Technology

2010-11-23

in colliding shells, and whether blazars are sources of ultra-high energy cosmic rays . Keywords. galaxies: jets, gamma rays : observations, gamma rays ...colliding shells ejected from the central supermassive black hole are made. The likelihood that blazars accelerate ultra-high energy cosmic rays is...colliding shells, and whether blazars are sources of ultra-high energy cosmic rays . 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF
Redshift measurement of Fermi blazars for the Cherenkov telescope array

NASA Astrophysics Data System (ADS)

Pita, S.; Goldoni, P.; Boisson, C.; Cotter, G.; Lefaucheur, J.; Lenain, J.-P.; Lindfors, E.; Williams, D. A.

2017-01-01

Blazars are active galactic nuclei, and the most numerous High Energy (HE) and Very High Energy (VHE) γ-ray emitters. Their optical emission is often dominated by non-thermal, and, in the case of BL Lacs, featureless continuum radiation. This makes the determination of their redshift extremely difficult. Indeed, as of today only about 50% of γ-ray blazars have a measured spectroscopic redshift. The knowledge of redshift is fundamental because it allows the precise modeling of the VHE emission and also of its interaction with the extragalactic background light (EBL). The beginning of the Cherenkov Telescope Array (CTA) operations in the near future will allow the detection of several hundreds of new blazars. Using the Fermi catalogue of sources above 50 GeV (2FHL), we performed simulations which indicate that a significant fraction of the 2FHL blazars detectable by CTA will not have a measured redshift. As a matter of fact, the organization of observing campaigns to measure the redshift of these blazars has been recognized as a necessary support for the AGN Key Science Project of CTA. We are planning such an observing campaign. In order to optimize our chances of success, we will perform preliminary deep imaging observations aimed at detecting or setting upper limits to the host galaxy. We will then take spectra of the candidates with the brightest host galaxies. Taking advantage of the recent success of an X-shooter GTO observing campaign, these observations will be different with respect to previous ones due to the use of higher resolution spectrographs and of 8 meter class telescopes. We are starting to submit proposals for these observations. In this paper we briefly describe how candidates are selected and the corresponding observation program.
X-Ray Absorbed, Broad-Lined, Red AGN and the Cosmic X-Ray Background

NASA Technical Reports Server (NTRS)

Mushotzky, Richard (Technical Monitor); Wilkes, Belinda

2005-01-01

We have obtained XMM spectra for five red, 2MASS AGN, selected from a sample observed by Chandra to be X-ray bright and to cover a range of hardness ratios. Our results confirm the presence of substantial absorbing material in three sources which have optical classifications ranging from Type 1 to Type 2, with an intrinsically flat (hard) power law continuum indicated in the other two. The presence of both X-ray absorption and broad optical emission lines with the usual strength suggests either a small (nuclear) absorber or a favored viewing angle so as to cover the X-ray source but not the broad emission line region (BELR). A soft excess is detected in all three Type 1 sources. We speculate that this soft X-ray emission may arise in an extended region of ionized gas, perhaps linked with the polarized (scattered) light which is a feature of these sources. The spectral complexity revealed by XMM emphasizes the limitations of the low S/N Chandra data. Overall, the new XMM results strengthen our conclusions (Wilkes et al. 2002) that the observed X-ray continua of red AGN are unusually hard at energies greater than 2 keV. Whether due to substantial line-of-sight absorption or to an intrinsically hard or reflection-dominated spectrum, these 'red' AGN have an observed spectral form consistent with contributing significantly to the missing had absorbed population of the Cosmic X-ray Background (CXRB). When absorption and or reflection is taken into account, all these AGN have power law slopes typical of broad-line (Type 1) AGN (Gamma approximately 1.9). This appears to resolve the spectral paradox which for so long has existed between the CXRB and the AGN thought to be the dominant contributors. It also suggests two scenarios whereby Type 1 AGN/QSOs may be responsible for a significant fraction of the CXRB at energies above 2 keV: 1) X-ray absorbed AGN/QSOs with visible broad emission lines; 2) AGN/QSOs with complex spectra whose hardness greater than 2 keV is not
Connecting blazars with ultrahigh-energy cosmic rays and astrophysical neutrinos

NASA Astrophysics Data System (ADS)

Resconi, E.; Coenders, S.; Padovani, P.; Giommi, P.; Caccianiga, L.

2017-06-01

We present a strong hint of a connection between high-energy γ-ray emitting blazars, very high energy neutrinos, and ultrahigh-energy cosmic rays. We first identify potential hadronic sources by filtering γ-ray emitters in spatial coincidence with the high-energy neutrinos detected by IceCube. The neutrino filtered γ-ray emitters are then correlated with the ultrahigh-energy cosmic rays from the Pierre Auger Observatory and the Telescope Array by scanning in γ-ray flux (Fγ) and angular separation (θ) between sources and cosmic rays. A maximal excess of 80 cosmic rays (42.5 expected) is found at θ ≤ 10° from the neutrino-filtered γ-ray emitters selected from the second hard Fermi-LAT catalogue (2FHL) and for Fγ(>50 GeV) ≥ 1.8 × 10-11 ph cm-2 s-1. The probability for this to happen is 2.4 × 10-5, which translates to ˜2.4 × 10-3 after compensation for all the considered trials. No excess of cosmic rays is instead observed for the complement sample of γ-ray emitters (I.e. not in spatial connection with IceCube neutrinos). A likelihood ratio test comparing the connection between the neutrino-filtered and the complement source samples with the cosmic rays favours a connection between neutrino-filtered emitters and cosmic rays with a probability of ˜1.8 × 10-3 (2.9σ) after compensation for all the considered trials. The neutrino-filtered γ-ray sources that make up the cosmic rays excess are blazars of the high synchrotron peak type. More statistics is needed to further investigate these sources as candidate cosmic ray and neutrino emitters.
On the origin of the soft X-ray background. [in cosmological observations

NASA Technical Reports Server (NTRS)

Wang, Q. D.; Mccray, Richard

1993-01-01

The angular autocorrelation function and spectrum of the soft X-ray background is studied below a discrete source detection limit, using two deep images from the Rosat X-ray satellite. The average spectral shape of pointlike sources, which account for 40 to 60 percent of the background intensity, is determined by using the autocorrelation function. The background spectrum, in the 0.5-0.9 keV band (M band), is decomposed into a pointlike source component characterized by a power law and a diffuse component represented by a two-temperature plasma. These pointlike sources cannot contribute more than 60 percent of the X-ray background intensity in the M band without exceeding the total observed flux in the R7 band. Spectral analysis has shown that the local soft diffuse component, although dominating the background intensity at energies not greater than 0.3 keV, contributes only a small fraction of the M band background intensity. The diffuse component may represent an important constituent of the interstellar or intergalactic medium.
On the large scale structure of X-ray background sources

NASA Technical Reports Server (NTRS)

Bi, H. G.; Meszaros, A.; Meszaros, P.

1991-01-01

The large scale clustering of the sources responsible for the X-ray background is discussed, under the assumption of a discrete origin. The formalism necessary for calculating the X-ray spatial fluctuations in the most general case where the source density contrast in structures varies with redshift is developed. A comparison of this with observational limits is useful for obtaining information concerning various galaxy formation scenarios. The calculations presented show that a varying density contrast has a small impact on the expected X-ray fluctuations. This strengthens and extends previous conclusions concerning the size and comoving density of large scale structures at redshifts 0.5 between 4.0.
Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event

DOE PAGES

Kadler, M.; Krauß, F.; Mannheim, K.; ...

2016-04-18

The astrophysical sources of the extraterrestrial, very high-energy neutrinos detected by the IceCube collaboration remain to be identified. Gamma-ray (γ-ray) blazars have been predicted to yield a cumulative neutrino signal exceeding the atmospheric background above energies of 100 TeV, assuming that both the neutrinos and the γ-ray photons are produced by accelerated protons in relativistic jets. As the background spectrum falls steeply with increasing energy, the individual events with the clearest signature of being of extraterrestrial origin are those at petaelectronvolt energies. Inside the large positional-uncertainty fields of the first two petaelectronvolt neutrinos detected by IceCube, the integrated emission ofmore » the blazar population has a sufficiently high electromagnetic flux to explain the detected IceCube events, but fluences of individual objects are too low to make an unambiguous source association. In this paper, we report that a major outburst of the blazar PKS B1424–418 occurred in temporal and positional coincidence with a third petaelectronvolt-energy neutrino event (HESE-35) detected by IceCube. On the basis of an analysis of the full sample of γ-ray blazars in the HESE-35 field, we show that the long-term average γ-ray emission of blazars as a class is in agreement with both the measured all-sky flux of petaelectronvolt neutrinos and the spectral slope of the IceCube signal. Finally, the outburst of PKS B1424–418 provides an energy output high enough to explain the observed petaelectronvolt event, suggestive of a direct physical association.« less

Correlation between low level fluctuations in the x ray background and faint galaxies

NASA Technical Reports Server (NTRS)

Tolstoy, Eline; Griffiths, R. E.

1993-01-01

A correlation between low-level x-ray fluctuations in the cosmic x-ray background flux and the large numbers of galaxies found in deep optical imaging, to m(sub v) is less than or equal to 24 - 26, is desired. These (faint) galaxies by their morphology and color in deep multi-color CCD images and plate material were optically identified. Statistically significant correlations between these galaxies and low-level x-ray fluctuations at the same positions in multiple deep Einstein HRI observations in PAVO and in a ROSAT PSPC field were searched for. Our aim is to test the hypothesis that faint 'star burst' galaxies might contribute significantly to the cosmic x-ray background (at approximately 1 keV).
Multiwavelength Observations of Markarian 421 During a TeV/X-Ray Flare

NASA Technical Reports Server (NTRS)

Bertsch, D. L.; Bruhweiler, F.; Macomb, D. J.; Cheng, K.-P.; Carter-Lewis, D. A.; Akerlof, C. W.; Aller, H. D.; Aller, M. F.; Buckley, J. H.; Cawley, M. F.

1995-01-01

A TeV flare from the BL Lac object Mrk 421 was detected in May of 1994 by the Whipple Observatory air Cherenkov experiment during which the flux above 250 GeV increased by nearly an order of magnitude over a 2-day period. Contemporaneous observations by ASCA showed the X-ray flux to be in a very high state. We present these results, combined with the first ever simultaneous or nearly simultaneous observations at GeV gamma-ray, UV, IR, mm, and radio energies for this nearest BL Lac object. While the GeV gamma-ray flux increased slightly, there is little evidence for variability comparable to that seen at TeV and X-ray energies. Other wavelengths show even less variability. This provides important constraints on the emission mechanisms at work. We present the multiwavelength spectrum of this gamma-ray blazar for both quiescent and flaring states and discuss the data in terms of current models of blazar emission.
Deriving the Contribution of Blazars to the Fermi-LAT Extragalactic γ-ray Background at E > 10 GeV with Efficiency Corrections and Photon Statistics

NASA Astrophysics Data System (ADS)

Di Mauro, M.; Manconi, S.; Zechlin, H.-S.; Ajello, M.; Charles, E.; Donato, F.

2018-04-01

The Fermi Large Area Telescope (LAT) Collaboration has recently released the Third Catalog of Hard Fermi-LAT Sources (3FHL), which contains 1556 sources detected above 10 GeV with seven years of Pass 8 data. Building upon the 3FHL results, we investigate the flux distribution of sources at high Galactic latitudes (| b| > 20^\\circ ), which are mostly blazars. We use two complementary techniques: (1) a source-detection efficiency correction method and (2) an analysis of pixel photon count statistics with the one-point probability distribution function (1pPDF). With the first method, using realistic Monte Carlo simulations of the γ-ray sky, we calculate the efficiency of the LAT to detect point sources. This enables us to find the intrinsic source-count distribution at photon fluxes down to 7.5 × 10‑12 ph cm‑2 s‑1. With this method, we detect a flux break at (3.5 ± 0.4) × 10‑11 ph cm‑2 s‑1 with a significance of at least 5.4σ. The power-law indexes of the source-count distribution above and below the break are 2.09 ± 0.04 and 1.07 ± 0.27, respectively. This result is confirmed with the 1pPDF method, which has a sensitivity reach of ∼10‑11 ph cm‑2 s‑1. Integrating the derived source-count distribution above the sensitivity of our analysis, we find that (42 ± 8)% of the extragalactic γ-ray background originates from blazars.
Background in X-ray astronomy proportional counters

NASA Technical Reports Server (NTRS)

Bower, C. R.; Dietz, K. L.; Ramsey, B. D.; Weisskopf, M. C.

1991-01-01

The authors report the results of an investigation into the nature of background events in proportional counters sensitive to X-ray photons having energy of less than 150 keV. Even with the use of thick shields composed of high-atomic-number material, a significant flux background in the detector's energy region can result from multiple Compton scattering in the mass surrounding the active region of the detector. The importance of the selection of detector components in the reduction of the background by more than an order of magnitude is emphasized. Experimental results are shown to agree qualitatively with Monte Carlo simulations. It is concluded that escape gating is a powerful means of determining the nature of background in flight detectors: the single/pair ratios reveal whether the detected events are charged particles or photons.
Contributions of late-type dwarf stars to the soft X-ray diffuse background

NASA Technical Reports Server (NTRS)

Schmitt, J. H. M. M.; Snowden, S. L.

1990-01-01

Comprehensive calculations of the contribution of late-type dwarf stars to the soft X-ray diffuse background are presented. The mean X-ray luminosity as derived from optically and X-ray selected samples is examined, using the Bahcall-Soneira Galaxy model to describe the spatial distribution of stars and recent results on the X-ray spectra. The model calculations are compared with the Wisconsin sky maps in the C, M1, M2, I and J bands to assess the uncertainties of the calculations. Contributions of up to 10 percent to the M2 and I band background at high Galactic latitudes are found, while at low Galactic latitudes late-type stars contribute up to 40 percent of the background. However, a Galactic ridge as well as a relatively isotropic component still remains unexplained, even with the added contribution of the extrapolated high-energy power law.
Deriving the Contribution of Blazars to the Fermi-LAT Extragalactic γ-ray Background at E > 10 GeV with Efficiency Corrections and Photon Statistics

DOE PAGES

Di Mauro, M.; Manconi, S.; Zechlin, H. -S.; ...

2018-03-29

Here, the Fermi Large Area Telescope (LAT) Collaboration has recently released the Third Catalog of Hard Fermi-LAT Sources (3FHL), which contains 1556 sources detected above 10 GeV with seven years of Pass 8 data. Building upon the 3FHL results, we investigate the flux distribution of sources at high Galactic latitudes (more » $$|b| \\gt 20^\\circ $$), which are mostly blazars. We use two complementary techniques: (1) a source-detection efficiency correction method and (2) an analysis of pixel photon count statistics with the one-point probability distribution function (1pPDF). With the first method, using realistic Monte Carlo simulations of the γ-ray sky, we calculate the efficiency of the LAT to detect point sources. This enables us to find the intrinsic source-count distribution at photon fluxes down to 7.5 × 10 –12 ph cm –2 s –1. With this method, we detect a flux break at (3.5 ± 0.4) × 10 –11 ph cm –2 s –1 with a significance of at least 5.4σ. The power-law indexes of the source-count distribution above and below the break are 2.09 ± 0.04 and 1.07 ± 0.27, respectively. This result is confirmed with the 1pPDF method, which has a sensitivity reach of ~10 –11 ph cm –2 s –1. Integrating the derived source-count distribution above the sensitivity of our analysis, we find that (42 ± 8)% of the extragalactic γ-ray background originates from blazars.« less
Deriving the Contribution of Blazars to the Fermi-LAT Extragalactic γ-ray Background at E > 10 GeV with Efficiency Corrections and Photon Statistics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Di Mauro, M.; Manconi, S.; Zechlin, H. -S.

Here, the Fermi Large Area Telescope (LAT) Collaboration has recently released the Third Catalog of Hard Fermi-LAT Sources (3FHL), which contains 1556 sources detected above 10 GeV with seven years of Pass 8 data. Building upon the 3FHL results, we investigate the flux distribution of sources at high Galactic latitudes (more » $$|b| \\gt 20^\\circ $$), which are mostly blazars. We use two complementary techniques: (1) a source-detection efficiency correction method and (2) an analysis of pixel photon count statistics with the one-point probability distribution function (1pPDF). With the first method, using realistic Monte Carlo simulations of the γ-ray sky, we calculate the efficiency of the LAT to detect point sources. This enables us to find the intrinsic source-count distribution at photon fluxes down to 7.5 × 10 –12 ph cm –2 s –1. With this method, we detect a flux break at (3.5 ± 0.4) × 10 –11 ph cm –2 s –1 with a significance of at least 5.4σ. The power-law indexes of the source-count distribution above and below the break are 2.09 ± 0.04 and 1.07 ± 0.27, respectively. This result is confirmed with the 1pPDF method, which has a sensitivity reach of ~10 –11 ph cm –2 s –1. Integrating the derived source-count distribution above the sensitivity of our analysis, we find that (42 ± 8)% of the extragalactic γ-ray background originates from blazars.« less
New Gener. High-Energy Spectra of the Blazar 3C 279 with XMM-Newton and GLAST

NASA Astrophysics Data System (ADS)

Collmar, Werner

2007-10-01

We propose two 20 ksec XMM-Newton observations of the X-ray bright gamma-ray blazar 3C~279 simultaneous with GLAST/LAT. The main goal is to measure its X-ray properties (spectrum, variability) in order to (1) improve our knowledge on the X-ray emission of the blazar, and (2) to supplement and correlate them to simultaneous GLAST/LAT Gamma-ray observations (30 MeV-300 GeV). Simultaneous GLAST observations of 3C 279 are guaranteed (assuming proper operation then). The high-energy data will be supplemented by ground-based measurements, adding finally up to multifrequency spectra which have unprecedented accuracy and will extend up to high-energy gamma-rays. Such high-quality SEDs will provide severe constraints on their modeling and have the potential to discriminate among models.
VERITAS Observations of Six Bright, Hard-Spectrum Fermi-LAT Blazars

NASA Technical Reports Server (NTRS)

E. Aliu; Archambault, S.; Arlen, T.; Aune, T.; Beilicke, M.; Benbow, W.; Boettcher, M.; Bouvier, A.; Buckley, J. H.; Bugaev, V.;

2012-01-01

We report on VERITAS very-high-energy (VHE; E >= 100 GeV) observations of six blazars selected from the Fermi Large Area Telescope First Source Catalog (1FGL). The gamma-ray emission from 1FGL sources was extrapolated up to the VHE band, taking gamma-ray absorption by the extragalactic background light into account. This allowed the selection of six bright, hard-spectrum blazars that were good candidate TeV emitters. Spectroscopic redshift measurements were attempted with the Keck Telescope for the targets without Sloan Digital Sky Survey (SDSS) spectroscopic data. No VHE emission is detected during the observations of the six sources described here. Corresponding TeV upper limits are presented, along with contemporaneous Fermi observations and non-concurrent Swift UVOT and XRT data. The blazar broadband spectral energy distributions (SEDs) are assembled and modeled with a single-zone synchrotron self-Compton model. The SED built for each of the six blazars show a synchrotron peak bordering between the intermediate- and high-spectrum-peak classifications, with four of the six resulting in particle-dominated emission region.

Multiwavelength Observations of the Blazar BL Lacertae: A New Fast TeV Gamma-Ray Flare

NASA Astrophysics Data System (ADS)

Abeysekara, A. U.; Benbow, W.; Bird, R.; Brantseg, T.; Brose, R.; Buchovecky, M.; Buckley, J. H.; Bugaev, V.; Connolly, M. P.; Cui, W.; Daniel, M. K.; Falcone, A.; Feng, Q.; Finley, J. P.; Fortson, L.; Furniss, A.; Gillanders, G. H.; Gunawardhana, I.; Hütten, M.; Hanna, D.; Hervet, O.; Holder, J.; Hughes, G.; Humensky, T. B.; Johnson, C. A.; Kaaret, P.; Kar, P.; Kertzman, M.; Krennrich, F.; Lang, M. J.; Lin, T. T. Y.; McArthur, S.; Moriarty, P.; Mukherjee, R.; O’Brien, S.; Ong, R. A.; Otte, A. N.; Park, N.; Petrashyk, A.; Pohl, M.; Pueschel, E.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Rulten, C.; Sadeh, I.; Santander, M.; Sembroski, G. H.; Shahinyan, K.; Wakely, S. P.; Weinstein, A.; Wells, R. M.; Wilcox, P.; Williams, D. A.; Zitzer, B.; The VERITAS Collaboration; Jorstad, S. G.; Marscher, A. P.; Lister, M. L.; Kovalev, Y. Y.; Pushkarev, A. B.; Savolainen, T.; Agudo, I.; Molina, S. N.; Gómez, J. L.; Larionov, V. M.; Borman, G. A.; Mokrushina, A. A.; Tornikoski, M.; Lähteenmäki, A.; Chamani, W.; Enestam, S.; Kiehlmann, S.; Hovatta, T.; Smith, P. S.; Pontrelli, P.

2018-04-01

Combined with measurements made by very-long-baseline interferometry, the observations of fast TeV gamma-ray flares probe the structure and emission mechanism of blazar jets. However, only a handful of such flares have been detected to date, and only within the last few years have these flares been observed from lower-frequency-peaked BL Lac objects and flat-spectrum radio quasars. We report on a fast TeV gamma-ray flare from the blazar BL Lacertae observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS). with a rise time of ∼2.3 hr and a decay time of ∼36 min. The peak flux above 200 GeV is (4.2 ± 0.6) × 10‑6 photon m‑2 s‑1 measured with a 4-minute-binned light curve, corresponding to ∼180% of the flux that is observed from the Crab Nebula above the same energy threshold. Variability contemporaneous with the TeV gamma-ray flare was observed in GeV gamma-ray, X-ray, and optical flux, as well as in optical and radio polarization. Additionally, a possible moving emission feature with superluminal apparent velocity was identified in Very Long Baseline Array observations at 43 GHz, potentially passing the radio core of the jet around the time of the gamma-ray flare. We discuss the constraints on the size, Lorentz factor, and location of the emitting region of the flare, and the interpretations with several theoretical models that invoke relativistic plasma passing stationary shocks.
An extended galactic population of low-luminosity x-ray sources (CVs?) and the diffuse x-ray background

NASA Technical Reports Server (NTRS)

Maoz, Eyal; Grindlay, Jonathan E.

1995-01-01

The incompatibility of the properties of the X-ray background (XRB) with active galactic nuclei (AGNs) contributing approximately greater than 60% at energies of a few keV has often been interpreted as being due to a substantial contribution of a new population of yet unrecognized X-ray sources. The existence of such population has been recently suggested also by an analysis of very deep ROSAT observations which revealed a considerable excess of faint X-ray sources over that expected from QSO evolution models, and that the average spectrum of the resolved sources becomes harder with decreasing flux limit. These sources could be extragalactic in origin, but if they make a substantial contribution to the XRB then they must exhibit much weaker clustering than galaxies or QSOs in order to be consistent with the stringent constraints on source clustering imposed by autocorrelation analyses of the unresolved XRB. We investigate the possibility that the indicated new population of X-ray sources is Galactic in origin. Examining spherical halo and thick disk distributions, we derive the allowed properties of such populations which would resolve the discrepancy found in the number counts of faint sources and be consistent with observational constraints on the total background intensity, the XRB anisotropy, the number of unidentified bright sources, the Galaxy's total X-ray luminosity, and with the results of fluctuation analyses of the unresolved XRB. We find that a flattened Galactic halo (or a thick disk) distribution with a scale height of a few kpc is consistent with all the above requirements. The typical X-ray luminosity of the sources is approximately equal to 10(exp 30-31)ergs/s in the 0.5-2 keV band, the number density of sources in the solar vicinity is approximately 10(exp -4.5)pc(exp -3), their total number in the Galaxy is approximately 10(exp 8.5), and their total contribution to the Galaxy's X-ray luminosity is approximately 10(exp 39) ergs/s. We discuss the
A physical classification scheme for blazars

NASA Astrophysics Data System (ADS)

Landt, Hermine; Padovani, Paolo; Perlman, Eric S.; Giommi, Paolo

2004-06-01

Blazars are currently separated into BL Lacertae objects (BL Lacs) and flat spectrum radio quasars based on the strength of their emission lines. This is performed rather arbitrarily by defining a diagonal line in the Ca H&K break value-equivalent width plane, following Marchã et al. We readdress this problem and put the classification scheme for blazars on firm physical grounds. We study ~100 blazars and radio galaxies from the Deep X-ray Radio Blazar Survey (DXRBS) and 2-Jy radio survey and find a significant bimodality for the narrow emission line [OIII]λ5007. This suggests the presence of two physically distinct classes of radio-loud active galactic nuclei (AGN). We show that all radio-loud AGN, blazars and radio galaxies, can be effectively separated into weak- and strong-lined sources using the [OIII]λ5007-[OII]λ3727 equivalent width plane. This plane allows one to disentangle orientation effects from intrinsic variations in radio-loud AGN. Based on DXRBS, the strongly beamed sources of the new class of weak-lined radio-loud AGN are made up of BL Lacs at the ~75 per cent level, whereas those of the strong-lined radio-loud AGN include mostly (~97 per cent) quasars.
Dissecting the Gamma-Ray Background in Search of Dark Matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cholis, Ilias; Hooper, Dan; McDermott, Samuel D.

2014-02-01

Several classes of astrophysical sources contribute to the approximately isotropic gamma-ray background measured by the Fermi Gamma-Ray Space Telescope. In this paper, we use Fermi's catalog of gamma-ray sources (along with corresponding source catalogs at infrared and radio wavelengths) to build and constrain a model for the contributions to the extragalactic gamma-ray background from astrophysical sources, including radio galaxies, star-forming galaxies, and blazars. We then combine our model with Fermi's measurement of the gamma-ray background to derive constraints on the dark matter annihilation cross section, including contributions from both extragalactic and galactic halos and subhalos. The resulting constraints are competitivemore » with the strongest current constraints from the Galactic Center and dwarf spheroidal galaxies. As Fermi continues to measure the gamma-ray emission from a greater number of astrophysical sources, it will become possible to more tightly constrain the astrophysical contributions to the extragalactic gamma-ray background. We project that with 10 years of data, Fermi's measurement of this background combined with the improved constraints on the astrophysical source contributions will yield a sensitivity to dark matter annihilations that exceeds the strongest current constraints by a factor of ~ 5 - 10.« less
Discovery of a GeV blazar shining through the galactic plane

DOE PAGES

Vandenbroucke, J.; Buehler, R.; Ajello, M.; ...

2010-07-14

The Fermi Large Area Telescope (LAT) discovered a new gamma-ray source near the Galactic plane, Fermi J0109+6134, when it flared brightly in 2010 February. The low Galactic latitude (b = –1more » $$ο\\atop{.}$$2) indicated that the source could be located within the Galaxy, which motivated rapid multi-wavelength follow-up including radio, optical, and X-ray observations. Here, we report the results of analyzing all 19 months of LAT data for the source, and of X-ray observations with both Swift and the Chandra X-ray Observatory. We determined the source redshift, z = 0.783, using a Keck Low-Resolution Imaging Spectrometer observation. Finally, we compiled a broadband spectral energy distribution (SED) from both historical and new observations contemporaneous with the 2010 February flare. The redshift, SED, optical line width, X-ray absorption, and multi-band variability indicate that this new GeV source is a blazar seen through the Galactic plane. Because several of the optical emission lines have equivalent width >5 Å, this blazar belongs in the flat-spectrum radio quasar category.« less
Characterization and Evolution of the Swift X-ray Telescope Instrumental Background

NASA Technical Reports Server (NTRS)

Hill, Joanne; Pagani, C.; Morris, D. C.; Racusin, J.; Grupe, D.; Vetere, L.; Stroh, M.; Falcone, A.; Kennea, J.; Burrows, D. N.;

2007-01-01

The X-ray telescope (XRT) on board the Swift Gamma Ray Burst Explorer has successfully operated since the spacecraft launch on 20 November 2004, automatically locating GRB afterglows, measuring their spectra and lightcurves and performing observations of high-energy sources. In this work we investigate the properties of the instrumental background, focusing on its dynamic behavior on both long and short timescales. The operational temperature of the CCD is the main factor that influences the XRT background level. After the failure of the Swift active on-board temperature control system, the XRT detector now operates at a temperature range between -75C and -45C thanks to a passive cooling Heat Rejection System. We report on the long-term effects on the background caused by radiation, consisting mainly of proton irradiation in Swift's low Earth orbit and on the short-term effects of transits through the South Atlantic Anomaly (SAA), which expose the detector to periods of intense proton flux. We have determined the fraction of the detector background that is due to the internal, instrumental background and the part that is due to unresolved astrophysical sources (the cosmic X-ray background) by investigating the degree of vignetting of the measured background and comparing it to the expected value from calibration data.

Correlations Between the Cosmic X-Ray and Microwave Backgrounds: Constraints on a Cosmological Constant

NASA Technical Reports Server (NTRS)

Boughn, S. P.; Crittenden, R. G.; Turok, N. G.

1998-01-01

In universes with significant curvature or cosmological constant, cosmic microwave background (CMB) anisotropies are created very recently via the Rees-Sciama or integrated Sachs-Wolfe effects. This causes the CMB anisotropies to become partially correlated with the local matter density (z less than 4). We examine the prospects of using the hard (2- 10 keV) X-ray background as a probe of the local density and the measured correlation between the HEAO1 A2 X-ray survey and the 4-year COBE-DMR map to obtain a constraint on the cosmological constant. The 95% confidence level upper limit on the cosmological constant is OMega(sub Lambda) less than or equal to 0.5, assuming that the observed fluctuations in the X-ray map result entirely from large scale structure. (This would also imply that the X-rays trace matter with a bias factor of b(sub x) approx. = 5.6 Omega(sub m, sup 0.53)). This bound is weakened considerably if a large portion of the X-ray fluctuations arise from Poisson noise from unresolved sources. For example, if one assumes that the X-ray bias is b(sub x) = 2, then the 95% confidence level upper limit is weaker, Omega(sub Lambda) less than or equal to 0.7. More stringent limits should be attainable with data from the next generation of CMB and X-ray background maps.
Cross-Correlation of the X-Ray Background with Nearby Galaxies: Erratum

NASA Astrophysics Data System (ADS)

Jahoda, Keith; Lahav, Ofer; Mushotzky, Richard F.; Boldt, Elihu

1992-11-01

In the Letter "Cross-Correlation of the X-Ray Background with Nearby Galaxies" by Keith Jahoda, Ofer Lahav, Richard F. Mushotzky, & Elihu Boldt (ApJ, 378, L37, [1991]) there is an error in the evaluation of equation(5): the numerical constant is too small by a factor of 4.5 (the solid angle of the HEAO 1 A2 beam). The revised X-ray emissivity values (over the volume sampled by the UGC and ESO galaxies) are as follows. For UGC (using the median of Table 1) ρ_x_ = (10.5 +/- 6.0) x 10^38^ h_50_ ergs s^-1^ Mpc^-3^, where the error reflects the scatter in Table 1 and the uncertainty in R_*_, the effective depth of the catalogs (the Hubble constant is in units of H_0_ = 50 h_50_ km s^-1^ Mpc^-1^). Similarly for ESO ρ_x = (14.5 +/- 8.0) x 10^38^ h_50_ ergs s^-1^ Mpc^-3^. For the combined data (UGC and ESO)our revised value is the mean of the two samples,ρ_x_ = (12.5 +/- 7.0) x 10^38^ h_50_ ergs s^-1^ Mpc^-3^. This correction has important consequences for the discussion section of the paper. First, the fraction of the X-ray background which can be produced by nonevolving X-ray sources distributed out to high redshift (assuming a look-back factor of f=0.5) can be as large as 50% +/- 30% and 70% +/- 40% for UGC and ESO, respectively. Second, this measurement of ρ_x_ exceeds the upper limit calculated by E. Boldt (IAU Colloq. 123,451 [1990]) based on an approximation of the total extragalactic X-ray dipole, unless b{OMEGA}^-0.6^<~ 1.3, less than about half the value derived for bright X-ray AGNs by T. Miyaji & E. Boldt (ApJ, 353, L3 [1990]) and T. Miyaji, K. Jahoda, & E. Boldt (AIP Conf. Proc. 222,431 [1991]). However, an improved determination of the extragalactic X-ray dipole, now obtained by performing a direct vector sum of the all-sky X-ray data (excluding only points near known Galactic point sources and their antipodes and points with |b| < 20^deg^), and subtracting the high-latitude contribution predicted by the Galactic model of D. Iwan et al. (ApJ, 260
Tev Blazars: Status of Observations

NASA Astrophysics Data System (ADS)

Krennrich, F.; Biller, S. D.; Bond, I. H.; Boyle, P. J.; Bradbury, S. M.; Breslin, A. C.; Buckley, J. H.; Burdett, A. M.; Bussons Gordo, J.; Carter-Lewis, D. A.; Catanese, M.; Cawley, M. F.; Fegan, D. J.; Finley, J. P.; Gaidos, J. A.; Hall, T.; Hillas, A. M.; Lamb, R. C.; Lessard, R. W.; Masterson, C.; McEnry, J. E.; Mohanty, G.; Moriarty, P.; Quinn, J.; Rodgers, A. J.; Rose, H. J.; Samuelson, F. W.; Sembroski, G. H.; Srinivasan, R.; Vassiliev, V. V.; Weekes, T. C.

The close relation between ground-based TeV observations and satellite borne $\\gamma$-ray measurements has been important for the understanding of blazars. The observations which involve the TeV component in blazar studies are reviewed.
Exploring Cosmic X-ray Source Polarization

NASA Technical Reports Server (NTRS)

Swank, Jean Hebb; Jahodal, K.; Kallman, T. R.; Kaaret, P.

2008-01-01

Cosmic X-ray sources are expected to be polarized, either because of their asymmetry and the role of scattering in their emission or the role of magnetic fields. Polarization at other wavelengths has been useful. X-ray polarization will provide a new handle on black hole parameters, in particular the spin, on accretion flows and outflows, on neutron star spin orientations and emission mechanisms, on the quantum mechanical effects of super-strong magnetic fields of magnetars, and on the structure of supernovae shocks. The proposed Gravity and Extreme Magnetism SMEX (GEMS) will use high efficiency polarimeters behind thin foil mirrors. The statistical sensitivity and control of systematics will allow measurement of polarization fractions as small as 1% from many galactic and extragalactic sources. Targets which should be polarized at the level that GEMS can easily measure include stellar black holes, Seyfert galaxies and quasars, blazars, rotation-powered and accretion-powered pulsars, magnetars, shell supernova remnants and pulsar wind nebulae. The polarimeters are Time Projection Chambers that allow reconstruction of images of photoelectron tracks for 2-10 keV Xrays. They can be deep without sacrificing modulation. These polarimeters do not image the sky, but the telescope point spread function and detector collimation allow structure to be resolved at the 10 arcmin level. Rotation of the spacecraft is not needed for the signal measurement in the Time Projection Chambers, but provides for measurement and correction of systematic errors. It also allows a small Bragg reflection soft X-ray experiment to be included that can be used for isolated neutron stars and blazars.
Hydrodynamic Simulation of the Cosmological X-Ray Background

NASA Astrophysics Data System (ADS)

Croft, Rupert A. C.; Di Matteo, Tiziana; Davé, Romeel; Hernquist, Lars; Katz, Neal; Fardal, Mark A.; Weinberg, David H.

2001-08-01

We use a hydrodynamic simulation of an inflationary cold dark matter model with a cosmological constant to predict properties of the extragalactic X-ray background (XRB). We focus on emission from the intergalactic medium (IGM), with particular attention to diffuse emission from warm-hot gas that lies in relatively smooth filamentary structures between galaxies and galaxy clusters. We also include X-rays from point sources associated with galaxies in the simulation, and we make maps of the angular distribution of the emission. Although much of the X-ray luminous gas has a filamentary structure, the filaments are not evident in the simulated maps because of projection effects. In the soft (0.5-2 keV) band, our calculated mean intensity of radiation from intergalactic and cluster gas is 2.3×10-12 ergs-1 cm-2 deg-2, 35% of the total softband emission. This intensity is compatible at the ~1 σ level with estimates of the unresolved soft background intensity from deep ROSAT and Chandra measurements. Only 4% of the hard (2-10 keV) emission is associated with intergalactic gas. Relative to active galactic nuclei flux, the IGM component of the XRB peaks at a lower redshift (median z~0.45) and spans a narrower redshift range, so its clustering makes an important contribution to the angular correlation function of the total emission. The clustering on the scales accessible to our simulation (0.1‧-10') is significant, with an amplitude roughly consistent with an extrapolation of recent ROSAT results to small scales. A cross-correlation analysis of the XRB against nearby galaxies taken from a simulated redshift survey also yields a strong signal from the IGM. Our conclusions about the soft background intensity differ from those of some recent papers that have argued that the expected emission from gas in galaxy, group, and cluster halos would exceed the observed background unless much of the gas is expelled by supernova feedback. We obtain reasonable compatibility with

OPTICAL SPECTROSCOPIC OBSERVATIONS OF GAMMA-RAY BLAZAR CANDIDATES. VI. FURTHER OBSERVATIONS FROM TNG, WHT, OAN, SOAR, AND MAGELLAN TELESCOPES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Álvarez Crespo, N.; Massaro, F.; Milisavljevic, D.

Blazars, one of the most extreme classes of active galaxies, constitute so far the largest known population of γ-ray sources, and their number is continuously growing in the Fermi catalogs. However, in the latest release of the Fermi catalog there is still a large fraction of sources that are classified as blazar candidates of uncertain type (BCUs) for which optical spectroscopic observations are necessary to confirm their nature and their associations. In addition, about one-third of the γ-ray point sources listed in the Third Fermi-LAT Source Catalog (3FGL) are still unassociated and lacking an assigned lower-energy counterpart. Since 2012 wemore » have been carrying out an optical spectroscopic campaign to observe blazar candidates to confirm their nature. In this paper, the sixth of the series, we present optical spectroscopic observations for 30 γ-ray blazar candidates from different observing programs we carried out with the Telescopio Nazionale Galileo, William Herschel Telescope, Observatorio Astronómico Nacional, Southern Astrophysical Research Telescope, and Magellan Telescopes. We found that 21 out of 30 sources investigated are BL Lac objects, while the remaining targets are classified as flat-spectrum radio quasars showing the typical broad emission lines of normal quasi-stellar objects. We conclude that our selection of γ-ray blazar candidates based on their multifrequency properties continues to be a successful way to discover potential low-energy counterparts of the Fermi unidentified gamma-ray sources and to confirm the nature of BCUs.« less
Broadband spectral fitting of blazars using XSPEC

NASA Astrophysics Data System (ADS)

Sahayanathan, Sunder; Sinha, Atreyee; Misra, Ranjeev

2018-03-01

The broadband spectral energy distribution (SED) of blazars is generally interpreted as radiation arising from synchrotron and inverse Compton mechanisms. Traditionally, the underlying source parameters responsible for these emission processes, like particle energy density, magnetic field, etc., are obtained through simple visual reproduction of the observed fluxes. However, this procedure is incapable of providing confidence ranges for the estimated parameters. In this work, we propose an efficient algorithm to perform a statistical fit of the observed broadband spectrum of blazars using different emission models. Moreover, we use the observable quantities as the fit parameters, rather than the direct source parameters which govern the resultant SED. This significantly improves the convergence time and eliminates the uncertainty regarding initial guess parameters. This approach also has an added advantage of identifying the degenerate parameters, which can be removed by including more observable information and/or additional constraints. A computer code developed based on this algorithm is implemented as a user-defined routine in the standard X-ray spectral fitting package, XSPEC. Further, we demonstrate the efficacy of the algorithm by fitting the well sampled SED of blazar 3C 279 during its gamma ray flare in 2014.
A Synthesis Of Cosmic X-ray And Infrared Background

NASA Astrophysics Data System (ADS)

Shi, Yong; Helou, G.; Armus, L.; Stierwalt, S.

2012-01-01

We present a synthesis model of cosmic IR and X-ray background, with the goal to derive a complete census of cosmic evolution of star formation (SF) and black-hole (BH) growth by complementing advantages of X-ray and IR surveys to each other. By assuming that individual galaxies are experiencing both SF and BH accretion, our model decomposes the total IR LF into SF and BH components while taking into account the luminosity-dependent SED and its dispersion of the SF component, and the extinction-dependent SED of the BH component. The best-fit parameters are derived by fitting to the number counts and redshift distributions at X-ray including both hard and soft bands, and mid-IR to submm bands including IRAS, Spitzer, Herschel, SCUBA, Aztec and MAMBO. Based on the fit result, our models provide a series of predictions on galaxy evolution and black-hole growth. For evolution of infrared galaxies, the model predicts that the total infrared luminosity function is best described through evolution in both luminosity and density. For evolution of AGN populations, the model predicts that the evolution of X-ray LF also shows luminosity and density dependent, that the type-1/type-2 AGN fraction is a function of both luminosity and redshift, and that the Compton-thick AGN number density evolves strongly with redshift, contributing about 20% to the total cosmic BH growth. For BH growth in IR galaxies, the model predicts that the majority of BH growth at z>1 occurs in infrared luminous galaxies and the AGN fraction as a function of IR survey is a strong function of the survey depth, ranging from >50% at bright end to below 10% at faint end. We also evaluates various AGN selection techniques at X-ray and IR wavelengths and offer predictions for future missions at X-ray and IR.
Measuring X-Ray Polarization in the Presence of Systematic Effects: Known Background

NASA Technical Reports Server (NTRS)

Elsner, Ronald F.; O'Dell, Stephen L.; Weisskopf, Martin C.

2012-01-01

The prospects for accomplishing x-ray polarization measurements of astronomical sources have grown in recent years, after a hiatus of more than 37 years. Unfortunately, accompanying this long hiatus has been some confusion over the statistical uncertainties associated with x-ray polarization measurements of these sources. We have initiated a program to perform the detailed calculations that will offer insights into the uncertainties associated with x-ray polarization measurements. Here we describe a mathematical formalism for determining the 1- and 2-parameter errors in the magnitude and position angle of x-ray (linear) polarization in the presence of a (polarized or unpolarized) background. We further review relevant statistics including clearly distinguishing between the Minimum Detectable Polarization (MDP) and the accuracy of a polarization measurement.
The Ultraluminous X-Ray Source X-37 Is a Background Quasar in the Antennae Galaxies

NASA Astrophysics Data System (ADS)

Clark, D. M.; Christopher, M. H.; Eikenberry, S. S.; Brandl, B. R.; Wilson, J. C.; Carson, J. C.; Henderson, C. P.; Hayward, T. L.; Barry, D. J.; Ptak, A. F.; Colbert, E. J. M.

2005-10-01

In this Letter we report that a bright, X-ray source in the Antennae galaxies (NGC 4038/9), previously identified as an ultraluminous X-ray source (ULX), is in fact a background quasar. We identify an isolated infrared and optical counterpart within 0.3" +/- 0.5" of the X-ray source X-37. After acquiring an optical spectrum of its counterpart, we use the narrow [O III] and broad Hα emission lines to identify X-37 as a quasar at a redshift of z=0.26. Through a U, V, and Ks photometric analysis, we demonstrate that most of the observable light along this line of sight is from the quasar. We discuss the implications of this discovery and the importance of acquiring spectra for optical and IR counterparts to ULXs.
Studies of the extreme ultraviolet/soft x-ray background

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stern, R.A.

1978-01-01

The results of an extensive sky survey of the extreme ultraviolet (EUV)/soft x-ray background are reported. The data were obtained with a focusing telescope designed and calibrated at U.C. Berkeley which observed EUV sources and the diffuse background as part of the Apollo-Soyuz mission in July, 1975. With a primary field-of-view of 2.3 + 0.1/sup 0/ FWHM and four EUV bandpass filters (16 to 25, 20 to 73, 80 to 108, and 80 to 250 eV) the EUV telescope obtained background data included in the final observational sample for 21 discrete sky locations and 11 large angular scans, as wellmore » as for a number of shorter observations. Analysis of the data reveals as intense flux above 80 eV energy, with upper limits to the background intensity given for the lower energy filters Ca 2 x 10/sup 4/ and 6 x 10/sup 2/ ph cm/sup -2/ sec/sup -1/ ster/sup -1/ eV/sup -1/ at 21 and 45 eV respectively). The 80 to 108 eV flux agrees within statistical errors with the earlier results of Cash, Malina and Stern (1976): the Apollo-Soyuz average reported intensity is 4.0 +- 1.3 ph cm/sup -2/ sec/sup -1/ ster/sup -1/ eV/sup -1/ at Ca 100 eV, or roughly a factor of ten higher than the corresponding 250 eV intensity. The uniformity of the background flux is uncertain due to limitations in the statistical accuracy of the data; upper limits to the point-to-point standard deviation of the background intensity are (..delta..I/I approximately less than 0.8 +- 0.4 (80 to 108 eV) and approximately less than 0.4 +- 0.2 (80 to 250 eV). No evidence is found for a correlation between the telescope count rate and earth-based parameters (zenith angle, sun angle, etc.) for E approximately greater than 80 eV (the lower energy bandpasses are significantly affected by scattered solar radiation. Unlike some previous claims for the soft x-ray background, no simple dependence upon galactic latitude is seen.« less
Does the Blazar Gamma-ray Spectrum Harden with Increasing Flux? - Analysis of Nine Years of EGRET Data

NASA Technical Reports Server (NTRS)

Nandikotkur, Giridhar; Jahoda, Keith M.; Hartman, R. C.; Mukherjee, R.; Sreekumar, P.; Boettcher, M.

2007-01-01

The Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (CGRO) discovered gamma-ray emission from more than 67 blazars during its nine-year lifetime. We conducted an exhaustive search of the EGRET archives and selected all the blazars that were observed multiple times and were bright enough to enable a spectral analysis using standard powerlaw models. The sample consists of 18 flat-spectrum radio quasars (FSRQs), 6 low-frequency-peaked BL Lacs (LBLs) and 2 high-frequency-peaked BL Lacs (HBLs). We do not detect any clear pattern in'the variation of spectral index with flux. Some of the blazars do not show any statistical evidence for spectral variability. The spectrum hardens with increasing flux in a few cases. There is also evidence for a flux-hardness anticorrelation at lo\\v fluxes in five blazars. The well observed blazars (3C 279,3C 273, PKS 0528-i-134, PKS 1622-297, PKS 0208- 512) do not show any overall trend in the long-term spectral dependence on flux, but the sample shows a mixture of hard and soft states. We observed spectral hysteresis at weekly timescales in all the three FSRQs for which data from flares lasting for 3 approx. 4 weeks were available. All three sources show a counterclockwise rotation despite the widely different flux profiles. Hysteresis in the spectral index vs. flux space has never been observed in FSRQs in gamma-rays at weekly timescales. itre analyze the observed spectral behavior in the context of various inverse-Compton mechanisms believed to be responsible for emission in the EGRET energy range. Our analysis uses the EGRET skymaps that were regenerated to include the changes in performance during the mission.
Monte-Carlo background simulations of present and future detectors in x-ray astronomy

NASA Astrophysics Data System (ADS)

Tenzer, C.; Kendziorra, E.; Santangelo, A.

2008-07-01

Reaching a low-level and well understood internal instrumental background is crucial for the scientific performance of an X-ray detector and, therefore, a main objective of the instrument designers. Monte-Carlo simulations of the physics processes and interactions taking place in a space-based X-ray detector as a result of its orbital environment can be applied to explain the measured background of existing missions. They are thus an excellent tool to predict and optimize the background of future observatories. Weak points of a design and the main sources of the background can be identified and methods to reduce them can be implemented and studied within the simulations. Using the Geant4 Monte-Carlo toolkit, we have created a simulation environment for space-based detectors and we present results of such background simulations for XMM-Newton's EPIC pn-CCD camera. The environment is also currently used to estimate and optimize the background of the future instruments Simbol-X and eRosita.
High redshift QSOs and the x ray background

NASA Technical Reports Server (NTRS)

Impey, Chris

1993-01-01

ROSAT pointed observations were made of 9 QSO's from the Large Bright Quasar Survey (LBQS). The LBQS is based on machine measurement of objective prism plates taken with the UK Schmidt Telescope. Software has been used to select QSO's by both color and by the presence of spectral features and continuum breaks. The probability of detection can be calculated as a function of magnitude, redshift and spectral features, and the completeness of the survey can be accurately estimated. Nine out of 1040 QSO's in the LBQS have z greater than 3. The observations will provide an important data point in the X-ray luminosity function of QSO's at high redshift. The QSO's with z greater than 3 span less than a magnitude in M(sub B), so can be combined as a homogeneous sample. This analysis is only possible with a sample drawn from a large and complete catalog such as the LBQS. Four of the 9 QSO's that were observed with the ROSAT PSPC for this proposal were detected, including one of the most luminous X-ray sources ever observed. The April 1992 version of the PROS DETECT package was used to reduce the data. The results have been used to search for evolution of the X-ray properties of QSO's in redshift. The 9 QSO's lie in the range -28.7 less than M(sub B) less than -27.8. When combined with data for 16 QSO's in a similar luminosity range at lower redshift correlations with luminosity and redshift can be separated out. The LBQS sample also yields a new constraint on the contribution of high redshift QSO's to the X-ray background. An initial requirement is knowledge of the X-ray properties (alpha(sub OX)) as a function of redshift. Integration over the evolving luminosity function of the LBQS then gives the QSO contribution to the source counts.
Apollo-Soyuz survey of the extreme-ultraviolet/soft X-ray background

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stern, R.; Bowyer, S.

1979-06-15

The results of an extensive sky survey of the extreme-ultraviolet (EUV)/soft X-ray background are reported. The data were obtained with a telescope, designed and calibrated at the University of California at Berkeley, which observed EUV sources and the diffuse background as part of the Apollo-Soyuz mission in 1975 July. With a primary field of view of 2 /sup 0/.3 +- 0 /sup 0/.1 FWHM and four EUV bandpass filters (16--25, 20--73, 80--108, and 80--250 eV), the EUV telescope obtained useful background data for 21 sky points, 11 large angle scans, and an additional group of short observations of both types.more » Analysis of the data reveals an intense 80--108 eV diffuse flux of 4.0 +- 1.3 photons cm/sup -2/ sr/sup -1/ eV/sup -1/ (broad-band weighted average). This is roughly a factor of 10 higher than the corresponding 150--280 eV average intensity and confirms the earlier results of Cash, Malina, and Stern. Galactic contributions to the background intensity at still lower energies are most likely masked by large fluxes of geocoronal or interplanetary solar-scattered resonance radiation; however, we drive upper limits to the local galactic background of 2 x 10/sup 4/ and 6 x 10/sup 2/ photons cm/sup -2/ sr/sup -1/ eV/sup -1/ averaged over the 16--25 eV and 20--73 eV bands, respectively. The uniformity of the background flux is uncertain due to limitations in the statistical accuracy of the data; we discuss probable upper limits to any spatial anisotropy. No evidence is found for a correlation between the telescope count rate and Earth-based parameters (zenith angle, Sun angle, etc.) for E> or approx. =80 eV. Unlike some previous claims for the soft X-ray background, no simple dependence upon galactic latitude is seen.Fitting models of thermal emission to the Apollo-Soyuz data yields constraints on model parameters that are consistent for a limited range of temperatures with the EUV results of Cash, Malina, and Stern and the soft X-ray data of Burstein et al.« less
On syntheses of the X-ray background with power-law sources

NASA Technical Reports Server (NTRS)

Dezotti, G.; Boldt, E. A.; Cavaliere, A.; Danese, L.; Franceschini, A.; Marshall, F. E.; Swank, J. H.; Szymkowiak, A. E.

1981-01-01

The conditions under which the combined emission from power law sources can mimic the X-ray background (XRB) spectrum in the 3-50 keV range are considered in view of HEAO 1 A-2 experiment measurements, and it is confirmed that a good fit may be obtained. The required spectral properties of the component sources differ, however, from those observed for local active galactic nuclei. Constraints are deduced for both the low luminosity extension and evolution of such local objects, and it is shown that any other class of sources contributing to the X-ray background must be characterized by an energy spectral index lower than about 0.4, which is the mean index of the XRB, and exhibit sleeper spectra at higher energies.
On syntheses of the X-ray background with power-law sources

NASA Astrophysics Data System (ADS)

De Zotti, G.; Boldt, E. A.; Cavaliere, A.; Danese, L.; Franceschini, A.; Marshall, F. E.; Swank, J. H.; Szymkowiak, A. E.

1981-08-01

The conditions under which the combined emission from power law sources can mimic the X-ray background (XRB) spectrum in the 3-50 keV range are considered in view of HEAO 1 A-2 experiment measurements, and it is confirmed that a good fit may be obtained. The required spectral properties of the component sources differ, however, from those observed for local active galactic nuclei. Constraints are deduced for both the low luminosity extension and evolution of such local objects, and it is shown that any other class of sources contributing to the X-ray background must be characterized by an energy spectral index lower than about 0.4, which is the mean index of the XRB, and exhibit sleeper spectra at higher energies.
Broadband Observations of High Redshift Blazars

NASA Astrophysics Data System (ADS)

Paliya, Vaidehi S.; Parker, M. L.; Fabian, A. C.; Stalin, C. S.

2016-07-01

We present a multi-wavelength study of four high redshift blazars, S5 0014+81 (z = 3.37), CGRaBS J0225+1846 (z = 2.69), BZQ J1430+4205 (z = 4.72), and 3FGL J1656.2-3303 (z = 2.40) using quasi-simultaneous data from the Swift, Nuclear Spectroscopic Telescope Array (NuSTAR) and the Fermi-Large Area Telescope (LAT) and also archival XMM-Newton observations. Other than 3FGL J1656.2-3303, none of the sources were known as γ-ray emitters, and our analysis of ˜7.5 yr of LAT data reveals the first time detection of statistically significant γ-ray emission from CGRaBS J0225+1846. We generate the broadband spectral energy distributions (SED) of all the objects, centering at the epoch of NuSTAR observations and reproduce them using a one-zone leptonic emission model. The optical-UV emission in all the objects can be explained by radiation from the accretion disk, whereas the X-ray to γ-ray windows of the SEDs are found to be dominated by inverse Compton scattering off the broad line region photons. All of them host black holes that are billions of solar masses. Comparing the accretion disk luminosity and the jet power of these sources with a large sample of blazars, we find them to occupy a high disk luminosity-jet power regime. We also investigate the X-ray spectral properties of the sources in detail with a major focus on studying the causes of soft X-ray deficit, a feature generally seen in high redshift radio-loud quasars. We summarize that this feature could be explained based on the intrinsic curvature in the jet emission rather than being due to the external effects predicted in earlier studies, such as host galaxy and/or warm absorption.
BROADBAND OBSERVATIONS OF HIGH REDSHIFT BLAZARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paliya, Vaidehi S.; Parker, M. L.; Fabian, A. C.

We present a multi-wavelength study of four high redshift blazars, S5 0014+81 ( z = 3.37), CGRaBS J0225+1846 ( z = 2.69), BZQ J1430+4205 ( z = 4.72), and 3FGL J1656.2−3303 ( z = 2.40) using quasi-simultaneous data from the Swift , Nuclear Spectroscopic Telescope Array ( NuSTAR ) and the Fermi -Large Area Telescope (LAT) and also archival XMM-Newton observations. Other than 3FGL J1656.2−3303, none of the sources were known as γ -ray emitters, and our analysis of ∼7.5 yr of LAT data reveals the first time detection of statistically significant γ -ray emission from CGRaBS J0225+1846. We generatemore » the broadband spectral energy distributions (SED) of all the objects, centering at the epoch of NuSTAR observations and reproduce them using a one-zone leptonic emission model. The optical−UV emission in all the objects can be explained by radiation from the accretion disk, whereas the X-ray to γ -ray windows of the SEDs are found to be dominated by inverse Compton scattering off the broad line region photons. All of them host black holes that are billions of solar masses. Comparing the accretion disk luminosity and the jet power of these sources with a large sample of blazars, we find them to occupy a high disk luminosity–jet power regime. We also investigate the X-ray spectral properties of the sources in detail with a major focus on studying the causes of soft X-ray deficit, a feature generally seen in high redshift radio-loud quasars. We summarize that this feature could be explained based on the intrinsic curvature in the jet emission rather than being due to the external effects predicted in earlier studies, such as host galaxy and/or warm absorption.« less
X-Ray Intraday Variability of Five TeV Blazars with NuSTAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandey, Ashwani; Gupta, Alok C.; Wiita, Paul J., E-mail: ashwanitapan@gmail.com, E-mail: acgupta30@gmail.com, E-mail: wiitap@tcnj.edu

We have examined 40 Nuclear Spectroscopic Telescope Array ( NuSTAR ) light curves (LCs) of five TeV emitting high synchrotron peaked blazars: 1ES 0229+200, Mrk 421, Mrk 501, 1ES 1959+650, and PKS 2155−304. Four of the blazars showed intraday variability in the NuSTAR energy range of 3–79 keV. Using an autocorrelation function analysis we searched for intraday variability timescales in these LCs and found indications of several between 2.5 and 32.8 ks in eight LCs of Mrk 421, a timescale around 8.0 ks for one LC of Mrk 501, and timescales of 29.6 and 57.4 ks in two LCs ofmore » PKS 2155-304. The other two blazars’ LCs do not show any evidence for intraday variability timescales shorter than the lengths of those observations; however, the data were both sparser and noisier for them. We found positive correlations with zero lag between soft (3–10 keV) and hard (10–79 keV) bands for most of the LCs, indicating that their emissions originate from the same electron population. We examined spectral variability using a hardness ratio analysis and noticed a general “harder-when-brighter” behavior. The 22 LCs of Mrk 421 observed between 2012 July and 2013 April show that this source was in a quiescent state for an extended period of time and then underwent an unprecedented double-peaked outburst while monitored on a daily basis during 2013 April 10–16. We briefly discuss models capable of explaining these blazar emissions.« less
CROSS-CORRELATION BETWEEN X-RAY AND OPTICAL/NEAR-INFRARED BACKGROUND INTENSITY FLUCTUATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitchell-Wynne, Ketron; Cooray, Asantha; Xue, Yongquan

Angular power spectra of optical and infrared background anisotropies at wavelengths between 0.5 and 5 μ m are a useful probe of faint sources present during reionization, in addition to faint galaxies and diffuse signals at low redshift. The cross-correlation of these fluctuations with backgrounds at other wavelengths can be used to separate some of these signals. A previous study on the cross-correlation between X-ray and Spitzer fluctuations at 3.6 μ m and 4.5 μ m has been interpreted as evidence for direct collapse black holes present at z > 12. Here we return to this cross-correlation and study its wavelengthmore » dependence from 0.5 to 4.5 μ m using Hubble and Spitzer data in combination with a subset of the 4 Ms Chandra observations in GOODS-S/ECDFS. Our study involves five Hubble bands at 0.6, 0.7, 0.85, 1.25, and 1.6 μ m, and two Spitzer -IRAC bands at 3.6 μ m and 4.5 μ m. We confirm the previously seen cross-correlation between 3.6 μ m (4.5 μ m) and X-rays with 3.7 σ (4.2 σ ) and 2.7 σ (3.7 σ ) detections in the soft [0.5–2] keV and hard [2–8] keV X-ray bands, respectively, at angular scales above 20 arcsec. The cross-correlation of X-rays with Hubble is largely anticorrelated, ranging between the levels of 1.4 σ –3.5 σ for all the Hubble and X-ray bands. This lack of correlation in the shorter optical/NIR bands implies the sources responsible for the cosmic infrared background at 3.6 and 4.5 μ m are at least partly dissimilar to those at 1.6 μ m and shorter.« less
HESS and Fermi-LAT discovery of γ-rays from the blazar 1ES 1312-423

DOE PAGES

Abramowski, A.; Acero, F.; Aharonian, F.; ...

2013-08-01

In this study, a deep observation campaign carried out by the High Energy Stereoscopic System (HESS) on Centaurus A enabled the discovery of γ-rays from the blazar 1ES 1312-423, 2° away from the radio galaxy. With a differential flux at 1 TeV of (Φ1 TeV) = (1.9 ± 0.6stat ± 0.4sys) × 10 -13 cm -2 s -1 TeV -1 corresponding to 0.5 percent of the Crab nebula differential flux and a spectral index Γ = 2.9 ± 0.5stat ± 0.2sys, 1ES 1312-423 is one of the faintest sources ever detected in the very high energy (E > 100 GeV)more » extragalactic sky. A careful analysis using three and a half years of Fermi Large Area Telescope (Fermi-LAT) data allows the discovery at high energies (E > 100 MeV) of a hard spectrum (Γ = 1.4 ± 0.4stat ± 0.2sys) source coincident with 1ES 1312-423. Radio, optical, UV and X-ray observations complete the spectral energy distribution of this blazar, now covering 16 decades in energy. Lastly, the emission is successfully fitted with a synchrotron self-Compton model for the non-thermal component, combined with a blackbody spectrum for the optical emission from the host galaxy.« less
The diffuse soft X-ray background as seen with the Einstein Observatory

NASA Technical Reports Server (NTRS)

Micela, G.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R., Jr.; Rosner, R.

1991-01-01

A systematic survey of the diffuse soft X-ray background as seen directly with the Einstein Observatory is presented. With the aid of 1633 selected 1 x 1 deg fields of view obtained by the IPC to provide about 5-percent sky coverage, with some bias toward the Galactic plane, the background in the 0.16-3.5 keV spectral region was spatially resolved on this angular scale. Maps of the background are characterized and produced at different energies within the Einstein passband. It is confirmed that the Galactic ridge is not present at energies below 0.33 keV and it is demonstrated that the appearance of the ridge above this energy is not due to hard Galactic sources with a flux above 10 exp -13 ergs/sq cm/s. A southern Galactic region is identified, with l between 80 and 180 deg and b less than -5 deg, where the mean background intensity has the lowest value and is homogeneous within better than 9 percent. The implications of these results for the Galactic structure and for the nature of the extragalactic X-ray background are discussed.
Time correlation between the radio and gamma-ray activity in blazars and the production site of the gamma-ray emission

DOE PAGES

Max-Moerbeck, W.; Hovatta, T.; Richards, J. L.; ...

2014-09-22

In order to determine the location of the gamma-ray emission site in blazars, we investigate the time-domain relationship between their radio and gamma-ray emission. Light-curves for the brightest detected blazars from the first 3 years of the mission of the Fermi Gamma-ray Space Telescope are cross-correlated with 4 years of 15GHz observations from the OVRO 40-m monitoring program. The large sample and long light-curve duration enable us to carry out a statistically robust analysis of the significance of the cross-correlations, which is investigated using Monte Carlo simulations including the uneven sampling and noise properties of the light-curves. Modeling the light-curvesmore » as red noise processes with power-law power spectral densities, we find that only one of 41 sources with high quality data in both bands shows correlations with significance larger than 3σ (AO0235+164), with only two more larger than even 2.25σ (PKS 1502+106 and B2 2308+34). Additionally, we find correlated variability in Mrk 421 when including a strong flare that occurred in July-September 2012. These results demonstrate very clearly the difficulty of measuring statistically robust multiwavelength correlations and the care needed when comparing light-curves even when many years of data are used. This should be a caution. In all four sources the radio variations lag the gamma-ray variations, suggesting that the gamma-ray emission originates upstream of the radio emission. Continuous simultaneous monitoring over a longer time period is required to obtain high significance levels in cross-correlations between gamma-ray and radio variability in most blazars.« less
The Diffuse Gamma-Ray Background from Type Ia Supernovae

NASA Technical Reports Server (NTRS)

Lien, Amy; Fields, Brian D.

2012-01-01

The origin of the diffuse extragalactic gamma-ray background (EGB) has been intensively studied but remains unsettled. Current popular source candidates include unresolved star-forming galaxies, starburst galaxies, and blazars. In this paper we calculate the EGB contribution from the interactions of cosmic rays accelerated by Type Ia supernovae, extending earlier work which only included core-collapse supernovae. We consider Type Ia events in star-forming galaxies, but also in quiescent galaxies that lack star formation. In the case of star-forming galaxies, consistently including Type Ia events makes little change to the star-forming EGB prediction, so long as both supernova types have the same cosmic-ray acceleration efficiencies in star-forming galaxies. Thus our updated EGB estimate continues to show that star-forming galaxies can represent a substantial portion of the signal measured by Fermi. In the case of quiescent galaxies, conversely, we find a wide range of possibilities for the EGB contribution. The dominant uncertainty we investigated comes from the mass in hot gas in these objects, which provides targets for cosmic rays: total gas masses are as yet poorly known, particularly at larger radii. Additionally, the EGB estimation is very sensitive to the cosmic-ray acceleration efficiency and confinement, especially in quiescent galaxies. In the most optimistic allowed scenarios, quiescent galaxies can be an important source of the EGB. In this case, star-forming galaxies and quiescent galaxies together will dominate the EGB and leave little room for other contributions. If other sources, such as blazars, are found to have important contributions to the EGB, then either the gas mass or cosmic-ray content of quiescent galaxies must be significantly lower than in their star-forming counterparts. In any case, improved Fermi EGB measurements will provide important constraints on hot gas and cosmic rays in quiescent galaxies.

THE BRIGHTEST GAMMA-RAY FLARING BLAZAR IN THE SKY: AGILE AND MULTI-WAVELENGTH OBSERVATIONS OF 3C 454.3 DURING 2010 NOVEMBER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vercellone, S.; Romano, P.; Striani, E.

2011-08-01

Since 2005, the blazar 3C 454.3 has shown remarkable flaring activity at all frequencies, and during the last four years it has exhibited more than one {gamma}-ray flare per year, becoming the most active {gamma}-ray blazar in the sky. We present for the first time the multi-wavelength AGILE, Swift, INTEGRAL, and GASP-WEBT data collected in order to explain the extraordinary {gamma}-ray flare of 3C 454.3 which occurred in 2010 November. On 2010 November 20 (MJD 55520), 3C 454.3 reached a peak flux (E >100 MeV) of F{sup p}{sub {gamma}} = (6.8 {+-} 1.0) x 10{sup -5} photons cm{sup -2} s{supmore » -1} on a timescale of about 12 hr, more than a factor of six higher than the flux of the brightest steady {gamma}-ray source, the Vela pulsar, and more than a factor of three brighter than its previous super-flare on 2009 December 2-3. The multi-wavelength data make possible a thorough study of the present event: the comparison with the previous outbursts indicates a close similarity to the one that occurred in 2009. By comparing the broadband emission before, during, and after the {gamma}-ray flare, we find that the radio, optical, and X-ray emission varies within a factor of 2-3, whereas the {gamma}-ray flux by a factor of 10. This remarkable behavior is modeled by an external Compton component driven by a substantial local enhancement of soft seed photons.« less
Optical photometric monitoring of gamma -ray loud blazars. II. Observations from November 1995 to June 1996

NASA Astrophysics Data System (ADS)

Raiteri, C. M.; Ghisellini, G.; Villata, M.; de Francesco, G.; Lanteri, L.; Chiaberge, M.; Peila, A.; Antico, G.

1998-02-01

New data from the optical monitoring of gamma -ray loud blazars at the Torino Astronomical Observatory are presented. Observations have been taken in the Johnson's B, V, and Cousins' R bands with the 1.05m REOSC telescope equipped with a 1242x1152 pixel CCD camera. Many of the 22 monitored sources presented here show noticeable magnitude variations. Periods corresponding to pointings of the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (CGRO) satellite are indicated on the light curves. The comparison of our data with those taken by CGRO in the gamma -ray band will contribute to better understand the mechanism of the gamma -ray emission. We finally show intranight light curves of 3C 66A and OJ 287, where microvariability was detected. Tables 2--21 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
Radio core dominance of Fermi blazars

NASA Astrophysics Data System (ADS)

Pei, Zhi-Yuan; Fan, Jun-Hui; Liu, Yi; Yuan, Yi-Hai; Cai, Wei; Xiao, Hu-Bing; Lin, Chao; Yang, Jiang-He

2016-07-01

During the first 4 years of mission, Fermi/LAT detected 1444 blazars (3FGL) (Ackermann et al. in Astrophys. J. 810:14, 2015). Fermi/LAT observations of blazars indicate that Fermi blazars are luminous and strongly variable with variability time scales, for some cases, as short as hours. Those observations suggest a strong beaming effect in Fermi/LAT blazars. In the present work, we will investigate the beaming effect in Fermi/LAT blazars using a core-dominance parameter, R = S_{core}/ S_{ext.}, where S_{core} is the core emission, while S_{ext.} is the extended emission. We compiled 1335 blazars with available core-dominance parameter, out of which 169 blazars have γ-ray emission (from 3FGL). We compared the core-dominance parameters, log R, between the 169 Fermi-detected blazars (FDBs) and the rest non-Fermi-detected blazars (non-FDBs), and we found that the averaged values are < log Rrangle = 0.99±0.87 for FDBs and < log Rrangle = -0.62±1.15 for the non-FDBs. A K-S test shows that the probability for the two distributions of FDBs and non-FDBs to come from the same parent distribution is near zero (P =9.12×10^{-52}). Secondly, we also investigated the variability index (V.I.) in the γ-ray band for FDBs, and we found V.I.=(0.12 ±0.07) log R+(2.25±0.10), suggesting that a source with larger log R has larger V.I. value. Thirdly, we compared the mean values of radio spectral index for FDBs and non-FDBs, and we obtained < α_{radio}rangle =0.06±0.35 for FDBs and < α_{radio}rangle =0.57±0.46 for non-FDBs. If γ-rays are composed of two components like radio emission (core and extended components), then we can expect a correlation between log R and the γ-ray spectral index. When we used the radio core-dominance parameter, log R, to investigate the relationship, we found that the spectral index for the core component is α_{γ}|_{core} = 1.11 (a photon spectral index of α_{γ}^{ph}|_{core} = 2.11) and that for the extended component is α_{γ}|_{ext.} = 0
Optical flare observed in the flaring gamma-ray blazar S5 1044+71

NASA Astrophysics Data System (ADS)

Pursimo, Tapio; Blay, Pere; Telting, John; Ojha, Roopesh

2017-01-01

We report optical photometry of the blazar S5 1044+71, obtained with the 2.56m Nordic Optical Telescope in La Palma, to look for any enhanced optical activity associated with a recent flare in the daily averaged gamma-ray flux (ATel#9928).
Characteristic Variability Timescales in the Gamma-ray Power Spectra of Blazars

NASA Astrophysics Data System (ADS)

Ryan, James Lee; Siemiginowska, Aneta; Sobolewska, Malgorzata; Grindlay, Jonathan E.

2018-01-01

We study the gamma-ray variability of 13 bright blazars observed with the Fermi Large Area Telescope in the 0.2-300 MeV band over 7.8 years.We find that continuous-time autoregressive moving average (CARMA) models provide adequate fits to the blazar light curves, and using the models we constrain the power spectral density (PSD) of each source.We also perform simulations to test the ability of CARMA modeling to recover the PSDs of artificial light curves with our data quality.Seven sources show evidence for a low-frequency break at an average timescale of ~1 year, with five of these sources showing evidence for an additional high-frequency break at an average timescale of ~7 days.We compare our results to previous studies, and discuss the possible physical interpretations of our results.
Signature of inverse Compton emission from blazars

NASA Astrophysics Data System (ADS)

Gaur, Haritma; Mohan, Prashanth; Wierzcholska, Alicja; Gu, Minfeng

2018-01-01

Blazars are classified into high-, intermediate- and low-energy-peaked sources based on the location of their synchrotron peak. This lies in infra-red/optical to ultra-violet bands for low- and intermediate-peaked blazars. The transition from synchrotron to inverse Compton emission falls in the X-ray bands for such sources. We present the spectral and timing analysis of 14 low- and intermediate-energy-peaked blazars observed with XMM-Newton spanning 31 epochs. Parametric fits to X-ray spectra help constrain the possible location of transition from the high-energy end of the synchrotron to the low-energy end of the inverse Compton emission. In seven sources in our sample, we infer such a transition and constrain the break energy in the range 0.6-10 keV. The Lomb-Scargle periodogram is used to estimate the power spectral density (PSD) shape. It is well described by a power law in a majority of light curves, the index being flatter compared to general expectation from active galactic nuclei, ranging here between 0.01 and 1.12, possibly due to short observation durations resulting in an absence of long-term trends. A toy model involving synchrotron self-Compton and external Compton (EC; disc, broad line region, torus) mechanisms are used to estimate magnetic field strength ≤0.03-0.88 G in sources displaying the energy break and infer a prominent EC contribution. The time-scale for variability being shorter than synchrotron cooling implies steeper PSD slopes which are inferred in these sources.
The Blazar 3C 66A in 2003-2004: hadronic versus leptonic model fits

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reimer, A.; Joshi, M.; Boettcher, M.

2008-12-24

The low-frequency peaked BL Lac object 3C 66A was the subject of an extensive multi-wavelength campaign from July 2003 till April 2004, which included quasi-simultaneous observations at optical, X-rays and very high energy gamma-rays. Here we apply the hadronic Synchrotron-Proton Blazar (SPB) model to the observed spectral energy distribution time-averaged over a flaring state, and compare the resulting model fits to those obtained from the application of the leptonic Synchrotron-Self-Compton (SSC) model. The results are used to identify diagnostic key predictions of the two blazar models for future multi-wavelength observations.
The New Surprising Behaviour of the Two 'Prototype' Blazars PKS 2155-304 and 3C 279

DOE Office of Scientific and Technical Information (OSTI.GOV)

Costamante, Luigi; /Stanford U., HEPL /KIPAC, Menlo Park; Aharonian, Felix

2011-11-21

Recent VHE observations have unveiled a surprising behaviour in two well-known blazars at opposite sides of the blazar sequence. PKS 2155-304 have shown for the first time in an HBL a large Compton dominance, high {gamma}-ray luminosities and a cubic relation between X-ray and VHE fluxes. 3C 279 is the first FSRQ detected at VHE. The high luminosity required to overcome the significant absorption caused by the BLR emission cannot be easily reconciled with the historical and quasi-simultaneous SED properties. Both cases shed a new light on the structure and ambient fields of blazars. Contrary to previous claims, it ismore » also shown that 3C 279 - as any FSRQ - cannot provide robust constraints on the EBL.« less
Constraints on the Location of γ-Ray Sample of Blazars with Radio Core-shift Measurements

NASA Astrophysics Data System (ADS)

Wu, Linhui; Wu, Qingwen; Yan, Dahai; Chen, Liang; Fan, Xuliang

2018-01-01

We model simultaneous or quasi-simultaneous multi-band spectral energy distributions (SEDs) for a sample of 25 blazars that have radio core-shift measurements, where a one-zone leptonic model and Markov chain Monte Carlo technique are adopted. In the SED fitting for 23 low-synchrotron-peaked (LSP) blazars, the seed photons from the broad-line (BLR) and molecular torus are considered respectively in the external Compton process. We find that the SED fitting with the seed photons from the torus are better than those utilizing BLR photons, which suggest that the γ-ray emitting region may be located outside the BLR. Assuming the magnetic field strength in the γ-ray emitting region as constrained from the SED fitting follows the magnetic field distribution as derived from the radio core-shift measurements (i.e., B{(R)≃ {B}1{pc}(R/1{pc})}-1, where R is the distance from the central engine and {B}1{pc} is the magnetic field strength at 1 pc), we further calculate the location of the γ-ray emitting region, {R}γ , for these blazars. We find that {R}γ ∼ 2× {10}4{R}{{S}}≃ 10 {R}{BLR} ({R}{{S}} is the Schwarzschild radius and {R}{BLR} is the BLR size), where {R}{BLR} is estimated from the broad-line luminosities using the empirical correlations obtained using the reverberation mapping methods.
Background radiation in inelastic X-ray scattering and X-ray emission spectroscopy. A study for Johann-type spectrometers

NASA Astrophysics Data System (ADS)

Paredes Mellone, O. A.; Bianco, L. M.; Ceppi, S. A.; Goncalves Honnicke, M.; Stutz, G. E.

2018-06-01

A study of the background radiation in inelastic X-ray scattering (IXS) and X-ray emission spectroscopy (XES) based on an analytical model is presented. The calculation model considers spurious radiation originated from elastic and inelastic scattering processes along the beam paths of a Johann-type spectrometer. The dependence of the background radiation intensity on the medium of the beam paths (air and helium), analysed energy and radius of the Rowland circle was studied. The present study shows that both for IXS and XES experiments the background radiation is dominated by spurious radiation owing to scattering processes along the sample-analyser beam path. For IXS experiments the spectral distribution of the main component of the background radiation shows a weak linear dependence on the energy for the most cases. In the case of XES, a strong non-linear behaviour of the background radiation intensity was predicted for energy analysis very close to the backdiffraction condition, with a rapid increase in intensity as the analyser Bragg angle approaches π / 2. The contribution of the analyser-detector beam path is significantly weaker and resembles the spectral distribution of the measured spectra. Present results show that for usual experimental conditions no appreciable structures are introduced by the background radiation into the measured spectra, both in IXS and XES experiments. The usefulness of properly calculating the background profile is demonstrated in a background subtraction procedure for a real experimental situation. The calculation model was able to simulate with high accuracy the energy dependence of the background radiation intensity measured in a particular XES experiment with air beam paths.
Masses, Dimensionless Kerr Parameters, and Emission Regions in GeV Gamma-Ray-loud Blazars

NASA Astrophysics Data System (ADS)

Xie, G.-Z.; Ma, L.; Liang, E.-W.; Zhou, S.-B.; Xie, Z.-H.

2003-11-01

We have compiled sample of 17 GeV γ-ray-loud blazars, for which rapid optical variability and γ-ray fluxes are well observed, from the literature. We derive estimates of the masses, the minimum Kerr parameters amin, and the size of the emission regions of the supermassive black holes (SMBHs) for the blazars in the sample from their minimum optical variability timescales and γ-ray fluxes. The results show that (1) the masses derived from the optical variability timescale (MH) are significantly correlated with the masses from the γ-ray luminosity (MKNH); (2) the values of amin of the SMBHs with masses MH>=108.3 Msolar (three out of 17 objects) range from ~0.5 to ~1.0, suggesting that these SMBHs are likely to be Kerr black holes. For the SMBHs with MH<108.3 Msolar, however, amin=0, suggesting that a nonrotating black hole model cannot be ruled out for these objects. In addition, the values of the size of the emission region, r*, for the two kinds of SMBHs are significantly different. For the SMBHs with amin>0, the sizes of the emission regions are almost within the horizon (2rG) and marginally bound orbit (4rG), while for those with amin=0 they are in the range (4.3-66.4)rG, extending beyond the marginally stable orbit (6rG). These results may imply that (1) the rotational state, the radiating regions, and the physical processes in the inner regions for the two kinds of SMBH are significantly different and (2) the emission mechanisms of GeV γ-ray blazars are related to the SMBHs in their centers but are not related to the two different kinds of SMBH.
Blazar Artist Concept

NASA Image and Video Library

2016-08-24

Black-hole-powered galaxies called blazars are the most common sources detected by NASA's Fermi Gamma-ray Space Telescope. As matter falls toward the supermassive black hole at the galaxy's center, some of it is accelerated outward at nearly the speed of light along jets pointed in opposite directions. When one of the jets happens to be aimed in the direction of Earth, as illustrated here, the galaxy appears especially bright and is classified as a blazar. http://photojournal.jpl.nasa.gov/catalog/PIA20912
Cosmic X-ray Physics: A Suborbital Investigation of the Diffuse X-ray Background Including Instrumentation Development

NASA Astrophysics Data System (ADS)

McCammon, Dan

We propose an investigation to improve our understanding of the Galactic diffuse X-ray background. The ultimate purpose of this is to determine the role of hot phases of the interstellar medium in mediating stellar feedback in star formation, in transport of metals, and in determining the structure and evolution of the Galaxy. This work will involve a flight of an existing payload with small modifications in Woomera, South Australia, to observe the Galactic soft X-ray bulge and attempt to determine its nature and emission mechanisms. It will also involve the development of detectors capable of 1-2 eV FWHM energy resolution in the 100-400 eV range with the intent of obtaining a scientifically useful spectrum on a sounding rocket flight of the emission from one million degree gas in this energy range. This will require a total area of 1-2 cm^2 for the detector array. With the collaboration and advice of microwave experts at the Goddard Space Flight Center, we will fabricate and test waveguide-below-cutoff filters to provide the necessary attenuation of infrared radiation for these detectors while still allowing relatively good x- ray transmission below 300 eV. The detectors, filters, and flight experience with the detector readouts are all relevant to future NASA major missions. The filters would be particularly valuable in allowing thermal detectors (microcalorimeters) similar to those used here in the X-ray range to be applied to the EUV and vacuum ultraviolet, where they offer large potential gains over existing detectors. These investigations will provide the primary training for our graduate students, and will involve a substantial number of undergraduates.
BL-Lacs in X-Ray Outburst

NASA Technical Reports Server (NTRS)

Remillard, Ronald A.; Urry, C. Megan; Aharonian, Felix; Pian, Elena; Sambruna, Rita; Coppi, Paolo

2000-01-01

We conducted a multifrequency campaign for the TeV blazar Markarian 421 in 1998 April. The campaign started from a pronounced high-amplitude flare recorded by BeppoSAX and Whipple; the Advanced Satellite for Cosmology and Astrophysics (ASCA) observation started three days later. In the X-ray data, we detected multiple flares, occurring on timescales of about one day. ASCA data clearly reveal spectral variability. The comparison of the data from ASCA, the Extreme Ultraviolet Explorer, and the Rossi X-Ray Timing Explorer indicates that the variability amplitudes in the low-energy synchrotron component are larger at higher photon energies. In TeV and gamma-rays, large intraday variations-which were correlated with the X-ray flux-were observed when results from three Cerenkov telescopes were combined. The rms variability of TeV and gamma-rays was similar to that observed in hard X-rays, above ten keV. The X-ray light curve reveals flares that are almost symmetric for most cases, implying that the dominant timescale is the light crossing time through the emitting region. The structure function analysis based on the continuous X-ray light curve of seven days indicates that the characteristic timescale is approx. 0.5 days. The analysis of ASCA light curves in various energy bands appears to show both soft (positive) and hard (negative) lags. These may not be real, as systematic effects could also produce these lags, which are all much smaller than an orbit. If the lags of both signs are real, these imply that the particle acceleration and X-ray cooling timescales are similar.
An Einstein survey of the 1 keV soft X-ray background in the Galactic plane

NASA Technical Reports Server (NTRS)

Stanford, John M.; Caillault, Jean-Pierre

1994-01-01

We have analyzed 56 Einstein Observatory Imaging Proportional Counter (IPC) observations within +/- 3 deg of the Galactic plane in order to determine the low-latitude soft X-ray background flux in the 0.56-1.73 keV band. Any detected X-ray point source which fell within our regions of study was removed from the image, enabling us to present maps of the background flux as a function of Galactic latitude along 18 meridians. These maps reveal considerable structure to the background in the Galactic plane on an angular scale of approximately 1 deg. Our results are compared with those of an earlier study of the 1 keV X-ray background along l = 25 deg by Kahn & Caillault. The double-peaked structure they found is not discernible in our results, possibly because of the presence of solar backscattered flux in their data. A model which takes into account contributions to the background by extragalactic and stellar sources, the distribution of both atomic and molecular absorbing material with the Galaxy, the energy dependence of the cross section for absorption of X-rays, and the energy dependence of the detector has been constructed and fitted to these new data to derive constraints on the scale height, temperature, and volume emissivity of the unaccounted-for X-ray-emitting material. The results of this model along l = 25 deg are roughly similar to those of the model of Kahn & Caillault along the same meridian.
LAMP: a micro-satellite based soft x-ray polarimeter for astrophysics

NASA Astrophysics Data System (ADS)

She, Rui; Feng, Hua; Muleri, Fabio; Soffitta, Paolo; Xu, Renxin; Li, Hong; Bellazzini, Ronaldo; Wang, Zhanshan; Spiga, Daniele; Minuti, Massimo; Brez, Alessandro; Spandre, Gloria; Pinchera, Michele; Sgrò, Carmelo; Baldini, Luca; Wen, Mingwu; Shen, Zhengxiang; Pareschi, Giovanni; Tagliaferri, Gianpiero; Tayabaly, Kashmira; Salmaso, Bianca; Zhan, Yafeng

2015-08-01

The Lightweight Asymmetry and Magnetism Probe (LAMP) is a micro-satellite mission concept dedicated for astronomical X-ray polarimetry and is currently under early phase study. It consists of segmented paraboloidal multilayer mirrors with a collecting area of about 1300 cm2 to reflect and focus 250 eV X-rays, which will be detected by position sensitive detectors at the focal plane. The primary targets of LAMP include the thermal emission from the surface of pulsars and synchrotron emission produced by relativistic jets in blazars. With the expected sensitivity, it will allow us to detect polarization or place a tight upper limit for about 10 pulsars and 20 blazars. In addition to measuring magnetic structures in these objects, LAMP will also enable us to discover bare quark stars if they exist, whose thermal emission is expected to be zero polarized, while the thermal emission from neutron stars is believed to be highly polarized due to plasma polarization and the quantum electrodynamics (QED) effect. Here we present an overview of the mission concept, its science objectives and simulated observational results.
The soft X-ray diffuse background observed with the HEAO 1 low-energy detectors

NASA Technical Reports Server (NTRS)

Garmire, G. P.; Nousek, J. A.; Apparao, K. M. V.; Burrows, D. N.; Fink, R. L.; Kraft, R. P.

1992-01-01

Results of a study of the diffuse soft-X-ray background as observed by the low-energy detectors of the A-2 experiment aboard the HEAO 1 satellite are reported. The observed sky intensities are presented as maps of the diffuse X-ray background sky in several energy bands covering the energy range 0.15-2.8 keV. It is found that the soft X-ray diffuse background (SXDB) between 1.5 and 2.8 keV, assuming a power law form with photon number index 1.4, has a normalization constant of 10.5 +/- 1.0 photons/sq cm s sr keV. Below 1.5 keV the spectrum of the SXDB exceeds the extrapolation of this power law. The low-energy excess for the NEP can be fitted with emission from a two-temperature equilibrium plasma model with the temperatures given by log I1 = 6.16 and log T2 = 6.33. It is found that this model is able to account for the spectrum below 1 keV, but fails to yield the observed Galactic latitude variation.
Comparison of Optical and Multi-Waveband Variations of Selected Gamma-ray Bright Blazars in 2012

NASA Astrophysics Data System (ADS)

Schultz, Benjamin; Jorstad, S. G.; Marscher, A. P.; Williamson, K. E.; Walker, G. E.

2013-01-01

We present multi-wavelength observations of several gamma-ray bright blazars. We combine optical data obtained with the 17-inch CCD telescope of Maria Mitchell Observatory with space- and ground-based observations carried out with a variety of instruments. These include a number of other optical telescopes, the Fermi Gamma-Ray Space Telescope at photon energies of 0.1-200 GeV, and the Swift satellite at 0.3-10 keV plus optical and UV wavelengths. Three of the observed blazars proved to be particularly active - BL Lac, Mrk501, and CTA-102. BL Lac was of special interest, displaying remarkable activity in multiple wavelengths during this observation period, including the optical, in which it underwent its largest observed flare in a number of years. In addition, CTA-102 has recently undergone an unprecedented multi-wavelength outburst. We cross-correlate the variations in the different wavebands in an effort to guide theoretical interpretations of the optical and high-energy emission from blazars. This project was supported by NSF/REU grant AST-0851892 and the Nantucket Maria Mitchell Association. The research at Boston University was supported in part by NSF grant AST-0907893 and by NASA through Fermi grant NNX11AQ03G.
INTEGRAL hard X-ray spectra of the cosmic X-ray background and Galactic ridge emission

NASA Astrophysics Data System (ADS)

Türler, M.; Chernyakova, M.; Courvoisier, T. J.-L.; Lubiński, P.; Neronov, A.; Produit, N.; Walter, R.

2010-03-01

Aims: We derive the spectra of the cosmic X-ray background (CXB) and of the Galactic ridge X-ray emission (GRXE) in the ~20-200 keV range from the data of the IBIS instrument aboard the INTEGRAL satellite obtained during the four dedicated Earth-occultation observations in early 2006. Methods: We analyze the modulation of the IBIS/ISGRI detector counts induced by the passage of the Earth through the field of view of the instrument. Unlike previous studies, we do not fix the spectral shape of the various contributions, but model instead their spatial distribution and derive for each of them the expected modulation of the detector counts. The spectra of the diffuse emission components are obtained by fitting the normalizations of the model lightcurves to the observed modulation in different energy bins. Because of degeneracy, we guide the fits with a realistic choice of the input parameters and a constraint for spectral smoothness. Results: The obtained CXB spectrum is consistent with the historic HEAO-1 results and falls slightly below the spectrum derived with Swift/BAT. A 10% higher normalization of the CXB cannot be completely excluded, but it would imply an unrealistically high albedo of the Earth. The derived spectrum of the GRXE confirms the presence of a minimum around 80 keV with improved statistics and yields an estimate of ~0.6 M⊙ for the average mass of white dwarfs in the Galaxy. The analysis also provides updated normalizations for the spectra of the Earth's albedo and the cosmic-ray induced atmospheric emission. Conclusions: This study demonstrates the potential of INTEGRAL Earth-occultation observations to derive the hard X-ray spectra of three fundamental components: the CXB, the GRXE and the Earth emission. Further observations would be extremely valuable to confirm our results with improved statistics.
Resolving the Extragalactic γ -Ray Background above 50 GeV with the Fermi Large Area Telescope

DOE PAGES

Ackermann, M.; Ajello, M.; Albert, A.; ...

2016-04-14

The Fermi Large Area Telescope (LAT) Collaboration has recently released a catalog of 360 sources detected above 50 GeV (2FHL). This catalog was obtained using 80 months of data re-processed with Pass 8, the newest event-level analysis, which significantly improves the acceptance and angular resolution of the instrument. Most of the 2FHL sources at high Galactic latitude are blazars. In this paper, using detailed Monte Carlo simulations, we measure, for the first time, the source count distribution, dN/dS, of extragalactic γ-ray sources at E > 50 GeV and find that it is compatible with a Euclidean distribution down to the lowest measured source flux in the 2FHL (~8 x 10 -12 ph cm -2s -1). We employ a one-point photon fluctuation analysis to constrain the behavior of dN/dS below the source detection threshold. Overall, the source count distribution is constrained over three decades in flux and found compatible with a broken power law with a break flux, S b, in the range [8 x 10 -12, 1.5 x 10 -11] ph cm -2s -1 and power-law indices below and above the break of α 2 ϵ [1.60, 1.75] and α 1 = 2.49 ± 0.12, respectively. Integration of dN/dS shows that point sources account for at least 86more » $$+16\\atop{-14}$$ % of the total extragalactic γ-ray background. The simple form of the derived source count distribution is consistent with a single population (i.e., blazars) dominating the source counts to the minimum flux explored by this analysis. Finally, we estimate the density of sources detectable in blind surveys that will be performed in the coming years by the Cherenkov Telescope Array.« less

CdZnTe detector for hard x-ray and low energy gamma-ray focusing telescope

NASA Astrophysics Data System (ADS)

Natalucci, L.; Alvarez, J. M.; Barriere, N.; Caroli, E.; Curado da Silva, R. M.; Del Sordo, S.; Di Cosimo, S.; Frutti, M.; Hernanz, M.; Lozano, M.; Quadrini, E.; Pellegrini, G.; Stephen, J. B.; Ubertini, P.; Uslenghi, M. C.; Zoglauer, A.

2008-07-01

The science drivers for a new generation soft gamma-ray mission are naturally focused on the detailed study of the acceleration mechanisms in a variety of cosmic sources. Through the development of high energy optics in the energy energy range 0.05-1 MeV it will be possible to achieve a sensitivity about two orders of magnitude better than the currently operating gamma-ray telescopes. This will open a window for deep studies of many classes of sources: from Galactic X-ray binaries to magnetars, from supernova remnants to Galaxy clusters, from AGNs (Seyfert, blazars, QSO) to the determination of the origin of the hard X-/gamma-ray cosmic background, from the study of antimatter to that of the dark matter. In order to achieve the needed performance, a detector with mm spatial resolution and very high peak efficiency is needed. The instrumental characteristics of this device could eventually allow to detect polarization in a number of objects including pulsars, GRBs and bright AGNs. In this work we focus on the characteristics of the focal plane detector, based on CZT or CdTe semiconductor sensors arranged in multiple planes and viewed by a side detector to enhance gamma-ray absorption in the Compton regime. We report the preliminary results of an optimization study based on simulations and laboratory tests, as prosecution of the former design studies of the GRI mission which constitute the heritage of this activity.
Fermi-LAT View of Bright Flaring Gamma-Ray Blazars

NASA Astrophysics Data System (ADS)

Bastieri, D.; Ciprini, S.; Gasparrini, D.

2011-06-01

The Fermi LAT provides a continuous and uniform monitoring of the Universe in the gamma-ray band. During the first year many gamma-ray blazar flares, some unidentified transients and emission by the Sun while in a quiet state were promptly detected. This is mainly due to the design of the mission, featuring a detector, the LAT with a wide field of view, and to the operation of the spacecraft itself, that can cover every region of the sky every 3 hours. Nevertheless, the scientific exploitation of this monitoring is more fruitful when early information about transients reaches a broader community. In this respect, the indefatigable activity of flare advocates, who worked on weekly shifts to validate the results and quickly broadcast information about flares and new detections, was the key to most scientific results.
Unusual flaring activity in the blazar PKS 1424-418 during 2008-2011

DOE PAGES

Buson, S.; Longo, F.; Larsson, S.; ...

2014-09-01

Context. Blazars are a subset of active galactic nuclei (AGN) with jets that are oriented along our line of sight. Variability and spectral energy distribution (SED) studies are crucial tools for understanding the physical processes responsible for observed AGN emission. Aims. We report peculiar behaviour in the bright γ-ray blazar PKS 1424-418 and use its strong variability to reveal information about the particle acceleration and interactions in the jet. Methods. Correlation analysis of the extensive optical coverage by the ATOM telescope and nearly continuous γ-ray coverage by the Fermi Large Area Telescope is combined with broadband, time-dependent modeling of themore » SED incorporating supplemental information from radio and X-ray observations of this blazar. Results. We analyse in detail four bright phases at optical-GeV energies. These flares of PKS 1424-418 show high correlation between these energy ranges, with the exception of one large optical flare that coincides with relatively low γ-ray activity. Although the optical/ γ-ray behaviour of PKS 1424-418 shows variety, the multiwavelength modeling indicates that these differences can largely be explained by changes in the flux and energy spectrum of the electrons in the jet that are radiating. We find that for all flares the SED is adequately represented by a leptonic model that includes inverse Compton emission from external radiation fields with similar parameters. Conclusions. Detailed studies of individual blazars like PKS 1424-418 during periods of enhanced activity in different wavebands are helping us identify underlying patterns in the physical parameters in this class of AGN.« less
NuSTAR Detection of the Blazar B2 1023+25 at Redshift 5.3

NASA Technical Reports Server (NTRS)

Sbarrato, T.; Tagliaferri, G.; Ghisellini, G.; Perri, M.; Puccetti, S.; Balokovic, M.; Nardini, M.; Stern, D.; Boggs, S. E.; Brandt, W. N.;

2013-01-01

B2 1023+25 is an extremely radio-loud quasar at zeta = 5.3 that was first identified as a likely high-redshift blazar candidate in the SDSS+FIRST quasar catalog. Here, we use the Nuclear Spectroscopic Telescope Array (NuSTAR) to investigate its non-thermal jet emission, whose high-energy component we detected in the hard X-ray energy band. The X-ray flux is approximately 5.5 × 10 (exp -14) erg cm(exp -2) s(exp -1) (5-10 keV) and the photon spectral index is Gamma(x) approx. =1.3-1.6. Modeling the full spectral energy distribution, we find that the jet is oriented close to the line of sight, with a viewing angle of approximately 3deg, and has significant Doppler boosting, with a large bulk Lorentz factor approximately 13, which confirms the identification of B2 1023+25 as a blazar. B2 1023+25 is the first object at redshift larger than 5 detected by NuSTAR, demonstrating the ability of NuSTAR to investigate the early X-ray universe and to study extremely active supermassive black holes located at very high redshift.

X-Ray Flux and Spectral Variability of Six TeV Blazars with NuSTAR

NASA Astrophysics Data System (ADS)

Pandey, Ashwani; Gupta, Alok C.; Wiita, Paul J.

2018-05-01

We report the first results of timing and spectral studies of Nuclear Spectroscopic Telescope Array observations of six TeV-emitting high-frequency peaked blazars: 1ES 0347-121, 1ES 0414+009, RGB J0710+591, 1ES 1101-232, 1ES 1218+304, and H 2356-309. Two out of these six TeV blazars, 1ES 1101‑232 and 1ES 1218+304, showed strong evidence of intraday variations in the 3–79 keV energy range during those observations. We also found a hint of an intraday variability timescale of 23.5 ks in the light curve of 1ES 1218+304 using an autocorrelation function analysis. We obtained a magnetic field B ∼ 0.03 G, electron Lorentz factor γ ∼ 2.16 × 106, and emission region size R ∼ 1.19 × 1016 cm for 1ES 1218+304 using that variability timescale. The other blazars’ light curves do not show any variability timescales shorter than their observation lengths; however, we note that the data were both noisier and sparser for them. We also investigated the spectral shape of these TeV blazars and found that the spectrum of 1ES 0414+009 is well described by a single power law with a photon index Γ ∼ 2.77. The spectra of the other five HBLs are somewhat better represented by log-parabola models with local photon indices (at 10 keV) α ∼ 2.23 ‑ 2.67 and curvature parameters β ∼ 0.27 ‑ 0.43.
Herschel PACS and SPIRE Observations of Blazar PKS 1510-089: A Case for Two Blazar Zones

DOE PAGES

Nalewajko, Krzysztof; Sikora, Marek; Madejski, Greg M.; ...

2012-11-06

In this paper, we present the results of observations of blazar PKS 1510–089 with the Herschel Space Observatory PACS and SPIRE instruments, together with multiwavelength data from Fermi/LAT, Swift, SMARTS, and Submillimeter Array. The source was found in a quiet state, and its far-infrared spectrum is consistent with a power law with a spectral index of α ≃ 0.7. Our Herschel observations were preceded by two "orphan" gamma-ray flares. The near-infrared data reveal the high-energy cutoff in the main synchrotron component, which cannot be associated with the main gamma-ray component in a one-zone leptonic model. This is because in suchmore » a model the luminosity ratio of the external-Compton (EC) and synchrotron components is tightly related to the frequency ratio of these components, and in this particular case an unrealistically high energy density of the external radiation would be implied. Therefore, we consider a well-constrained two-zone blazar model to interpret the entire data set. Finally, in this framework, the observed infrared emission is associated with the synchrotron component produced in the hot-dust region at the supra-parsec scale, while the gamma-ray emission is associated with the EC component produced in the broad-line region at the sub-parsec scale. In addition, the optical/UV emission is associated with the accretion disk thermal emission, with the accretion disk corona likely contributing to the X-ray emission.« less
Suzaku Observations of Luminous Quasars: Revealing the Nature of High-Energy Blazar Emission in Low-level activity States

DOE PAGES

Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

2010-05-21

We present the results from the Suzaku X-ray observations of five flat-spectrum radio quasars (FSRQs), namely PKS 0208–512, Q 0827+243, PKS 1127–145, PKS 1510–089, and 3C 454.3. Here, all these sources were additionally monitored simultaneously or quasi-simultaneously by the Fermi satellite in gamma rays and the Swift UVOT in the UV and optical bands, respectively. Here, we constructed their broadband spectra covering the frequency range from 10 14 Hz up to 10 25 Hz, and those reveal the nature of high-energy emission of luminous blazars in their low-activity states. The analyzed X-ray spectra are well fitted by a power-law modelmore » with photoelectric absorption. In the case of PKS 0208–512, PKS 1127–145, and 3C 454.3, the X-ray continuum showed indication of hardening at low energies. Moreover, when compared with the previous X-ray observations, we see a significantly increasing contribution of low-energy photons to the total X-ray fluxes when the sources are getting fainter. The same behavior can be noted in the Suzaku data alone. A likely explanation involves a variable, flat-spectrum component produced via inverse-Compton emission, plus an additional, possibly steady soft X-ray component prominent when the source gets fainter. This soft X-ray excess is represented either by a steep power-law (photon indices Γ ~ 3-5) or a blackbody-type emission with temperatures kT ~ 0.1-0.2 keV. We model the broadband spectra of the five observed FSRQs using synchrotron self-Compton and/or external-Compton radiation models. Lastly, our modeling suggests that the difference between the low- and high-activity states in luminous blazars is due to the different total kinetic power of the jet, most likely related to varying bulk Lorentz factor of the outflow within the blazar emission zone.« less
Chandra and the VLT Jointly Investigate the Cosmic X-Ray Background

NASA Astrophysics Data System (ADS)

2001-03-01

Summary Important scientific advances often happen when complementary investigational techniques are brought together . In the present case, X-ray and optical/infrared observations with some of the world's foremost telescopes have provided the crucial information needed to solve a 40-year old cosmological riddle. Very detailed observations of a small field in the southern sky have recently been carried out, with the space-based NASA Chandra X-Ray Observatory as well as with several ground-based ESO telescopes, including the Very Large Telescope (VLT) at the Paranal Observatory (Chile). Together, they have provided the "deepest" combined view at X-ray and visual/infrared wavelengths ever obtained into the distant Universe. The concerted observational effort has already yielded significant scientific results. This is primarily due to the possibility to 'identify' most of the X-ray emitting objects detected by the Chandra X-ray Observatory on ground-based optical/infrared images and then to determine their nature and distance by means of detailed (spectral) observations with the VLT . In particular, there is now little doubt that the so-called 'X-ray background' , a seemingly diffuse short-wave radiation first detected in 1962, in fact originates in a vast number of powerful black holes residing in active nuclei of distant galaxies . Moreover, the present investigation has permitted to identify and study in some detail a prime example of a hitherto little known type of object, a distant, so-called 'Type II Quasar' , in which the central black hole is deeply embedded in surrounding gas and dust. These achievements are just the beginning of a most fruitful collaboration between "space" and "ground". It is yet another impressive demonstration of the rapid progress of modern astrophysics, due to the recent emergence of a new generation of extremely powerful instruments. PR Photo 09a/01 : Images of a small part of the Chandra Deep Field South , obtained with ESO telescopes
Starburst Galaxies: Hard X-ray spectra and contribution to the diffuse background

NASA Technical Reports Server (NTRS)

Gruber, Duane E.

1993-01-01

During the period of this grant two main tasks were performed: a determination of a selection criterion for starburst galaxies most likely to emit X-rays, and performance of a pilot study of the X-ray emission from nine such systems. Starburst galaxies may be expected to emit flat-spectrum X-ray at energies above 10 keV resulting from the various remnants of the short-lived massive stars which characterize the starburst. The investigation to determine the optimum sample resulted in a change from an X-ray selected (HEAO-2) sample to infrared selection based on the IRAS catalogue. A much broader sample thereby available for study, and selection could be limited to only the nearest objects and still obtain a reasonably large sample. A sample of 99 of the brightest infrared starburst galaxies was settled on for the X-ray survey. For a set of practical size, this was then reduced to a subset of 53, based on luminosity and nearness. X-ray emission from these objects was individually measured from the UCSD HEAO-1 all-sky survey in four energy bands between 13 keV to 160 keV. This data base consists of about 20 optical disk volumes. Net significance for the result was roughly two sigma, and a very hard spectral shape is indicated for the net spectrum of the surveyed galaxies. With the possibility of detection of the class, it was then felt worthwhile to examine fluxes from these sources in other archival data. This was performed with the HEAO-1 A2 data and the HEAO-2 (EINSTEIN) main archive and slew survey. Positive results were also obtained for the sample, but again at weak significance. With three independent measures of weak X-ray fluxes from nearby starburst galaxies, we wrote a letter to the Astrophysical Journal (enclosed) discussing these results and their likely significance, in particular, for the contribution to the cosmic diffuse x-ray background, perhaps as much as 25 percent.
SPECTRAL ANALYSIS OF FERMI -LAT BLAZARS ABOVE 50 GEV

DOE PAGES

Domínguez, Alberto; Ajello, Marco

2015-11-04

We present an analysis of the intrinsic (unattenuated by the extragalactic background light, EBL) power-law spectral indices of 128 extragalactic sources detected up to z ~ 2 with the Fermi-Large Area Telescope (LAT) at very high energies (VHEs, E ≥50 GeV). The median of the intrinsic index distribution is 2.20 (versus 2.54 for the observed distribution). We also analyze the observed spectral breaks (i.e., the difference between the VHE and high energy, HE, 100 MeV ≤ E ≤ 300 GeV, spectral indices). The Fermi-LAT has now provided a large sample of sources detected both at VHE and HE with comparablemore » exposure that allows us to test models of extragalactic γ-ray photon propagation. We find that our data are compatible with simulations that include intrinsic blazar curvature and EBL attenuation. There is also no evidence of evolution with redshift of the physics that drives the photon emission in high-frequency synchrotron peak (HSP) blazars. This makes HSP blazars excellent probes of the EBL.« less
CXBN: a blueprint for an improved measurement of the cosmological x-ray background

NASA Astrophysics Data System (ADS)

Simms, Lance M.; Jernigan, J. G.; Malphrus, Benjamin K.; McNeil, Roger; Brown, Kevin Z.; Rose, Tyler G.; Lim, Hyoung S.; Anderson, Steven; Kruth, Jeffrey A.; Doty, John P.; Wampler-Doty, Matthew; Cominsky, Lynn R.; Prasad, Kamal S.; Thomas, Eric T.; Combs, Michael S.; Kroll, Robert T.; Cahall, Benjamin J.; Turba, Tyler T.; Molton, Brandon L.; Powell, Margaret M.; Fitzpatrick, Jonathan F.; Graves, Daniel C.; Gaalema, Stephen D.; Sun, Shunming

2012-10-01

A precise measurement of the Cosmic X-ray Background (CXB) is crucial for constraining models of the evolution and composition of the universe. While several large, expensive satellites have measured the CXB as a secondary mission, there is still disagreement about normalization of its spectrum. The Cosmic X-ray Background NanoSat (CXBN) is a small, low-cost satellite whose primary goal is to measure the CXB over its two-year lifetime. Benefiting from a low instrument-induced background due to its small mass and size, CXBN will use a novel, pixelated Cadmium Zinc Telluride (CZT) detector with energy resolution < 1 keV over the range 1-60 keV to measure the CXBN with unprecedented accuracy. This paper describes CXBN and its science payload, including the GEANT4 model that has been used to predict overall performance and the backgrounds from secondary particles in Low Earth Orbit. It also addresses the strategy for scanning the sky and calibrating the data, and presents the expected results over the two-year mission lifetime.
The Influence of Plasma Effects of Pair Beams on the Intergalactic Cascade Emission of Blazars

NASA Astrophysics Data System (ADS)

Menzler, Ulf; Schlickeiser, Reinhard

2014-03-01

The attenuation of TeV γ-rays from distant blazars by the extragalactic background light (EBL) produces relativistic electron-positron pair beams. It has been shown by Broderick et. al. (2012) and Schlickeiser et. al (2012) that a pair beam traversing the intergalactic medium is unstable to linear two-stream instabilities of both electrostatic and electromagnetic nature. While for strong blazars all free pair energy is dissipated in heating the intergalactic medium and a potential electromagnetic cascade via inverse-Compton scattering with the cosmic microwave background is suppressed, we investigate the case of weak blazars where the back reaction of generated electrostatic turbulence leads to a plateauing of the electron energy spectrum. In the ultra-relativistic Thomson limit we analytically calculate the inverse-Compton spectral energy distribution for both an unplateaued and a plateaued beam scenario, showing a peak reduction factor of Rpeak ≈ 0.345. This is consistent with the FERMI non-measurements of a GeV excess in the spectrum of EBL attenuated TeV blazars. Claims on the lower bound of the intergalactic magnetic field strengths, made by several authors neglecting plasma effects, are thus put into question.
Broad-Band Continuum and Line Emission of the gamma-Ray Blazar PKS 0537-441

NASA Technical Reports Server (NTRS)

Pian, E.; Falomo, R.; Hartman, R. C.; Maraschi, L.; Tavecchio, F.; Tornikoski, M.; Treves, A.; Urry, C. M.; Ballo, L.; Mukherjee, R.;

2002-01-01

PKS 0537-441, a bright gamma ray emitting blazar was observed at radio, optical, UV and X-ray frequencies during various EGRET paintings, often quasi-simultaneously. In 1995 the object was found in an intense emission state at all wavelengths. BeppoSAX observations made in 1998, non-simultaneously with exposures at other frequencies, allow us to characterize precisely the spectral shape of the high energy blazer component, which we attribute to inverse Compton scatter in The optical-to-gamma-ray spectral energy distributions at the different epochs show that the gamma-ray luminosity dominates the barometric output. This, together with the presence of optical and UV line emission, suggests that, besides the synchrotron self-Compton mechanism, the Compton upscattering of photons external to the jet (e.g., in the broad line region) may have a significant role for high energy radiation. The multiwavelength variability can be reproduced by changes of the plasma bulk Lorentz factor. The spectrum secured by ICE in 1995 appears to be partially absorbed shortward of approximately 1700 Angstroms. However, this signature is not detected in the HST spectrum taker during a lower state of the source. The presence of intervening absorbers is not supported by optical imaging and spectroscopy of the field.

Optical Spectroscopic Observations of γ-Ray Blazar Candidates. III. The 2013/2014 Campaign in the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Landoni, M.; Massaro, F.; Paggi, A.; D'Abrusco, R.; Milisavljevic, D.; Masetti, N.; Smith, H. A.; Tosti, G.; Chomiuk, L.; Strader, J.; Cheung, C. C.

2015-05-01

We report the results of our exploratory program carried out with the southern Astrophysical Research telescope aimed at associating counterparts and establishing the nature of the Fermi Unidentified γ-ray Sources (UGSs). We selected the optical counterparts of six UGSs from the Fermi catalog on the basis of our recently discovered tight connection between infrared and γ-ray emission found for the γ-ray blazars detected by the Wide-Field Infrared Survey Explorer in its all-sky survey. We perform for the first time a spectroscopic study of the low-energy counterparts of the Fermi UGSs, in the optical band, confirming the blazar-like nature of the whole sample. We also present new spectroscopic observations of six active galaxies of uncertain type associated with Fermi sources which appear to be BL Lac objects. Finally, we report the spectra collected for six known γ-ray blazars belonging to the Roma BZCAT that were obtained to establish their nature or better estimate their redshifts. Two interesting cases of high redshift and extremely luminous BL Lac objects (z ≥ 1.18 and z ≥ 1.02, based on the detection of Mg ii intervening systems) are also discussed. Based on observations obtained at the southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).
A color gradient in the soft X-ray diffuse background

NASA Technical Reports Server (NTRS)

Snowden, S. L.; Schmitt, J. H. M. M.; Edwards, B. C.

1990-01-01

It is shown that the deviations of the soft X-ray diffuse background B band to C band intensity ratio from a constant value can be described as a simple dipole-like variation across the sky. In terms of the observed Wisconsin B/C band intensity ratio, the mean value is 0.355, the dipole magnitude is 0.106, and the positive dipole axis points toward l = 168.7 deg, b = 11.2 deg, almost in the galactic anticenter direction. This gradient in the spectral hardness can be due to several causes; the simplest is a temperature gradient in the X-ray emitting plasma of the local cavity from about 10 exp 6.2 K toward the galactic center to about 10 exp 5.9 K in the anticenter direction. While the physical origin of such a temperature gradient is uncertain, the alignment of the dipole with the higher temperature (and absorbed) Loop I region may be significant.
Simultaneous Multiwavelength Observations of the Blazar 1ES 1959+650 at a Low TeV Flux

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tagliaferri, G.; Ghisellini, G.; Foschini, L.

We present the results from a multiwavelength campaign on the TeV blazar 1ES 1959+650, performed in 2006 May. Data from the optical, UV, soft- and hard-X-ray, and very high energy (VHE) gamma-ray (E > 100 GeV) bands were obtained with the Suzaku and Swift satellites, the MAGIC telescope, and other ground-based facilities. The source spectral energy distribution (SED), derived from Suzaku and MAGIC observations at the end of 2006 May, shows the usual double hump shape, with the synchrotron peak at a higher flux level than the Compton peak. With respect to historical values, during our campaign the source exhibitedmore » a relatively high state in X-rays and optical, while in the VHE band it was at one of the lowest level so far recorded. We also monitored the source for flux spectral variability on a time window of 10 days in the optical-UV and X-ray bands and 7 days in the VHE band. The source varies more in the X-ray than in the optical band, with the 2-10 keV X-ray flux varying by a factor of {approx}2. The synchrotron peak is located in the X-ray band and moves to higher energies as the source gets brighter, with the X-ray fluxes above it varying more rapidly than the X-ray fluxes at lower energies. The variability behavior observed in the X-ray band cannot be produced by emitting regions varying independently and suggests instead some sort of 'standing shock' scenario. The overall SED is well represented by a homogeneous one-zone synchrotron inverse Compton emission model, from which we derive physical parameters that are typical of high-energy peaked blazars.« less
IGR J12319-0749: Evidence for Another Extreme Blazar Found with INTEGRAL

NASA Technical Reports Server (NTRS)

Bassani, L.; Landi, R.; Marshall, F. E.; Malizia, A.; Bazzano, A.; Bird, A. J.; Gehrels, N.; Ubertini, P.; Masetti, N.

2012-01-01

We report on the identification of a new soft gamma-ray source, IGR J12319 C0749, detected with the IBIS imager on board the INTEGRAL satellite. The source, which has an observed 20 C100 keV flux of 8.3 10.12 erg cm.2 s.1, is spatially coincident with an AGN at redshift z = 3.12. The broad-band continuum, obtained by combining XRT and IBIS data, is flat ( =1.3) with evidence for a spectral break around 25 keV (100 keV in the source rest frame). X-ray observations indicate flux variability which is further supported by a comparison with a previous ROSAT measurement. IGR J12319 C0749 is also a radio emitting object likely characterized by a flat spectrum and high radio loudness; optically it is a broad-line emitting object with a massive black hole (2.8 109 solar masses) at its center. The source Spectral Energy Distribution is similar to another high redshift blazar, 225155+2217 at z = 3.668: both objects are bright, with a large accretion disk luminosity and a Compton peak located in the hard X-ray/soft gamma-ray band. IGR J12319 C0749 is likely the second most distant blazar detected so far by INTEGRAL.
High-energy sources at low radio frequency: the Murchison Widefield Array view of Fermi blazars

DOE PAGES

Giroletti, M.; Massaro, F.; D’Abrusco, R.; ...

2016-04-01

Low-frequency radio arrays are opening a new window for the study of the sky, both to study new phenomena and to better characterize known source classes. Being flat-spectrum sources, blazars are so far poorly studied at low radio frequencies. In this paper, we characterize the spectral properties of the blazar population at low radio frequency, compare the radio and high-energy properties of the gamma-ray blazar population, and search for radio counterparts of unidentified gamma-ray sources. We cross-correlated the 6100 deg 2 Murchison Widefield Array Commissioning Survey catalogue with the Roma blazar catalogue, the third catalogue of active galactic nuclei detectedmore » by Fermi-LAT, and the unidentified members of the entire third catalogue of gamma-ray sources detected by Fermi-LAT. When available, we also added high-frequency radio data from the Australia Telescope 20 GHz catalogue. We find low-frequency counterparts for 186 out of 517 (36%) blazars, 79 out of 174 (45%) gamma-ray blazars, and 8 out of 73 (11%) gamma-ray blazar candidates. The mean low-frequency (120–180 MHz) blazar spectral index is (α low) = 0.57 ± 0.02: blazar spectra are flatter than the rest of the population of low-frequency sources, but are steeper than at ~GHz frequencies. Low-frequency radio flux density and gamma-ray energy flux display a mildly significant and broadly scattered correlation. Ten unidentified gamma-ray sources have a (probably fortuitous) positional match with low radio frequency sources. Low-frequency radio astronomy provides important information about sources with a flat radio spectrum and high energy. However, the relatively low sensitivity of the present surveys still misses a significant fraction of these objects. Finally, upcoming deeper surveys, such as the GaLactic and Extragalactic All-Sky MWA (GLEAM) survey, will provide further insight into this population.« less
High-energy sources at low radio frequency: the Murchison Widefield Array view of Fermi blazars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giroletti, M.; Massaro, F.; D’Abrusco, R.

Low-frequency radio arrays are opening a new window for the study of the sky, both to study new phenomena and to better characterize known source classes. Being flat-spectrum sources, blazars are so far poorly studied at low radio frequencies. In this paper, we characterize the spectral properties of the blazar population at low radio frequency, compare the radio and high-energy properties of the gamma-ray blazar population, and search for radio counterparts of unidentified gamma-ray sources. We cross-correlated the 6100 deg 2 Murchison Widefield Array Commissioning Survey catalogue with the Roma blazar catalogue, the third catalogue of active galactic nuclei detectedmore » by Fermi-LAT, and the unidentified members of the entire third catalogue of gamma-ray sources detected by Fermi-LAT. When available, we also added high-frequency radio data from the Australia Telescope 20 GHz catalogue. We find low-frequency counterparts for 186 out of 517 (36%) blazars, 79 out of 174 (45%) gamma-ray blazars, and 8 out of 73 (11%) gamma-ray blazar candidates. The mean low-frequency (120–180 MHz) blazar spectral index is (α low) = 0.57 ± 0.02: blazar spectra are flatter than the rest of the population of low-frequency sources, but are steeper than at ~GHz frequencies. Low-frequency radio flux density and gamma-ray energy flux display a mildly significant and broadly scattered correlation. Ten unidentified gamma-ray sources have a (probably fortuitous) positional match with low radio frequency sources. Low-frequency radio astronomy provides important information about sources with a flat radio spectrum and high energy. However, the relatively low sensitivity of the present surveys still misses a significant fraction of these objects. Finally, upcoming deeper surveys, such as the GaLactic and Extragalactic All-Sky MWA (GLEAM) survey, will provide further insight into this population.« less
Blazar emission modeling: going beyond spherical cows

NASA Astrophysics Data System (ADS)

Giannios, Dimitrios

Blazars are a subclass of Active Galactic Nuclei with non-thermal, variable emission extending over most of the electromagnetic spectrum, i.e., from radio up to gamma-rays. The blazar emission is believed to originate in relativistic jets emerging from supermassive black holes at galactic centers, when the jet points close to the line of sight. Because of their very high-energy emission and high luminosity, blazars have long been considered as prime candidates for the acceleration of ultra-high-energy cosmic rays (UHECRs). It comes as no surprise, therefore, that blazars have been the target of multiple observational campaigns. NASA satellite missions in synergy with ground-based facilities have led to huge observational progress in recent years. Yet, the theoretical understanding of the non-thermal processes responsible for the blazar emission lags far behind the observational progress. There is no reliable theory built from first principles for the energy dissipation and particle acceleration mechanisms at work in blazar jets. As a result, there exists no broadly-accepted framework for the particle distribution, geometry and magnetic field in the high-energy emitting regions in blazars. Over the past several years, Co-PI Giannios has argued that blazar emission can be understood as the result of magnetic energy dissipation via magnetic reconnection. In particular, the physical properties in the reconnection layer - where the emission is assumed to take place - can naturally reproduce the extreme energetics and timescales of the observed flaring episodes in blazars. Here, we propose to put the theory of magnetic reconnection in the context of blazar emission on a much more robust footing by capitalizing on new observational constraints and large progress in fully-kinetic particlein-cell (PIC) simulations led by Co-PI Sironi. Thanks to large-scale PIC simulations, we have recently demonstrated that reconnection can satisfy all the basic conditions for the blazar

Gamma rays from blazars

NASA Astrophysics Data System (ADS)

Tavecchio, Fabrizio

2017-01-01

Blazars are high-energy engines providing us natural laboratories to study particle acceleration, relativistic plasma processes, magnetic field dynamics, black hole physics. Key informations are provided by observations at high-energy (in particular by Fermi/LAT) and very-high energy (by Cherenkov telescopes). I give a short account of the current status of the field, with particular emphasis on the theoretical challenges connected to the observed ultra-fast variability events and to the emission of flat spectrum radio quasars in the very high energy band.
Cosmological Implications of the Effects of X-Ray Clusters on the Cosmic Microwave Background

NASA Technical Reports Server (NTRS)

Forman, William R.

1996-01-01

We have been carrying forward a program to confront X-ray observations of clusters and their evolution as derived from X-ray observatories with observations of the cosmic microwave background radiation (CMBR). In addition to the material covered in our previous reports (including three published papers), most recently we have explored the effects of a cosmological constant on the predicted Sunyaev-Zel'dovich effect from the ensemble of clusters. In this report we summarize that work from which a paper will be prepared.
Cosmic x ray physics

NASA Technical Reports Server (NTRS)

Mccammon, Dan; Cox, D. P.; Kraushaar, W. L.; Sanders, W. T.

1990-01-01

The annual progress report on Cosmic X Ray Physics is presented. Topics studied include: the soft x ray background, proportional counter and filter calibrations, the new sounding rocket payload: X Ray Calorimeter, and theoretical studies.
RoboPol: Unveiling the Physics of Blazar Jets from Skinakas

NASA Astrophysics Data System (ADS)

Pavlidou, V.

2016-06-01

Blazars are powered by relativistic jets and radiate exclusively through extreme, nonthermal particle interactions, energized by accretion onto supermassive black holes. Despite intensive observational and theoretical efforts over the last four decades, the details of blazar astrophysics remain elusive. The launch of NASA's Fermi Gammaray Space Telescope in 2008 provided an unprecedented opportunity for the systematic study of blazar jets and has prompted large-scale blazar monitoring efforts across wavelengths. In such a multi-wavelength campaign, a novel effect was discovered: fast changes in the optical polarization during gamma-ray flares. Optical emission from blazars is significantly polarized and the polarization probes the magnetic field structure in the jet. For this reason, such polarization rotations reveal important information about the evolution of disturbances responsible for blazar flares. The RoboPol program for the polarimetric monitoring of statistically complete samples of blazars was developed in 2013 to systematically study this class of events. RoboPol is a collaboration between the University of Crete, Caltech, the Max-Planck Institute for Radio Astronomy, the Inter-University Centre for Astronomy and Astrophysics in India, and the Nicolaus Copernicus University in Poland. Using a novel polarimeter operating at the 1.3m telescope of the Skinakas Observatory in Crete, it has succeeded in its 3 years of operation in taking optopolarimetric rotations of blazars from novelty status to a well-studied phenomenon that can be used to answer long-standing questions in our theoretical understanding of jets. We review the RoboPol program and its most important results in the classification of the optopolarimetric properties of blazars, the statistical properties of polarization rotations, and their relation to gamma-ray activity in blazar jets.
Spectral properties of bright Fermi-detected blazars in the gamma-ray band

DOE PAGES

Abdo, A. A.

2010-01-28

We investigated the gamma-ray energy spectra of bright blazars of the LAT Bright AGN Sample (LBAS) using Fermi-LAT data. Spectral properties (hardness, curvature, and variability) established using a data set accumulated over 6 months of operation are presented and discussed for different blazar classes and subclasses: flat spectrum radio quasars (FSRQs), low-synchrotron peaked BLLacs (LSP-BLLacs), intermediate-synchrotron peaked BLLacs (ISP-BLLacs), and high-synchrotron peaked BLLacs (HSP-BLLacs). Furthermore, the distribution of photon index (Γ, obtained from a power-law fit above 100 MeV) is found to correlate strongly with blazar subclass. The change in spectral index from that averaged over the 6 months observingmore » period is < 0.2-0.3 when the flux varies by about an order of magnitude, with a tendency toward harder spectra when the flux is brighter for FSRQs and LSP-BLLacs. A strong departure from a single power-law spectrum appears to be a common feature for FSRQs. Finally, we present this feature for some high-luminosity LSP-BLLacs, and a small number of ISP-BLLacs. It is absent in all LBAS HSP-BLLacs. For 3C 454.3 and AO 0235+164, the two brightest FSRQ source and LSP-BLLac source, respectively, a broken power law (BPL) gives the most acceptable of power law, BPL, and curved forms. The consequences of these findings are discussed.« less
Detection of very high energy gamma-ray emission from the gravitationally lensed blazar QSO B0218+357 with the MAGIC telescopes

NASA Astrophysics Data System (ADS)

Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.; Antoranz, P.; Arcaro, C.; Babic, A.; Banerjee, B.; Bangale, P.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Berti, A.; Biasuzzi, B.; Biland, A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Buson, S.; Carosi, A.; Chatterjee, A.; Clavero, R.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; de Oña Wilhelmi, E.; Di Pierro, F.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher Glawion, D.; Elsaesser, D.; Engelkemeier, M.; Fallah Ramazani, V.; Fernández-Barral, A.; Fidalgo, D.; Fonseca, M. V.; Font, L.; Frantzen, K.; Fruck, C.; Galindo, D.; García López, R. J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Giammaria, P.; Godinović, N.; Gora, D.; Guberman, D.; Hadasch, D.; Hahn, A.; Hayashida, M.; Herrera, J.; Hose, J.; Hrupec, D.; Hughes, G.; Idec, W.; Kodani, K.; Konno, Y.; Kubo, H.; Kushida, J.; La Barbera, A.; Lelas, D.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; López-Coto, R.; Majumdar, P.; Makariev, M.; Mallot, K.; Maneva, G.; Manganaro, M.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Miranda, J. M.; Mirzoyan, R.; Moralejo, A.; Moretti, E.; Nakajima, D.; Neustroev, V.; Niedzwiecki, A.; Nievas Rosillo, M.; Nilsson, K.; Nishijima, K.; Noda, K.; Nogués, L.; Paiano, S.; Palacio, J.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Paredes-Fortuny, X.; Pedaletti, G.; Peresano, M.; Perri, L.; Persic, M.; Poutanen, J.; Prada Moroni, P. G.; Prandini, E.; Puljak, I.; Garcia, J. R.; Reichardt, I.; Rhode, W.; Ribó, M.; Rico, J.; Saito, T.; Satalecka, K.; Schroeder, S.; Schweizer, T.; Shore, S. N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Stamerra, A.; Strzys, M.; Surić, T.; Takalo, L.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Torres, D. F.; Toyama, T.; Treves, A.; Vanzo, G.; Verguilov, V.; Vovk, I.; Ward, J. E.; Will, M.; Wu, M. H.; Zanin, R.; Desiante, R.

2016-11-01

Context. QSO B0218+357 is a gravitationally lensed blazar located at a redshift of 0.944. The gravitational lensing splits the emitted radiation into two components that are spatially indistinguishable by gamma-ray instruments, but separated by a 10-12 day delay. In July 2014, QSO B0218+357 experienced a violent flare observed by the Fermi-LAT and followed by the MAGIC telescopes. Aims: The spectral energy distribution of QSO B0218+357 can give information on the energetics of z 1 very high energy gamma-ray sources. Moreover the gamma-ray emission can also be used as a probe of the extragalactic background light at z 1. Methods: MAGIC performed observations of QSO B0218+357 during the expected arrival time of the delayed component of the emission. The MAGIC and Fermi-LAT observations were accompanied by quasi-simultaneous optical data from the KVA telescope and X-ray observations by Swift-XRT. We construct a multiwavelength spectral energy distribution of QSO B0218+357 and use it to model the source. The GeV and sub-TeV data obtained by Fermi-LAT and MAGIC are used to set constraints on the extragalactic background light. Results: Very high energy gamma-ray emission was detected from the direction of QSO B0218+357 by the MAGIC telescopes during the expected time of arrival of the trailing component of the flare, making it the farthest very high energy gamma-ray source detected to date. The observed emission spans the energy range from 65 to 175 GeV. The combined MAGIC and Fermi-LAT spectral energy distribution of QSO B0218+357 is consistent with current extragalactic background light models. The broadband emission can be modeled in the framework of a two-zone external Compton scenario, where the GeV emission comes from an emission region in the jet, located outside the broad line region.
Detection of very high energy gamma-ray emission from the gravitationally lensed blazar QSO B0218+357 with the MAGIC telescopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.

QSO B0218+357 is a gravitationally lensed blazar located at a redshift of 0.944. The gravitational lensing splits the emitted radiation into two components that are spatially indistinguishable by gamma-ray instruments, but separated by a 10–12 day delay. In July 2014, QSO B0218+357 experienced a violent flare observed by the Fermi-LAT and followed by the MAGIC telescopes. The spectral energy distribution of QSO B0218+357 can give information on the energetics of z ~ 1 very high energy gamma-ray sources. Furthermore, the gamma-ray emission can also be used as a probe of the extragalactic background light at z ~ 1. MAGIC performedmore » observations of QSO B0218+357 during the expected arrival time of the delayed component of the emission. The MAGIC and Fermi-LAT observations were accompanied by quasi-simultaneous optical data from the KVA telescope and X-ray observations by Swift-XRT. We construct a multiwavelength spectral energy distribution of QSO B0218+357 and use it to model the source. The GeV and sub-TeV data obtained by Fermi-LAT and MAGIC are used to set constraints on the extragalactic background light. We detected very high energy gamma-ray emission from the direction of QSO B0218+357 by the MAGIC telescopes during the expected time of arrival of the trailing component of the flare, making it the farthest very high energy gamma-ray source detected to date. We also observed emission spans the energy range from 65 to 175 GeV. The combined MAGIC and Fermi-LAT spectral energy distribution of QSO B0218+357 is consistent with current extragalactic background light models. The broadband emission can be modeled in the framework of a two-zone external Compton scenario, where the GeV emission comes from an emission region in the jet, located outside the broad line region.« less
Detection of very high energy gamma-ray emission from the gravitationally lensed blazar QSO B0218+357 with the MAGIC telescopes

DOE PAGES

Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.; ...

2016-11-04

QSO B0218+357 is a gravitationally lensed blazar located at a redshift of 0.944. The gravitational lensing splits the emitted radiation into two components that are spatially indistinguishable by gamma-ray instruments, but separated by a 10–12 day delay. In July 2014, QSO B0218+357 experienced a violent flare observed by the Fermi-LAT and followed by the MAGIC telescopes. The spectral energy distribution of QSO B0218+357 can give information on the energetics of z ~ 1 very high energy gamma-ray sources. Furthermore, the gamma-ray emission can also be used as a probe of the extragalactic background light at z ~ 1. MAGIC performedmore » observations of QSO B0218+357 during the expected arrival time of the delayed component of the emission. The MAGIC and Fermi-LAT observations were accompanied by quasi-simultaneous optical data from the KVA telescope and X-ray observations by Swift-XRT. We construct a multiwavelength spectral energy distribution of QSO B0218+357 and use it to model the source. The GeV and sub-TeV data obtained by Fermi-LAT and MAGIC are used to set constraints on the extragalactic background light. We detected very high energy gamma-ray emission from the direction of QSO B0218+357 by the MAGIC telescopes during the expected time of arrival of the trailing component of the flare, making it the farthest very high energy gamma-ray source detected to date. We also observed emission spans the energy range from 65 to 175 GeV. The combined MAGIC and Fermi-LAT spectral energy distribution of QSO B0218+357 is consistent with current extragalactic background light models. The broadband emission can be modeled in the framework of a two-zone external Compton scenario, where the GeV emission comes from an emission region in the jet, located outside the broad line region.« less
Cosmic x ray physics

NASA Technical Reports Server (NTRS)

Mccammon, Dan; Cox, D. P.; Kraushaar, W. L.; Sanders, W. T.

1991-01-01

The annual progress report on Cosmic X Ray Physics for the period 1 Jan. to 31 Dec. 1990 is presented. Topics studied include: soft x ray background, new sounding rocket payload: x ray calorimeter, and theoretical studies.
MULTIBAND DIAGNOSTICS OF UNIDENTIFIED 1FGL SOURCES WITH SUZAKU AND SWIFT X-RAY OBSERVATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takeuchi, Y.; Kataoka, J.; Maeda, K.

2013-10-01

We have analyzed all the archival X-ray data of 134 unidentified (unID) gamma-ray sources listed in the first Fermi/LAT (1FGL) catalog and subsequently followed up by the Swift/XRT. We constructed the spectral energy distributions (SEDs) from radio to gamma-rays for each X-ray source detected, and tried to pick up unique objects that display anomalous spectral signatures. In these analyses, we target all the 1FGL unID sources, using updated data from the second Fermi/LAT (2FGL) catalog on the Large Area Telescope (LAT) position and spectra. We found several potentially interesting objects, particularly three sources, 1FGL J0022.2–1850, 1FGL J0038.0+1236, and 1FGL J0157.0–5259,more » which were then more deeply observed with Suzaku as a part of an AO-7 program in 2012. We successfully detected an X-ray counterpart for each source whose X-ray spectra were well fitted by a single power-law function. The positional coincidence with a bright radio counterpart (currently identified as an active galactic nucleus, AGN) in the 2FGL error circles suggests these sources are definitely the X-ray emission from the same AGN, but their SEDs show a wide variety of behavior. In particular, the SED of 1FGL J0038.0+1236 is not easily explained by conventional emission models of blazars. The source 1FGL J0022.2–1850 may be in a transition state between a low-frequency peaked and a high-frequency peaked BL Lac object, and 1FGL J0157.0–5259 could be a rare kind of extreme blazar. We discuss the possible nature of these three sources observed with Suzaku, together with the X-ray identification results and SEDs of all 134 sources observed with the Swift/XRT.« less
Probing dissipation mechanisms in BL Lac jets through X-ray polarimetry

NASA Astrophysics Data System (ADS)

Tavecchio, F.; Landoni, M.; Sironi, L.; Coppi, P.

2018-06-01

The dissipation of energy flux in blazar jets plays a key role in the acceleration of relativistic particles. Two possibilities are commonly considered for the dissipation processes, magnetic reconnection - possibly triggered by instabilities in magnetically-dominated jets - , or shocks - for weakly magnetized flows. We consider the polarimetric features expected for the two scenarios analyzing the results of state-of-the-art simulations. For the magnetic reconnection scenario we conclude, using results from global relativistic MHD simulations, that the emission likely occurs in turbulent regions with unstructured magnetic fields, although the simulations do not allow us to draw firm conclusions. On the other hand, with local particle-in-cell simulations we show that, for shocks with a magnetic field geometry suitable for particle acceleration, the self-generated magnetic field at the shock front is predominantly orthogonal to the shock normal and becomes quasi-parallel downstream. Based on this result we develop a simplified model to calculate the frequency-dependent degree of polarization, assuming that high-energy particles are injected at the shock and cool downstream. We apply our results to HBLs, blazars with the maximum of their synchrotron output at UV-soft X-ray energies. While in the optical band the predicted degree of polarization is low, in the X-ray emission it can ideally reach 50%, especially during active/flaring states. The comparison between measurements in the optical and in the X-ray band made during active states (feasible with the planned IXPE satellite) are expected to provide valuable constraints on the dissipation and acceleration processes.
RoboPol: first season rotations of optical polarization plane in blazars

DOE PAGES

Blinov, D.; Pavlidou, V.; Papadakis, I.; ...

2015-08-26

Here, we present first results on polarization swings in optical emission of blazars obtained by RoboPol, a monitoring programme of an unbiased sample of gamma-ray bright blazars specially designed for effective detection of such events. A possible connection of polarization swing events with periods of high activity in gamma-rays is investigated using the data set obtained during the first season of operation. It was found that the brightest gamma-ray flares tend to be located closer in time to rotation events, which may be an indication of two separate mechanisms responsible for the rotations. Blazars with detected rotations during non-rotating periodsmore » have significantly larger amplitude and faster variations of polarization angle than blazars without rotations. Our simulations show that the full set of observed rotations is not a likely outcome (probability ≤1.5 × 10 -2) of a random walk of the polarization vector simulated by a multicell model. Furthermore, it is highly unlikely (~5 × 10 -5) that none of our rotations is physically connected with an increase in gamma-ray activity.« less
The X-ray spectra of blazars: Analysis of the complete EXOSAT archive

NASA Technical Reports Server (NTRS)

Sambruna, Rita M.; Barr, Paul; Giommi, Paolo; Maraschi, Laura; Tagliaferri, Gianpiero; Treves, Aldo

1994-01-01

We analyzed the 0.1-10 keV spectra of 26 blazars (21 BL Lac objects and 5 highly polarized quasars), on the basis of 93 exposures taken from the EXOSAT archives. Fits were performed first with a single power-law model. Indications are found that better fits can be obtained with models where the slope steepens at higher energies. We therefore considered a broken power law and found that in a large fraction of the spectra the fit is significantly improved. Fits with a power law + oxygen edge at 0.6 keV are also explored.
Through the Ring of Fire: A Study of the Origin of Orphan Gamma-ray Flares in Blazars

NASA Astrophysics Data System (ADS)

MacDonald, Nicholas R.; Marscher, Alan P.; Jorstad, Svetlana G.; Joshi, Manasvita

2014-06-01

Blazars exhibit flares across the electromagnetic spectrum. Many gamma-ray flares are highly correlated with flares detected at optical wavelengths; however, a small subset appear to occur in isolation, with no counterpart in the other wave bands. These "orphan" gamma-ray flares challenge current models of blazar variability, most of which are unable to reproduce this type of behavior. We present numerical calculations of the time variable emission of a blazar based on a proposal by Marscher et al. (2010) to explain such events. In this model, a plasmoid ("blob") consisting of a power-law distribution of electrons propagates relativistically along the spine of a blazar jet and passes through a synchrotron emitting ring of electrons representing a shocked portion of the jet sheath. This ring supplies a source of seed photons that are inverse-Compton scattered by the electrons in the moving blob. As the blob approaches the ring, the photon density in the co-moving frame of the plasma increases, resulting in an orphan gamma-ray flare that then dissipates as the blob passes through and then moves away from the ring. The model includes the effects of radiative cooling and a spatially varying magnetic field. Support for the plausibility of this model is provided by observations by Marscher et al.(2010) of an isolated gamma-ray flare that was correlated with the passage of a superluminal knot through the inner jet of quasar PKS 1510-089. Synthetic light-curves produced by this new model are compared to the observed light-curves from this event. In addition, we present polarimetric observations that point to the existence of a jet sheath in the quasar 3C 273. A rough estimate of the bolometric luminosity of the sheath results in a value of ~10^45 erg s^-1 10% of the jet luminosity). This inferred sheath luminosity indicates that the jet sheath in 3C 273 can provide a significant source of seed photons that need to be taken into account when modeling the non
The Nuclear Spectroscopic Telescope Array (NuSTAR) High-Energy X-ray Mission

NASA Technical Reports Server (NTRS)

Harrison, Fiona A.; Craig, Willliam W.; Christensen, Finn E.; Hailey, Charles J.; Zhang, William W.; Boggs, Steven E.; Stern, Daniel; Cook, W. Rick; Forster, Karl; Giommi, Paolo;

2013-01-01

High-energy X-ray telescope in orbit. NuSTAR operates in the band from 3 to 79 keV, extending the sensitivity of focusing far beyond the 10 keV high-energy cutoff achieved by all previous X-ray satellites. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than 100-fold improvement in sensitivity over the collimated or coded mask instruments that have operated in this bandpass. Using its unprecedented combination of sensitivity and spatial and spectral resolution, NuSTAR will pursue five primary scientific objectives: (1) probe obscured active galactic nucleus (AGN) activity out to thepeak epoch of galaxy assembly in the universe (at z 2) by surveying selected regions of the sky; (2) study the population of hard X-ray-emitting compact objects in the Galaxy by mapping the central regions of the Milky Way; (3) study the non-thermal radiation in young supernova remnants, both the hard X-ray continuum and the emission from the radioactive element 44Ti; (4) observe blazars contemporaneously with ground-based radio, optical, and TeV telescopes, as well as with Fermi and Swift, to constrain the structure of AGN jets; and (5) observe line and continuum emission from core-collapse supernovae in the Local Group, and from nearby Type Ia events, to constrain explosion models. During its baseline two-year mission, NuSTAR will also undertake a broad program of targeted observations. The observatory consists of two co-aligned grazing-incidence X-ray telescopes pointed at celestial targets by a three-axis stabilized spacecraft. Deployed into a 600 km, near-circular, 6 inclination orbit, the observatory has now completed commissioning, and is performing consistent with pre-launch expectations. NuSTAR is now executing its primary science mission, and with an expected orbit lifetime of 10 yr, we anticipate proposing a guest investigator program, to begin in late 2014.

VizieR Online Data Catalog: Blazars equivalent widths and radio luminosity (Landt+, 2004)

NASA Astrophysics Data System (ADS)

Landt, H.; Padovani, P.; Perlman, E. S.; Giommi, P.

2004-07-01

Blazars are currently separated into BL Lacertae objects (BL Lacs) and flat spectrum radio quasars based on the strength of their emission lines. This is performed rather arbitrarily by defining a diagonal line in the Ca H&K break value-equivalent width plane, following Marcha et al. (1996MNRAS.281..425M). We readdress this problem and put the classification scheme for blazars on firm physical grounds. We study ~100 blazars and radio galaxies from the Deep X-ray Radio Blazar Survey (DXRBS, Cat. and ) and 2-Jy radio survey and find a significant bimodality for the narrow emission line [OIII]{lambda}5007. This suggests the presence of two physically distinct classes of radio-loud active galactic nuclei (AGN). We show that all radio-loud AGN, blazars and radio galaxies, can be effectively separated into weak- and strong-lined sources using the [OIII]{lambda}5007-[OII]{lambda}3727 equivalent width plane. This plane allows one to disentangle orientation effects from intrinsic variations in radio-loud AGN. Based on DXRBS, the strongly beamed sources of the new class of weak-lined radio-loud AGN are made up of BL Lacs at the ~75 per cent level, whereas those of the strong-lined radio-loud AGN include mostly (~97 per cent) quasars. (4 data files).
A search for a cosmological component of the soft X-ray background in the direction of M31

NASA Technical Reports Server (NTRS)

Margon, B.; Bowyer, S.; Cruddace, R.; Heiles, C.; Lampton, M.; Troland, T.

1974-01-01

Results of an experiment to search for absorption of the soft diffuse X-ray background by M31, the Andromeda Nebula, are presented. Both X-ray and 21-cm observations were obtained with high spatial resolution; the X-ray detector had a 2-degree field of view, and the 21-cm data were taken with 20-minute resolution. The results establish that at least 48 percent of the soft X-ray flux has a local source, but that the remainder may be of distant origin and therefore of cosmological significance.
A high resolution spectrum of the diffuse soft X-ray background

NASA Astrophysics Data System (ADS)

Crowder, S. Gwynne

Galactic contributions to the diffuse X-ray background were believed to largely come from thermal emission of hot gas and models of the Galactic neighborhood within ˜ 100 pc reflected this belief. However, recent observations led to the realization that emission from charge exchange within the Solar System might produce comparable intensities to that of thermal emission. A high resolution spectrum of the diffuse X-ray background from 0.1 to 1 keV was obtained for a ˜ 1 sr region of the sky centered at l = 90°, b = +60° in May 2008 using a 36 pixel array of microcalorimeters flown on a sounding rocket. With an energy resolution of 11 eV FWHM below 1 keV, the spectrum can be used to separate charge exchange contributions originating within the heliosphere from thermal emission of hot gas in the interstellar medium. The X-ray sensitivity below 1 keV was reduced about a factor of four by contamination that occurred early in the flight, limiting the significance of the results. The observed ratio of helium-like O VII forbidden plus intercombination to resonance lines is 1.2 +/- 1.2 at 90% confidence. This indicates that at least 67% of the emission is thermal. On the other hand, the observed ratio of C VI Lygamma to Lyalpha is 0.3+0.3-0.2 , requiring at least a 33% contribution from charge exchange. In addition to these astrophysical results, I present experimental improvements from the addition of a gold coating to the detector array substrate which greatly reduces extraneous signals and from the use of silicon support meshes which improves blocking filter robustness. I also detail a new optimal filtering analysis technique that preserves spectral resolution and live time in the presence of pulse overlap.
Swift detection of increased X-ray activity from gamma-ray flaring blazar PKS 1424-41

NASA Astrophysics Data System (ADS)

Ciprini, Stefano; Cutini, Sara

2013-01-01

Following enduring gamma-ray flaring activity of the flat spectrum radio quasar PKS 1424-41 (also known as 2FGL J1428.0-4206, Nolan et al. 2012, ApJS, 199, 31) detected by Fermi LAT during January 2013, two Swift target of opportunity observations were performed on January 24 and 27, 2013. Recent gamma-ray and X-ray flaring activity from the source was observed on January 6 and January 7 (ATel#4714 and ATel #4717).
Measurement of the EBL spectral energy distribution using the VHE γ-ray spectra of H.E.S.S. blazars

NASA Astrophysics Data System (ADS)

H. E. S. S. Collaboration; Abdalla, H.; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A. G.; Andersson, T.; Angüner, E. O.; Arakawa, M.; Arrieta, M.; Aubert, P.; Backes, M.; Balzer, A.; Barnard, M.; Becherini, Y.; Tjus, J. Becker; Berge, D.; Bernhard, S.; Bernlöhr, K.; Blackwell, R.; Böttcher, M.; Boisson, C.; Bolmont, J.; Bonnefoy, S.; Bordas, P.; Bregeon, J.; Brun, F.; Brun, P.; Bryan, M.; Büchele, M.; Bulik, T.; Capasso, M.; Carr, J.; Casanova, S.; Cerruti, M.; Chakraborty, N.; Chaves, R. C. G.; Chen, A.; Chevalier, J.; Coffaro, M.; Colafrancesco, S.; Cologna, G.; Condon, B.; Conrad, J.; Cui, Y.; Davids, I. D.; Decock, J.; Degrange, B.; Deil, C.; Devin, J.; de Wilt, P.; Dirson, L.; Djannati-Ataï, A.; Domainko, W.; Donath, A.; Drury, L. O.'C.; Dutson, K.; Dyks, J.; Edwards, T.; Egberts, K.; Eger, P.; Ernenwein, J.-P.; Eschbach, S.; Farnier, C.; Fegan, S.; Fernandes, M. V.; Fiasson, A.; Fontaine, G.; Förster, A.; Funk, S.; Füßling, M.; Gabici, S.; Gallant, Y. A.; Garrigoux, T.; Giavitto, G.; Giebels, B.; Glicenstein, J. F.; Gottschall, D.; Goyal, A.; Grondin, M.-H.; Hahn, J.; Haupt, M.; Hawkes, J.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hinton, J. A.; Hofmann, W.; Hoischen, C.; Holch, T. L.; Holler, M.; Horns, D.; Ivascenko, A.; Iwasaki, H.; Jacholkowska, A.; Jamrozy, M.; Janiak, M.; Jankowsky, D.; Jankowsky, F.; Jingo, M.; Jogler, T.; Jouvin, L.; Jung-Richardt, I.; Kastendieck, M. A.; Katarzyński, K.; Katsuragawa, M.; Katz, U.; Kerszberg, D.; Khangulyan, D.; Khélifi, B.; King, J.; Klepser, S.; Klochkov, D.; Kluźniak, W.; Kolitzus, D.; Komin, Nu.; Kosack, K.; Krakau, S.; Kraus, M.; Krüger, P. P.; Laffon, H.; Lamanna, G.; Lau, J.; Lees, J.-P.; Lefaucheur, J.; Lefranc, V.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J.-P.; Leser, E.; Lohse, T.; Lorentz, M.; Liu, R.; López-Coto, R.; Lypova, I.; Marandon, V.; Marcowith, A.; Mariaud, C.; Marx, R.; Maurin, G.; Maxted, N.; Mayer, M.; Meintjes, P. J.; Meyer, M.; Mitchell, A. M. W.; Moderski, R.; Mohamed, M.; Mohrmann, L.; Morå, K.; Moulin, E.; Murach, T.; Nakashima, S.; de Naurois, M.; Niederwanger, F.; Niemiec, J.; Oakes, L.; O'Brien, P.; Odaka, H.; Ohm, S.; Ostrowski, M.; Oya, I.; Padovani, M.; Panter, M.; Parsons, R. D.; Pekeur, N. W.; Pelletier, G.; Perennes, C.; Petrucci, P.-O.; Peyaud, B.; Piel, Q.; Pita, S.; Poon, H.; Prokhorov, D.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raab, S.; Rauth, R.; Reimer, A.; Reimer, O.; Renaud, M.; de los Reyes, R.; Richter, S.; Rieger, F.; Romoli, C.; Rowell, G.; Rudak, B.; Rulten, C. B.; Sahakian, V.; Saito, S.; Salek, D.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Schlickeiser, R.; Schüssler, F.; Schulz, A.; Schwanke, U.; Schwemmer, S.; Seglar-Arroyo, M.; Settimo, M.; Seyffert, A. S.; Shafi, N.; Shilon, I.; Simoni, R.; Sol, H.; Spanier, F.; Spengler, G.; Spies, F.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Stycz, K.; Sushch, I.; Takahashi, T.; Tavernet, J.-P.; Tavernier, T.; Taylor, A. M.; Terrier, R.; Tibaldo, L.; Tiziani, D.; Tluczykont, M.; Trichard, C.; Tsuji, N.; Tuffs, R.; Uchiyama, Y.; van der Walt, D. J.; van Eldik, C.; van Rensburg, C.; van Soelen, B.; Vasileiadis, G.; Veh, J.; Venter, C.; Viana, A.; Vincent, P.; Vink, J.; Voisin, F.; Völk, H. J.; Vuillaume, T.; Wadiasingh, Z.; Wagner, S. J.; Wagner, P.; Wagner, R. M.; White, R.; Wierzcholska, A.; Willmann, P.; Wörnlein, A.; Wouters, D.; Yang, R.; Zaborov, D.; Zacharias, M.; Zanin, R.; Zdziarski, A. A.; Zech, A.; Zefi, F.; Ziegler, A.; Żywucka, N.

2017-10-01

Very high-energy γ rays (VHE, E ≳ 100 GeV) propagating over cosmological distances can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron pairs. The transparency of the Universe to VHE γ rays is then directly related to the spectral energy distribution (SED) of the EBL. The observation of features in the VHE energy spectra of extragalactic sources allows the EBL to be measured, which otherwise is very difficult. An EBL model-independent measurement of the EBL SED with the H.E.S.S. array of Cherenkov telescopes is presented. It was obtained by extracting the EBL absorption signal from the reanalysis of high-quality spectra of blazars. From H.E.S.S. data alone the EBL signature is detected at a significance of 9.5σ, and the intensity of the EBL obtained in different spectral bands is presented together with the associated γ-ray horizon.

Multiwavelength studies of the blazars detected by AGILE

NASA Astrophysics Data System (ADS)

Filippo D'Ammando

2010-02-01

activity states of the two flavours of blazars, but going into details of the single observation more complex scenarios sometimes are requested. The possibility to obtain information over the entire electromagnetic spectrum during the multifrequency campaigns organized by AGILE gave me also the opportunity to investigate in some blazars the presence of Seyfert-like features, such as the little and big blue bumps (PKS 1510-089) and the Compton reflection component (3C 273). Moreover, we revealed in the FSRQ PKS 1510-089 some features typical of High-frequency peaked BL Lac objects, such a X-ray harder-when-brighter behaviour during March 2008 and a shift of the synchrotron peak towards higher frequencies during the huge flare of March 2009. Emission in optical and gamma-ray bands seems to be correlated during high activity states of blazars, but not strongly, with a possible lag of the gamma-ray flux with respect to optical one less than one day, both for FSRQs (e.g. 3C 454.3) and BL Lacs (S5 0716+714). On the other hand, during March 2009 a possible delay of the optical emission with respect to the gamma-ray one is detected for PKS 1510-089, suggesting a more complex behaviour in the optical/gamma-ray correlation, especially for FSRQs, where also a contribution of the thermal disk emission is clearly visible.
The 105-Month Swift-BAT All-Sky Hard X-Ray Survey

NASA Technical Reports Server (NTRS)

Oh, Kyuseok; Koss, Michael; Markwardt, Craig B.; Schawinski, Kevin; Baumgartner, Wayne H.; Barthelmy, Scott D.; Cenko, S. Bradley; Gehrels, Neil; Mushotzky, Richard; Petulante, Abigail;

2018-01-01

We present a catalog of hard X-ray sources detected in the first 105 months of observations with the Burst Alert Telescope (BAT) coded-mask imager on board the Swift observatory. The 105-month Swift-BAT survey is a uniform hard X-ray all-sky survey with a sensitivity of 8.40 x 10(exp -12) erg s(exp -1) cm(exp -2) over 90% of the sky and 7.24 x 10(exp -12) erg s(exp -1) cm(exp -2) over 50% of the sky in the 14-195 keV band. The Swift-BAT 105-month catalog provides 1632 (422 new detections) hard X-ray sources in the 14-195 keV band above the 4.8 sigma significance level. Adding to the previously known hard X-ray sources, 34% (144/422) of the new detections are identified as Seyfert active galactic nuclei (AGNs) in nearby galaxies (z < 0.2). The majority of the remaining identified sources are X-ray binaries (7%, 31) and blazars/BL Lac objects (10%, 43). As part of this new edition of the Swift-BAT catalog, we release eight-channel spectra and monthly sampled light curves for each object in the online journal and at the Swift-BAT 105-month website.

IGR J12319-0749: Evidence for Another Extreme Blazar Found with INTEGRAL

NASA Technical Reports Server (NTRS)

Bassani, L.; Landi, R.; Marshall, F. E.; Malizia, A.; Bazzano, A.; Bird, A. J.; Gehrels, N.; Ubertini, P.; Masetti, N.

2012-01-01

We report on the identification of a new soft gamma-ray source, IGR J12319-0749, detected with the IBIS imager on board the INTEGRAL satellite. The source, which has an observed 20-100 keV flux of approx 8.3 × 10(exp -12) erg/sq. cm/ s, is spatially coincident with an active galactic nucleus (AGN) at redshift z = 3.12. The broad-band continuum, obtained by combining XRT and IBIS data, is flat (Gamma = 1.3) with evidence for a spectral break around 25 keV (100 keV in the source restframe). X-ray observations indicate flux variability, which is also supported by a comparison with a previous ROSAT measurement. IGR J12319-0749 is also a radio-emitting object likely characterised by a flat spectrum and high radio loudness; optically it is a broad-line emitting object with a massive black hole (2.8 × 10(exp 9) solar masses) at its centre. The source spectral energy distribution is similar to another high-redshift blazar, 225155+2217 at z = 3.668: both objects are bright, with a high accretion disk luminosity and a Compton peak located in the hard X-ray/soft gamma-ray band. IGR J12319-0749 is likely the second-most distant blazar detected so far by INTEGRAL.
Spatial Fluctuations in the Diffuse Cosmic X-Ray Background. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Shafer, R. A.

1983-01-01

The bright, essentially isotropic, X-ray sky flux above 2 keV yields information on the universe at large distances. However, a definitive understanding of the origin of the flux is lacking. Some fraction of the total flux is contributed by active galactic nuclei and clusters of galaxies, but less than one percent of the total is contributed by the or approximately 3 keV band resolved sources, which is the band where the sky flux is directly observed. Parametric models of AGN (quasar) luminosity function evolution are examined. Most constraints are by the total sky flux. The acceptability of particular models hinges on assumptions currently not directly testable. The comparison with the Einstein Observatory 1 to keV low flux source counts is hampered by spectral uncertainties. A tentative measurement of a large scale dipole anisotropy is consistent with the velocity and direction derived from the dipole in the microwave background. The impact of the X-ray anisotropy limits for other scales on studies of large-scale structure in the universe is sketched. Models of the origins of the X-ray sky flux are reviewed, and future observational programs outlined.
Is 4C+29.48 a γ-ray source?

NASA Astrophysics Data System (ADS)

Gabányi, K. É.; Frey, S.; An, T.

2018-05-01

Context. The Fermi Large Area Telescope revealed that the extragalactic γ-ray sky is dominated by blazars, active galactic nuclei (AGN) whose jet is seen at very small angle to the line of sight. To associate and then classify the γ-ray sources, data have been collected from lower frequency surveys and observations. Since those have superior angular resolution and positional accuracy compared to the γ-ray observations, some associations are not straightforward. Aims: The γ-ray source 3FGL J1323.0+2942 is associated with the radio source 4C+29.48 and classified as a blazar of unknown type, lacking optical spectrum and redshift. The higher-resolution radio data showed that 4C+29.48 comprises three bright radio-emitting features located within a 1'-diameter area. We aim to reveal their nature and pinpoint the origin of the γ-ray emission. Methods: We (re-)analyzed archival Very Large Array (VLA) and unpublished very long baseline interferometry (VLBI) observations conducted by the Very Long Baseline Array (VLBA) and the European VLBI Network of 4C+29.48. We also collected data form optical, infrared and X-ray surveys. Results: According to the VLBI data, the northernmost complex of 4C+29.48 contains a blazar with a high brightness temperature compact core and a steep-spectrum jet feature. The blazar is positionally coincident with an optical source at a redshift of 1.142. Its mid-infrared colors also support its association with a γ-ray emitting blazar. The two other radio complexes have steep radio spectra similar to AGN-related lobes and do not have optical or infrared counterparts in currently available surveys. Based on the radio morphology, they are unlikely to be related to the blazar. There is an optical source between the two radio features, also detected in infrared wavebands. We discuss the possibilities whether the two radio features are lobes of a radio galaxy, or gravitationally lensed images of a background source. Conclusions: We propose to
My 35 Years in X-ray Astronomy (Not)

NASA Astrophysics Data System (ADS)

Urry, C. M.

2013-01-01

My contact with X-ray astronomy started with HEAO-1, just before launch, when I was a summer student at the Harvard/Smithsonian Center for Astrophysics. Another summer position followed at NASA’s Goddard Space Flight Center, where I later did my PhD thesis on HEAO1 and HEAO2 (and IUE) data. Next I was a postdoc at MIT working with Einstein and Ginga observations, and I then continued observing blazars and other AGN with ASCA, Exosat, RXTE, Chandra, XMM, Swift, Suzaku, and Fermi. I have also witnessed or participated in many proposals for future X-ray missions. Fortunately for the audience, I will not recall all these times... So many photons, so little time! But this long history does mean I met most of the great figures in X-ray astronomy when they were young and I probably have embarrassing stories to tell about many of them. For my 2-minute vignette in a panel discussion, I will entertain you with one of the more interesting (and pertinent) memories. Acknowledgement: Thank you to all my high-energy astrophysics colleagues, who taught me a great deal, and to NASA for the hit parade of high-energy missions.
The particle background observed by the X-ray detectors onboard Copernicus

NASA Technical Reports Server (NTRS)

Davison, P. J. N.

1974-01-01

The design and characteristics of low energy detectors on the Copernicus satellite are described. The functions of the sensors in obtaining data on the particle background. The procedure for processing the data obtained by the satellite is examined. The most significant positive deviations are caused by known weak X-ray sources in the field of view. In addition to small systemic effects, occasional random effects where the count rate increases suddenly and decreases within a few frames are analyzed.
The Study on the Physical Properties of Blazar Jets

NASA Astrophysics Data System (ADS)

Kang, S. J.

2017-09-01

Active galactic nuclei (AGNs) belong to a special class of active galaxies, and have violent active phenomena and intense physical processes in the nuclei. Blazar is a subclass of AGNs, and has a relativistic jet with a small jet viewing angle. Therefore, the boosting effect is very important, and almost all the observed radiation is dominated by the jet. The relativistic jet physics is not very clear yet, such as the jet formation, collimation, and matter content etc. The multi-waveband radiation of blazar is dominated by jet, which provides an ideal laboratory for studying the jet physics. The first chapter of this thesis introduces the recent progress of AGNs and blazars. We further introduce the jet model that commonly used in blazars in the second chapter. In the third chapter, we fit simultaneously (or quasi-simultaneously) the multi-waveband spectral energy distributions (SEDs) for a sample of low-synchrotron-peaked (LSP) blazars with the jet model and χ2 procedure, which takes into account different soft photon fields (broad line region or a molecular torus). We find that the SED fitting with an external soft photon from IR torus is systematically better than that from the broad line region (BLR) based on a χ2 test, which suggests that the γ-ray emitting region most possibly stays outside the BLR. The minimum electron Lorentz factor, γmin, is constrained from the modeling of these LSP blazars with good soft X-ray data, and in a range from 5 to 160 (with a median value of 55), which plays a key role in jet power estimation. Assuming one-to-one ratio of proton and electron, we find that the jet power for LSP blazars is systematically higher than that of Fanaroff-Riley type II (FR II) radio galaxies. A possible reason for this is that there are some positrons in the jets of these blazars. If this is the case, the jet power will be reduced. Therefore, we propose a mixed composition of e±-p in the jets of these LSP blazars. If we assume that the jet power
Can the cosmic x ray and gamma ray background be due to reflection of a steep power law spectrum and Compton scattering by relativistic electrons?

NASA Technical Reports Server (NTRS)

Zycki, Piotr T.; Zdziarski, Andrzej A.; Svensson, Roland

1991-01-01

We reconsider the recent model for the origin in the cosmic X-ray and gamma-ray background by Rogers and Field. The background in the model is due to an unresolved population of AGNs. An individual AGN spectrum contains three components: a power law with the energy index of alpha = 1.1, an enhanced reflection component, and a component from Compton scattering by relativistic electrons with a low energy cutoff at some minimum Lorentz factor, gamma(sub min) much greater than 1. The MeV bump seen in the gamma-ray background is then explained by inverse Compton emission by the electrons. We show that the model does not reproduce the shape of the observed X-ray and gamma-ray background below 10 MeV and that it overproduces the background at larger energies. Furthermore, we find the assumptions made for the Compton component to be physically inconsistent. Relaxing the inconsistent assumptions leads to model spectra even more different from that of the observed cosmic background. Thus, we can reject the hypothesis that the high-energy cosmic background is due to the described model.
Time-dependent Models for Blazar Emission with the Second-order Fermi Acceleration

NASA Astrophysics Data System (ADS)

Asano, Katsuaki; Takahara, Fumio; Kusunose, Masaaki; Toma, Kenji; Kakuwa, Jun

2014-01-01

The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101-232. For other blazars that show softer spectra, the Fermi-II model requires radial evolution of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from the radio to the X-ray regime. The photon spectrum in the GeV energy range of Mrk 421 is hard to fit with a synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of 4.9 × 1038 erg s-1, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.
Time-dependent models for blazar emission with the second-order Fermi acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asano, Katsuaki; Takahara, Fumio; Toma, Kenji

The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101–232. For other blazars that show softer spectra, the Fermi-II model requires radial evolution of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from the radio to the X-ray regime. The photon spectrum in the GeV energy range ofmore » Mrk 421 is hard to fit with a synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of 4.9 × 10{sup 38} erg s{sup –1}, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.« less
Establishing the spectral turnover of blazar PKS 2155-304 as an outcome of radiative losses

NASA Astrophysics Data System (ADS)

Jagan, Sitha K.; Sahayanathan, S.; Misra, R.; Ravikumar, C. D.; Jeena, K.

2018-07-01

The broad-band optical/UV and X-ray spectra of blazars have been often modelled as synchrotron component arising from a broken power-law distribution of electrons. A broken power-law distribution is expected, since the high-energy electrons undergo radiative losses effectively. The change in the energy index should then be ≈1 and corresponds to a spectral index difference of 0.5. However, one of the long outstanding problems has been that the observed index change is significantly different. On the other hand, recent high-quality observations of blazars suggest that their local spectra may not be a power law, instead have a slight curvature and often represented by a log-parabola model. Using XMM-Newtonobservations spanning over 12 yr for the BL Lac PKS 2155-304, we show that the optical/UV and X-ray spectra can be well represented by a broken log-parabola model. Further, we show that such a spectrum can indicate the energy dependence of the electron escape time-scale from the main acceleration zone. This novel approach, besides addressing the observed difference in the photon spectral indices, also tries to explain the spectral turn over in far-UV/soft X-rays as a result of the radiative losses.
Establishing the spectral turnover of blazar PKS 2155-304 as an outcome of radiative losses

NASA Astrophysics Data System (ADS)

Jagan, Sitha K.; Sahayanathan, S.; Misra, R.; Ravikumar, C. D.; Jeena, K.

2018-06-01

The broad-band optical/UV and X-ray spectra of blazars have been often modelled as synchrotron component arising from a broken power-law distribution of electrons. A broken power-law distribution is expected, since the high energy electrons undergo radiative losses effectively. The change in the energy index should then be ≈1 and corresponds to a spectral index difference of 0.5. However, one of the long outstanding problems has been that the observed index change is significantly different. On the other hand, recent high quality observations of blazars suggest that their local spectra may not be a power-law, instead have a slight curvature and often represented by a log parabola model. Using XMM-Newton observations spanning over 12 years for the BL Lac PKS 2155-304, we show that the optical/UV and X-ray spectra can be well represented by a broken log parabola model. Further, we show that such a spectrum can indicate the energy dependence of the electron escape time-scale from the main acceleration zone. This novel approach, besides addressing the observed difference in the photon spectral indices, also tries to explain the spectral turn over in far-UV/soft X-rays as a result of the radiative losses.
The Electrostatic Instability for Realistic Pair Distributions in Blazar/EBL Cascades

NASA Astrophysics Data System (ADS)

Vafin, S.; Rafighi, I.; Pohl, M.; Niemiec, J.

2018-04-01

This work revisits the electrostatic instability for blazar-induced pair beams propagating through the intergalactic medium (IGM) using linear analysis and PIC simulations. We study the impact of the realistic distribution function of pairs resulting from the interaction of high-energy gamma-rays with the extragalactic background light. We present analytical and numerical calculations of the linear growth rate of the instability for the arbitrary orientation of wave vectors. Our results explicitly demonstrate that the finite angular spread of the beam dramatically affects the growth rate of the waves, leading to the fastest growth for wave vectors quasi-parallel to the beam direction and a growth rate at oblique directions that is only a factor of 2–4 smaller compared to the maximum. To study the nonlinear beam relaxation, we performed PIC simulations that take into account a realistic wide-energy distribution of beam particles. The parameters of the simulated beam-plasma system provide an adequate physical picture that can be extrapolated to realistic blazar-induced pairs. In our simulations, the beam looses only 1% of its energy, and we analytically estimate that the beam would lose its total energy over about 100 simulation times. An analytical scaling is then used to extrapolate the parameters of realistic blazar-induced pair beams. We find that they can dissipate their energy slightly faster by the electrostatic instability than through inverse-Compton scattering. The uncertainties arising from, e.g., details of the primary gamma-ray spectrum are too large to make firm statements for individual blazars, and an analysis based on their specific properties is required.
Investigating Possible Outliers in the Fermi Blazar AGN Sample

NASA Astrophysics Data System (ADS)

Shrader, Chris

2018-01-01

The Fermi Gamma-Ray Space Telescope (Fermi) has cataloged over 3000 gamma-ray (>100 MeV) point sources of which more than 1100 are likely AGN. These AGN are predominantly among the radio-loud “blazar” subclass. Recently however, a significant sample of bright (F_15GHz >1.5 Jy), radio selected AGN was found to overlap with Fermi at only the ~80% level (Lister et. al., 2015). This could be a result of some selection bias or it could be due to deficient Doppler boosting among that ~20%. Additionally, a recent survey of high-latitude gamma-ray sources by Schinzel et al. (2017) reveals a sample of ~100 objects which are not detected in the 4-10 GHz radio band to a limiting flux of about 2mJy. This apparent lack of radio flux is puzzling, and may indicate either an extreme Compton-dominated sample, or copious gamma-ray emission from a heretofore unknown population such as a subclass of radio-quiet AGN. Speculatively, these radio-loud/gamma-quiet and gamma-loud/radio quiet samples could be odd cases of the blazar phenomena which reside outside of the well-known blazar sequence. To explore this problem further we have undertaken a study to construct or constrain individual source SEDs as a first step towards their classification. In this contribution we present results from our search for emission in the Swift-BAT 15-100-keV hard X-ray band for each of these samples.
Through the Ring of Fire: Gamma-Ray Variability in Blazars by a Moving Plasmoid Passing a Local Source of Seed Photons

NASA Astrophysics Data System (ADS)

MacDonald, Nicholas R.; Marscher, Alan P.; Jorstad, Svetlana G.; Joshi, Manasvita

2015-05-01

Blazars exhibit flares across the electromagnetic spectrum. Many γ-ray flares are highly correlated with flares detected at optical wavelengths; however, a small subset appears to occur in isolation, with little or no variability detected at longer wavelengths. These “orphan” γ-ray flares challenge current models of blazar variability, most of which are unable to reproduce this type of behavior. We present numerical calculations of the time-variable emission of a blazar based on a proposal by Marscher et al. to explain such events. In this model, a plasmoid (“blob”) propagates relativistically along the spine of a blazar jet and passes through a synchrotron-emitting ring of electrons representing a shocked portion of the jet sheath. This ring supplies a source of seed photons that are inverse-Compton scattered by the electrons in the moving blob. The model includes the effects of radiative cooling, a spatially varying magnetic field, and acceleration of the blob's bulk velocity. Synthetic light curves produced by our model are compared to the observed light curves from an orphan flare that was coincident with the passage of a superluminal knot through the inner jet of the blazar PKS 1510-089. In addition, we present Very Long Baseline Array polarimetric observations that point to the existence of a jet sheath in PKS 1510-089, thus providing further observational support for the plausibility of our model. An estimate of the bolometric luminosity of the sheath within PKS 1510-089 is made, yielding {{L}sh}˜ 3× {{10}45} erg {{s}-1}. This indicates that the sheath within PKS 1510-089 is potentially a very important source of seed photons.
The 105-Month Swift-BAT All-sky Hard X-Ray Survey

NASA Astrophysics Data System (ADS)

Oh, Kyuseok; Koss, Michael; Markwardt, Craig B.; Schawinski, Kevin; Baumgartner, Wayne H.; Barthelmy, Scott D.; Cenko, S. Bradley; Gehrels, Neil; Mushotzky, Richard; Petulante, Abigail; Ricci, Claudio; Lien, Amy; Trakhtenbrot, Benny

2018-03-01

We present a catalog of hard X-ray sources detected in the first 105 months of observations with the Burst Alert Telescope (BAT) coded-mask imager on board the Swift observatory. The 105-month Swift-BAT survey is a uniform hard X-ray all-sky survey with a sensitivity of 8.40× {10}-12 {erg} {{{s}}}-1 {cm}}-2 over 90% of the sky and 7.24× {10}-12 {erg} {{{s}}}-1 {cm}}-2 over 50% of the sky in the 14–195 keV band. The Swift-BAT 105-month catalog provides 1632 (422 new detections) hard X-ray sources in the 14–195 keV band above the 4.8σ significance level. Adding to the previously known hard X-ray sources, 34% (144/422) of the new detections are identified as Seyfert active galactic nuclei (AGNs) in nearby galaxies (z< 0.2). The majority of the remaining identified sources are X-ray binaries (7%, 31) and blazars/BL Lac objects (10%, 43). As part of this new edition of the Swift-BAT catalog, we release eight-channel spectra and monthly sampled light curves for each object in the online journal and at the Swift-BAT 105-month website.
Exploring the X-Ray Universe

NASA Astrophysics Data System (ADS)

Seward, Frederick D.; Charles, Philip A.

1995-11-01

Exploring the X-Ray Universe describes the view of the stars and galaxies that is obtained through X-ray telescopes. X-rays, which are invisible to human sight, are created in the cores of active galaxies, in cataclysmic stellar explosions, and in streams of gas expelled by the Sun and stars. The window on the heavens used by the X-ray astronomers shows the great drama of cosmic violence on the grandest scale.
This account of X-ray astronomy incorporates the latest findings from several observatories operating in space. These include the Einstein Observatory operated by NASA, and the EXOSAT satellite of the European Space Agency. The book covers the entire field, with chapters on stars, supernova remnants, normal and active galaxies, clusters of galaxies, the diffuse X-ray background, and much more. The authors review basic principles, include the necessary historical background, and explain exactly what we know from X-ray observations of the Universe.
The average X-ray/gamma-ray spectra of Seyfert galaxies from Ginga and OSSE and the origin of the cosmic X-ray background

NASA Technical Reports Server (NTRS)

Zdziarski, Andrzej A.; Johnson, W. Neil; Done, Chris; Smith, David; Mcnaron-Brown, Kellie

1995-01-01

We have obtained the first average 2-500 keV spectra of Seyfert galaxies, using the data from Ginga and Compton Gamma-Ray Observatory's (CGRO) Oriented Scintillation Spectrometer Experiment (OSSE). Our sample contains three classes of objects with markedly different spectra: radio-quiet Seyfert 1's and 2's, and radio-loud Seyfert 1's. The average radio-quiet Seyfert 1 spectrum is well-fitted by a power law continuum with the energy spectral index alpha approximately equals 0.9, a Compton reflection component corresponding to a approximately 2 pi covering solid angle, and ionized absorption. There is a high-energy cutoff in the incident power law continuum: the e-folding energy is E(sub c) approximately equals 0.6(sup +0.8 sub -0.3) MeV. The simplest model that describes this spectrum is Comptonization in a relativistic optically-thin thermal corona above the surface of an accretion disk. Radio-quiet Seyfert 2's show strong netural absorption, and there is an indication that their X-ray power laws are intrinsically harder. Finally, the radio-loud Seyfert spectrum has alpha approximately equals 0.7, moderate neutral absorption E(sub C) = 0.4(sup +0.7 sub -0.2) MeV, and no or little Compton reflection. This is incompatible with the radio-quiet Seyfert 1 spectrum, and probably indicating that the X-rays are beamed away from the accretion disk in these objects. The average spectra of Seyferts integrated over redshift with a power-law evolution can explain the hard X-ray spectrum of the cosmic background.
X-ray Survey of Centaurus A.

PubMed

Byram, E T; Chubb, T A; Friedman, H

1970-07-24

An x-ray survey of Centaurus A has given marginal evidence of its x-ray flux. If taken as an upper limit on inverse Compton x-rays generated by scattering interactions between relativistic electrons and cosmological background photons, the observation implies an upper limit of close to 3 degrees K for the background radiation temperature.

PATCHY BLAZAR HEATING: DIVERSIFYING THE THERMAL HISTORY OF THE INTERGALACTIC MEDIUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lamberts, Astrid; Chang, Philip; Pfrommer, Christoph

TeV-blazars potentially heat the intergalactic medium (IGM) as their gamma rays interact with photons of the extragalactic background light to produce electron–positron pairs, which lose their kinetic energy to the surrounding medium through plasma instabilities. This results in a heating mechanism that is only weakly sensitive to the local density, and therefore approximately spatially uniform, naturally producing an inverted temperature–density relation in underdense regions. In this paper we go beyond the approximation of uniform heating and quantify the heating rate fluctuations due to the clustered distribution of blazars and how this impacts the thermal history of the IGM. We analyticallymore » compute a filtering function that relates the heating rate fluctuations to the underlying dark matter density field. We implement it in the cosmological code GADGET-3 and perform large-scale simulations to determine the impact of inhomogeneous heating. We show that because of blazar clustering, blazar heating is inhomogeneous for z ≳ 2. At high redshift, the temperature–density relation shows an important scatter and presents a low temperature envelope of unheated regions, in particular at low densities and within voids. However, the median temperature of the IGM is close to that in the uniform case, albeit slightly lower at low redshift. We find that blazar heating is more complex than initially assumed and that the temperature–density relation is not unique. Our analytic model for the heating rate fluctuations couples well with large-scale simulations and provides a cost-effective alternative to subgrid models.« less
Optical polarimetry and photometry of X-ray selected BL Lacertae objects

NASA Technical Reports Server (NTRS)

Jannuzi, Buell T.; Smith, Paul S.; Elston, Richard

1993-01-01

We present the data from 3 years of monitoring the optical polarization and apparent brightness of 37 X-ray-selected BL Lacertae objects. The monitored objects include a complete sample drawn from the Einstein Extended Medium Sensitivity Survey. We confirm the BL Lac identifications for 15 of these 22 objects. We include descriptions of the objects and samples in our monitoring program and of the existing complete samples of BL Lac objects, highly polarized quasars, optically violent variable quasars, and blazars.
ANTARES constrains a blazar origin of two IceCube PeV neutrino events

NASA Astrophysics Data System (ADS)

ANTARES Collaboration; Adrián-Martínez, S.; Albert, A.; André, M.; Anton, G.; Ardid, M.; Aubert, J.-J.; Baret, B.; Barrios, J.; Basa, S.; Bertin, V.; Biagi, S.; Bogazzi, C.; Bormuth, R.; Bou-Cabo, M.; Bouwhuis, M. C.; Bruijn, R.; Brunner, J.; Busto, J.; Capone, A.; Caramete, L.; Carr, J.; Chiarusi, T.; Circella, M.; Coniglione, R.; Costantini, H.; Coyle, P.; Creusot, A.; De Rosa, G.; Dekeyser, I.; Deschamps, A.; De Bonis, G.; Distefano, C.; Donzaud, C.; Dornic, D.; Dorosti, Q.; Drouhin, D.; Dumas, A.; Eberl, T.; Enzenhöfer, A.; Escoffier, S.; Fehn, K.; Felis, I.; Fermani, P.; Folger, F.; Fusco, L. A.; Galatà, S.; Gay, P.; Geißelsöder, S.; Geyer, K.; Giordano, V.; Gleixner, A.; Gómez-González, J. P.; Gracia-Ruiz, R.; Graf, K.; van Haren, H.; Heijboer, A. J.; Hello, Y.; Hernández-Rey, J. J.; Herrero, A.; Hößl, J.; Hofestädt, J.; Hugon, C.; James, C. W.; de Jong, M.; Kalekin, O.; Katz, U.; Kießling, D.; Kooijman, P.; Kouchner, A.; Kulikovskiy, V.; Lahmann, R.; Lattuada, D.; Lefèvre, D.; Leonora, E.; Loehner, H.; Loucatos, S.; Mangano, S.; Marcelin, M.; Margiotta, A.; Martínez-Mora, J. A.; Martini, S.; Mathieu, A.; Michael, T.; Migliozzi, P.; Neff, M.; Nezri, E.; Palioselitis, D.; Păvălaş, G. E.; Perrina, C.; Piattelli, P.; Popa, V.; Pradier, T.; Racca, C.; Riccobene, G.; Richter, R.; Roensch, K.; Rostovtsev, A.; Saldaña, M.; Samtleben, D. F. E.; Sánchez-Losa, A.; Sanguineti, M.; Sapienza, P.; Schmid, J.; Schnabel, J.; Schulte, S.; Schüssler, F.; Seitz, T.; Sieger, C.; Spies, A.; Spurio, M.; Steijger, J. J. M.; Stolarczyk, Th.; Taiuti, M.; Tamburini, C.; Tayalati, Y.; Trovato, A.; Tselengidou, M.; Tönnis, C.; Vallage, B.; Vallée, C.; Van Elewyck, V.; Visser, E.; Vivolo, D.; Wagner, S.; de Wolf, E.; Yepes, H.; Zornoza, J. D.; Zúñiga, J.; TANAMI Collaboration; Krauß, F.; Kadler, M.; Mannheim, K.; Schulz, R.; Trüstedt, J.; Wilms, J.; Ojha, R.; Ros, E.; Baumgartner, W.; Beuchert, T.; Blanchard, J.; Bürkel, C.; Carpenter, B.; Edwards, P. G.; Eisenacher Glawion, D.; Elsässer, D.; Fritsch, U.; Gehrels, N.; Gräfe, C.; Großberger, C.; Hase, H.; Horiuchi, S.; Kappes, A.; Kreikenbohm, A.; Kreykenbohm, I.; Langejahn, M.; Leiter, K.; Litzinger, E.; Lovell, J. E. J.; Müller, C.; Phillips, C.; Plötz, C.; Quick, J.; Steinbring, T.; Stevens, J.; Thompson, D. J.; Tzioumis, A. K.

2015-04-01

Context. The source(s) of the neutrino excess reported by the IceCube Collaboration is unknown. The TANAMI Collaboration recently reported on the multiwavelength emission of six bright, variable blazars which are positionally coincident with two of the most energetic IceCube events. Objects like these are prime candidates to be the source of the highest-energy cosmic rays, and thus of associated neutrino emission. Aims: We present an analysis of neutrino emission from the six blazars using observations with the ANTARES neutrino telescope. Methods: The standard methods of the ANTARES candidate list search are applied to six years of data to search for an excess of muons - and hence their neutrino progenitors - from the directions of the six blazars described by the TANAMI Collaboration, and which are possibly associated with two IceCube events. Monte Carlo simulations of the detector response to both signal and background particle fluxes are used to estimate the sensitivity of this analysis for different possible source neutrino spectra. A maximum-likelihood approach, using the reconstructed energies and arrival directions of through-going muons, is used to identify events with properties consistent with a blazar origin. Results: Both blazars predicted to be the most neutrino-bright in the TANAMI sample (1653-329 and 1714-336) have a signal flux fitted by the likelihood analysis corresponding to approximately one event. This observation is consistent with the blazar-origin hypothesis of the IceCube event IC 14 for a broad range of blazar spectra, although an atmospheric origin cannot be excluded. No ANTARES events are observed from any of the other four blazars, including the three associated with IceCube event IC20. This excludes at a 90% confidence level the possibility that this event was produced by these blazars unless the neutrino spectrum is flatter than -2.4. Figures 2, 3 and Appendix A are available in electronic form at http://www.aanda.org
Fingerprints of the first black holes? Crosscorrelationg the Near-Infrared and X-ray background in COSMOS

NASA Astrophysics Data System (ADS)

Hasinger, Guenther

Unresolved cosmic backgrounds carry information about the populations of stars and black holes not accessible by any other current observational technique. Studies using both Spitzer and AKARI have revealed large-scale fluctuations in the Cosmic Infrared Background (CIB) after subtracting resolved sources to faint levels. The signal, which is stronger than all foreground contributions, has been attributed to the earliest light in the universe. Other teams, by using Spitzer and CIBER, suggested that this signal could originate from stars tidally stripped from their parent galaxies at low redshift as a result of mergers. Only sensitive multi-wavelength observations can distinguish between these radically different interpretations. Recently our team discovered an intriguing cross-correlation signal between the unresolved CIB and X-ray background (CXB) suggesting significant black hole populations among the CIB sources (C13). The analysis used data from Spitzer and Chandra in an overlapping 8'x45' region of the All-Wavelength Extended Groth strip International Survey (AEGIS), probing the clustering of the underlying sources to angular scales 20', but the experiment is limited by the size and the elongated configuration of the field. Here we propose to use the much more extended multiwavelength observations in the COSMOS field to obtain new constraints on this important debate. Spitzer has recently completed the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH), which observed the full 2 square degree COSMOS field to about half the depth of the AEGIS field, but a 20 times larger sky area. SPLASH, focusing on the COSMOS field with excellent multi-wavelength coverage from space and ground-based observatories, is ideally suited to study the CIB to better precision and at larger scales than available so far. We propose to cross-correlate the Spitzer unresolved CIB to the unresolved CXB observed by Chandra and XMM-Newton. Chandra has covered the full 2 deg2 COSMOS
Observations of recent flares of the blazar 1ES1959+650 with VERITAS

NASA Astrophysics Data System (ADS)

Zhou, Yuyang; Santander, Marcos; VERITAS Collaboration

2017-01-01

VERITAS (Very Energetic Radiation Imaging Telescope Array System) is a an array of imaging atmospheric Cherenkov telescopes that carries out an extensive observation program of the gamma-ray sky at energies above 0.1 TeV. Blazars, active galactic nuclei powered by supermassive black holes, are gamma-ray sources of major interest. The relativistic jets they emit are among the most energetic phenomena in the universe and constitute a significant amount of study in high energy astrophysics. In particular, the blazar 1ES 1959+650 (z=0.048) has garnered special attention due to its emission of an ``orphan'' flare in 2002. An orphan flare is an extremely bright emission in gamma rays that is not coupled to X-rays. This phenomenon is incompatible with our current model of gamma-ray production, the self-synchrotron Compton (SSC) process. This study aims to characterize recent TeV flares of this source by analyzing the time variability of its light curve and spectrum and comparing these findings to observations made in other wavelengths. We hope to determine if these recent flares have also been orphan in nature, put an upper limit on the size of the emission region, and understand the nature of the gamma-ray emission in the source.
Synchrotron pair halo and echo emission from blazars in the cosmic web: application to extreme TeV blazars

NASA Astrophysics Data System (ADS)

Oikonomou, Foteini; Murase, Kohta; Kotera, Kumiko

2014-08-01

High frequency peaked, high redshift blazars, are extreme in the sense that their spectrum is particularly hard and peaks at TeV energies. Standard leptonic scenarios require peculiar source parameters and/or a special setup in order to account for these observations. Electromagnetic cascades seeded by ultra-high energy cosmic rays (UHECR) in the intergalactic medium have also been invoked, assuming a very low intergalactic magnetic field (IGMF). Here we study the synchrotron emission of UHECR secondaries produced in blazars located in magnetised environments, and show that it can provide an alternative explanation to these challenged channels, for sources embedded in structured regions with magnetic field strengths of the order of 10-7 G. To demonstrate this, we focus on three extreme blazars: 1ES 0229+200, RGB J0710+591, and 1ES 1218+304. We model the expected gamma-ray signal from these sources through a combination of numerical Monte Carlo simulations and solving the kinetic equations of the particles in our simulations, and explore the UHECR source and intergalactic medium parameter space to test the robustness of the emission. We show that the generated synchrotron-pair halo and echo flux at the peak energy is not sensitive to variations in the overall IGMF strength. This signal is unavoidable in contrast to the inverse Compton-pair halo and echo intensity, which is appealing in view of the large uncertainties on the IGMF in voids of large scale structure. It is also shown that the variability of blazar gamma-ray emission can be accommodated by the synchrotron emission of secondary products of UHE neutral beams if these are emitted by UHECR accelerators inside magnetised regions.
Characteristics of Gamma-Ray Loud Blazars in the VLBA Imaging and Polarimetry Survey

NASA Technical Reports Server (NTRS)

Linford, J. D.; Taylor, G. B.; Romani, R. W.; Healey, S. E.; Helmboldt, J. F.; Readhead, A. C.; Reeves, R.; Richards, J. L.; Cotter, G.

2010-01-01

The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed as part of the VLBA Imaging and Polarimetry Survey. This large, flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong gamma-ray emission. At lower flux levels, radio flux density does not directly correlate with gamma-ray flux. We find that the LAT-detected BL Lac objects tend to be similar to the non-LAT BL Lac objects, but that the LAT-detected FSRQs are often significantly different from the non-LAT FSRQs. The differences between the gamma-ray loud and quiet FSRQS can be explained by Doppler boosting; these objects appear to require larger Doppler factors than those of the BL Lac objects. It is possible that the gamma-ray loud FSRQs are fundamentally different from the gamma-ray quiet FSRQs. Strong polarization at the base of the jet appears to be a signature for gamma-ray loud AGNs.
Looking for blazars in a sample of unidentified high-energy emitting Fermi sources

NASA Astrophysics Data System (ADS)

Marchesini, E. J.; Masetti, N.; Chavushyan, V.; Cellone, S. A.; Andruchow, I.; Bassani, L.; Bazzano, A.; Jiménez-Bailón, E.; Landi, R.; Malizia, A.; Palazzi, E.; Patiño-Álvarez, V.; Rodríguez-Castillo, G. A.; Stephen, J. B.; Ubertini, P.

2016-11-01

Context. Based on their overwhelming dominance among associated Fermi γ-ray catalogue sources, it is expected that a large fraction of the unidentified Fermi objects are blazars. Through crossmatching between the positions of unidentified γ-ray sources from the First Fermi Catalog of γ-ray sources emitting above 10 GeV (1FHL) and the ROSAT and Swift/XRT catalogues of X-ray objects and between pointed XRT observations, a sample of 36 potential associations was found in previous works with less than 15 arcsec of positional offset. One-third of them have recently been classified; the remainder, though believed to belong to the blazar class, still lack spectroscopic classifications. Aims: We study the optical spectrum of the putative counterparts of these unidentified gamma-ray sources in order to find their redshifts and to determine their nature and main spectral characteristics. Methods: An observational campaign was carried out on the putative counterparts of 13 1FHL sources using medium-resolution optical spectroscopy from the Osservatorio Astronomico di Bologna in Loiano, Italy; the Telescopio Nazionale Galileo and the Nordic Optical Telescope, both in the Canary Islands, Spain; and the Observatorio Astronómico Nacional San Pedro Mártir in Baja California, Mexico. Results: We were able to classify 14 new objects based on their continuum shapes and spectral features. Conclusions: Twelve new blazars were found, along with one new quasar and one new narrow line Seyfert 1 (NLS1) to be potentially associated with the 1FHL sources of our sample. Redshifts or lower limits were obtained when possible alongside central black hole mass and luminosity estimates for the NLS1 and the quasar.
γ-Ray And Parsec-Scale Jet Properties Of A Complete Sample Of Blazars From The Mojave Program

DOE PAGES

Lister, M. L.

2011-11-02

We investigate the Fermi LAT -ray and 15 GHz VLBA radio properties of a joint -ray- and radio-selected sample of AGNs obtained during the first 11 months of the Fermi mission (2008 Aug 4 - 2009 Jul 5). Our sample contains the brightest 173 AGNs in these bands above declination -30° during this period, and thus probes the full range of -ray loudness ( -ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least four orders ofmagnitude, reflecting a wide range of spectral energy distribution (SED) parameters in the bright blazar population. Themore » BL Lac objects, however, display a linear correlation of increasing -ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class. The synchrotron self-Compton model is favored for the -ray emission in these BL Lacs over external seed photon models, since the latter predict a dependence of Compton dominance on Doppler factor that would destroy any observed synchrotron SED peak - -ray loudness correlation. The high-synchrotron peaked (HSP) BL Lac objects are distinguished by lower than average radio core brightness temperatures, and none display large radio modulation indices or high linear core polarization levels. No equivalent trends are seen for the flat-spectrum radio quasars (FSRQ) in our sample. Given the association of such properties with relativistic beaming, we suggest that the HSP BL Lacs have generally lower Doppler factors than the lower-synchrotron peaked BL Lacs or FSRQs in our sample.« less
Gamma-Ray and Parsec-Scale Jet Properties of a Complete Sample of Blazars from the MOJAVE Program

NASA Technical Reports Server (NTRS)

Lister, M.L.; Aller, M.; Aller, H.; Hovatta, T.; Kellermann, K. I.; Kovalev, Y. Y.; Meyer, E. T.; Pushkarev, A. B.; Ros, E.; Ackermann, M.;

2011-01-01

We investigate the Fermi LAT gamma-ray and 15 GHz VLBA radio properties of a joint gamma-ray- and radio-selected sample of AGNs obtained during the first 11 months of the Fermi mission (2008 Aug 4 - 2009 Jul 5). Our sample contains the brightest 173 AGNs in these bands above declination -300 during this period, and thus probes the full range of gamma-ray loudness (gamma-ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least four orders of magnitude, reflecting a wide range of spectral energy distribution (SED) parameters in the bright blazar population. The BL Lac objects, however, display a linear correlation of increasing gamma-ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class. The synchrotron self-Compton model is favored for the gamma-ray emission in these BL Lacs over external seed photon models, since the latter predict a dependence of Compton dominance on Doppler factor that would destroy any observed synchrotron SED peak - gamma-ray loudness correlation. The high-synchrotron peaked (HSP) BL Lac objects are distinguished by lower than average radio core brightness temperatures, and none display large radio modulation indices or high linear core polarization levels. No equivalent trends are seen for the flat-spectrum radio quasars (FSRQ) in our sample. Given the association of such properties with relativistic beaming, we suggest that the HSP BL Lacs have generally lower Doppler factors than the lower-synchrotron peaked BL Lacs or FSRQs in our sample.

The All-Sky Swift - INTEGRAL X-Ray Survey

NASA Astrophysics Data System (ADS)

Michelson, Peter

All-sky surveys at hard X-ray energies (above 15 keV) have proven to be a powerful technique in detecting Galactic and extragalactic source populations. Most of the radiation at hard X-ray energies originates in non-thermal processes. These processes take place in extreme conditions of gravitational fields, of electromagnetic field, and also in explosive events. Such extreme conditions can be found in the Milk Way in the vicinity of neutron stars, black holes, and supernovae. Also extragalactic sources are known to be hard X-ray emitters like Active Galactic Nuclei (AGNs), blazars, and Clusters of Galaxies. Currently the most sensitive flying hard X-ray detectors are the Burst Alert Telescope (BAT) on board the NASA mission Swift and the INTEGRAL Soft-Gamma Ray Imager (IBIS/ISGRI) on board the ESA mission INTEGRAL. BAT and IBIS/ISGRI are coded- mask telescopes that shed continuously light on the Galactic and the extragalactic source populations. However, coded-mask telescopes suffer from heavy systematic effects (errors) preventing them from reaching their theoretical limiting sensitivity. Furthermore, by design, they block ~50% of the incident photons causing and increase of statistical noise. As a consequence BAT and IBIS/ISGRI are not sensitive enough to detect faint objects. In addition it has been proven that the Galactic survey of these instruments is limited by systematic uncertainties. Therefore, further observations on the Galactic plane will not improve the sensitivity of the survey of BAT and IBIS/ISGRI. In this project we show that it is possible to overcome the limits of BAT and of IBIS/ISGRI by combining their observations in the 18 55 keV energy range. We call it the SIX survey that stands for Swift - INTEGRAL X-ray survey. Two major advantages are obtained by merging the observations of BAT and IBIS/ISGRI: 1) the exposure is greatly enhanced (sum of BAT and IBIS/ISGRI) and therefore the sensitivity is improved; 2) the systematic errors of both
Background studies in gas ionizing x ray detectors

NASA Technical Reports Server (NTRS)

Eldridge, Hudson B.

1989-01-01

The background response of a gas ionizing proportional x ray detector is estimated by solving the one dimensional photon transport equation for two regions using Monte Carlo techniques. The solution was effected using the SSL VAX 780 and the CRAY XMP computers at Marshall Space Flight Center. The isotropic photon energy spectrum encompassing the range from 1 to 1000 KeV incident onto the first region, the shield, is taken so as to represent the measured spectrum at an altitude of 3 mb over Palastine, Texas. The differential energy spectrum deposited in the gas region, xenon, over the range of 0 to 100 KeV is written to an output file. In addition, the photon flux emerging from the shield region, tin, over the range of 1 to 1000 KeV is also tabulated and written to a separate file. Published tabular cross sections for photoelectric, elastic and inelastic Compton scattering as well as the total absorption coefficient are used. Histories of each incident photon as well as secondary photons from Compton and photoelectric interactions are followed until the photon either is absorbed or exits from the regions under consideration. The effect of shielding thickness upon the energy spectrum deposited in the xenon region for this background spectrum incident upon the tin shield was studied.
Status of the Simbol-X Background Simulation Activities

NASA Astrophysics Data System (ADS)

Tenzer, C.; Briel, U.; Bulgarelli, A.; Chipaux, R.; Claret, A.; Cusumano, G.; Dell'Orto, E.; Fioretti, V.; Foschini, L.; Hauf, S.; Kendziorra, E.; Kuster, M.; Laurent, P.; Tiengo, A.

2009-05-01

The Simbol-X background simulation group is working towards a simulation based background and mass model which can be used before and during the mission. Using the Geant4 toolkit, a Monte-Carlo code to simulate the detector background of the Simbol-X focal plane instrument has been developed with the aim to optimize the design of the instrument. Achieving an overall low instrument background has direct impact on the sensitivity of Simbol-X and thus will be crucial for the success of the mission. We present results of recent simulation studies concerning the shielding of the detectors with respect to the diffuse cosmic hard X-ray background and to the cosmic-ray proton induced background. Besides estimates of the level and spectral shape of the remaining background expected in the low and high energy detector, also anti-coincidence rates and resulting detector dead time predictions are discussed.
X-Ray Spectral Variability Signatures of Flares in BL Lac Objects

NASA Technical Reports Server (NTRS)

Boettcher, Markus; Chiang, James; White, Nicholas E. (Technical Monitor)

2002-01-01

We are presenting a detailed parameter study of the time-dependent electron injection and kinematics and the self-consistent radiation transport in jets of intermediate and low-frequency peaked BL Lac objects. Using a time-dependent, combined synchrotron-self-Compton and external-Compton jet model, we study the influence of variations of several essential model parameters, such as the electron injection compactness, the relative contribution of synchrotron to external soft photons to the soft photon compactness, the electron- injection spectral index, and the details of the time profiles of the electron injection episodes giving rise to flaring activity. In the analysis of our results, we focus on the expected X-ray spectral variability signatures in a region of parameter space particularly well suited to reproduce the broadband spectral energy distributions of intermediate and low-frequency peaked BL Lac objects. We demonstrate that SSC- and external-Compton dominated models for the gamma-ray emission from blazars are producing significantly different signatures in the X-ray variability, in particular in the soft X-ray light curves and the spectral hysteresis at soft X-ray energies, which can be used as a powerful diagnostic to unveil the nature of the high-energy emission from BL Lac objects.
Possible Accretion Disk Origin of the Emission Variability of a Blazar Jet

NASA Astrophysics Data System (ADS)

Chatterjee, Ritaban; Roychowdhury, Agniva; Chandra, Sunil; Sinha, Atreyee

2018-06-01

We analyze X-ray light curves of the blazar Mrk 421 obtained from the Soft X-ray Imaging Telescope (SXT) and the Large Area X-ray Proportional Counter (LAXPC) instrument on board the Indian space telescope AstroSat and archival observations from Swift. We show that the X-ray power spectral density (PSD) is a piece-wise power-law with a break; i.e., the index becomes more negative below a characteristic “break timescale.” Galactic black hole (BH) X-ray binaries and Seyfert galaxies exhibit a similar characteristic timescale in their X-ray variability that is proportional to their respective BH mass. X-rays in these objects are produced in the accretion disk or corona. Hence, such a timescale is believed to be linked to the properties of the accretion flow. Any relation observed between events in the accretion disk and those in the jet can be used to characterize the disk–jet connection. However, evidence of such a link has been scarce and indirect. Mrk 421 is a BL Lac object that has a prominent jet pointed toward us and a weak disk emission, and it is assumed that most of its X-rays are generated in the jet. Hence, the existence of the break in its X-ray PSD may indicate that changes in the accretion disk, which may be the source of the break timescale, are translating into the jet where the X-rays are produced.
DISCOVERY OF VERY HIGH ENERGY gamma-RAYS FROM THE BLAZAR S5 0716+714

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderhub, H.; Biland, A.; Antonelli, L. A.

The MAGIC Collaboration reports the detection of the blazar S5 0716+714 (z = 0.31 +- 0.08) in very high energy gamma rays. The observations were performed in 2007 November and in 2008 April, and were triggered by the Kungliga Vetenskapliga Akademi telescope due to the high optical state of the object. An overall significance of the signal accounts to S = 5.8sigma for 13.1 hr of data. Most of the signal (S = 6.9sigma) comes from the 2008 April data sample during a higher optical state of the object suggesting a possible correlation between the Very High Energy gamma-ray andmore » optical emissions. The differential energy spectrum of the 2008 data sample follows a power law with a photon index of GAMMA = 3.45 +- 0.54{sub stat} +- 0.2{sub syst}, and the integral flux above 400 GeV is at the level of (7.5 +- 2.2{sub stat} +- 2.3{sub syst}) x 10{sup -12} cm{sup -2} s{sup -1}, corresponding to a 9% Crab Nebula flux. Modeling of the broadband spectral energy distribution indicates that a structured jet model appears to be more promising in describing the available data than a simple one-zone synchrotron self-Compton model.« less
The TANAMI Multiwavelength Program: Dynamic spectral energy distributions of southern blazars

DOE PAGES

Krauß, F.; Wilms, J.; Kadler, M.; ...

2016-06-28

Simultaneous broadband spectral and temporal studies of blazars are an important tool for investigating active galactic nuclei (AGN) jet physics. Aims. Here, we study the spectral evolution between quiescent and flaring periods of 22 radio-loud AGN through multiepoch, quasi-simultaneous broadband spectra. For many of these sources these are the first broadband studies. We also use a Bayesian block analysis of Fermi/LAT light curves to determine time ranges of constant flux for constructing quasi-simultaneous spectral energy distributions (SEDs). The shapes of the resulting 81 SEDs are described by two logarithmic parabolas and a blackbody spectrum where needed. The peak frequencies andmore » luminosities agree well with the blazar sequence for low states with higher luminosity implying lower peak frequencies. This is not true for sources in high states. The γ-ray photon index in Fermi/LAT correlates with the synchrotron peak frequency in low and intermediate states. No correlation is present in high states. The black hole mass cannot be determined from the SEDs. Surprisingly, the thermal excess often found in FSRQs at optical/UV wavelengths can be described by blackbody emission and not an accretion disk spectrum. The so-called harder-when-brighter trend, typically seen in X-ray spectra of flaring blazars, is visible in the blazar sequence. Furthermore, our results for low and intermediate states, as well as the Compton dominance, are in agreement with previous results. Black hole mass estimates using recently published parameters are in agreement with some of the more direct measurements. For two sources, estimates disagree by more than four orders of magnitude, possibly owing to boosting effects. The shapes of the thermal excess seen predominantly in flat spectrum radio quasars are inconsistent with a direct accretion disk origin.« less
VizieR Online Data Catalog: Gamma-ray bright blazars spectrophotometry (Williamson+, 2014)

NASA Astrophysics Data System (ADS)

Williamson, K. E.; Jorstad, S. G.; Marscher, A. P.; Larionov, V. M.; Smith, P. S.; Agudo, I.; Arkharov, A. A.; Blinov, D. A.; Casadio, C.; Efimova, N. V.; Gomez, J. L.; Hagen-Thorn, V. A.; Joshi, M.; Konstantinova, T. S.; Kopatskaya, E. N.; Larionova, E. G.; Larionova, L. V.; Malmrose, M. P.; McHardy, I. M.; Molina, S. N.; Morozova, D. A.; Schmidt, G. D.; Taylor, B. W.; Troitsky, I. S.

2017-03-01

Since 2007, we have been collecting multi-waveband fluxes, polarization measurements, and radio images of blazars to provide the data for understanding the physics of the jets (see, e.g., Marscher 2012, arXiv:1201.5402). This study includes 28 of the original 30 objects selected for the monitoring campaign, confirmed as γ-ray sources by EGRET (Energetic γ-Ray Experiment Telescope) on the Compton Gamma Ray Observatory, have an R-band brightness exceeding 18 mag (bright enough for optical polarization measurements at a 1-2 m class optical telescope without needing excessive amounts of telescope time), exceed 0.5 Jy at 43 GHz, and have a declination accessible to the collaboration's observatories (> - 30°). Three additional BL Lacs (1055+018, 1308+326, and 1749+096) and two FSRQs (3C345 and 3C446) included in this analysis were among those added when they were detected as γ-ray sources by the Fermi LAT (Abdo et al. 2009, J/ApJ/700/597). (4 data files).
Characterizing the Optical Variability of Bright Blazars: Variability-based Selection of Fermi Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Ruan, John J.; Anderson, Scott F.; MacLeod, Chelsea L.; Becker, Andrew C.; Burnett, T. H.; Davenport, James R. A.; Ivezić, Željko; Kochanek, Christopher S.; Plotkin, Richard M.; Sesar, Branimir; Stuart, J. Scott

2012-11-01

We investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, in part to aid in the identification of blazar counterparts to the ~30% of γ-ray sources in the Fermi 2FGL catalog still lacking reliable associations. Using data from the optical LINEAR asteroid survey, we characterize the optical variability of blazars by fitting a damped random walk model to individual light curves with two main model parameters, the characteristic timescales of variability τ, and driving amplitudes on short timescales \\hat{\\sigma }. Imposing cuts on minimum τ and \\hat{\\sigma } allows for blazar selection with high efficiency E and completeness C. To test the efficacy of this approach, we apply this method to optically variable LINEAR objects that fall within the several-arcminute error ellipses of γ-ray sources in the Fermi 2FGL catalog. Despite the extreme stellar contamination at the shallow depth of the LINEAR survey, we are able to recover previously associated optical counterparts to Fermi active galactic nuclei with E >= 88% and C = 88% in Fermi 95% confidence error ellipses having semimajor axis r < 8'. We find that the suggested radio counterpart to Fermi source 2FGL J1649.6+5238 has optical variability consistent with other γ-ray blazars and is likely to be the γ-ray source. Our results suggest that the variability of the non-thermal jet emission in blazars is stochastic in nature, with unique variability properties due to the effects of relativistic beaming. After correcting for beaming, we estimate that the characteristic timescale of blazar variability is ~3 years in the rest frame of the jet, in contrast with the ~320 day disk flux timescale observed in quasars. The variability-based selection method presented will be useful for blazar identification in time-domain optical surveys and is also a probe of jet physics.
Prediction of ECS and SSC Models for Flux-Limited Samples of Gamma-Ray Blazars

NASA Technical Reports Server (NTRS)

Lister, Matthew L.; Marscher, Alan P.

1999-01-01

The external Compton scattering (ECS) and synchrotron self-Compton (SSC) models make distinct predictions for the amount of Doppler boosting of high-energy gamma-rays emitted by Nazar. We examine how these differences affect the predicted properties of active galactic nucleus (AGN) samples selected on the basis of Murray emission. We create simulated flux-limited samples based on the ECS and SSC models, and compare their properties to those of identified EGRET blazars. We find that for small gamma-ray-selected samples, the two models make very similar predictions, and cannot be reliably distinguished. This is primarily due to the fact that not only the Doppler factor, but also the cosmological distance and intrinsic luminosity play a role in determining whether an AGN is included in a flux-limited gamma-ray sample.

Analysis of XMM-Newton Data from Extended Sources and the Diffuse X-Ray Background

NASA Technical Reports Server (NTRS)

Snowden, Steven

2011-01-01

Reduction of X-ray data from extended objects and the diffuse background is a complicated process that requires attention to the details of the instrumental response as well as an understanding of the multiple background components. We present methods and software that we have developed to reduce data from XMM-Newton EPIC imaging observations for both the MOS and PN instruments. The software has now been included in the Science Analysis System (SAS) package available through the XMM-Newton Science Operations Center (SOC).
Exploring the Variability of the Fermi LAT Blazar Population

NASA Astrophysics Data System (ADS)

Macomb, Daryl J.; Shrader, C. R.

2014-01-01

The flux variability of the approximately 2000 point sources cataloged by the Fermi Gamma-Ray Space Telescope provide important clues to population characteristics. This is particularly true of the more than 1100 source that are likely AGN. By characterizing the intrinsic flux variability and distinguishing this variability from flaring behavior, we can better address questions of flare amplitudes, durations, recurrence times, and temporal profiles. A better understanding of the responsible physical environments, such as the scale and location of jet structures responsible for the high-energy emission, may emerge from such studies. Assessing these characteristics as a function of blazar sub-class is a further goal in order to address questions about the fundamentals of blazar AGN physics. Here we report on progress made in categorizing blazar flare behavior, and correlate these behaviors with blazar sub-type and other source parameters.
Background simulations for the wide field imager aboard the ATHENA X-ray Observatory

NASA Astrophysics Data System (ADS)

Hauf, Steffen; Kuster, Markus; Hoffmann, Dieter H. H.; Lang, Philipp-Michael; Neff, Stephan; Pia, Maria Grazia; Strüder, Lothar

2012-09-01

The ATHENA X-ray observatory was a European Space Agency project for a L-class mission. ATHENA was to be based upon a simplified IXO design with the number of instruments and the focal length of the Wolter optics being reduced. One of the two instruments, the Wide Field Imager (WFI) was to be a DePFET based focal plane pixel detector, allowing for high time and spatial resolution spectroscopy in the energy-range between 0.1 and 15 keV. In order to fulfill the mission goals a high sensitivity is essential, especially to study faint and extended sources. Thus a detailed understanding of the detector background induced by cosmic ray particles is crucial. During the mission design generally extensive Monte-Carlo simulations are used to estimate the detector background in order to optimize shielding components and software rejection algorithms. The Geant4 toolkit1,2 is frequently the tool of choice for this purpose. Alongside validation of the simulation environment with XMM-Newton EPIC-pn and Space Shuttle STS-53 data we present estimates for the ATHENA WFI cosmic ray induced background including long-term activation, which demonstrate that DEPFET-technology based detectors are able to achieve the required sensitivity.
Cosmic X-ray Physics: Sounding rocket investigations of the diffuse X-ray background, including instrument development

NASA Astrophysics Data System (ADS)

McCammon, Dan

We propose an investigation to improve our understanding of the Galactic diffuse X-ray background. The ultimate purpose of this is to determine the role of hot phases of the interstellar medium in mediating stellar feedback in star formation, in transport of metals, and in determining the structure and evolution of the Galaxy. It directly addresses SMD's astrophysics goal No. 2, to explore the origin and evolution of the galaxies, stars and planets that make up our universe. This work will involve a flight of an existing payload with small modifications in Woomera, South Australia, to observe the Galactic soft X-ray bulge and attempt to determine its nature and emission mechanisms. This flight should also either confirm or put strict upper limits on the "sterile neutrino" model for the 3.5 keV signal observed near the Galactic Center by XMM-Newton. Our investigation includes the development of thermal detectors with superconducting transition edge thermometers capable of 1-2 eV FWHM energy resolution in the 100-400 eV range with the intent of obtaining a scientifically useful spectrum on a sounding rocket flight of the emission from one million degree gas in this energy range. This will require a total area of 1-2 square centimeters for the detector array. To enable routine testing of such detectors in the lab and for necessary in-flight gain and resolution monitoring, we are trying to develop a pulsed-UV laser calibration source. In collaboration with Goddard Space Flight Center, we are investigating the practicality of waveguide-below-cutoff filters to provide the necessary attenuation of infrared radiation for these detectors while still allowing good x-ray transmission below 150 eV. The detectors, calibration source, filters, optimal high-rate pulse analysis and flight experience with the detector readouts are all relevant to future NASA major missions. The detectors we're working on for a low-energy sounding rocket flight would be an excellent match to what is
Blazar flaring patterns (B-FlaP) classifying blazar candidate of uncertain type in the third Fermi-LAT catalogue by artificial neural networks

NASA Astrophysics Data System (ADS)

Chiaro, G.; Salvetti, D.; La Mura, G.; Giroletti, M.; Thompson, D. J.; Bastieri, D.

2016-11-01

The Fermi-Large Area Telescope (LAT) is currently the most important facility for investigating the GeV γ-ray sky. With Fermi-LAT, more than three thousand γ-ray sources have been discovered so far. 1144 (˜40 per cent) of the sources are active galaxies of the blazar class, and 573 (˜20 per cent) are listed as blazar candidate of uncertain type (BCU), or sources without a conclusive classification. We use the empirical cumulative distribution functions and the artificial neural networks for a fast method of screening and classification for BCUs based on data collected at γ-ray energies only, when rigorous multiwavelength analysis is not available. Based on our method, we classify 342 BCUs as BL Lacs and 154 as flat-spectrum radio quasars, while 77 objects remain uncertain. Moreover, radio analysis and direct observations in ground-based optical observatories are used as counterparts to the statistical classifications to validate the method. This approach is of interest because of the increasing number of unclassified sources in Fermi catalogues and because blazars and in particular their subclass high synchrotron peak objects are the main targets of atmospheric Cherenkov telescopes.
SMARTScience Tools: Interacting With Blazar Data In The Web Browser

NASA Astrophysics Data System (ADS)

Hasan, Imran; Isler, Jedidah; Urry, C. Megan; MacPherson, Emily; Buxton, Michelle; Bailyn, Charles D.; Coppi, Paolo S.

2014-08-01

The Yale-SMARTS blazar group has accumulated 6 years of optical-IR photometry of more than 70 blazars, mostly bright enough in gamma-rays to be detected with Fermi. Observations were done with the ANDICAM instrument on the SMARTS 1.3 m telescope at the Cerro Tololo Inter-American Observatory. As a result of this long-term, multiwavelength monitoring, we have produced a calibrated, publicly available data set (see www.astro.yale.edu/smarts/glast/home.php), which we have used to find that (i) optical-IR and gamma-ray light curves are well correlated, supporting inverse-Compton models for gamma-ray production (Bonning et al. 2009, 2012), (ii) at their brightest, blazar jets can contribute significantly to the photoionization of the broad-emission-line region, indicating that gamma-rays are produced within 0.1 pc of the black hole in at least some cases (Isler et al. 2014), and (iii) optical-IR and gamma-ray flares are symmetric, implying the time scales are dominated by light-travel-time effects rather than acceleration or cooling (Chatterjee et al. 2012). The volume of data and diversity of projects for which it is used calls out for an efficient means of visualization. To this end, we have developed a suite of visualization tools called SMARTScience Tools, which allow users to interact dynamically with our dataset. The SMARTScience Tools is publicly available via our webpage and can be used to customize multiwavelength light curves and color magnitude diagrams quickly and intuitively. Users can choose specific bands to construct plots, and the plots include features such as band-by-band panning, dynamic zooming, and direct mouse interaction with individual data points. Human and machine readable tables of the plotted data can be directly printed for the user's convenience and for further independent study. The SMARTScience Tools significantly improves the public’s ability to interact with the Yale-SMARTS 6-year data base of blazar photometry, and should make
{gamma}-RAY AND PARSEC-SCALE JET PROPERTIES OF A COMPLETE SAMPLE OF BLAZARS FROM THE MOJAVE PROGRAM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lister, M. L.; Hovatta, T.; Aller, M.

We investigate the Fermi Large Area Telescope {gamma}-ray and 15 GHz Very Long Baseline Array radio properties of a joint {gamma}-ray and radio-selected sample of active galactic nuclei (AGNs) obtained during the first 11 months of the Fermi mission (2008 August 4-2009 July 5). Our sample contains the brightest 173 AGNs in these bands above declination -30 Degree-Sign during this period, and thus probes the full range of {gamma}-ray loudness ({gamma}-ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least 4 orders of magnitude, reflecting a wide range of spectral energy distribution (SED)more » parameters in the bright blazar population. The BL Lac objects, however, display a linear correlation of increasing {gamma}-ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class. The synchrotron self-Compton model is favored for the {gamma}-ray emission in these BL Lac objects over external seed photon models, since the latter predict a dependence of Compton dominance on Doppler factor that would destroy any observed synchrotron SED-peak-{gamma}-ray-loudness correlation. The high-synchrotron peaked (HSP) BL Lac objects are distinguished by lower than average radio core brightness temperatures, and none display large radio modulation indices or high linear core polarization levels. No equivalent trends are seen for the flat-spectrum radio quasars (FSRQs) in our sample. Given the association of such properties with relativistic beaming, we suggest that the HSP BL Lac objects have generally lower Doppler factors than the lower-synchrotron peaked BL Lac objects or FSRQs in our sample.« less
γ-Ray and Parsec-scale Jet Properties of a Complete Sample of Blazars From the MOJAVE Program

NASA Astrophysics Data System (ADS)

Lister, M. L.; Aller, M.; Aller, H.; Hovatta, T.; Kellermann, K. I.; Kovalev, Y. Y.; Meyer, E. T.; Pushkarev, A. B.; Ros, E.; MOJAVE Collaboration; Ackermann, M.; Antolini, E.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Boeck, M.; Bonamente, E.; Borgland, A. W.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Casandjian, J. M.; Cavazzuti, E.; Cecchi, C.; Chang, C. S.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; de Palma, F.; Dermer, C. D.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Finke, J.; Focke, W. B.; Fortin, P.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Guiriec, S.; Hadasch, D.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Jóhannesson, G.; Johnson, A. S.; Kadler, M.; Katagiri, H.; Kataoka, J.; Knödlseder, J.; Kuss, M.; Lande, J.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Mizuno, T.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Nishino, S.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ozaki, M.; Paneque, D.; Parent, D.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Pivato, G.; Rainò, S.; Readhead, A.; Reimer, A.; Reimer, O.; Richards, J. L.; Ritz, S.; Sadrozinski, H. F.-W.; Sgrò, C.; Shaw, M. S.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Takahashi, H.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tosti, G.; Tramacere, A.; Troja, E.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Zimmer, S.; Fermi LAT Collaboration

2011-11-01

We investigate the Fermi Large Area Telescope γ-ray and 15 GHz Very Long Baseline Array radio properties of a joint γ-ray and radio-selected sample of active galactic nuclei (AGNs) obtained during the first 11 months of the Fermi mission (2008 August 4-2009 July 5). Our sample contains the brightest 173 AGNs in these bands above declination -30° during this period, and thus probes the full range of γ-ray loudness (γ-ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least 4 orders of magnitude, reflecting a wide range of spectral energy distribution (SED) parameters in the bright blazar population. The BL Lac objects, however, display a linear correlation of increasing γ-ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class. The synchrotron self-Compton model is favored for the γ-ray emission in these BL Lac objects over external seed photon models, since the latter predict a dependence of Compton dominance on Doppler factor that would destroy any observed synchrotron SED-peak-γ-ray-loudness correlation. The high-synchrotron peaked (HSP) BL Lac objects are distinguished by lower than average radio core brightness temperatures, and none display large radio modulation indices or high linear core polarization levels. No equivalent trends are seen for the flat-spectrum radio quasars (FSRQs) in our sample. Given the association of such properties with relativistic beaming, we suggest that the HSP BL Lac objects have generally lower Doppler factors than the lower-synchrotron peaked BL Lac objects or FSRQs in our sample.
RoboPol: blazar astrophysics from Skinakas with a unique optical

NASA Astrophysics Data System (ADS)

Pavlidou, V.

2013-09-01

Blazars are the most active galaxies known. They are powered by relativistic jets of matter speeding towards us almost head-on at the speed of light, radiating exclusively through extreme, non-thermal particle interactions, energized by accretion onto supermassive black holes. Despite intensive observational and theoretical efforts over the last four decades, the details of blazar astrophysics remain elusive. The launch of NASA's Fermi Gamma-ray Space Telescope in 2008 has provided an unprecedented opportunity for the systematic study of blazar jets and has prompted large-scale blazar monitoring efforts across wavelengths. In such a multi-wavelength campaign, a novel effect was discovered: fast changes in the optical polarization during gamma-ray flares. Such events probe the magnetic field structure in the jet and the evolution of disturbances responsible for blazar flares. Their systematic study can answer long-standing questions in our theoretical understanding of jets; however, until recently, optical polarimetry programs in operation were not adequate to find and follow similar events with the efficiency and time-resolution needed. RoboPol is a massive program of optical polarimetric monitoring of over 100 blazars, using an innovative, specially-designed and built polarimeter mounted on the 1.3 m telescope at Skinakas Observatory, a dynamical observing schedule, and a large amount of dedicated telescope time. The program is a collaboration between the University of Crete and the Foundation for Research and Technology - Hellas in Greece, the Max-Planck Institute for Radioastronomy in Germany, Caltech in the US, the Nicolaus Copernicus University in Poland, and the Inter-University Centre for Astronomy and Astrophysics in India. The instrument was successfully commissioned in March of 2013 and has been taking data since. In this talk we will review the RoboPol program, its potential for discovery in blazar astrophysics, and we will present results from its first
The Ringo2 Optical Polarisation Catalogue of 13 High-Energy Blazars

NASA Astrophysics Data System (ADS)

Barres de Almeida, Ulisses; Jermak, Helen; Mundell, Carole; Lindfors, Elina; Nilsson, Kari; Steele, Iain

2015-08-01

We present the findings of the Ringo2 3-year survey of 13 blazars (3 FSRQs and 10 BL Lacs) with regular coverage and reasonably fast cadence of one to three observations a week. Ringo2 was installed on the Liverpool Robotic Telescope (LT) on the Canary Island of La Palma between 2009 and 2012 and monitored thirteen high-energy-emitting blazars in the northern sky. The objects selected as well as the observational strategy were tuned to maximise the synergies with high-energy X- to gamma-ray observations. Therefore this sample stands out as a well-sampled, long-term view of high-energy AGN jets in polarised optical light. Over half of the sources exhibited an increase in optical flux during this period and almost a quarter were observed in outburst. We compare the optical data to gamma (Fermi/LAT) and X-ray data during these periods of outburst. In this talk we present the data obtained for all sources over the lifetime of Ringo2 with additional optical data from the KVA telescope and the SkyCamZ wide-field camera (on the LT), we explore the relationship between the change in polarisation angle as a function of time (dEVPA/dMJD), flux and polarisation degree along with cross correlation comparisons of optical and high-energy flux.
SUZAKU X-RAY FOLLOW-UP OBSERVATIONS OF SEVEN UNASSOCIATED FERMI-LAT GAMMA-RAY SOURCES AT HIGH GALACTIC LATITUDES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takahashi, Y.; Kataoka, J.; Nakamori, T.

2012-03-01

We report on our second-year campaign of X-ray follow-up observations of unidentified Fermi Large Area Telescope (LAT) {gamma}-ray sources at high Galactic latitudes (|b| > 10 Degree-Sign ) using the X-ray Imaging Spectrometer on board the Suzaku X-ray Observatory. In this second year of the project, seven new targets were selected from the First Fermi-LAT Catalog, and studied with 20-40 ks effective Suzaku exposures. We detected an X-ray point source coincident with the position of the recently discovered millisecond pulsar (MSP) PSR J2302+4442 within the 95% confidence error circle of 1FGL J2302.8+4443. The X-ray spectrum of the detected counterpart wasmore » well fit by a blackbody model with temperature of kT {approx_equal} 0.3 keV, consistent with an origin of the observed X-ray photons from the surface of a rotating magnetized neutron star. For four other targets that were also recently identified with a normal pulsar (1FGL J0106.7+4853) and MSPs (1FGL J1312.6+0048, J1902.0-5110, and J2043.2+1709), only upper limits in the 0.5-10 keV band were obtained at the flux levels of {approx_equal} 10{sup -14} erg cm{sup -2} s{sup -1}. A weak X-ray source was found in the field of 1FGL J1739.4+8717, but its association with the variable {gamma}-ray emitter could not be confirmed with the available Suzaku data alone. For the remaining Fermi-LAT object 1FGL J1743.8-7620 no X-ray source was detected within the LAT 95% error ellipse. We briefly discuss the general properties of the observed high Galactic-latitude Fermi-LAT objects by comparing their multiwavelength properties with those of known blazars and MSPs.« less
PKS 1502+106: A new and distant gamma-ray blazar in outburst discovered by the Fermi Large Area Telescope

DOE PAGES

Abdo, A. A.

2010-01-22

The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope discovered a rapid (~5 days duration), high-energy (E > 100 MeV) gamma-ray outburst from a source identified with the blazar PKS 1502+106 (OR 103, S3 1502+10, z = 1.839) starting on 2008 August 5 (~23 UTC, MJD 54683.95), and followed by bright and variable flux over the next few months. Our results on the gamma-ray localization and identification, as well as spectral and temporal behavior during the first months of the Fermi all-sky survey, are reported here in conjunction with a multiwaveband characterization as a result of onemore » of the first Fermi multifrequency campaigns. The campaign included a Swift ToO (followed up by a 16 day observation on August 7-22, MJD 54685-54700), VLBA (within the MOJAVE program), Owens Valley Radio Observatory (OVRO) 40 m, Effelsberg-100 m, Metsähovi-14 m, RATAN-600, and Kanata-Hiroshima radio/optical observations. Results from the analysis of archival observations by INTEGRAL, XMM-Newton, and Spitzer space telescopes are reported for a more complete picture of this new gamma-ray blazar. PKS 1502+106 is a sub-GeV peaked, powerful flat spectrum radio quasar (luminosity at E > 100 MeV, L γ, is about 1.1 × 10 49 erg s –1, and black hole mass likely close to 10 9 M ⊙), exhibiting marked gamma-ray bolometric dominance, in particular during the asymmetric outburst (L γ/L opt ~ 100, and 5 day averaged flux F E > 100 MeV = 2.91 ± 1.4 × 10 –6 ph cm –2 s –1), which was characterized by a factor greater than 3 of flux increase in less than 12 hr. The outburst was observed simultaneously from optical to X-ray bands (F 0.3 – 10 keV = 2.18 +0.15 –0.12 × 10 –12 erg cm –2 s –1, and hard photon index ~1.5, similar to past values) with a flux increase of less than 1 order of magnitude with respect to past observations, and was likely controlled by Comptonization of external-jet photons produced in the broad-line region (BLR) in the gamma-ray
Quasi-stellar objects in the intergalactic medium: Source for the cosmic X-ray background

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sherman, R.D.

1980-06-15

QSOs are regarded as sources of both electromagnetic radiation and ejected matter that heat and ionize a dense intergalactic medium (IGM). Using current estimates of QSO luminosity, number density, evolution, and spectral index, we study three viable models: the diffuse cosmic X-ray background is (1) due entirely to thermal Bremsstrahlung of the IGM, (2) completely supplied by QSO X-radiation, (3) or a combination of both. The upper limits on an IGM fractional density with respect to closure are ..cap omega..=0.26, 0.24, and 0.21 for pure collisional, photo/collisional mixture, and pure photoionization, respectively. These calculations give emission spectra, Compton distortion ofmore » the cosmic microwave background, and optical depths to distant OSOs for comparison with relevant data.« less
Femtosecond X-ray coherent diffraction of aligned amyloid fibrils on low background graphene.

PubMed

Seuring, Carolin; Ayyer, Kartik; Filippaki, Eleftheria; Barthelmess, Miriam; Longchamp, Jean-Nicolas; Ringler, Philippe; Pardini, Tommaso; Wojtas, David H; Coleman, Matthew A; Dörner, Katerina; Fuglerud, Silje; Hammarin, Greger; Habenstein, Birgit; Langkilde, Annette E; Loquet, Antoine; Meents, Alke; Riek, Roland; Stahlberg, Henning; Boutet, Sébastien; Hunter, Mark S; Koglin, Jason; Liang, Mengning; Ginn, Helen M; Millane, Rick P; Frank, Matthias; Barty, Anton; Chapman, Henry N

2018-05-09

Here we present a new approach to diffraction imaging of amyloid fibrils, combining a free-standing graphene support and single nanofocused X-ray pulses of femtosecond duration from an X-ray free-electron laser. Due to the very low background scattering from the graphene support and mutual alignment of filaments, diffraction from tobacco mosaic virus (TMV) filaments and amyloid protofibrils is obtained to 2.7 Å and 2.4 Å resolution in single diffraction patterns, respectively. Some TMV diffraction patterns exhibit asymmetry that indicates the presence of a limited number of axial rotations in the XFEL focus. Signal-to-noise levels from individual diffraction patterns are enhanced using computational alignment and merging, giving patterns that are superior to those obtainable from synchrotron radiation sources. We anticipate that our approach will be a starting point for further investigations into unsolved structures of filaments and other weakly scattering objects.
Modeling Blazar Spectra by Solving an Electron Transport Equation

NASA Astrophysics Data System (ADS)

Lewis, Tiffany; Finke, Justin; Becker, Peter A.

2018-01-01

Blazars are luminous active galaxies across the entire electromagnetic spectrum, but the spectral formation mechanisms, especially the particle acceleration, in these sources are not well understood. We develop a new theoretical model for simulating blazar spectra using a self-consistent electron number distribution. Specifically, we solve the particle transport equation considering shock acceleration, adiabatic expansion, stochastic acceleration due to MHD waves, Bohm diffusive particle escape, synchrotron radiation, and Compton radiation, where we implement the full Compton cross-section for seed photons from the accretion disk, the dust torus, and 26 individual broad lines. We used a modified Runge-Kutta method to solve the 2nd order equation, including development of a new mathematical method for normalizing stiff steady-state ordinary differential equations. We show that our self-consistent, transport-based blazar model can qualitatively fit the IR through Fermi g-ray data for 3C 279, with a single-zone, leptonic configuration. We use the solution for the electron distribution to calculate multi-wavelength SED spectra for 3C 279. We calculate the particle and magnetic field energy densities, which suggest that the emitting region is not always in equipartition (a common assumption), but sometimes matter dominated. The stratified broad line region (based on ratios in quasar reverberation mapping, and thus adding no free parameters) improves our estimate of the location of the emitting region, increasing it by ~5x. Our model provides a novel view into the physics at play in blazar jets, especially the relative strength of the shock and stochastic acceleration, where our model is well suited to distinguish between these processes, and we find that the latter tends to dominate.
Small scale H I structure and the soft X-ray background

NASA Technical Reports Server (NTRS)

Jahoda, K.; Mccammon, D.; Lockman, F. J.

1986-01-01

The observed anticorrelation between diffuse soft X-ray flux and H I column density has been explained as absorption of soft X-rays produced in a hot galactic halo, assuming that the neutral interstellar material is sufficiently clumped to reduce the soft X-ray absorption cross section by a factor of two to three. A 21 cm emission line study of H I column density variations at intermediate and high galactic latitudes to 10' spatial resolution has been done. The results confirm conclusions from preliminary work at coarser resolution, and in combination with other data appear to rule out the hypothesis that clumping of neutral interstellar matter on any angular scale significantly reduces X-ray absorption cross sections in the 0.13 - 0.28 keV energy range. It is concluded therefore that the observed anticorrelation is not primarily a consequence of absorption of soft X-rays produced in a hot galactic halo.
Disentangling Hadronic and Leptonic Cascade Scenarios from the Very-High-Energy Gamma-Ray Emission of Distant Hard-Spectrum Blazars

DOE PAGES

Takami, Hajime; Murase, Kohta; Dermer, Charles D.

2013-06-26

We show that recent data from the Fermi Large Area Telescope have revealed about a dozen distant hard-spectrum blazars that have very-high-energy (VHE; ≳ 100 eV) photons associated with them, but most of them have not yet been detected by imaging atmospheric Cherenkov Telescopes. Most of these high-energy gamma-ray spectra, like those of other extreme high-frequency peaked BL Lac objects, can be well explained either by gamma rays emitted at the source or by cascades induced by ultra-high-energy cosmic rays, as we show specifically for KUV 00311–1938. We consider the prospects for detection of the VHE sources by the plannedmore » Cherenkov Telescope Array (CTA) and show how it can distinguish the two scenarios by measuring the integrated flux above ~500 GeV (depending on source redshift) for several luminous sources with z ≲ 1 in the sample. Strong evidence for the origin of ultra-high-energy cosmic rays could be obtained from VHE observations with CTA. Depending on redshift, if the often quoted redshift of KUV 00311–1938 (z = 0.61) is believed, then preliminary H.E.S.S. data favor cascades induced by ultra-high-energy cosmic rays. Lastly, accurate redshift measurements of hard-spectrum blazars are essential for this study.« less
The classification of flaring states of blazars

NASA Astrophysics Data System (ADS)

Resconi, E.; Franco, D.; Gross, A.; Costamante, L.; Flaccomio, E.

2009-08-01

Aims: The time evolution of the electromagnetic emission from blazars, in particular high-frequency peaked sources (HBLs), displays irregular activity that has not yet been understood. In this work we report a methodology capable of characterizing the time behavior of these variable objects. Methods: The maximum likelihood blocks (MLBs) is a model-independent estimator that subdivides the light curve into time blocks, whose length and amplitude are compatible with states of constant emission rate of the observed source. The MLBs yield the statistical significance in the rate variations and strongly suppresses the noise fluctuations in the light curves. We applied the MLBs for the first time on the long term X-ray light curves (RXTE/ASM) of Mkn 421, Mkn 501, 1ES 1959+650, and 1ES 2155-304, more than 10 years of observational data (1996-2007). Using the MLBs interpretation of RXTE/ASM data, the integrated time flux distribution is determined for each single source considered. We identify in these distributions the characteristic level, as well as the flaring states of the blazars. Results: All the distributions show a significant component at negative flux values, most probably caused by an uncertainty in the background subtraction and by intrinsic fluctuations of RXTE/ASM. This effect concerns in particular short time observations. To quantify the probability that the intrinsic fluctuations give rise to a false identification of a flare, we study a population of very faint sources and their integrated time-flux distribution. We determine duty cycle or fraction of time a source spent in the flaring state of the source Mkn 421, Mkn 501, 1ES 1959+650 and 1ES 2155-304. Moreover, we study the random coincidences between flares and generic sporadic events such as high-energy neutrinos or flares in other wavelengths.
Optical flare observed in the flaring gamma-ray blazar CGRaBS J0809+5341 (87GB 080551.6+535010)

NASA Astrophysics Data System (ADS)

Pursimo, Tapio; Galindo-Guil, F. J.; Serrano, Pere Blay; Ojha, Roopesh

2017-11-01

We report optical photometry of the blazar CGRaBS J0809+5341 (87GB 080551.6+535010), obtained with the 2.56m Nordic Optical Telescope in La Palma, to look for any enhanced optical activity associated with a recent flare in the daily averaged gamma-ray flux (ATel#10905).
Investigating broadband variability of the TeV blazar 1ES 1959+650

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aliu, E.; Archambault, S.; Arlen, T.

We summarize broadband observations of the TeV-emitting blazar 1ES 1959 650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift UVOT, X-ray observations by the Swift X-ray Telescope, high-energy gamma-ray observations with the Fermi Large Area Telescope, and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 2012 April 17 and 2012 June 1 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that the parameters requiredmore » to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not required to explain the observed variability pattern, represents one possible scenario which can describe the observations. As applied to an elevated VHE state of 66% of the Crab Nebula flux, observed on a single night during the observation period, the reflected emission scenario does not support a purely leptonic non-thermal emission mechanism. The reflected model does, however, predict a reflected photon field with sufficient energy to enable elevated gamma-ray emission via pion production with protons of energies between 10 and 100 TeV.« less

INVESTIGATING BROADBAND VARIABILITY OF THE TeV BLAZAR 1ES 1959+650

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aliu, E.; Archambault, S.; Arlen, T.

We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift Ultraviolet and Optical Telescope, X-ray observations by the Swift X-ray Telescope, high-energy gamma-ray observations with the Fermi Large Area Telescope, and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 2012 April 17 and 2012 June 1 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that themore » parameters required to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not required to explain the observed variability pattern, represents one possible scenario which can describe the observations. As applied to an elevated VHE state of 66% of the Crab Nebula flux, observed on a single night during the observation period, the reflected emission scenario does not support a purely leptonic non-thermal emission mechanism. The reflected emission model does, however, predict a reflected photon field with sufficient energy to enable elevated gamma-ray emission via pion production with protons of energies between 10 and 100 TeV.« less
INVESTIGATING BROADBAND VARIABILITY OF THE TeV BLAZAR 1ES 1959+650

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aliu, E.; Archambault, S.; Arlen, T.

We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift Ultraviolet and Optical Telescope, X-ray observations by the Swift X-ray Telescope, high-energy gamma-ray observations with the Fermi Large Area Telescope, and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 2012 April 17 and 2012 June 1 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that themore » parameters required to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not required to explain the observed variability pattern, represents one possible scenario which can describe the observations. As applied to an elevated VHE state of 66% of the Crab Nebula flux, observed on a single night during the observation period, the reflected emission scenario does not support a purely leptonic non-thermal emission mechanism. The reflected emission model does, however, predict a reflected photon field with sufficient energy to enable elevated gamma-ray emission via pion production with protons of energies between 10 and 100 TeV.« less
Investigating broadband variability of the TeV blazar 1ES 1959+650

DOE PAGES

Aliu, E.; Archambault, S.; Arlen, T.; ...

2014-12-03

We summarize broadband observations of the TeV-emitting blazar 1ES 1959 650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift UVOT, X-ray observations by the Swift X-ray Telescope, high-energy gamma-ray observations with the Fermi Large Area Telescope, and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 2012 April 17 and 2012 June 1 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that the parameters requiredmore » to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not required to explain the observed variability pattern, represents one possible scenario which can describe the observations. As applied to an elevated VHE state of 66% of the Crab Nebula flux, observed on a single night during the observation period, the reflected emission scenario does not support a purely leptonic non-thermal emission mechanism. The reflected model does, however, predict a reflected photon field with sufficient energy to enable elevated gamma-ray emission via pion production with protons of energies between 10 and 100 TeV.« less
Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program

NASA Astrophysics Data System (ADS)

Jorstad, Svetlana G.; Marscher, Alan P.; Morozova, Daria A.; Troitsky, Ivan S.; Agudo, Iván; Casadio, Carolina; Foord, Adi; Gómez, José L.; MacDonald, Nicholas R.; Molina, Sol N.; Lähteenmäki, Anne; Tammi, Joni; Tornikoski, Merja

2017-09-01

We analyze the parsec-scale jet kinematics from 2007 June to 2013 January of a sample of γ-ray bright blazars monitored roughly monthly with the Very Long Baseline Array at 43 GHz. In a total of 1929 images, we measure apparent speeds of 252 emission knots in 21 quasars, 12 BL Lacertae objects (BLLacs), and 3 radio galaxies, ranging from 0.02c to 78c; 21% of the knots are quasi-stationary. Approximately one-third of the moving knots execute non-ballistic motions, with the quasars exhibiting acceleration along the jet within 5 pc (projected) of the core, and knots in BLLacs tending to decelerate near the core. Using the apparent speeds of the components and the timescales of variability from their light curves, we derive the physical parameters of 120 superluminal knots, including variability Doppler factors, Lorentz factors, and viewing angles. We estimate the half-opening angle of each jet based on the projected opening angle and scatter of intrinsic viewing angles of knots. We determine characteristic values of the physical parameters for each jet and active galactic nucleus class based on the range of values obtained for individual features. We calculate the intrinsic brightness temperatures of the cores, {T}{{b},{int}}{core}, at all epochs, finding that the radio galaxies usually maintain equipartition conditions in the cores, while ˜30% of {T}{{b},{int}}{core} measurements in the quasars and BLLacs deviate from equipartition values by a factor >10. This probably occurs during transient events connected with active states. In the Appendix, we briefly describe the behavior of each blazar during the period analyzed.
Long-term multiwavelength studies of high-redshift blazar 0836+710

DOE PAGES

Akyuz, A.; Thompson, D. J.; Donato, D.; ...

2013-07-30

The observation of γ-ray flares from blazar 0836+710 in 2011, following a period of quiescence, offered an opportunity to study correlated activity at different wavelengths for a high-redshift (z = 2.218) active galactic nucleus. Here, optical and radio monitoring, plus Fermi-LAT γ-ray monitoring provided 20082–2012 coverage, while Swift offered auxiliary optical, ultraviolet, and X-ray information. Other contemporaneous observations were used to construct a broad-band spectral energy distribution. As a result, there is evidence of correlation but not a measurable lag between the optical and γ-ray flaring emission. In contrast, there is no clear correlation between radio and γ-ray activity, indicatingmore » radio emission regions that are unrelated to the parts of the jet that produce the γ rays. In conclusion, the γ-ray energy spectrum is unusual in showing a change of shape from a power law to a curved spectrum when going from the quiescent state to the active state.« less
Is There Evidence for X-Ray Emitting Plasma Very Close to the Photospheres of O Stars?

NASA Technical Reports Server (NTRS)

Leutenegger, Maurice A.

2008-01-01

Aims. We reexamine the implications of the recent HESS observations of the blazar 1ES0229+200 for constraining the extragalactic mid-infrared background radiation. Methods. We examine the effect of gamma-ray absorption by the extragalactic infrared radiation on predicted intrinsic spectra for this blazar and compare our results with the observational data. Results. We find agreement with our previous results on the shape of the infrared spectral energy distribution, contrary to the recent assertion of the HESS group. Our analysis indicates that 1ES0229+200 has a very hard intrinsic spectrum with a spectral index between 1.1 +/- 0.3 and 1.5 +/- 0.3 in the energy range between approx.0.5 TeV and approx.15 TeV. Conclusions. Under the assumptions that (1) the models of Stecker et al. (2006, ApJ, 648, 774) as derived from numerous detailed infrared observations are reasonable, and (2) spectral indexes in the range 1 < gamma < 1.5 are obtainable from relativistic shock acceleration under the astrophysical conditions extant in blazar flares (Stecker et al. 2007, ApJ, 667, L29), the fits to the observations of 1ES0229+200 using our previous infrared spectral energy distributions are consistent with both the infrared and gamma-ray observations. Our analysis presents evidence indicating that the energy spectrum of relativistic particles in 1ES0229+200 is produced by relativistic shock acceleration, producing an intrinsic -ray spectrum with index 1 < gamma < 1.5 and with no evidence of a peak in the spectral energy distribution up to energies approx.15 TeV.
Gamma-ray background induced by atmospheric neutrons

NASA Astrophysics Data System (ADS)

Ma, Y.-Q.

1984-03-01

A small piggyback detector system is used to study the reduction of gamma-ray background induced by atmospheric neutrons in the type of actively shielded gamma-ray spectroscopes. The system consists of two 1.5 x 1.5 arcsec NaI crystal units, one of which is surrounded by some neutron shield material. The results of a balloon flight in 1981 are presented. The data show that a shield of 3 cm-thick pure paraffin cannot reduce the gamma-ray background. On the contrary, it may even cause some enhancement.
The Chandra Deep Field-North Survey and the cosmic X-ray background.

PubMed

Brandt, W Nielsen; Alexander, David M; Bauer, Franz E; Hornschemeier, Ann E

2002-09-15

Chandra has performed a 1.4 Ms survey centred on the Hubble Deep Field-North (HDF-N), probing the X-ray Universe 55-550 times deeper than was possible with pre-Chandra missions. We describe the detected point and extended X-ray sources and discuss their overall multi-wavelength (optical, infrared, submillimetre and radio) properties. Special attention is paid to the HDF-N X-ray sources, luminous infrared starburst galaxies, optically faint X-ray sources and high-to-extreme redshift active galactic nuclei. We also describe how stacking analyses have been used to probe the average X-ray-emission properties of normal and starburst galaxies at cosmologically interesting distances. Finally, we discuss plans to extend the survey and argue that a 5-10 Ms Chandra survey would lay key groundwork for future missions such as XEUS and Generation-X.
A Luminous and Isolated Gamma-Ray Flare from the Blazar B2 1215+30

DOE PAGES

Abeysekara, A. U.; Archambault, S.; Archer, A.; ...

2017-02-21

We report that B2 1215+30 is a BL-Lac-type blazar that was first detected at TeV energies by the MAGIC atmospheric Cherenkov telescopes and subsequently confirmed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory with data collected between 2009 and 2012. In 2014 February 08, VERITAS detected a large-amplitude flare from B2 1215+30 during routine monitoring observations of the blazar 1ES 1218+304, located in the same field of view. The TeV flux reached 2.4 times the Crab Nebula flux with a variability timescale ofmore » $$\\lt 3.6\\,\\mathrm{hr}$$. Multiwavelength observations with Fermi-LAT, Swift, and the Tuorla Observatory revealed a correlated high GeV flux state and no significant optical counterpart to the flare, with a spectral energy distribution where the gamma-ray luminosity exceeds the synchrotron luminosity. Lastly, when interpreted in the framework of a one-zone leptonic model, the observed emission implies a high degree of beaming, with Doppler factor $$\\delta \\gt 10$$, and an electron population with spectral index $$p\\lt 2.3$$.« less
The Diffuse X-ray Background, from Earth's Exosphere to the Edge of the Universe: Or, One Astronomer's Signal is Another Astronomer's Contamination

NASA Technical Reports Server (NTRS)

Snowden, Steve

2007-01-01

The "X-ray background" means various things to various people. It's origin is comprised of emission from objects as close as Earth's exosphere to as far away as the most distant clusters of galaxies. It is comprised of the emission of truly diffusely distributed plasmas and the superposition of the emission from unresolved point-like objects. To add to the confusion, in general there is no redshift information so there is very little information on where an individual X-ray may originate. This talk will address the evolution of our understanding of origin of the X-ray background and the current best-guess about what is really going on.
Cosmic X-ray physics

NASA Technical Reports Server (NTRS)

Mccammon, D.; Cox, D. P.; Kraushaar, W. L.; Sanders, W. T.

1985-01-01

A progress report of research activities carried out in the area of cosmic X-ray physics is presented. The Diffuse X-ray Spectrometer DXS which has been flown twice as a rocket payload is described. The observation times proved to be too small for meaningful X-ray data to be obtained. Data collection and reduction activities from the Ultra-Soft X-ray background (UXT) instrument are described. UXT consists of three mechanically-collimated X-ray gas proportional counters with window/filter combinations which allow measurements in three energy bands, Be (80-110 eV), B (90-187 eV), and O (e84-532 eV). The Be band measurements provide an important constraint on local absorption of X-rays from the hot component of the local interstellar medium. Work has also continued on the development of a calorimetric detector for high-resolution spectroscopy in the 0.1 keV - 8keV energy range.
Intrinsic Correlations for Flaring Blazars Detected by Fermi

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, J. H.; Xiao, H. B.; Lin, C.

2017-02-01

Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the timescale of their radio flares. In this Letter, we use multiwavelength data and Doppler factors reported in the literature for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distributions and investigate the correlations among observed and intrinsic data.more » Quite interestingly, intrinsic data show a positive correlation between luminosity and peak frequency, in contrast with the behavior of observed data, and a tighter correlation between γ -ray luminosity and the lower-energy ones. For flaring blazars detected by Fermi , we conclude that (1) observed emissions are strongly beamed; (2) the anti-correlation between luminosity and peak frequency from the observed data is an apparent result, the correlation between intrinsic data being positive; and (3) intrinsic γ -ray luminosity is strongly correlated with other intrinsic luminosities.« less
Gamma-Ray Light Curves And Variability Of Bright Fermi -Detected Blazars

DOE PAGES

Abdo, A. A.

2010-09-22

This paper presents light curves as well as the first systematic characterization of variability of the 106 objects in the high-confidence Fermi Large Area Telescope Bright AGN Sample (LBAS). Weekly light curves of this sample, obtained during the first 11 months of the Fermi survey (2008 August 4-2009 July 4), are tested for variability and their properties are quantified through autocorrelation function and structure function analysis. For the brightest sources, 3 or 4 day binned light curves are extracted in order to determine power density spectra (PDSs) and to fit the temporal structure of major flares. More than 50% ofmore » the sources are found to be variable with high significance, where high states do not exceed 1/4 of the total observation range. Variation amplitudes are larger for flat spectrum radio quasars and low/intermediate synchrotron frequency peaked BL Lac objects. Autocorrelation timescales derived from weekly light curves vary from four to a dozen of weeks. Variable sources of the sample have weekly and 3-4 day bin light curves that can be described by 1/f α PDS, and show two kinds of gamma-ray variability: (1) rather constant baseline with sporadic flaring activity characterized by flatter PDS slopes resembling flickering and red noise with occasional intermittence and (2)—measured for a few blazars showing strong activity—complex and structured temporal profiles characterized by long-term memory and steeper PDS slopes, reflecting a random walk underlying mechanism. The average slope of the PDS of the brightest 22 FSRQs and of the 6 brightest BL Lacs is 1.5 and 1.7, respectively. The study of temporal profiles of well-resolved flares observed in the 10 brightest LBAS sources shows that they generally have symmetric profiles and that their total duration vary between 10 and 100 days. Results presented here can assist in source class recognition for unidentified sources and can serve as reference for more detailed analysis of the
MULTIWAVELENGTH EVIDENCE FOR QUASI-PERIODIC MODULATION IN THE GAMMA-RAY BLAZAR PG 1553+113

DOE PAGES

Ackerman, M.

2015-11-10

We report for the first time a γ-ray and multiwavelength nearly-periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope (LAT) we have discovered an apparent quasi-periodicity in the γ-ray flux (E > 100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18±0.08 year-period γ-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the OVRO, Tuorla, KAIT, and CSS monitoring programs and Swift UVOT. The optical cycle appearing in ~ 10 years of data has a similar period, while the 15 GHz oscillationmore » is less regular than seen in the other bands. Further long-term multi-wavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity.« less
Very high energy γ-rays from the universe's middle age: detection of the z = 0.940 blazar PKS 1441+25 with magic

DOE PAGES

Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.; ...

2015-12-15

The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is detected between 40 and 250 GeV with a significance of 25.5σ using the MAGIC telescopes. Together with the gravitationally lensed blazar QSO B0218+357 (z = 0.944), PKS 1441+25 is the most distant very high energy (VHE) blazar detected to date. The observations were triggered by an outburst in 2015 April seen at GeV energies with the Large Area Telescope on board Fermi. Multi-wavelength observations suggest a subdivision of the high state into two distinct flux states. In the band covered by MAGIC, the variability timescale ismore » estimated to be 6.4 ± 1.9 days. Modeling the broadband spectral energy distribution with an external Compton model, the location of the emitting region is understood as originating in the jet outside the broad-line region (BLR) during the period of high activity, while being partially within the BLR during the period of low (typical) activity. In conclusion, the observed VHE spectrum during the highest activity is used to probe the extragalactic background light at an unprecedented distance scale for ground-based gamma-ray astronomy.« less
The Cambridge-Cambridge X-ray Serendipity Survey: I X-ray luminous galaxies

NASA Technical Reports Server (NTRS)

Boyle, B. J.; Mcmahon, R. G.; Wilkes, B. J.; Elvis, M.

1994-01-01

We report on the first results obtained from a new optical identification program of 123 faint X-ray sources with S(0.5-2 keV) greater than 2 x 10(exp -14) erg/s/sq cm serendipitously detected in ROSAT PSPC pointed observations. We have spectroscopically identified the optical counterparts to more than 100 sources in this survey. Although the majority of the sample (68 objects) are QSO's, we have also identified 12 narrow emission line galaxies which have extreme X-ray luminosities (10(exp 42) less than L(sub X) less than 10(exp 43.5) erg/s). Subsequent spectroscopy reveals them to be a mixture of star-burst galaxies and Seyfert 2 galaxies in approximately equal numbers. Combined with potentially similar objects identified in the Einstein Extended Medium Sensitivity Survey, these X-ray luminous galaxies exhibit a rate of cosmological evolution, L(sub X) varies as (1 + z)(exp 2.5 +/- 1.0), consistent with that derived for X-ray QSO's. This evolution, coupled with the steep slope determined for the faint end of the X-ray luminosity function (Phi(L(sub X)) varies as L(sub X)(exp -1.9)), implies that such objects could comprise 15-35% of the soft (1-2 keV) X-ray background.
Suzaku observations of γ-ray bright radio galaxies: Origin of the x-ray emission and broadband modeling

DOE PAGES

Fukazawa, Yasushi; Finke, Justin; Stawarz, Łukasz; ...

2014-12-24

Here, we performed a systematic X-ray study of eight nearby γ-ray bright radio galaxies with Suzaku in order to understand the origins of their X-ray emissions. The Suzaku spectra for five of those have been presented previously, while the remaining three (M87, PKS 0625–354, and 3C 78) are presented here for the first time. Based on the Fe-K line strength, X-ray variability, and X-ray power-law photon indices, and using additional information on the [O III] line emission, we argue for a jet origin of the observed X-ray emission in these three sources. We also analyzed five years of Fermi Largemore » Area Telescope (LAT) GeV gamma-ray data on PKS 0625–354 and 3C 78 to understand these sources within the blazar paradigm. We found significant γ-ray variability in the former object. Overall, we note that the Suzaku spectra for both PKS 0625–354 and 3C 78 are rather soft, while the LAT spectra are unusually hard when compared with other γ-ray detected low-power (FR I) radio galaxies. We demonstrate that the constructed broadband spectral energy distributions of PKS 0625–354 and 3C 78 are well described by a one-zone synchrotron/synchrotron self-Compton model. The results of the modeling indicate lower bulk Lorentz factors compared to those typically found in other BL Lacertae (BL Lac) objects, but consistent with the values inferred from modeling other LAT-detected FR I radio galaxies. Interestingly, the modeling also implies very high peak (~10 16 Hz) synchrotron frequencies in the two analyzed sources, contrary to previously suggested scenarios for Fanaroff-Riley (FR) type I/BL Lac unification. Finally, we discuss the implications of our findings in the context of the FR I/BL Lac unification schemes.« less
The ISM From the Soft X-ray Background Perspective

NASA Technical Reports Server (NTRS)

Snowden, S. L.

2003-01-01

In the past few years progress in understanding the local and Galactic ISM in terms of the diffuse X-ray background has been as much about what hasn't been seen as it has been about detections. High resolution spectra of the local SXRB have been observed, but are inconsistent with current thermal emission models. An excess over the extrapolation of the high-energy (most clearly visible at E greater than 1.5 keV) extragalactic power law down to 3/4 keV has been observed but only at the level consistent with cosmological models, implying the absence of at least a bright hot Galactic halo. A very recent FUSE result indicates that O VI emission from the Local Hot Bubble is insignificant, if it exists at all, a result which is also inconsistent with current thermal emission models. A short review of the current status of our (well, at least my) understanding of the Galactic SXRB and ISM is presented here.
Some Aspects of the Radio Emission of EGRET-Detected Blazars

NASA Technical Reports Server (NTRS)

Lin, Y. C.; Bertsch, D. L.; Bloom, S. D.; Esposito, J. A.; Hartman, R. C.; Hunter, S. D.; Kniffen, D. A.; Kanbach, G.; Mayer-Hasselwander, H. A.; Michelson, P. F.

1999-01-01

It has long been recognized that the high-latitude Energetic Gamma Ray Experiment Telescope (EGRET) sources can be identified with blazars of significant radio emission. Many aspects of the relation between high-energy gamma-ray emission and radio emission of EGRET-detected blazars remain uncertain. In this paper, we use the results of the recently published Third EGRET Source Catalog to examine in more detail to what extent the EGRET flux and the radio flux are correlated. In particular we examine the correlation (or the lack of it) in flux level, spectral shape, temporal variation, and detection limit. Many significant previous studies in these areas are also evaluated.
Deep Extragalactic X-Ray Surveys

NASA Astrophysics Data System (ADS)

Brandt, W. N.; Hasinger, G.

2005-09-01

Deep surveys of the cosmic X-ray background are reviewed in the context of observational progress enabled by the Chandra X-Ray Observatory and the X-Ray Multi-Mirror Mission-Newton. The sources found by deep surveys are described along with their redshift and luminosity distributions, and the effectiveness of such surveys at selecting active galactic nuclei (AGN) is assessed. Some key results from deep surveys are highlighted, including (a) measurements of AGN evolution and the growth of supermassive black holes, (b) constraints on the demography and physics of high-redshift AGN, (c) the X-ray AGN content of infrared and submillimeter galaxies, and (d) X-ray emission from distant starburst and normal galaxies. We also describe some outstanding problems and future prospects for deep extragalactic X-ray surveys.

Frontiers of X-Ray Astronomy

NASA Astrophysics Data System (ADS)

Fabian, Andrew C.; Pounds, Kenneth A.; Blandford, Roger D.

2004-07-01

Preface; 1. Forty years on from Aerobee 150: a personal perspective K. Pounds; 2. X-ray spectroscopy of astrophysical plasmas S. M. Kahn, E. Behar, A. Kinkhabwala and D. W. Savin; 3. X-rays from stars M. Gudel; 4. X-ray observations of accreting white-dwarf systems M. Cropper, G. Ramsay, C. Hellier, K. Mukai, C. Mauche and D. Pandel; 5. Accretion flows in X-ray binaries C. Done; 6. Recent X-ray observations of supernova remnants C. R. Canizares; 7. Luminous X-ray sources in spiral and star-forming galaxies M. Ward; 8. Cosmological constraints from Chandra observations of galaxy clusters S. W. Allen; 9. Clusters of galaxies: a cosmological probe R. Mushotzky; 10. Obscured active galactic nuclei: the hidden side of the X-ray Universe G. Matt; 11. The Chandra Deep Field-North Survey and the cosmic X-ray background W. N. Brandt, D. M. Alexander, F. E. Bauer and A. E. Hornschemeier; 12. Hunting the first black holes G. Hasinger; 13. X-ray astronomy in the new millennium: a summary R. D. Blandford.
NuSTAR and multifrequency study of the two high-redshift blazars S5 0836+710 and PKS 2149-303

DOE PAGES

Tagliaferri, Gianpiero; Ghisellini, G.; Perri, M.; ...

2015-07-09

Powerful blazars are flat-spectrum radio quasars whose emission is dominated by a Compton component peaking between a few hundred keV and a few hundred MeV. We observed two bright blazars, PKS 2149–306 at redshift z = 2.345 and S5 0836+710 at z = 2.172, in the hard X-ray band with the Nuclear Spectroscopic Telescope Array satellite. Simultaneous soft-X-rays and UV–optical observations were performed with the Swift satellite, while near-infrared (near-IR) data were obtained with the Rapid Eye Mount telescope. To study their variability, we repeated these observations for both sources on a timescale of a few months. While no fastmore » variability was detected during a single observation, both sources were variable in the X-ray band, up to 50%, between the two observations, with larger variability at higher energies. No variability was detected in the optical/NIR band. These data, together with Fermi-Large Area Telescope, Wide-field Infrared Survey Explorer, and other literature data, are then used to study the overall spectral energy distributions (SEDs) of these blazars. Although the jet nonthermal emission dominates the SED, it leaves the UV band unhidden, allowing us to detect the thermal emission of the disk and to estimate the black hole mass. The nonthermal emission is well reproduced by a one-zone leptonic model by the synchrotron, self-Compton, and external Compton processes. Our data are better reproduced if we assume that the location of the dissipation region of the jet, R diss, is in between the torus and the broad-line region. As a result, the observed variability is explained by changing a minimum number of model parameters by a very small amount.« less
NuSTAR and multifrequency study of the two high-redshift blazars S5 0836+710 and PKS 2149-303

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tagliaferri, Gianpiero; Ghisellini, G.; Perri, M.

Powerful blazars are flat-spectrum radio quasars whose emission is dominated by a Compton component peaking between a few hundred keV and a few hundred MeV. We observed two bright blazars, PKS 2149–306 at redshift z = 2.345 and S5 0836+710 at z = 2.172, in the hard X-ray band with the Nuclear Spectroscopic Telescope Array satellite. Simultaneous soft-X-rays and UV–optical observations were performed with the Swift satellite, while near-infrared (near-IR) data were obtained with the Rapid Eye Mount telescope. To study their variability, we repeated these observations for both sources on a timescale of a few months. While no fastmore » variability was detected during a single observation, both sources were variable in the X-ray band, up to 50%, between the two observations, with larger variability at higher energies. No variability was detected in the optical/NIR band. These data, together with Fermi-Large Area Telescope, Wide-field Infrared Survey Explorer, and other literature data, are then used to study the overall spectral energy distributions (SEDs) of these blazars. Although the jet nonthermal emission dominates the SED, it leaves the UV band unhidden, allowing us to detect the thermal emission of the disk and to estimate the black hole mass. The nonthermal emission is well reproduced by a one-zone leptonic model by the synchrotron, self-Compton, and external Compton processes. Our data are better reproduced if we assume that the location of the dissipation region of the jet, R diss, is in between the torus and the broad-line region. As a result, the observed variability is explained by changing a minimum number of model parameters by a very small amount.« less
Broadband radio jet emission and variability of γ-ray blazars

NASA Astrophysics Data System (ADS)

Nestoras, Ioannis

2015-07-01

AGN (Active Galactic Nuclei) and in particular their subclass blazars, are among the most energetic objects observed in the universe, featuring extreme phenomenological characteristics such as rapid broadband flux density and polarization variability, fast super--luminal motion, high degree of polarization and a broadband, double-humped spectral energy distribution (SED). The details of the emission processes and violent variability of blazars are still poorly understood. Variability studies give important clues about the size, structure, physics and dynamics of the emitting region making AGN/blazar monitoring programs of uttermost importance in providing the necessary constraints for understanding the origin of energy production. In this framework the F-gamma program was initiated, monitoring monthly 60 fermi detected AGN/blazars at 12 frequencies between 2.6 and 345GHz since 2007. For the thesis in hand observations and data analysis were performed within the realms of the F-gamma program, using the Effelsberg (EB) 100m and Pico Veleta (PV) 30m telescopes at 10 frequency bands ranging from 2.64 to 142GHz. The cm to short-mm variability/spectral characteristics are monitored for a sample of 59 sources for a period of five years enabling for the first time a detailed study of the observed flaring activity in both the light curve and spectral domains for such a large number of sources and such high cadence. Also the observing systems and methods are introduced as well as the data reduction techniques. The thesis at hand is structured as follows: Chapter 3 presents the reduction methods and post measurement corrections applied to the data such as pointing offsets, gain--elevation and sensitivity corrections as well as specific corrections applied for each of the Effelsberg and Pico Veleta observing systems respectively. Chapter 4 presents the analysis tools and methods that were used such as: variability characteristics, flare amplitudes with a new method for
Description of small-scale fluctuations in the diffuse X-ray background.

NASA Technical Reports Server (NTRS)

Cavaliere, A.; Friedland, A.; Gursky, H.; Spada, G.

1973-01-01

An analytical study of the fluctuations on a small angular scale expected in the diffuse X-ray background in the presence of unresolved sources is presented. The source population is described by a function N(S), giving the number of sources per unit solid angle and unit apparent flux S. The distribution of observed flux, s, in each angular resolution element of a complete sky survey is represented by a function Q(s). The analytical relation between the successive, higher-order moments of N(S) and Q(s) is described. The goal of reconstructing the source population from the study of the moments of Q(s) of order higher than the second (i.e., the rms fluctuations) is discussed.
Cosmic x ray physics

NASA Technical Reports Server (NTRS)

Mccammon, Dan; Cox, D. P.; Kraushaar, W. L.; Sanders, W. T.

1992-01-01

This final report covers the period 1 January 1985 - 31 March 1992. It is divided into the following sections: the soft x-ray background; proportional counter and filter calibrations; sounding rocket flight preparations; new sounding rocket payload: x-ray calorimeter; and theoretical studies. Staff, publications, conference proceedings, invited talks, contributed talks, colloquia and seminars, public service lectures, and Ph. D. theses are listed.
Mildly obscured active galaxies and the cosmic X-ray background

NASA Astrophysics Data System (ADS)

Esposito, V.; Walter, R.

2016-05-01

Context. The diffuse cosmic X-ray background (CXB) is the sum of the emission of discrete sources, mostly massive black-holes accreting matter in active galactic nuclei (AGN). The CXB spectrum differs from the integration of the spectra of individual sources, calling for a large population, undetected so far, of strongly obscured Compton-thick AGN. Such objects are predicted by unified models, which attribute most of the AGN diversity to their inclination on the line of sight, and play an important role for the understanding of the growth of black holes in the early Universe. Aims: The percentage of strongly obscured Compton-thick AGN at low redshift can be derived from the observed CXB spectrum, if we assume AGN spectral templates and luminosity functions. Methods: We show that high signal-to-noise stacked hard X-ray spectra, derived from more than a billion seconds of effective exposure time with the Swift/BAT instrument, imply that mildly obscured Compton-thin AGN feature a strong reflection and contribute massively to the CXB. Results: A population of Compton-thick AGN larger than that which is effectively detected is not required to reproduce the CXB spectrum, since no more than 6% of the CXB flux can be attributed to them. The stronger reflection observed in mildly obscured AGN suggests that the covering factor of the gas and dust surrounding their central engines is a key factor in shaping their appearance. These mildly obscured AGN are easier to study at high redshift than Compton-thick sources are.
Handbook of X-Ray Astronomy

NASA Technical Reports Server (NTRS)

Arnaud, Keith A. (Editor); Smith, Randall K.; Siemiginowska, Aneta

2011-01-01

X-ray astronomy was born in the aftermath of World War II as military rockets were repurposed to lift radiation detectors above the atmosphere for a few minutes at a time. These early flights detected and studied X-ray emission from the Solar corona. The first sources beyond the Solar System were detected during a rocket flight in 1962 by a team headed by Riccardo Giaccom at American Science and Engineering, a company founded by physicists from MIT. The rocket used Geiger counters with a system designed to reduce non-X-ray backgrounds and collimators limiting the region of sky seen by the counters. As the rocket spun, the field of view (FOV) happened to pass over what was later found to be the brightest non-Solar X-ray source; later designated See X-1. It also detected a uniform background glow which could not be resolved into individual sources. A follow-up campaign using X-ray detectors with better spatial resolution and optical telescopes identified See X-1 as an interacting binary with a compact (neutron star) primary. This success led to further suborbital rocket flights by a number of groups. More X-ray binaries were discovered, as well as X-ray emission from supernova remnants, the radio galaxies M87 and Cygnus-A, and the Coma cluster. Detectors were improved and Geiger counters were replaced by proportional counters, which provided information about energy spectra of the sources. A constant challenge was determining precise positions of sources as only collimators were available.
The Nature of the Unresolved Extragalactic Cosmic Soft X-Ray Background

NASA Technical Reports Server (NTRS)

Cappelluti, N.; Ranalli, P.; Roncarelli, M.; Arevalo, P.; Zamorani, G.; Comastri, A.; Gilli, R.; Rovilos, E.; Vignali, C.; Allevato, V.;

2013-01-01

In this paper we investigate the power spectrum of the unresolved 0.5-2 keV cosmic X-ray background (CXB) with deep Chandra 4-Msec (Ms) observations in the Chandra Deep Field South (CDFS). We measured a signal that, on scales >30 arcsec, is significantly higher than the shot noise and is increasing with angular scale. We interpreted this signal as the joint contribution of clustered undetected sources like active galactic nuclei (AGN), galaxies and the intergalactic medium (IGM). The power of unresolved cosmic source fluctuations accounts for approximately 12 per cent of the 0.5-2 keV extragalactic CXB. Overall, our modelling predicts that approximately 20 per cent of the unresolved CXB flux is produced by low-luminosity AGN, approximately 25 per cent by galaxies and approximately 55 per cent by the IGM. We do not find any direct evidence of the so-called 'warm hot intergalactic medium' (i.e. matter with 10(exp 5) less than T less than 10(exp 7) K and density contrast delta less than 1000), but we estimated that it could produce about 1/7 of the unresolved CXB. We placed an upper limit on the space density of postulated X-ray-emitting early black holes at z greater than 7.5 and compared it with supermassive black hole evolution models.

Second-Order Fermi Acceleration and Emission in Blazar Jets

NASA Astrophysics Data System (ADS)

Asano, Katsuaki; Takahara, Fumio; Toma, Kenji; Kusunose, Masaaki; Kakuwa, Jun

The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations, adopt it for 1ES 1101-232, and Mrk 421. The Fermi-II model with radial evolution of the electron injection rate and/or diffusion coefficient can reproduce the spectra from the radio to the gamma-ray regime. For Mrk 421, an external radio photon field with a luminosity of 4.9 begin{math} {times} 10 (38) erg s (-1) is required to agree with the observed GeV flux. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.
A time dependent approach to model X-ray and γ-ray light curves of Mrk 421 observed during the flare in February 2010

NASA Astrophysics Data System (ADS)

Singh, K. K.; Sahayanathan, S.; Sinha, A.; Bhatt, N.; Tickoo, A. K.; Yadav, K. K.; Rannot, R. C.; Chandra, P.; Venugopal, K.; Marandi, P.; Kumar, N.; Goyal, H. C.; Goyal, A.; Agarwal, N. K.; Kothari, M.; Chanchalani, K.; Dhar, V. K.; Chouhan, N.; Bhat, C. K.; Koul, M. K.; Koul, R.

2017-07-01

Strong X-ray and γ-ray flares have been detected in February 2010 from the high synchrotron peaked blazar Mrk 421 (z = 0.031). With the motivation of understanding the physics involved in this flaring activity, we study the variability of the source in X-ray and γ-ray energy bands during the period February 10-23, 2010 (MJD 55237-55250). We use near simultaneous X-ray data collected by MAXI, Swift-XRT and γ-ray data collected by Fermi-LAT and TACTIC along with the optical V-band observations by SPOLat Steward Observatory. We observe that the variation in the one day averaged flux from the source during the flare is characterized by fast rise and slow decay. Besides, the TeV γ-ray flux shows a strong correlation with the X-ray flux, suggesting the former to be an outcome of synchrotron self Compton emission process. To model the observed X-ray and γ-ray light curves, we numerically solve the kinetic equation describing the evolution of particle distribution in the emission region. The injection of particle distribution into the emission region, from the putative acceleration region, is assumed to be a time dependent power law. The synchrotron and synchrotron self Compton emission from the evolving particle distribution in the emission region are used to reproduce the X-ray and γ-ray flares successfully. Our study suggests that the flaring activity of Mrk 421 can be an outcome of an efficient acceleration process associated with the increase in underlying non-thermal particle distribution.
A Multiwavelength View of the TeV Blazar Markarian 421: Correlated Variability, Flaring, and Spectral Evolution

NASA Astrophysics Data System (ADS)

Błażejowski, M.; Blaylock, G.; Bond, I. H.; Bradbury, S. M.; Buckley, J. H.; Carter-Lewis, D. A.; Celik, O.; Cogan, P.; Cui, W.; Daniel, M.; Duke, C.; Falcone, A.; Fegan, D. J.; Fegan, S. J.; Finley, J. P.; Fortson, L.; Gammell, S.; Gibbs, K.; Gillanders, G. G.; Grube, J.; Gutierrez, K.; Hall, J.; Hanna, D.; Holder, J.; Horan, D.; Humensky, B.; Kenny, G.; Kertzman, M.; Kieda, D.; Kildea, J.; Knapp, J.; Kosack, K.; Krawczynski, H.; Krennrich, F.; Lang, M.; LeBohec, S.; Linton, E.; Lloyd-Evans, J.; Maier, G.; Mendoza, D.; Milovanovic, A.; Moriarty, P.; Nagai, T. N.; Ong, R. A.; Power-Mooney, B.; Quinn, J.; Quinn, M.; Ragan, K.; Reynolds, P. T.; Rebillot, P.; Rose, H. J.; Schroedter, M.; Sembroski, G. H.; Swordy, S. P.; Syson, A.; Valcarel, L.; Vassiliev, V. V.; Wakely, S. P.; Walker, G.; Weekes, T. C.; White, R.; Zweerink, J.; VERITAS Collaboration; Mochejska, B.; Smith, B.; Aller, M.; Aller, H.; Teräsranta, H.; Boltwood, P.; Sadun, A.; Stanek, K.; Adams, E.; Foster, J.; Hartman, J.; Lai, K.; Böttcher, M.; Reimer, A.; Jung, I.

2005-09-01

We report results from an intensive multiwavelength monitoring campaign on the TeV blazar Mrk 421 over the period of 2003-2004. The source was observed simultaneously at TeV energies with the Whipple 10 m telescope and at X-ray energies with the Rossi X-Ray Timing Explorer (RXTE) during each clear night within the Whipple observing windows. Supporting observations were also frequently carried out at optical and radio wavelengths to provide simultaneous or contemporaneous coverages. The large amount of simultaneous data has allowed us to examine the variability of Mrk 421 in detail, including cross-band correlation and broadband spectral variability, over a wide range of flux. The variabilities are generally correlated between the X-ray and gamma-ray bands, although the correlation appears to be fairly loose. The light curves show the presence of flares with varying amplitudes on a wide range of timescales at both X-ray and TeV energies. Of particular interest is the presence of TeV flares that have no coincident counterparts at longer wavelengths, because the phenomenon seems difficult to understand in the context of the proposed emission models for TeV blazars. We have also found that the TeV flux reached its peak days before the X-ray flux did during a giant flare (or outburst) in 2004 (with the peak flux reaching ~135 mcrab in X-rays, as seen by the RXTE ASM, and ~3 crab in gamma rays). Such a difference in the development of the flare presents a further challenge to both the leptonic and hadronic emission models. Mrk 421 varied much less at optical and radio wavelengths. Surprisingly, the normalized variability amplitude in the optical seems to be comparable to that in the radio, perhaps suggesting the presence of different populations of emitting electrons in the jet. The spectral energy distribution of Mrk 421 is seen to vary with flux, with the two characteristic peaks moving toward higher energies at higher fluxes. We have failed to fit the measured
COLLISION-INDUCED MAGNETIC RECONNECTION AND A UNIFIED INTERPRETATION OF POLARIZATION PROPERTIES OF GRBs AND BLAZARS

DOE PAGES

Deng; Zhang; Zhang; ...

2016-04-11

The jet composition and energy dissipation mechanism of gamma-ray bursts (GRBs) and blazars are fundamental questions that remain not fully understood. One plausible model is to interpret the γ-ray emission of GRBs and optical emission of blazars as synchrotron radiation of electrons accelerated from the collision-induced magnetic dissipation regions in Poynting-flux-dominated jets. The polarization observation is an important and independent information to test this model. Based on our recent 3D relativistic MHD simulations of collision-induced magnetic dissipation of magnetically dominated blobs, here we perform calculations of the polarization properties of the emission in the dissipation region and apply the resultsmore » to model the polarization observational data of GRB prompt emission and blazar optical emission. In this article, we show that the same numerical model with different input parameters can reproduce well the observational data of both GRBs and blazars, especially the 90° polarization angle (PA) change in GRB 100826A and the 180° PA swing in blazar 3C279. This supports a unified model for GRB and blazar jets, suggesting that collision-induced magnetic reconnection is a common physical mechanism to power the relativistic jet emission from events with very different black hole masses.« less
Gamma-Ray Flaring Activity from the Gravitationally Lensed Blazar PKS 1830-211 Observed by Fermi LAT

NASA Astrophysics Data System (ADS)

Abdo, A. A.; Ackermann, M.; Ajello, M.; Allafort, A.; Amin, M. A.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Blandford, R. D.; Bonamente, E.; Borgland, A. W.; Bregeon, J.; Brigida, M.; Buehler, R.; Bulmash, D.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Cheung, C. C.; Chiang, J.; Chiaro, G.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Corbet, R. H. D.; Cutini, S.; D'Ammando, F.; de Angelis, A.; de Palma, F.; Dermer, C. D.; Drell, P. S.; Drlica-Wagner, A.; Favuzzi, C.; Finke, J.; Focke, W. B.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Grenier, I. A.; Grove, J. E.; Guiriec, S.; Hadasch, D.; Hayashida, M.; Hays, E.; Hughes, R. E.; Inoue, Y.; Jackson, M. S.; Jogler, T.; Jóhannesson, G.; Johnson, A. S.; Kamae, T.; Knödlseder, J.; Kuss, M.; Lande, J.; Larsson, S.; Latronico, L.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Mazziotta, M. N.; Mehault, J.; Michelson, P. F.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nemmen, R.; Nuss, E.; Ohno, M.; Ohsugi, T.; Paneque, D.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Reyes, L. C.; Ritz, S.; Romoli, C.; Roth, M.; Saz Parkinson, P. M.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Takahashi, H.; Takeuchi, Y.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Tronconi, V.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Werner, M.; Winer, B. L.; Wood, K. S.

2015-02-01

The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope routinely detects the MeV-peaked flat-spectrum radio quasar PKS 1830-211 (z = 2.507). Its apparent isotropic γ-ray luminosity (E > 100 MeV), averaged over ~3 years of observations and peaking on 2010 October 14/15 at 2.9 × 1050 erg s-1, makes it among the brightest high-redshift Fermi blazars. No published model with a single lens can account for all of the observed characteristics of this complex system. Based on radio observations, one expects time-delayed variability to follow about 25 days after a primary flare, with flux about a factor of 1.5 less. Two large γ-ray flares of PKS 1830-211 have been detected by the LAT in the considered period, and no substantial evidence for such a delayed activity was found. This allows us to place a lower limit of about 6 on the γ-ray flux ratio between the two lensed images. Swift XRT observations from a dedicated Target of Opportunity program indicate a hard spectrum with no significant correlation of X-ray flux with the γ-ray variability. The spectral energy distribution can be modeled with inverse Compton scattering of thermal photons from the dusty torus. The implications of the LAT data in terms of variability, the lack of evident delayed flare events, and different radio and γ-ray flux ratios are discussed. Microlensing effects, absorption, size and location of the emitting regions, the complex mass distribution of the system, an energy-dependent inner structure of the source, and flux suppression by the lens galaxy for one image path may be considered as hypotheses for understanding our results.
Gamma-ray flaring activity from the gravitationally lensed blazar PKS 1830-211 observed by Fermi LAT

DOE PAGES

Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

2015-01-23

We present that the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope routinely detects the MeV-peaked flat-spectrum radio quasar PKS 1830–211 (z = 2.507). Its apparent isotropic γ-ray luminosity (E > 100 MeV), averaged over ~3 years of observations and peaking on 2010 October 14/15 at 2.9 × 10 50 erg s –1, makes it among the brightest high-redshift Fermi blazars. No published model with a single lens can account for all of the observed characteristics of this complex system. Based on radio observations, one expects time-delayed variability to follow about 25 days after a primary flare,more » with flux about a factor of 1.5 less. Two large γ-ray flares of PKS 1830–211 have been detected by the LAT in the considered period, and no substantial evidence for such a delayed activity was found. This allows us to place a lower limit of about 6 on the γ-ray flux ratio between the two lensed images. Swift XRT observations from a dedicated Target of Opportunity program indicate a hard spectrum with no significant correlation of X-ray flux with the γ-ray variability. The spectral energy distribution can be modeled with inverse Compton scattering of thermal photons from the dusty torus. The implications of the LAT data in terms of variability, the lack of evident delayed flare events, and different radio and γ-ray flux ratios are discussed. Lastly, microlensing effects, absorption, size and location of the emitting regions, the complex mass distribution of the system, an energy-dependent inner structure of the source, and flux suppression by the lens galaxy for one image path may be considered as hypotheses for understanding our results.« less
MULTIWAVELENGTH EVIDENCE FOR QUASI-PERIODIC MODULATION IN THE GAMMA-RAY BLAZAR PG 1553+113

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackermann, M.; Buehler, R.; Ajello, M.

2015-11-10

We report for the first time a γ-ray and multiwavelength nearly periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope we have discovered an apparent quasi-periodicity in the γ-ray flux (E > 100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 ± 0.08 year period γ-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the Owens Valley Radio Observatory, Tuorla, Katzman Automatic Imaging Telescope, and Catalina Sky Survey monitoring programs and Swift-UVOT. The optical cycle appearing in ∼10 years of datamore » has a similar period, while the 15 GHz oscillation is less regular than seen in the other bands. Further long-term multiwavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity.« less
VERY HIGH ENERGY γ-RAYS FROM THE UNIVERSE’S MIDDLE AGE: DETECTION OF THE z = 0.940 BLAZAR PKS 1441+25 WITH MAGIC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahnen, M. L.; Biland, A.; Ansoldi, S.

2015-12-20

The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is detected between 40 and 250 GeV with a significance of 25.5σ using the MAGIC telescopes. Together with the gravitationally lensed blazar QSO B0218+357 (z = 0.944), PKS 1441+25 is the most distant very high energy (VHE) blazar detected to date. The observations were triggered by an outburst in 2015 April seen at GeV energies with the Large Area Telescope on board Fermi. Multi-wavelength observations suggest a subdivision of the high state into two distinct flux states. In the band covered by MAGIC, the variability timescale is estimated to bemore » 6.4 ± 1.9 days. Modeling the broadband spectral energy distribution with an external Compton model, the location of the emitting region is understood as originating in the jet outside the broad-line region (BLR) during the period of high activity, while being partially within the BLR during the period of low (typical) activity. The observed VHE spectrum during the highest activity is used to probe the extragalactic background light at an unprecedented distance scale for ground-based gamma-ray astronomy.« less
The soft X-ray background as a supernova blast wave viewed from inside - Solar abundance models

NASA Technical Reports Server (NTRS)

Edgar, R. J.

1986-01-01

A model of the soft X-ray background is presented in which the sun is assumed to be inside an active supernova blast wave. The blast wave evolves in a preexisting cavity. The broad band surface brightnesses is explained by such a blast wave with an explosion energy of E sub approximately 5 x 10 to the 50th power ergs and radius 80 to 100 pc, using solar abundances. An approach to treating the problem of large anisotropies in the ambient medium is also explored, accommodating the observed anticorrelation between the soft X-ray surface brightness and the 21 cm column density. It is found that only for post shock temperatures below 10 to the 6 power K a shock propagating into a density enhancement will be dimmer than a similar shock in a lower density region.
VLT/X-Shooter spectrum of the blazar TXS 0506+056 (located inside the IceCube-170922A error box)

NASA Astrophysics Data System (ADS)

Coleiro, Alexis; Chaty, Sylvain

2017-10-01

The blazar TXS 0506+056 (PMN J0509+0541) is currently reported to show increased gamma-ray and optical activity (ATel #10791, #10792, #10794, #10799, #10801, #10817, #10830, #10831, #10838) and has been proposed as the counterpart to the high-energy neutrino event IceCube-170922A (https://gcn.gsfc.nasa.gov/notices_amon/50579430_130033.amon).
NuSTAR AND MULTIFREQUENCY STUDY OF THE TWO HIGH-REDSHIFT BLAZARS S5 0836+710 AND PKS 2149–306

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tagliaferri, G.; Ghisellini, G.; Covino, S.

Powerful blazars are flat-spectrum radio quasars whose emission is dominated by a Compton component peaking between a few hundred keV and a few hundred MeV. We observed two bright blazars, PKS 2149–306 at redshift z = 2.345 and S5 0836+710 at z = 2.172, in the hard X-ray band with the Nuclear Spectroscopic Telescope Array satellite. Simultaneous soft-X-rays and UV–optical observations were performed with the Swift satellite, while near-infrared (near-IR) data were obtained with the Rapid Eye Mount telescope. To study their variability, we repeated these observations for both sources on a timescale of a few months. While no fastmore » variability was detected during a single observation, both sources were variable in the X-ray band, up to 50%, between the two observations, with larger variability at higher energies. No variability was detected in the optical/NIR band. These data, together with Fermi-Large Area Telescope, Wide-field Infrared Survey Explorer, and other literature data, are then used to study the overall spectral energy distributions (SEDs) of these blazars. Although the jet nonthermal emission dominates the SED, it leaves the UV band unhidden, allowing us to detect the thermal emission of the disk and to estimate the black hole mass. The nonthermal emission is well reproduced by a one-zone leptonic model by the synchrotron, self-Compton, and external Compton processes. Our data are better reproduced if we assume that the location of the dissipation region of the jet, R{sub diss}, is in between the torus and the broad-line region. The observed variability is explained by changing a minimum number of model parameters by a very small amount.« less

Kiloparsec Jet Properties of Hybrid, Low-, and High-Synchrotron-Peaked Blazars

NASA Astrophysics Data System (ADS)

Stanley, Ethan C.

Blazars are a rare class of active galactic nucleus (AGN) with relativistic jets closely aligned with the line of sight. Many aspects of the environments and kiloparsec-scale jet structure are not fully understood. Hybrid and high synchrotron peaked (HSP) blazars are two types of blazar that provide unique opportunities to study these jets. Hybrid blazars appear to have jets of differing morphology on each side of their core, suggesting that external factors shape their jet morphology. Three hybrid sources were investigated in radio, optical, and X-ray wavelengths: 8C 1849+670, PKS 2216-038, and PKS 1045-188. For all three, X-ray emission was detected only from the approaching jet. All three had jet radio flux densities and emission mechanisms similar to higher-power FR II sources, but two had approaching jets similar to lower-power FR I sources. None of the three showed definitive signs of asymmetry in their external environments. These results agree with previous multiwavelength studies of hybrid sources that show a dominance of FR I approaching jets and FR II emission mechanisms. With the addition of these three hybrid sources, 13 have been studied in total. Eleven have FR I approaching jets, and eight of those have FR II emission mechanisms. These trends may be due to small number statistics, or they may indicate other factors are creating hybrid-like appearances. High synchrotron peaked blazars are defined by the frequency of the peak of their jet synchrotron emission. Some have shown extreme variability which would imply incredibly-powerful and well-aligned jets, but VLBA observations have measured only modest jet speeds. A radio survey was performed to measure the extended radio luminosity of a large sample of HSP sources. These sources were compared to the complete radio flux density limited MOJAVE 1.5 Jy sample. Flat spectrum radio quasars (FSRQs) showed significant overlap with low synchrotron peaked (LSP) BL Lacs in multiple parameters, which may suggest
X-ray astronomy from Uhuru to HEAO-1

NASA Technical Reports Server (NTRS)

Clark, G. W.

1981-01-01

The nature of galactic and extragalactic X-ray sources is investigated using observations made with nine satellites and several rockets. The question of X-ray pulsars being neutron stars or white dwarfs is considered, as is the nature of Population II and low-luminosity X-ray stars, the diffuse X-ray emission from clusters of galaxies, the unidentified high-galactic-latitude (UHGL) sources, and the unresolved soft X-ray background. The types of sources examined include binary pulsars, Population II X-ray stars (both nonbursters and bursters) inside and outside globular clusters, coronal X-ray emitters, and active galactic nuclei. It is concluded that: (1) X-ray pulsars are strongly magnetized neutron stars formed in the evolution of massive close binaries; (2) all Population II X-ray stars are weakly magnetized or nonmagnetic neutron stars accreting from low-mass companions in close binary systems; (3) the diffuse emission from clusters is thermal bremsstrahlung of hot matter processed in stars and swept out by ram pressure exerted by the intergalactic gas; (4) most or all of the UHGL sources are active galactic nuclei; and (5) the soft X-ray background is emission from a hot component of the interstellar medium.
Fermi LAT detection of a GeV gamma-ray flare from blazar CGRaBS J0809+5341 (87GB 080551.6+535010)

NASA Astrophysics Data System (ADS)

Gasparrini, Dario

2017-10-01

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray emission from a source positionally consistent with the flat spectrum radio quasar CGRaBS J0809+5341 (also known as 87GB 080551.6+535010, BZQ J0809+5341 and 3FGL J0809.5+5342) with radio coordinates (J2000) R.A.: 122.4238862 deg, Dec.: 53.6903033 deg (Petrov et al. 2011, AJ, 142, 89). This blazar has a redshift z = 2.133 (Healey et al. 2008, ApJS, 175, 97). Preliminary analysis indicates that on 2017 October 26, CGRaBS J0809+5341 was in a high state with a daily averaged gamma-ray flux (E > 100 MeV) of (0.23+/-0.15) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 20 times greater than its four-year average flux reported in the third Fermi-LAT source catalog (3FGL, Acero et al. 2015, ApJS, 218, 23). Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue.
Probing stochastic inter-galactic magnetic fields using blazar-induced gamma ray halo morphology

NASA Astrophysics Data System (ADS)

Duplessis, Francis; Vachaspati, Tanmay

2017-05-01

Inter-galactic magnetic fields can imprint their structure on the morphology of blazar-induced gamma ray halos. We show that the halo morphology arises through the interplay of the source's jet and a two-dimensional surface dictated by the magnetic field. Through extensive numerical simulations, we generate mock halos created by stochastic magnetic fields with and without helicity, and study the dependence of the halo features on the properties of the magnetic field. We propose a sharper version of the Q-statistics and demonstrate its sensitivity to the magnetic field strength, the coherence scale, and the handedness of the helicity. We also identify and explain a new feature of the Q-statistics that can further enhance its power.
The ever-surprising blazar OJ 287: multi-wavelength study and appearance of a new component in X-rays

NASA Astrophysics Data System (ADS)

Kushwaha, Pankaj; Gupta, Alok C.; Wiita, Paul J.; Pal, Main; Gaur, Haritma; de Gouveia Dal Pino, E. M.; Kurtanidze, O. M.; Semkov, E.; Damljanovic, G.; Hu, S. M.; Uemura, M.; Vince, O.; Darriba, A.; Gu, M. F.; Bachev, R.; Chen, Xu; Itoh, R.; Kawabata, M.; Kurtanidze, S. O.; Nakaoka, T.; Nikolashvili, M. G.; Sigua, L. A.; Strigachev, A.; Zhang, Z.

2018-06-01

We present a multi-wavelength spectral and temporal investigation of OJ 287 emission during its strong optical-to-X-ray activity between July 2016 - July 2017. The daily γ-ray fluxes from Fermi-LAT are consistent with no variability. The strong optical-to-X-ray variability is accompanied by a change in power-law spectral index of the X-ray spectrum from <2 to >2, with variations often associated with changes in optical polarization properties. Cross-correlations between optical-to-X-ray emission during four continuous segments show simultaneous optical-ultraviolet (UV) variations while the X-ray and UV/optical are simultaneous only during the middle two segments. In the first segment, the results suggest X-rays lag the optical/UV, while in the last segment X-rays lead by ˜ 5-6 days. The last segment also shows a systematic trend with variations appearing first at higher energies followed by lower energy ones. The LAT spectrum before the VHE activity is similar to preceding quiescent state spectrum while it hardens during VHE activity period and is consistent with the extrapolated VHE spectrum during the latter. Overall, the broadband spectral energy distributions (SEDs) during high activity periods are a combination of a typical OJ 287 SED and an HBL SED, and can be explained in a two-zone leptonic model, with the second zone located at parsec scales, beyond the broad line region, being responsible for the HBL-like spectrum. The change of polarization properties from systematic to chaotic and back to systematic, before, during and after the VHE activity, suggest dynamic roles for magnetic fields and turbulence.
Soft X-ray excess in the Coma cluster from a Cosmic Axion Background

DOE Office of Scientific and Technical Information (OSTI.GOV)

Angus, Stephen; Conlon, Joseph P.; Marsh, M.C. David

2014-09-01

We show that the soft X-ray excess in the Coma cluster can be explained by a cosmic background of relativistic axion-like particles (ALPs) converting into photons in the cluster magnetic field. We provide a detailed self-contained review of the cluster soft X-ray excess, the proposed astrophysical explanations and the problems they face, and explain how a 0.1- 1 keV axion background naturally arises at reheating in many string theory models of the early universe. We study the morphology of the soft excess by numerically propagating axions through stochastic, multi-scale magnetic field models that are consistent with observations of Faraday rotation measuresmore » from Coma. By comparing to ROSAT observations of the 0.2- 0.4 keV soft excess, we find that the overall excess luminosity is easily reproduced for g{sub aγγ} ∼ 2 × 10{sup -13} Ge {sup -1}. The resulting morphology is highly sensitive to the magnetic field power spectrum. For Gaussian magnetic field models, the observed soft excess morphology prefers magnetic field spectra with most power in coherence lengths on O(3 kpc) scales over those with most power on O(12 kpc) scales. Within this scenario, we bound the mean energy of the axion background to 50 eV∼< ( E{sub a} ) ∼< 250 eV, the axion mass to m{sub a} ∼< 10{sup -12} eV, and derive a lower bound on the axion-photon coupling g{sub aγγ} ∼> √(0.5/Δ N{sub eff}) 1.4 × 10{sup -13} Ge {sup -1}.« less
DETECTION OF VERY HARD γ -RAY SPECTRUM FROM THE TEV BLAZAR MRK 501

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shukla, A.; Chitnis, V. R.; Acharya, B. S.

2016-12-01

The occasional hardening of the GeV-to-TeV spectrum observed from the blazar Mrk 501 has reopened the debate on the physical origin of radiation and particle acceleration processes in TeV blazars. We have used the ∼7 years of Fermi -LAT data to search for the time intervals with unusually hard spectra from the nearby TeV blazar Mrk 501. We detected hard spectral components above 10 GeV with photon index <1.5 at a significance level of more than 5 sigma on 17 occasions, each with 30 day integration time. The photon index of the hardest component reached a value of 0.89 ± 0.29. We interpretmore » these hard spectra as signatures of intermittent injection of sharply peaked and localized particle distributions from the base of the jet.« less
Observational Aspects of Hard X-ray Polarimetry

NASA Astrophysics Data System (ADS)

Chattopadhyay, Tanmoy

2016-04-01

Sensitive polarization measurements in X-ray may address a wealth of astrophysical phenomena, which so far remain beyond our understanding through available X-ray spectroscopic, imaging, and timing studies. Though scientific potential of X-ray polarimetry was realized long ago, there has not been any significant advancement in this field for the last four decades since the birth of X-ray astronomy. The only successful polarization measurement in X-rays dates back to 1976, when a Bragg polarimeter onboard OSO-8 measured polarization of Crab nebula. Primary reason behind the lack in progress is its extreme photon hungry nature, which results in poor sensitivity of the polarimeters. Recently, in the last decade or so, with the advancement in detection technology, X-ray polarimetry may see a significant progress in near future, especially in soft X-rays with the invention of photoelectron tracking polarimeters. Though photoelectric polarimeters are expected to provide sensitive polarization measurements of celestial X-ray sources, they are sensitive only in soft X-rays, where the radiation from the sources is dominated by thermal radiation and therefore expected to be less polarized. On the other hand, in hard X-rays, sources are ex-pected to be highly polarized due to the dominance of nonthermal emission over its thermal counterpart. Moreover, polarization measurements in hard X-rays promises to address few interesting scientific issues regarding geometry of corona for black hole sources, emission mechanism responsible for the higher energy peak in the blazars, accretion geometry close to the magnetic poles in accreting neutron star systems and acceleration mechanism in solar flares. Compton polarimeters provide better sensitivity than photoelectric polarimeters in hard X-rays with a broad energy band of operation. Recently, with the development of hard X-ray focusing optics e.g. NuSTAR, Astro-H, it is now possible to conceive Compton polarimeters at the focal plane
Simultaneous Constraints on the Spectrum of the Extragalactic Background Light and the Intrinsic TeV Spectra of Markarian 421, Markarian 501, and H1426+428

NASA Astrophysics Data System (ADS)

Dwek, Eli; Krennrich, Frank

2005-01-01

Very high energy (~TeV) γ-rays from blazars are attenuated by photons from the extragalactic background light (EBL). Observations of blazars can therefore provide an ideal opportunity for determining the EBL intensity if their intrinsic spectrum is known. Conversely, knowledge of the EBL intensity can be used to determine the intrinsic blazar spectrum. Unfortunately, neither the EBL intensity nor the intrinsic blazar spectrum is known with high enough precision to accurately derive one quantity from the other. In this paper we use the most recent data on the EBL to construct 12 different realizations representing all possible permutations between EBL limits and the detections in the different wavelength regions. These realizations explore a significantly larger range of allowable EBL spectra than any previous studies. We show that these realizations can be used to explore the effects of the EBL on the inferred spectra of blazars. Concentrating on the two relatively nearby (z~0.03) blazars Mrk 421 and 501, we derive their intrinsic spectra and peak γ-ray energies for the different EBL realizations. Some EBL spectra give rise to ``unphysical'' intrinsic blazar spectra, characterized by an exponential rise at high TeV energies. We use the F-test to show that some of these exponential rises are statistically insignificant. Consequently, statements regarding the existence of an ``IR background-TeV γ-ray crisis'' are unfounded on the basis of our present knowledge of the EBL. EBL spectra that do give rise to unphysical blazar spectra are regarded as invalid realizations of the EBL. Those that do not thus define new constraints on the EBL spectrum and are used to derive new limits on the intensity and the peak γ-ray energy of these two blazars. In particular, we derive an upper limit of ~15 nW m-2 sr-1 on the 60 μm EBL intensity and find the peak energies of the Mrk 421 and Mrk 501 sources to be very similar, between 0.5-1.2 and 0.8-2.5 TeV, respectively. We also
Polarization swings reveal magnetic energy dissipation in blazars

DOE PAGES

Zhang, Haocheng; Chen, Xuhui; Böttcher, Markus; ...

2015-05-01

The polarization signatures of blazar emissions are known to be highly variable. In addition to small fluctuations of the polarization angle around a mean value, large (≳ 180°) polarization angle swings are observed. We suggest that such phenomena can be interpreted as arising from light-travel-time effects within an underlying axisymmetric emission region. We present the first simultaneous fitting of the multi-wavelength spectrum, variability, and time-dependent polarization features of a correlated optical and gamma-ray flaring event of the prominent blazar 3C279, which was accompanied by a drastic change in its polarization signatures. This unprecedented combination of spectral, variability, and polarization informationmore » in a coherent physical model allows us to place stringent constraints on the particle acceleration and magnetic-field topology in the relativistic jet of a blazar, strongly favoring a scenario in which magnetic energy dissipation is the primary driver of the flare event.« less
Mrk 421 after the Giant X-Ray Outburst in 2013

NASA Astrophysics Data System (ADS)

Kapanadze, B.; Dorner, D.; Romano, P.; Vercellone, S.; Kapanadze, S.; Tabagari, L.

2017-10-01

We present the results of the Swift observations of the nearby BL Lac object Mrk 421 during 2013 November-2015 June. The source exhibited a strong long-term variability in the 0.3-10 keV band, with a maximum-to-minimum flux ratio of 13, and underwent X-ray flares by a factor of 1.8-5.2 on timescales of a few weeks or shorter. The source showed 48 instances of intraday flux variability in this period, which sometimes was observed within the 1 ks observational run. It was characterized by fractional amplitudes of 1.5(0.3)%-38.6(0.4)% and flux doubling/halving times of 2.6-20.1 hr. The X-ray flux showed a lack of correlation with the TeV flux on some occasions (strong TeV flares were not accompanied by comparable X-ray activity and vice versa), indicating that the high-energy emission in Mrk 421 was generated from an emission region more complex than a single zone. The best fits of the 0.3-10 keV spectra were mainly obtained using the log-parabola model, showing a strong spectral variability that generally followed a “harder-when-brighter” trend. The position of the synchrotron spectral energy distribution peak showed an extreme range from a few eV to ˜10 keV that happens rarely in blazars.
Multiwavelength variability properties of Fermi blazar S5 0716+714

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liao, N. H.; Bai, J. M.; Liu, H. T.

S5 0716+714 is a typical BL Lacertae object. In this paper we present the analysis and results of long-term simultaneous observations in the radio, near-infrared, optical, X-ray, and γ-ray bands, together with our own photometric observations for this source. The light curves show that the variability amplitudes in γ-ray and optical bands are larger than those in the hard X-ray and radio bands and that the spectral energy distribution (SED) peaks move to shorter wavelengths when the source becomes brighter, which is similar to other blazars, i.e., more variable at wavelengths shorter than the SED peak frequencies. Analysis shows thatmore » the characteristic variability timescales in the 14.5 GHz, the optical, the X-ray, and the γ-ray bands are comparable to each other. The variations of the hard X-ray and 14.5 GHz emissions are correlated with zero lag, and so are the V band and γ-ray variations, which are consistent with the leptonic models. Coincidences of γ-ray and optical flares with a dramatic change of the optical polarization are detected. Hadronic models do not have the same natural explanation for these observations as the leptonic models. A strong optical flare correlating a γ-ray flare whose peak flux is lower than the average flux is detected. The leptonic model can explain this variability phenomenon through simultaneous SED modeling. Different leptonic models are distinguished by average SED modeling. The synchrotron plus synchrotron self-Compton (SSC) model is ruled out because of the extreme input parameters. Scattering of external seed photons, such as the hot-dust or broad-line region emission, and the SSC process are probably both needed to explain the γ-ray emission of S5 0716+714.« less
QUASI-PERIODICITIES AT YEAR-LIKE TIMESCALES IN BLAZARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sandrinelli, A.; Treves, A.; Covino, S.

2016-03-15

We searched for quasi-periodicities on year-like timescales in the light curves of six blazars in the optical—near-infrared bands and we made a comparison with the high energy emission. We obtained optical/NIR light curves from Rapid Eye Mounting photometry plus archival Small and Moderate Aperture Research Telescope System data and we accessed the Fermi light curves for the γ-ray data. The periodograms often show strong peaks in the optical and γ-ray bands, which in some cases may be inter-related. The significance of the revealed peaks is then discussed, taking into account that the noise is frequency dependent. Quasi-periodicities on a year-likemore » timescale appear to occur often in blazars. No straightforward model describing these possible periodicities is yet available, but some plausible interpretations for the physical mechanisms causing periodic variabilities of these sources are examined.« less
The RINGO2 and DIPOL optical polarization catalogue of blazars

NASA Astrophysics Data System (ADS)

Jermak, H.; Steele, I. A.; Lindfors, E.; Hovatta, T.; Nilsson, K.; Lamb, G. P.; Mundell, C.; Barres de Almeida, U.; Berdyugin, A.; Kadenius, V.; Reinthal, R.; Takalo, L.

2016-11-01

We present ˜2000 polarimetric and ˜3000 photometric observations of 15 γ-ray bright blazars over a period of 936 days (2008-10-11 to 2012-10-26) using data from the Tuorla blazar monitoring program (KVA DIPOL) and Liverpool Telescope (LT) RINGO2 polarimeters (supplemented with data from SkyCamZ (LT) and Fermi-LAT γ-ray data). In 11 out of 15 sources we identify a total of 19 electric vector position angle (EVPA) rotations and 95 flaring episodes. We group the sources into subclasses based on their broad-band spectral characteristics and compare their observed optical and γ-ray properties. We find that (1) the optical magnitude and γ-ray flux are positively correlated, (2) EVPA rotations can occur in any blazar subclass, four sources show rotations that go in one direction and immediately rotate back, (3) we see no difference in the γ-ray flaring rates in the sample; flares can occur during and outside of rotations with no preference for this behaviour, (4) the average degree of polarization (DoP), optical magnitude and γ-ray flux are lower during an EVPA rotation compared with during non-rotation and the distribution of the DoP during EVPA rotations is not drawn from the same parent sample as the distribution outside rotations, (5) the number of observed flaring events and optical polarization rotations are correlated, however we find no strong evidence for a temporal association between individual flares and rotations and (6) the maximum observed DoP increases from ˜10 per cent to ˜30 per cent to ˜40 per cent for subclasses with synchrotron peaks at high, intermediate and low frequencies, respectively.
GSFC Contributions to the NATO X-ray Astronomy Institute, Erice, July 1979. [X-ray spectra of supernova remants, galactic X-ray sources, active galactic nuclei, and clusters of galaxies

NASA Technical Reports Server (NTRS)

Holt, S. S.; Mushotzky, R. F.

1979-01-01

An overview of X-ray astronomical spectroscopy in general is presented and results obtained by HEAO 1 and 2 as well as earlier spacecraft are examined. Particular emphasis is given to the spectra of supernova remnants; galactic binary X-ray sources, cataclysmic variables, bulges, pulsars, and stars; the active nuclei of Seyfert 1 galaxy, BL Lac, and quasars; the diffuse X-ray background; and galactic clusters.
Search for Magnetically Broadened Cascade Emission from Blazars with VERITAS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Archambault, S.; Griffin, S.; Archer, A.

2017-02-01

We present a search for magnetically broadened gamma-ray emission around active galactic nuclei (AGNs), using VERITAS observations of seven hard-spectrum blazars. A cascade process occurs when multi-TeV gamma-rays from an AGN interact with extragalactic background light (EBL) photons to produce electron–positron pairs, which then interact with cosmic microwave background photons via inverse-Compton scattering to produce gamma-rays. Due to the deflection of the electron–positron pairs, a non-zero intergalactic magnetic field (IGMF) would potentially produce detectable effects on the angular distribution of the cascade emission. In particular, an angular broadening compared to the unscattered emission could occur. Through non-detection of angularly broadenedmore » emission from 1ES 1218+304, the source with the largest predicted cascade fraction, we exclude a range of IGMF strengths around 10{sup −14} G at the 95% confidence level. The extent of the exclusion range varies with the assumptions made about the intrinsic spectrum of 1ES 1218+304 and the EBL model used in the simulation of the cascade process. All of the sources are used to set limits on the flux due to extended emission.« less
Planetary X ray experiment

NASA Technical Reports Server (NTRS)

Anderson, K. A.

1972-01-01

Design studies for an X-ray experiment using solid state detectors and for an experiment using a proportional counter for investigating Jovian and Saturnian magnetospheres are reported. Background counting rates through the forward aperture and leakage fluxes are discussed for each design. It is concluded that the best choice of instrument appears to have following the characteristics: (1) two separate multiwire proportional counters for redundancy; (2) passive collimation to restrict the field to about 5 deg, wiregrid modulation collimation to about 0.1 deg angular resolution; (3) no active shielding system around the counter body; and (4) light passive shielding around any portion of the counter body exposed to space to absorb most of the cosmic X-ray background.
Tomographic image via background subtraction using an x-ray projection image and a priori computed tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang Jin; Yi Byongyong; Lasio, Giovanni

Kilovoltage x-ray projection images (kV images for brevity) are increasingly available in image guided radiotherapy (IGRT) for patient positioning. These images are two-dimensional (2D) projections of a three-dimensional (3D) object along the x-ray beam direction. Projecting a 3D object onto a plane may lead to ambiguities in the identification of anatomical structures and to poor contrast in kV images. Therefore, the use of kV images in IGRT is mainly limited to bony landmark alignments. This work proposes a novel subtraction technique that isolates a slice of interest (SOI) from a kV image with the assistance of a priori information frommore » a previous CT scan. The method separates structural information within a preselected SOI by suppressing contributions to the unprocessed projection from out-of-SOI-plane structures. Up to a five-fold increase in the contrast-to-noise ratios (CNRs) was observed in selected regions of the isolated SOI, when compared to the original unprocessed kV image. The tomographic image via background subtraction (TIBS) technique aims to provide a quick snapshot of the slice of interest with greatly enhanced image contrast over conventional kV x-ray projections for fast and accurate image guidance of radiation therapy. With further refinements, TIBS could, in principle, provide real-time tumor localization using gantry-mounted x-ray imaging systems without the need for implanted markers.« less
Probing Large-scale Coherence between Spitzer IR and Chandra X-Ray Source-subtracted Cosmic Backgrounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cappelluti, N.; Urry, M.; Arendt, R.

2017-09-20

We present new measurements of the large-scale clustering component of the cross-power spectra of the source-subtracted Spitzer -IRAC cosmic infrared background and Chandra -ACIS cosmic X-ray background surface brightness fluctuations Our investigation uses data from the Chandra Deep Field South, Hubble Deep Field North, Extended Groth Strip/AEGIS field, and UDS/SXDF surveys, comprising 1160 Spitzer hours and ∼12 Ms of Chandra data collected over a total area of 0.3 deg{sup 2}. We report the first (>5 σ ) detection of a cross-power signal on large angular scales >20″ between [0.5–2] keV and the 3.6 and 4.5 μ m bands, at ∼5more » σ and 6.3 σ significance, respectively. The correlation with harder X-ray bands is marginally significant. Comparing the new observations with existing models for the contribution of the known unmasked source population at z < 7, we find an excess of about an order of magnitude at 5 σ confidence. We discuss possible interpretations for the origin of this excess in terms of the contribution from accreting early black holes (BHs), including both direct collapse BHs and primordial BHs, as well as from scattering in the interstellar medium and intra-halo light.« less
The Impact of Electromagnetic Cascades of Very-high Energy Gamma Rays on the Extragalactic Gamma-ray Background

NASA Technical Reports Server (NTRS)

Venters, Tonia

2012-01-01

As very high energy (VHE) photons propagate through the extragalactic background light (EBL), they interact with the soft photons of the EBL and initiate electromagnetic cascades of photons and electrons. The collective intensity of a cosmological population emitting at VHEs (such as blazars) will be attenuated at the highest energies through interactions with the EBL and enhanced at lower energies by the resulting cascade. As such, depending on the space density and spectra of the sources and the model of the EBL, cascade radiation can provide a significant contribution to the extragalactic gamma-ray background (EGB). Through deflections of the charged particles of the cascade, an intergalactic magnetic field (IGMF) may leave an imprint on the anisotropy properties of the EGB. The impact of a strong IGMF is to isotropize lower energy cascade photons, inducing a modulation in the anisotropy energy spectrum of the EGB. We discuss the implications of cascade radiation for the origins of the EGB and the nature of the IGMF, as well as insight that will be provided by data from the Fermi Large Area Telescope in the upcoming years.

Probing stochastic inter-galactic magnetic fields using blazar-induced gamma ray halo morphology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duplessis, Francis; Vachaspati, Tanmay, E-mail: fdupless@asu.edu, E-mail: tvachasp@asu.edu

Inter-galactic magnetic fields can imprint their structure on the morphology of blazar-induced gamma ray halos. We show that the halo morphology arises through the interplay of the source's jet and a two-dimensional surface dictated by the magnetic field. Through extensive numerical simulations, we generate mock halos created by stochastic magnetic fields with and without helicity, and study the dependence of the halo features on the properties of the magnetic field. We propose a sharper version of the Q-statistics and demonstrate its sensitivity to the magnetic field strength, the coherence scale, and the handedness of the helicity. We also identify andmore » explain a new feature of the Q-statistics that can further enhance its power.« less
A significant hardening and rising shape detected in the MeV/GeV νF ν spectrum from the recently discovered very-high-energy blazar S4 0954+65 during the bright optical flare in 2015 February

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanaka, Yasuyuki T.; Becerra Gonzalez, Josefa; Itoh, Ryosuke

2016-05-23

In this paper, we report on Fermi Large Area Telescope (LAT) and multi-wavelength results on the recently discovered very-high-energy (VHE, E > 100 GeV) blazar S4 0954+65 (z = 0.368) during an exceptionally bright optical flare in 2015 February. During the time period (2015 February 13/14, or MJD 57067) when the MAGIC telescope detected VHE γ-ray emission from the source, the Fermi-LAT data indicated a significant spectral hardening at GeV energies, with a power-law photon index of 1.8 ± 0.1—compared with the 3FGL (The Fermi LAT 4-Year Point Source Catalog) value (averaged over four years of observation) of 2.34 ±more » 0.04. In contrast, Swift X-Ray Telescope data showed a softening of the X-ray spectrum, with a photon index of 1.72 ± 0.08 (compared with 1.38 ± 0.03 averaged during the flare from MJD 57066 to 57077), possibly indicating a modest contribution of synchrotron photons by the highest-energy electrons superposed on the inverse Compton component. Fitting of the quasi-simultaneous (<1 d) broad-band spectrum with a one-zone synchrotron plus inverse-Compton model revealed that GeV/TeV emission could be produced by inverse-Compton scattering of external photons from the dust torus. Finally, we emphasize that a flaring blazar showing high flux of ≳1.0 × 10 -6 photons cm -2s -1 (E > 100 MeV) and a hard spectral index of ΓGeV < 2.0 detected by Fermi-LAT on daily timescales is a promising target for TeV follow-up by ground-based Cherenkov telescopes to discover high-redshift blazars, investigate their temporal variability and spectral features in the VHE band, and also constrain the intensity of the extragalactic background light.« less
The Disk-Jet Connection in Radio-Loud AGN: The X-Ray Perspective

NASA Technical Reports Server (NTRS)

Sambruna, Rita

2008-01-01

Unification schemes assume that radio-loud active galactic nuclei (AGN) contain an accretion disk and a relativistic jet perpendicular to the disk, and an obscuring molecular torus. The jet dominance decreases with larger viewing angles from blazars to Broad-Line and Narrow-Line Radio Galaxies. A fundamental question is how accretion and ejecta are related. The X-rays provide a convenient window to study these issues, as they originate in the innermost nuclear regions and penetrate large obscuring columns. I review the data, using observations by Chandra but also from other currently operating high-energy experiments. Synergy with the upcoming GLAST mission will also be highlighted.
Extragalactic Hard X-ray Surveys: From INTEGRAL to Simbol-X

NASA Astrophysics Data System (ADS)

Paltani, S.; Dwelly, T.; Walter, R.; McHardy, I. M.; Courvoisier, T. J.-L.

2009-05-01

We present some results of the deepest extragalactic survey performed by the INTEGRAL satellite. The fraction of very absorbed AGN is quite large. The sharp decrease in the absorption fraction with X-ray luminosity observed at lower-energy X-rays is not observed. The current lack of truly Compton-thick objects, with an upper limit of 14% to the size of this population, is just compatible with recent modeling of the cosmic X-ray background. We also study the prospects for a future hard X-ray serendipitous survey with Simbol-X. We show that Simbol-X will easily detect a large number of serendipitous AGN, allowing us to study the evolution of AGN up to redshifts about 2, opening the door to the cosmological study of hard X-ray selected AGN, which is barely possible with existing satellites like Swift and INTEGRAL.
Impact of Improved Heat Sinking of an X-Ray Calorimeter Array on Crosstalk, Noise, and Background Events

NASA Technical Reports Server (NTRS)

Kilbourne, C. A.; Adams, J. S.; Brekosky, R. P.; Chervenak, J. A.; Chiao, M. P.; Kelley, R. L.; Kelly, D. P.; Porter, F. S.

2011-01-01

The x-ray calorimeter array of the Soft X-ray Spectrometer (SXS) of the Astro-H satellite will incorporate a silicon thermistor array produced during the development of the X-Ray Spectrometer (XRS) of the Suzaku satellite. On XRS, inadequate heat sinking of the array led to several non-ideal effects. The thermal crosstalk, while too small to be confused with x-ray signals, nonetheless contributed a noise term that could be seen as a degradation in energy resolution at high flux. When energy was deposited in the silicon frame around the active elements of the array, such as by a cosmic ray, the resulting pulse in the temperature of the frame resulted in coincident signal pulses on most of the pixels. In orbit, the resolution was found to depend on the particle background rate. In order to minimize these effects on SXS, heat-sinking gold was applied to areas on the front and back of the array die, which was thermally anchored to the gold of its fanout board via gold wire bonds. The thermal conductance from the silicon chip to the fanout board was improved over that of XRS by an order of magnitude. This change was sufficient for essentially eliminating frame events and allowing high-resolution to be attained at much higher counting rates. We will present the improved performance, the measured crosstalk, and the results of the thermal characterization of such arrays.
Extragalactic background light measurements and applications.

PubMed

Cooray, Asantha

2016-03-01

This review covers the measurements related to the extragalactic background light intensity from γ-rays to radio in the electromagnetic spectrum over 20 decades in wavelength. The cosmic microwave background (CMB) remains the best measured spectrum with an accuracy better than 1%. The measurements related to the cosmic optical background (COB), centred at 1 μm, are impacted by the large zodiacal light associated with interplanetary dust in the inner Solar System. The best measurements of COB come from an indirect technique involving γ-ray spectra of bright blazars with an absorption feature resulting from pair-production off of COB photons. The cosmic infrared background (CIB) peaking at around 100 μm established an energetically important background with an intensity comparable to the optical background. This discovery paved the way for large aperture far-infrared and sub-millimetre observations resulting in the discovery of dusty, starbursting galaxies. Their role in galaxy formation and evolution remains an active area of research in modern-day astrophysics. The extreme UV (EUV) background remains mostly unexplored and will be a challenge to measure due to the high Galactic background and absorption of extragalactic photons by the intergalactic medium at these EUV/soft X-ray energies. We also summarize our understanding of the spatial anisotropies and angular power spectra of intensity fluctuations. We motivate a precise direct measurement of the COB between 0.1 and 5 μm using a small aperture telescope observing either from the outer Solar System, at distances of 5 AU or more, or out of the ecliptic plane. Other future applications include improving our understanding of the background at TeV energies and spectral distortions of CMB and CIB.
Extragalactic background light measurements and applications

PubMed Central

Cooray, Asantha

2016-01-01

This review covers the measurements related to the extragalactic background light intensity from γ-rays to radio in the electromagnetic spectrum over 20 decades in wavelength. The cosmic microwave background (CMB) remains the best measured spectrum with an accuracy better than 1%. The measurements related to the cosmic optical background (COB), centred at 1 μm, are impacted by the large zodiacal light associated with interplanetary dust in the inner Solar System. The best measurements of COB come from an indirect technique involving γ-ray spectra of bright blazars with an absorption feature resulting from pair-production off of COB photons. The cosmic infrared background (CIB) peaking at around 100 μm established an energetically important background with an intensity comparable to the optical background. This discovery paved the way for large aperture far-infrared and sub-millimetre observations resulting in the discovery of dusty, starbursting galaxies. Their role in galaxy formation and evolution remains an active area of research in modern-day astrophysics. The extreme UV (EUV) background remains mostly unexplored and will be a challenge to measure due to the high Galactic background and absorption of extragalactic photons by the intergalactic medium at these EUV/soft X-ray energies. We also summarize our understanding of the spatial anisotropies and angular power spectra of intensity fluctuations. We motivate a precise direct measurement of the COB between 0.1 and 5 μm using a small aperture telescope observing either from the outer Solar System, at distances of 5 AU or more, or out of the ecliptic plane. Other future applications include improving our understanding of the background at TeV energies and spectral distortions of CMB and CIB. PMID:27069645
Small-Scale Spatial Fluctuations in the Soft X-Ray Background. Degree awarded by Maryland Univ., 2000

NASA Technical Reports Server (NTRS)

Kuntz, K. D.; White, Nicolas E. (Technical Monitor)

2001-01-01

In order to isolate the diffuse extragalactic component of the soft X-ray background, we have used a combination of ROSAT All-Sky Survey and IRAS 100 micron data to separate the soft X-ray background into five components. We find a Local Hot Bubble similar to that described by Snowden et al (1998). We make a first calculation of the contribution by unresolved Galactic stars to the diffuse background. We constrain the normalization of the Extragalactic Power Law (the contribution of the unresolved extragalactic point sources such as AGN, QSO'S, and normal galaxies) to 9.5 +/- 0.9 keV/(sq cm s sr keV), assuming a power-law index of 1.46. We show that the remaining emission, which is some combination of Galactic halo emission and the putative diffuse extragalactic emission, must be composed of at least two components which we have characterized by thermal spectra. The softer component has log T - 6.08 and a patchy distribution; thus it is most probably part of the Galactic halo. The harder component has log T - 6.46 and is nearly isotropic; some portion may be due to the Galactic halo and some portion may be due to the diffuse extragalactic emission. The maximum upper limit to the strength of the emission by the diffuse extragalactic component is the total of the hard component, approx. 7.4 +/- 1.0 keV/(sq cm s sr keV) in the 3/4 keV band. We have made the first direct measure of the fluctuations due to the diffuse extragalactic emission in the 3/4 keV band. Physical arguments suggest that small angular scale (approx. 10') fluctuations in the Local Hot Bubble or the Galactic halo will have very short dissipation times (about 10(exp 5) years). Therefore, the fluctuation spectrum of the soft X-ray background should measure the distribution of the diffuse extragalactic emission. Using mosaics of deep, overlapping PSPC pointings, we find an autocorrelation function value of approx. 0.0025 for 10' < theta < 20', and a value consistent with zero on larger scales
High Spectral Resolution Observation of the Soft Diffuse X-ray Background in the Direction of the Galactic Anti-Center

NASA Astrophysics Data System (ADS)

Wulf, Dallas; Eckart, Mega E.; Galeazzi, Massimiliano; Jaeckel, Felix; Kelley, Richard L.; Kilbourne, Caroline A.; McCammon, Dan; Morgan, Kelsey M.; Porter, Frederick S.; Szymkowiak, Andrew E.

2018-01-01

High spectral resolution observations in the soft x-rays are necessary for understanding and modelling the hot component of the interstellar medium and its contribution to the Soft X-ray Background (SXRB). This extended source emission cannot be resolved with most wavelength dispersive spectrometers, making energy dispersive microcalorimeters the ideal choice for these observations. We present here the analysis of the most recent sounding rocket flight of the University of Wisconsin-Madison/Goddard Space Flight Center X-ray Quantum Calorimeter (XQC), a large area silicon thermistor microcalorimeter. This 111 second observation integrates a nearly 1 steradian field of view in the direction of the galactic anti-center (l, b = 165°, -5°) and features ~5 eV spectral resolution below 1 keV. Direct comparison will also be made to the previous, high-latitude observations.
A new background subtraction method for energy dispersive X-ray fluorescence spectra using a cubic spline interpolation

NASA Astrophysics Data System (ADS)

Yi, Longtao; Liu, Zhiguo; Wang, Kai; Chen, Man; Peng, Shiqi; Zhao, Weigang; He, Jialin; Zhao, Guangcui

2015-03-01

A new method is presented to subtract the background from the energy dispersive X-ray fluorescence (EDXRF) spectrum using a cubic spline interpolation. To accurately obtain interpolation nodes, a smooth fitting and a set of discriminant formulations were adopted. From these interpolation nodes, the background is estimated by a calculated cubic spline function. The method has been tested on spectra measured from a coin and an oil painting using a confocal MXRF setup. In addition, the method has been tested on an existing sample spectrum. The result confirms that the method can properly subtract the background.
X-ray properties of quasars

NASA Technical Reports Server (NTRS)

Ku, W. H.-M.; Helfand, D. J.; Lucy, L. B.

1980-01-01

The X-ray properties of 111 catalogued quasars have been examined with the imaging proportional counter on board the Einstein Observatory. Thirty-five of the objects, of redshift between 0.064 and 3.53, were detected as X-ray sources. The 0.5-4.5-keV X-ray properties of these quasars are correlated with their optical and radio continuum properties and with their redshifts and variability characteristics. The X-ray luminosity of quasars tends to be highest for those objects which are bright in the optical and radio regimes and which exhibit optically violent variability. These observations suggest that quasars should be divided into two classes on the basis of radio luminosities, spectra, evolution and underlying morphology and that quasars can make up a significant portion of the diffuse soft X-ray background only if the slope of the optical quasar log N-log S relation is steeper than 2 to m sub b of about 21.5.
Cross-correlating Cosmic IR and X-ray Background Fluctuations: Evidence of Significant Black Hole Populations Among the CIB Sources

NASA Technical Reports Server (NTRS)

Cappelluti, N.; Kashlinsky, A.; Arendt, R. G.; Comastri, A.; Fazio, G. G.; Finoguenov, A.; Hasinger, G.; Mather, J. C.; Miyaji, T; Moseley, S. H.

2013-01-01

In order to understand the nature of the sources producing the recently uncovered cosmic infrared background (CIB) fluctuations, we study cross-correlations between the fluctuations in the source-subtracted CIB from Spitzer/IRAC data and the unresolved cosmic X-ray background from deep Chandra observations. Our study uses data from the EGS/AEGIS field, where both data sets cover an approx = 8' x 45' region of the sky. Our measurement is the cross-power spectrum between the IR and X-ray data. The cross-power signal between the IRAC maps at 3.6 micron and 4.5 micron and the Chandra [0.5-2] keV data has been detected, at angular scales approx >20'', with an overall significance of approx = 3.8 sigma and approx. = 5.6 sigma, respectively. At the same time we find no evidence of significant cross-correlations at the harder Chandra bands. The cross-correlation signal is produced by individual IR sources with 3.6 micron and 4.5 micron magnitudes m(sub AB) approx. > 25-26 and [0.5-2] keV X-ray fluxes << 7 × 10(exp -177 erg sq. cm/ s. We determine that at least 15%-25% of the large scale power of the CIB fluctuations is correlated with the spatial power spectrum of the X-ray fluctuations. If this correlation is attributed to emission from accretion processes at both IR and X-ray wavelengths, this implies a much higher fraction of accreting black holes than among the known populations. We discuss the various possible origins for the cross-power signal and show that neither local foregrounds nor the known remaining normal galaxies and active galactic nuclei can reproduce the measurements. These observational results are an important new constraint on theoretical modeling of the near-IR CIB fluctuations. local foregrounds, nor the known remaining normal galaxies and active galactic nuclei (AGN) can reproduce the measurements. These observational results are an important new constraint on theoretical modeling of the near-IR CIB fluctuations
Detection of significant cm to sub-mm band radio and γ-ray correlated variability in Fermi bright blazars

DOE PAGES

Fuhrmann, L.; Larsson, S.; Chiang, J.; ...

2014-05-12

The exact location of the γ-ray emitting region in blazars is still controversial. In order to attack this problem we present first results of a cross-correlation analysis between radio (11 cm to 0.8 mm wavelength, F-GAMMA programme) and γ-ray (0.1–300 GeV) ~3.5 yr light curves of 54 Fermi-bright blazars. We perform a source stacking analysis and estimate significances and chance correlations using mixed source correlations. These results reveal: (i) the first highly significant multiband radio and γ-ray correlations (radio lagging γ rays) when averaging over the whole sample, (ii) average time delays (source frame: 76 ± 23 to 7 ±more » 9 d), systematically decreasing from cm to mm/sub-mm bands with a frequency dependence τr, γ(ν) ∝ ν -1, in good agreement with jet opacity dominated by synchrotron self-absorption, (iii) a bulk γ-ray production region typically located within/upstream of the 3 mm core region (τ3mm, γ = 12 ± 8 d), (iv) mean distances between the region of γ-ray peak emission and the radio ‘τ = 1 photosphere’ decreasing from 9.8 ± 3.0 pc (11 cm) to 0.9 ± 1.1 pc (2 mm) and 1.4 ± 0.8 pc (0.8 mm), (v) 3 mm/γ-ray correlations in nine individual sources at a significance level where one is expected by chance (probability: 4 × 10 -6), (vi) opacity and ‘time lag core shift’ estimates for quasar 3C 454.3 providing a lower limit for the distance of the bulk γ-ray production region from the supermassive black hole (SMBH) of ~0.8–1.6 pc, i.e. at the outer edge of the broad-line region (BLR) or beyond. A 3 mm τ = 1 surface at ~2–3 pc from the jet base (i.e. well outside the ‘canonical BLR’) finally suggests that BLR material extends to several parsec distances from the SMBH.« less
Discovery of very high energy gamma-ray emission from the blazar 1ES 1727+502 with the MAGIC Telescopes

DOE PAGES

Aleksić, J.; Antonelli, L. A.; Antoranz, P.; ...

2014-03-14

Motivated by the prediction of a high TeV luminosity we investigated whether the blazar 1ES 1727+502 (z = 0.055) is emitting very high energy (VHE, E > 100 GeV) γ rays. Here, we observed the BL Lac object 1ES 1727+502 in stereoscopic mode with the two MAGIC telescopes for 14 nights between May 6th and June 10th 2011, for a total effective observing time of 12.6 h. To study the multiwavelength spectral energy distribution (SED), we also oused simultaneous optical R-band data from the KVA telescope, archival UV/optical and X-ray observations from instruments UVOT and XRT on board of themore » Swift satellite, and high energy (HE, 0.1 GeV–100 GeV) γ-ray data from the Fermi-LAT instrument. We detected, for the first time, VHE γ-ray emission from 1ES 1727+502 at a statistical significance of 5.5σ. The integral flux above 150 GeV is estimated to be (2.1 ± 0.4)% of the Crab nebula flux and the de-absorbed VHE spectrum has a photon index of (2.7 ± 0.5). Furthermore, there were no significant short-term variability found in any of the wavebands presented here. We model the SED using a one-zone synchrotron self-Compton model obtaining parameters typical for this class of sources.« less
Multi-wavelength Observations of Blazar AO 0235+164 in the 2008-2009 Flaring State

NASA Astrophysics Data System (ADS)

Ackermann, M.; Ajello, M.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Casandjian, J. M.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Cutini, S.; D'Ammando, F.; de Palma, F.; Dermer, C. D.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Dubois, R.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Fuhrmann, L.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Guiriec, S.; Hadasch, D.; Hayashida, M.; Hughes, R. E.; Itoh, R.; Jóhannesson, G.; Johnson, A. S.; Katagiri, H.; Kataoka, J.; Knödlseder, J.; Kuss, M.; Lande, J.; Larsson, S.; Lee, S.-H.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Mazziotta, M. N.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Nishino, S.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ozaki, M.; Paneque, D.; Panetta, J. H.; Pelassa, V.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Rando, R.; Rastawicki, D.; Razzano, M.; Readhead, A.; Reimer, A.; Reimer, O.; Reyes, L. C.; Richards, J. L.; Sbarra, C.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Szostek, A.; Takahashi, H.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Winer, B. L.; Wood, K. S.; Yang, Z.; Zimmer, S.; Fermi-LAT Collaboration; Moderski, R.; Nalewajko, K.; Sikora, M.; Villata, M.; Raiteri, C. M.; Aller, H. D.; Aller, M. F.; Arkharov, A. A.; Benítez, E.; Berdyugin, A.; Blinov, D. A.; Boettcher, M.; Bravo Calle, O. J. A.; Buemi, C. S.; Carosati, D.; Chen, W. P.; Diltz, C.; Di Paola, A.; Dolci, M.; Efimova, N. V.; Forné, E.; Gurwell, M. A.; Heidt, J.; Hiriart, D.; Jordan, B.; Kimeridze, G.; Konstantinova, T. S.; Kopatskaya, E. N.; Koptelova, E.; Kurtanidze, O. M.; Lähteenmäki, A.; Larionova, E. G.; Larionova, L. V.; Larionov, V. M.; Leto, P.; Lindfors, E.; Lin, H. C.; Morozova, D. A.; Nikolashvili, M. G.; Nilsson, K.; Oksman, M.; Roustazadeh, P.; Sievers, A.; Sigua, L. A.; Sillanpää, A.; Takahashi, T.; Takalo, L. O.; Tornikoski, M.; Trigilio, C.; Troitsky, I. S.; Umana, G.; GASP-WEBT Consortium; Angelakis, E.; Krichbaum, T. P.; Nestoras, I.; Riquelme, D.; F-GAMMA; Krips, M.; Trippe, S.; Iram-PdBI; Arai, A.; Kawabata, K. S.; Sakimoto, K.; Sasada, M.; Sato, S.; Uemura, M.; Yamanaka, M.; Yoshida, M.; Kanata; Belloni, T.; Tagliaferri, G.; RXTE; Bonning, E. W.; Isler, J.; Urry, C. M.; SMARTS; Hoversten, E.; Falcone, A.; Pagani, C.; Stroh, M.; (Swift-XRT

2012-06-01

The blazar AO 0235+164 (z = 0.94) has been one of the most active objects observed by Fermi Large Area Telescope (LAT) since its launch in Summer 2008. In addition to the continuous coverage by Fermi, contemporaneous observations were carried out from the radio to γ-ray bands between 2008 September and 2009 February. In this paper, we summarize the rich multi-wavelength data collected during the campaign (including F-GAMMA, GASP-WEBT, Kanata, OVRO, RXTE, SMARTS, Swift, and other instruments), examine the cross-correlation between the light curves measured in the different energy bands, and interpret the resulting spectral energy distributions in the context of well-known blazar emission models. We find that the γ-ray activity is well correlated with a series of near-IR/optical flares, accompanied by an increase in the optical polarization degree. On the other hand, the X-ray light curve shows a distinct 20 day high state of unusually soft spectrum, which does not match the extrapolation of the optical/UV synchrotron spectrum. We tentatively interpret this feature as the bulk Compton emission by cold electrons contained in the jet, which requires an accretion disk corona with an effective covering factor of 19% at a distance of 100 R g. We model the broadband spectra with a leptonic model with external radiation dominated by the infrared emission from the dusty torus.
First Search for an X-Ray-Optical Reverberation Signal in an Ultraluminous X-Ray Source

NASA Technical Reports Server (NTRS)

Pasham, Dheeraj R.; Strohmayer, Tod E.; Cenko, S. Bradley; Trippe, Margaret L.; Mushotzky, Richard F.; Gandhi, Poshak

2016-01-01

Using simultaneous optical (VLT/FORS2) and X-ray (XMM-Newton) data of NGC 5408, we present the first ever attempt to search for a reverberation signal in an ultraluminous X-ray source (NGC 5408 X-1). The idea is similar to active galactic nucleus broad line reverberation mapping where a lag measurement between the X-ray and the optical flux combined with a Keplerian velocity estimate should enable us to weigh the central compact object. We find that although NGC 5408 X-1's X-rays are variable on a timescale of a few hundred seconds (rms of 9.0 +/- 0.5%), the optical emission does not show any statistically significant variations. We set a 3s upper limit on the rms optical variability of 3.3%. The ratio of the X-ray to the optical variability is an indicator of X-ray reprocessing efficiency. In X-ray binaries, this ratio is roughly 5. Assuming a similar ratio for NGC 5408 X-1, the expected rms optical variability is approximately equal to 2%, which is still a factor of roughly two lower than what was possible with the VLT observations in this study. We find marginal evidence (3 sigma) for optical variability on an approximately 24 hr timescale. Our results demonstrate that such measurements can be made, but photometric conditions, low sky background levels, and longer simultaneous observations will be required to reach optical variability levels similar to those of X-ray binaries.
On the incidence of Mg II absorbers along the blazar sightlines

NASA Astrophysics Data System (ADS)

Mishra, S.; Chand, H.; Krishna, Gopal-; Joshi, R.; Shchekinov, Y. A.; Fatkhullin, T. A.

2018-02-01

It is widely believed that the cool gas clouds traced by Mg II absorption, within a velocity offset of 5000 km s-1 relative to the background quasar are mostly associated with the quasar itself, whereas the absorbers seen at larger velocity offsets towards us are intervening absorber systems and hence their existence is completely independent of the background quasar. Recent evidence by Bergeron et al. (hereinafter BBM) has seriously questioned this paradigm, by showing that the number density of intervening Mg II absorbers towards the 45 blazars in their sample is nearly two times the expectation based on the Mg II absorption systems seen towards normal quasars (QSOs). Given its serious implications, it becomes important to revisit this finding, by enlarging the blazar sample and subjecting it to an independent analysis. Here, we first report the outcome of our re-analysis of the available spectroscopic data for the BBM sample itself. Our analysis of the BBM sample reproduces their claimed factor of 2 excess of dN/dz along blazar sightlines, vis-à-vis normal QSOs. We have also assembled an approxmately three times larger sample of blazars, albeit with moderately sensitive optical spectra. Using this sample together with the BBM sample, our analysis shows that the dN/dz of the Mg II absorbers statistically matches that known for normal QSO sightlines. Further, the analysis indicates that associated absorbers might be contributing significantly to the estimated dN/dz up to offset speeds Δv ∼ 0.2c relative to the blazar.
X-ray Diffraction Gratings for Astrophysics

NASA Astrophysics Data System (ADS)

Paerels, Frits

2010-12-01

Over the past year, we have celebrated the tenth anniversary of the Chandra and XMM-Newton X-ray observatories. Both carry powerful, novel diffraction grating spectrometers, which have opened true X-ray spectroscopy for astrophysics. I will describe the design and operation of these instruments, as the background to some of the beautiful results they have produced. But these designs do not exhaust the versatility and essential simplicity of diffraction grating spectrometers, and I will discuss applications for the International X-ray Observatory IXO.
Mrk 421 after the Giant X-Ray Outburst in 2013

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kapanadze, B.; Kapanadze, S.; Tabagari, L.

2017-10-20

We present the results of the Swift observations of the nearby BL Lac object Mrk 421 during 2013 November–2015 June. The source exhibited a strong long-term variability in the 0.3–10 keV band, with a maximum-to-minimum flux ratio of 13, and underwent X-ray flares by a factor of 1.8–5.2 on timescales of a few weeks or shorter. The source showed 48 instances of intraday flux variability in this period, which sometimes was observed within the 1 ks observational run. It was characterized by fractional amplitudes of 1.5(0.3)%–38.6(0.4)% and flux doubling/halving times of 2.6–20.1 hr. The X-ray flux showed a lack ofmore » correlation with the TeV flux on some occasions (strong TeV flares were not accompanied by comparable X-ray activity and vice versa), indicating that the high-energy emission in Mrk 421 was generated from an emission region more complex than a single zone. The best fits of the 0.3–10 keV spectra were mainly obtained using the log-parabola model, showing a strong spectral variability that generally followed a “harder-when-brighter” trend. The position of the synchrotron spectral energy distribution peak showed an extreme range from a few eV to ∼10 keV that happens rarely in blazars.« less
Another X-ray Flare in TeV-detected blazar 1ES 1959+650

NASA Astrophysics Data System (ADS)

Kapanadze, Bidzina

2017-05-01

Since 2015 August, the nearby TeV-detected HBL source 1ES 1959+650 (z=0.048) is in a phase of enhanced X-ray activity compared to the previous years (Kapanadze et al. 2016, MNRAS, 461, L26; ATel #8014, #8289, #8342, #8468, #9121, #9205, #9694, #9949, and http://www.swift.psu.edu/monitoring/source.php?source=1ES1959+650 for the historical 0.3-10 keV light curve).

Monitoring X-Ray Emission from X-Ray Bursters

NASA Technical Reports Server (NTRS)

Halpern, Jules P.; Kaaret, Philip

1999-01-01

The scientific goal of this project was to monitor a selected sample of x-ray bursters using data from the All-Sky Monitor (ASM) on the Rossi X-Ray Timing Explorer together with data from the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory to study the long-term temporal evolution of these sources in the x-ray and hard x-ray bands. The project was closely related to "Long-Term Hard X-Ray Monitoring of X-Ray Bursters", NASA project NAG5-3891, and and "Hard x-ray emission of x-ray bursters", NASA project NAG5-4633, and shares publications in common with both of these. The project involved preparation of software for use in monitoring and then the actual monitoring itself. These efforts have lead to results directly from the ASM data and also from Target of Opportunity Observations (TOO) made with the Rossi X-Ray Timing Explorer based on detection of transient hard x-ray outbursts with the ASM and BATSE.
Techniques to improve the accuracy of noise power spectrum measurements in digital x-ray imaging based on background trends removal.

PubMed

Zhou, Zhongxing; Gao, Feng; Zhao, Huijuan; Zhang, Lixin

2011-03-01

Noise characterization through estimation of the noise power spectrum (NPS) is a central component of the evaluation of digital x-ray systems. Extensive works have been conducted to achieve accurate and precise measurement of NPS. One approach to improve the accuracy of the NPS measurement is to reduce the statistical variance of the NPS results by involving more data samples. However, this method is based on the assumption that the noise in a radiographic image is arising from stochastic processes. In the practical data, the artifactuals always superimpose on the stochastic noise as low-frequency background trends and prevent us from achieving accurate NPS. The purpose of this study was to investigate an appropriate background detrending technique to improve the accuracy of NPS estimation for digital x-ray systems. In order to achieve the optimal background detrending technique for NPS estimate, four methods for artifactuals removal were quantitatively studied and compared: (1) Subtraction of a low-pass-filtered version of the image, (2) subtraction of a 2-D first-order fit to the image, (3) subtraction of a 2-D second-order polynomial fit to the image, and (4) subtracting two uniform exposure images. In addition, background trend removal was separately applied within original region of interest or its partitioned sub-blocks for all four methods. The performance of background detrending techniques was compared according to the statistical variance of the NPS results and low-frequency systematic rise suppression. Among four methods, subtraction of a 2-D second-order polynomial fit to the image was most effective in low-frequency systematic rise suppression and variances reduction for NPS estimate according to the authors' digital x-ray system. Subtraction of a low-pass-filtered version of the image led to NPS variance increment above low-frequency components because of the side lobe effects of frequency response of the boxcar filtering function. Subtracting two
SBS 0846+513: a New Gamma-ray Emitting Narrow-line Seyfert 1 Galaxy

NASA Technical Reports Server (NTRS)

D'Ammando, F.; Orienti, M.; Finke, J.; Raiteri, C. M.; Angelakis, E.; Fuhrmann, L.; Giroletti, M.; Hovatta, T.; Max-Moerbeck, W.; Perkins, J. S.;

2012-01-01

We report Fermi-LAT observations of the radio-loud AGN SBS 0846+513 (z=0.5835), optically classified as a Narrow-Line Seyfert 1 galaxy, together with new and archival radio-to-X-ray data. The source was not active at ?-ray energies during the first two years of Fermi operation. A significant increase in activity was observed during 2010 October-2011 August. In particular a strong gamma-ray flare was observed in 2011 June reaching an isotropic ?-ray luminosity (0.1-300 GeV) of 1.0×10(sup 48) erg s(sup -1), comparable to that of the brightest flat spectrum radio quasars, and showing spectral evolution in gamma rays. An apparent superluminal velocity of (8.2+/-1.5)c in the jet was inferred from 2011-2012 VLBA images, suggesting the presence of a highly relativistic jet. Both the power released by this object during the flaring activity and the apparent superluminal velocity are strong indications of the presence of a relativistic jet as powerful as those of blazars. In addition, variability and spectral properties in radio and gamma-ray bands indicate blazar-like behaviour, suggesting that, except for some distinct optical characteristics, SBS 0846+513 could be considered as a young blazar at the low end of the blazar's black hole mass distribution.

BLAZAR SPECTRAL PROPERTIES AT 74 MHz

DOE Office of Scientific and Technical Information (OSTI.GOV)

Massaro, F.; Funk, S.; Giroletti, M.

2013-10-01

Blazars are the most extreme class of active galactic nuclei. Despite a previous investigation at 102 MHz for a small sample of BL Lac objects and our recent analysis of blazars detected in the Westerbork Northern Sky Survey, a systematic study of the blazar spectral properties at frequencies below 100 MHz has been never carried out. In this paper, we present the first analysis of the radio spectral behavior of blazars based on the recent Very Large Array Low-frequency Sky Survey (VLSS) at 74 MHz. We search for blazar counterparts in the VLSS catalog, confirming that they are detected atmore » 74 MHz. We then show that blazars present radio-flat spectra (i.e., radio spectral indices of ∼0.5) when evaluated, which also about an order of magnitude in frequency lower than previous analyses. Finally, we discuss the implications of our findings in the context of the blazars-radio galaxies connection since the low-frequency radio data provide a new diagnostic tool to verify the expectations of the unification scenario for radio-loud active galaxies.« less
Near-equipartition Jets with Log-parabola Electron Energy Distribution and the Blazar Spectral-index Diagrams

NASA Astrophysics Data System (ADS)

Dermer, Charles D.; Yan, Dahai; Zhang, Li; Finke, Justin D.; Lott, Benoit

2015-08-01

Fermi-LAT analyses show that the γ-ray photon spectral indices {{{Γ }}}γ of a large sample of blazars correlate with the ν {F}ν peak synchrotron frequency {ν }s according to the relation {{{Γ }}}γ =d-k{log} {ν }s. The same function, with different constants d and k, also describes the relationship between {{{Γ }}}γ and peak Compton frequency {ν }{{C}}. This behavior is derived analytically using an equipartition blazar model with a log-parabola description of the electron energy distribution (EED). In the Thomson regime, k={k}{EC}=3b/4 for external Compton (EC) processes and k={k}{SSC}=9b/16 for synchrotron self-Compton (SSC) processes, where b is the log-parabola width parameter of the EED. The BL Lac object Mrk 501 is fit with a synchrotron/SSC model given by the log-parabola EED, and is best fit away from equipartition. Corrections are made to the spectral-index diagrams for a low-energy power-law EED and departures from equipartition, as constrained by absolute jet power. Analytic expressions are compared with numerical values derived from self-Compton and EC scattered γ-ray spectra from Lyα broad-line region and IR target photons. The {{{Γ }}}γ versus {ν }s behavior in the model depends strongly on b, with progressively and predictably weaker dependences on γ-ray detection range, variability time, and isotropic γ-ray luminosity. Implications for blazar unification and blazars as ultra-high energy cosmic-ray sources are discussed. Arguments by Ghisellini et al. that the jet power exceeds the accretion luminosity depend on the doubtful assumption that we are viewing at the Doppler angle.
Fermi-LAT Detection of Gravitational Lens Delayed Gamma-Ray Flares from Blazar B0218+357

NASA Technical Reports Server (NTRS)

Cheung, C. C.; Larsson, S.; Scargle, J. D.; Amin, M. A.; Blandford, R. D.; Bulmash, D.; Chiang, J.; Ciprini, S.; Corbet, R. D. H.; Falco, E. E.;

2014-01-01

Using data from the Fermi Large Area Telescope (LAT), we report the first clear gamma-ray measurement of a delay between flares from the gravitationally lensed images of a blazar. The delay was detected in B0218+357, a known double-image lensed system, during a period of enhanced gamma-ray activity with peak fluxes consistently observed to reach greater than 20-50 times its previous average flux. An auto-correlation function analysis identified a delay in the gamma-ray data of 11.46 plus or minus 0.16 days (1 sigma) that is approximately 1 day greater than previous radio measurements. Considering that it is beyond the capabilities of the LAT to spatially resolve the two images, we nevertheless decomposed individual sequences of superposing gamma-ray flares/delayed emissions. In three such approximately 8-10 day-long sequences within an approximately 4-month span, considering confusion due to overlapping flaring emission and flux measurement uncertainties, we found flux ratios consistent with approximately 1, thus systematically smaller than those from radio observations. During the first, best-defined flare, the delayed emission was detailed with a Fermi pointing, and we observed flux doubling timescales of approximately 3-6 hours implying as well extremely compact gamma-ray emitting regions.

Development of Compton X-ray spectrometer for high energy resolution single-shot high-flux hard X-ray spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kojima, Sadaoki, E-mail: kojima-s@ile.osaka-u.ac.jp, E-mail: sfujioka@ile.osaka-u.ac.jp; Ikenouchi, Takahito; Arikawa, Yasunobu

Hard X-ray spectroscopy is an essential diagnostics used to understand physical processes that take place in high energy density plasmas produced by intense laser-plasma interactions. A bundle of hard X-ray detectors, of which the responses have different energy thresholds, is used as a conventional single-shot spectrometer for high-flux (>10{sup 13} photons/shot) hard X-rays. However, high energy resolution (Δhv/hv < 0.1) is not achievable with a differential energy threshold (DET) X-ray spectrometer because its energy resolution is limited by energy differences between the response thresholds. Experimental demonstration of a Compton X-ray spectrometer has already been performed for obtaining higher energy resolutionmore » than that of DET spectrometers. In this paper, we describe design details of the Compton X-ray spectrometer, especially dependence of energy resolution and absolute response on photon-electron converter design and its background reduction scheme, and also its application to the laser-plasma interaction experiment. The developed spectrometer was used for spectroscopy of bremsstrahlung X-rays generated by intense laser-plasma interactions using a 200 μm thickness SiO{sub 2} converter. The X-ray spectrum obtained with the Compton X-ray spectrometer is consistent with that obtained with a DET X-ray spectrometer, furthermore higher certainly of a spectral intensity is obtained with the Compton X-ray spectrometer than that with the DET X-ray spectrometer in the photon energy range above 5 MeV.« less
Observed Limits on Charge Exchange Contributions to the Diffuse X-Ray Background

NASA Technical Reports Server (NTRS)

Crowder, S. G.; Barger, K. A.; Brandl, D. E.; Eckart, M. E.; Galeazzi, M.; Kelley, R. L.; Kilbourne, C. A.; McCammon, D.; Pfendner, C. G.; Porter, F. S.;

2012-01-01

We present a high-resolution spectrum of the diffuse X-ray background from 0.1 to 1 keV for an approximately 1 sr region of the sky centered at l = 90 degrees b = +60 degrees using a 36 pixel array of microcalorimeters flown on a sounding rocket. With an energy resolution of 11 eV FWHM below 1 keV, the spectrum s observed line ratios help separate charge exchange contributions originating within the heliosphere from thermal emission of hot gas in the interstellar medium. The X-ray sensitivity below 1 keV was reduced by about a factor of four from contamination that occurred early in the flight, limiting the significance of the results. The observed centroid of helium-like O VII is 568 (sup +2 (sub -3) eV at 90% confidence. Since the centroid expected for thermal emission is 568.4 eV and for charge exchange is 564.2 eV, thermal emission appears to dominate for this line complex. The dominance of thermal emission is consistent with much of the high-latitude O VII emission originating in 2-3 x 10(exp 6) K gas in the Galactic halo. On the other hand, the observed ratio of C VI Lygamma to Lyalpha is 0.3 plus or minus 0.2. The expected ratios are 0.04 for thermal emission and 0.24 for charge exchange, indicating that charge exchange must contribute strongly to this line and therefore potentially to the rest of the ROSAT R12 band usually associated with 10(sup 6) K emission from the Local Hot Bubble. The limited statistics of this experiment and systematic uncertainties due to the contamination require only greater than 32% thermal emission for O VII and greater than 20% from charge exchange for C VI at the 90% confidence level. An experimental gold coating on the silicon substrate of the array greatly reduced extraneous signals induced on nearby pixels from cosmic rays passing through the substrate, reducing the triggered event rate by a factor of 15 from a previous flight of the instrument.

Multiwavelength Observations of Blazars

NASA Technical Reports Server (NTRS)

Sambruna, Rita

2007-01-01

The last decade has seen formidable progress in our understanding of blazar jets, thanks to the advent of several higher-sensitivity observatories. I will review the status of the art for blazar jets focusing especially on the latest multiwavelength campaigns.
Quasar X-Ray Spectra At z=1.5

NASA Technical Reports Server (NTRS)

Siemiginowska, Aneta

2001-01-01

The predicted counts for ASCA observation was much higher than actually observed counts in the quasar. However, there are three weak hard x-ray sources in the GIS field. We are adding them to the source counts in modeling of hard x-ray background. The work is in progress. We have published a paper in Ap.J. on the luminosity function and the quasar evolution. Based on the theory described in this paper we are predicting a number of sources and their contribution to the x-ray background at different redshifts. These model predictions will be compared to the observed data in the final paper.
Revisiting Quasi-periodic Modulation in γ -Ray Blazar PKS 2155-304 with Fermi Pass 8 Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Peng-fei; Liao, Neng-hui; Yan, Da-hai

We examine the gamma-ray quasi-periodic variability of PKS 2155-304 with the latest publicly available Fermi -LAT Pass 8 data, which covers the years from 2008 August to 2016 October. We produce the light curves in two ways: the exposure-weighted aperture photometry and the maximum likelihood optimization. The light curves are then analyzed by using Lomb-Scargle Periodogram (LSP) and Weighted Wavelet Z-transform, and the results reveal a significant quasi-periodicity with a period of 1.74±0.13 years and a significance of ∼4.9 σ . The constraint of multifrequencies quasi-periodic variabilities on blazar emission model is discussed.
Apollo-Soyuz pamphlet no. 2: X-rays, gamma-rays. [experimental design

NASA Technical Reports Server (NTRS)

Page, L. W.; From, T. P.

1977-01-01

The nature of high energy radiation and its penetration through earth's atmosphere is examined with emphasis on X-rays, gamma rays, and cosmic radiation and the instruments used in their detection. The history of radio astronomy and the capabilities of the Uhuru satellite are summarized. The ASTP soft X-ray experiment (MA-048) designed to study the spectra in the range from 0.1 to 10 keV and survey the background over a large section of the sky is described, as well as the determination of SMC C-1 as an X-ray pulsar. The crystal activation experiment (MA-151) used to measure the radioactive isotopes created by cosmic rays in crystals used for gamma ray detectors is also discussed.
Gamma-Ray "Raindrops" from Flaring Blazar

NASA Image and Video Library

2017-12-08

This visualization shows gamma rays detected during 3C 279's big flare by the LAT instrument on NASA's Fermi satellite. Gamma rays are represented as expanding circles reminiscent of raindrops on water. The flare is an abrupt shower of "rain" that trails off toward the end of the movie. Both the maximum size of the circle and its color represent the energy of the gamma ray, with white lowest and magenta highest. In a second version of the visualization, a background map shows how the LAT detects 3C 279 and other sources by accumulating high-energy photons over time (brighter squares reflect higher numbers of gamma rays). The movie starts on June 14 and ends June 17. The area shown is a region of the sky five degrees on a side and centered on the position of 3C 279. Read more: go.nasa.gov/1TqximF Credits: NASA/DOE/Fermi LAT Collaboration
Fermi Spots a Record Flare from Blazar

NASA Image and Video Library

2015-07-10

Blazar 3C 279's historic gamma-ray flare can be seen in this image from the Large Area Telescope (LAT) on NASA's Fermi satellite. Gamma rays with energies from 100 million to 100 billion electron volts (eV) are shown; for comparison, visible light has energies between 2 and 3 eV. The image spans 150 degrees, is shown in a stereographic projection, and represents an exposure from June 11 at 00:28 UT to June 17 at 08:17 UT. Credit: NASA/DOE/Fermi LAT Collaboration
X-ray filter for x-ray powder diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sinsheimer, John Jay; Conley, Raymond P.; Bouet, Nathalie C. D.

Technologies are described for apparatus, methods and systems effective for filtering. The filters may comprise a first plate. The first plate may include an x-ray absorbing material and walls defining first slits. The first slits may include arc shaped openings through the first plate. The walls of the first plate may be configured to absorb at least some of first x-rays when the first x-rays are incident on the x-ray absorbing material, and to output second x-rays. The filters may comprise a second plate spaced from the first plate. The second plate may include the x-ray absorbing material and wallsmore » defining second slits. The second slits may include arc shaped openings through the second plate. The walls of the second plate may be configured to absorb at least some of second x-rays and to output third x-rays.« less
A Method for Localizing Energy Dissipation in Blazars Using Fermi Variability

NASA Technical Reports Server (NTRS)

Dotson, Amanda; Georganopoulos, Markos; Kazanas, Demosthenes; Perlman, Eric S.

2013-01-01

The distance of the Fermi-detected blazar gamma-ray emission site from the supermassive black hole is a matter of active debate. Here we present a method for testing if the GeV emission of powerful blazars is produced within the sub-pc scale broad line region (BLR) or farther out in the pc-scale molecular torus (MT) environment. If the GeV emission takes place within the BLR, the inverse Compton (IC) scattering of the BLR ultraviolet (UV) seed photons that produces the gamma-rays takes place at the onset of the Klein-Nishina regime. This causes the electron cooling time to become practically energy independent and the variation of the gamma-ray emission to be almost achromatic. If on the other hand the -ray emission is produced farther out in the pc-scale MT, the IC scattering of the infrared (IR) MT seed photons that produces the gamma-rays takes place in the Thomson regime, resulting to energy-dependent electron cooling times, manifested as faster cooling times for higher Fermi energies. We demonstrate these characteristics and discuss the applicability and limitations of our method.
Explosives detection using photoneutrons produced by X-rays

NASA Astrophysics Data System (ADS)

Yang, Yigang; Li, Yuanjing; Wang, Haidong; Li, Tiezhu; Wu, Bin

2007-08-01

The detection of explosives has become a critical issue after recent terrorist attacks. This paper describes research on explosives detection using photoneutrons from a photoneutron convertor that consists of 20 kg heavy water in an aluminum container whose shape was optimized to most effectively convert X-rays to photoneutrons. The X-rays were produced by a 9 MeV electron accelerator with an average electron current of 100 μA, resulted in a photoneutron yield of >10 11 n/s. Monte-Carlo simulations show that the radiation field is composed of X-ray pulses, fast neutron pulses and thermal neutrons. Both the X-ray and fast neutron pulses are 5 μs wide with a 300 Hz repetition frequency. The thermal neutron flux, which is higher than 10 4 n/cm 2/s, is essentially time invariant. A time shielding circuit was developed for the spectrometry system to halt the sampling process during the intense X-ray pulses. Paraffin, boron carbide and lead were used to protect the detector from interference from the X-rays, fast neutrons, thermal neutrons and background γ-rays coming from the system materials induced by photoneutrons. 5″×5″ NaI (Tl) scintillators were chosen as the detectors to detect the photoneutrons induced γ-rays from the inspected explosive simulant. Nitrogen (6.01 cps) 10.828 MeV γ-rays were detected with one detector from a 50 kg carbamide block placed 60 cm in front of the detector. A collimator was used to reduce the number of background 10.828 MeV γ-rays coming from the nitrogen in the air to improve the signal to background ratio from 0.136 to 1.81. A detector array of seven 5″×5″ NaI (Tl) detectors was used to measure the 2-D distributions of N and H in the sample. The combination of photoneutron analysis and X-ray imaging shows promise for enhancing explosives detection capabilities.
Bulk Comptonization: new hints from the luminous blazar 4C+25.05

NASA Astrophysics Data System (ADS)

Kammoun, E. S.; Nardini, E.; Risaliti, G.; Ghisellini, G.; Behar, E.; Celotti, A.

2018-01-01

Blazars are often characterized by a spectral break at soft X-rays, whose origin is still debated. While most sources show a flattening, some exhibit a blackbody-like soft excess with temperatures of the order of ∼0.1 keV, similar to low-luminosity, non-jetted Seyferts. Here, we present the analysis of the simultaneous XMM-Newton and NuSTAR observations of the luminous flat-spectrum radio quasar 4C+25.05 (z = 2.368). The observed 0.3-30 keV spectrum is best described by the sum of a hard X-ray power law (Γ = 1.38_{-0.03}^{+0.05}) and a soft component, approximated by a blackbody with kT_BB = 0.66_{-0.04}^{+0.05} keV (rest frame). If the spectrum of 4C+25.05 is interpreted in the context of bulk Comptonization by cold electrons of broad-line region photons emitted in the direction of the jet, such an unusual temperature implies a bulk Lorentz factor of the jet of Γbulk ∼ 11.7. Bulk Comptonization is expected to be ubiquitous on physical grounds, yet no clear signature of it has been found so far, possibly due to its transient nature and the lack of high-quality, broad-band X-ray spectra.
VizieR Online Data Catalog: Fermi blazars with Doppler factors (Fan+, 2017)

NASA Astrophysics Data System (ADS)

Fan, J. H.; Yang, J. H.; Xiao, H. B.; Lin, C.; Constantin, D.; Luo, G. Y.; Pei, Z. Y.; Hao, J. M.; Mao, Y. W.

2017-09-01

Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the timescale of their radio flares. In this Letter, we use multiwavelength data and Doppler factors reported in the literature for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distributions and investigate the correlations among observed and intrinsic data. Quite interestingly, intrinsic data show a positive correlation between luminosity and peak frequency, in contrast with the behavior of observed data, and a tighter correlation between γ-ray luminosity and the lower-energy ones. For flaring blazars detected by Fermi, we conclude that (1) observed emissions are strongly beamed; (2) the anti-correlation between luminosity and peak frequency from the observed data is an apparent result, the correlation between intrinsic data being positive; and (3) intrinsic γ-ray luminosity is strongly correlated with other intrinsic luminosities. (2 data files).
On the modulation of X ray fluxes in thunderstorms

NASA Technical Reports Server (NTRS)

Mccarthy, Michael P.; Parks, George K.

1992-01-01

The production of X-ray fluxes in thunderstorms has been attributed to bremsstrahlung. Assuming this, another question arises. How can a thunderstorm modulate the number density of electrons which are sufficiently energetic to produce X-rays? As a partial answer to this question, the effects of typical thunderstorm electric fields on a background population of energetic electrons, such as produced by cosmic ray secondaries and their decays or the decay of airborne radionuclides, are considered. The observed variation of X-ray flux is shown to be accounted for by a simple model involving typical electric field strengths. A necessary background electron number density is found from the model and is determined to be more than 2 orders of magnitude higher than that available from radon decay and a factor of 8 higher than that available from cosmic ray secondaries. The ionization enhancement due to energetic electrons and X-rays is discussed.

TOPICAL REVIEW: Human soft tissue analysis using x-ray or gamma-ray techniques

NASA Astrophysics Data System (ADS)

Theodorakou, C.; Farquharson, M. J.

2008-06-01

This topical review is intended to describe the x-ray techniques used for human soft tissue analysis. X-ray techniques have been applied to human soft tissue characterization and interesting results have been presented over the last few decades. The motivation behind such studies is to provide improved patient outcome by using the data obtained to better understand a disease process and improve diagnosis. An overview of theoretical background as well as a complete set of references is presented. For each study, a brief summary of the methodology and results is given. The x-ray techniques include x-ray diffraction, x-ray fluorescence, Compton scattering, Compton to coherent scattering ratio and attenuation measurements. The soft tissues that have been classified using x-rays or gamma rays include brain, breast, colon, fat, kidney, liver, lung, muscle, prostate, skin, thyroid and uterus.
X-ray metal film filters at cryogenic temperatures

NASA Technical Reports Server (NTRS)

Keski-Kuha, Ritva A. M.

1989-01-01

Thin aluminum foil filters have been evaluated at cryogenic temperatures. The results of the test program, including cold cycling and vibration testing, indicate that these filters are fully successful at cryogenic temperatures and can provide the high X-ray transmittance and high background rejection required for the blocking filters which are being developed for the X-Ray Spectrometer, one of the focal plane instruments on the Advanced X-Ray Astrophysics Facility.
How gravitational lensing helps γ-ray photons avoid γ – γ absorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnacka, Anna; Böttcher, Markus; Sushch, Iurii, E-mail: abarnacka@cfa.harvard.edu, E-mail: Markus.Bottcher@nwu.ac.za

2014-08-01

We investigate potential γ – γ absorption of γ-ray emission from blazars arising from inhomogeneities along the line of sight, beyond the diffuse Extragalactic Background Light (EBL). As plausible sources of excess γ – γ opacity, we consider (1) foreground galaxies, including cases in which this configuration leads to strong gravitational lensing, (2) individual stars within these foreground galaxies, and (3) individual stars within our own galaxy, which may act as lenses for microlensing events. We found that intervening galaxies close to the line of sight are unlikely to lead to significant excess γ – γ absorption. This opens upmore » the prospect of detecting lensed gamma-ray blazars at energies above 10 GeV with their gamma-ray spectra effectively only affected by the EBL. The most luminous stars located either in intervening galaxies or in our galaxy provide an environment in which these gamma-rays could, in principle, be significantly absorbed. However, despite a large microlensing probability due to stars located in intervening galaxies, γ-rays avoid absorption by being deflected by the gravitational potentials of such intervening stars to projected distances ({sup i}mpact parameters{sup )} where the resulting γ – γ opacities are negligible. Thus, neither of the intervening excess photon fields considered here, provide a substantial source of excess γ – γ opacity beyond the EBL, even in the case of very close alignments between the background blazar and a foreground star or galaxy.« less
Yet another NIR flare of the Blazar BZBJ1454+5124

NASA Astrophysics Data System (ADS)

Carrasco, L.; Porras, A.; Recillas, E.; Escobedo, G.; Chavushyan, V.

2018-05-01

We call attention on our recent observation of the Gamma Ray source 3FGLJ1454.5+5124 related with the quasar SBS1452+516 (z=1.0831) On March 28th,2018,(JD24582015.0015), we found this blazar to be in a new outburst.
Sounding-rocket experiment to study the diffuse soft X-ray background using a Si(Li) detector

NASA Technical Reports Server (NTRS)

Delvaille, J. P.

1981-01-01

Soft X-ray background in the energy range 0.4 to 10 keV was studied. A payload was developed which uses a wide angle, windowless, cooled, Si(Li) semiconductor detector system. With a resolution of less than 150 eV between 0.3 and 2.0 keV, the system is sensitive to an emission equivalent width of about 10 eV. Carbon and oxygen line emission were detected from the vicinity of the North Galactic Pole and the North Polar Spur.
THE OUTBURST OF THE BLAZAR S5 0716+71 IN 2011 OCTOBER: SHOCK IN A HELICAL JET

DOE Office of Scientific and Technical Information (OSTI.GOV)

Larionov, V. M.; Jorstad, S. G.; Morozova, D. A.

We present the results of optical (R band) photometric and polarimetric monitoring and Very Long Baseline Array (VLBA) imaging of the blazar S5 0716+714 along with Fermi {gamma}-ray data during a multi-waveband outburst in 2011 October. We analyze total and polarized intensity images of the blazar obtained with the VLBA at 43 GHz during and after the outburst. Monotonic rotation of the linear polarization vector at a rate of {approx}> 50 Degree-Sign per night coincided with a sharp maximum in {gamma}-ray and optical flux. At the same time, within the uncertainties, a new superluminal knot appeared with an apparent speedmore » of 21 {+-} 2c. The general multi-frequency behavior of the outburst can be explained within the framework of a shock wave propagating along a helical path in the blazar's jet.« less
SBS 0846+513: a new γ-ray-emitting narrow-line Seyfert 1 galaxy

DOE PAGES

D'Ammando, F.; Orienti, M.; Finke, J.; ...

2012-10-11

In this paper, we report Fermi Large Area Telescope (LAT) observations of the radio-loud active galactic nucleus SBS 0846+513 (z = 0.5835), optically classified as a narrow-line Seyfert 1 galaxy, together with new and archival radio-to-X-ray data. The source was not active at γ-ray energies during the first two years of Fermi operation. A significant increase in activity was observed during 2010 October–2011 August. In particular, a strong γ-ray flare was observed in 2011 June reaching an isotropic γ-ray luminosity (0.1–300 GeV) of 1.0 × 10 48 erg s -1, comparable to that of the brightest flat spectrum radio quasars,more » and showing spectral evolution in γ rays. An apparent superluminal velocity of (8.2 ± 1.5)c in the jet was inferred from 2011 to 2012 Very Long Baseline Array (VLBA) images, suggesting the presence of a highly relativistic jet. Finally, both the power released by this object during the flaring activity and the apparent superluminal velocity are strong indications of the presence of a relativistic jet as powerful as those of blazars. In addition, variability and spectral properties in radio and γ-ray bands indicate blazar-like behaviour, suggesting that, except for some distinct optical characteristics, SBS 0846+513 could be considered as a young blazar at the low end of the blazar's black hole mass distribution.« less
Observed Limits on Charge Exchange Contributions to the Diffuse X-Ray Background

NASA Astrophysics Data System (ADS)

Crowder, S. G.; Barger, K. A.; Brandl, D. E.; Eckart, M. E.; Galeazzi, M.; Kelley, R. L.; Kilbourne, C. A.; McCammon, D.; Pfendner, C. G.; Porter, F. S.; Rocks, L.; Szymkowiak, A. E.; Teplin, I. M.

2012-10-01

We present a high-resolution spectrum of the diffuse X-ray background from 0.1 to 1 keV for a ~1 sr region of the sky centered at l = 90°, b = +60° using a 36 pixel array of microcalorimeters flown on a sounding rocket. With an energy resolution of 11 eV FWHM below 1 keV, the spectrum's observed line ratios help separate charge exchange contributions originating within the heliosphere from thermal emission of hot gas in the interstellar medium. The X-ray sensitivity below 1 keV was reduced by about a factor of four from contamination that occurred early in the flight, limiting the significance of the results. The observed centroid of helium-like O VII is 568+2 - 3 eV at 90% confidence. Since the centroid expected for thermal emission is 568.4 eV and for charge exchange is 564.2 eV, thermal emission appears to dominate for this line complex. The dominance of thermal emission is consistent with much of the high-latitude O VII emission originating in 2-3 × 106 K gas in the Galactic halo. On the other hand, the observed ratio of C VI Lyγ to Lyα is 0.3 ± 0.2. The expected ratios are 0.04 for thermal emission and 0.24 for charge exchange, indicating that charge exchange must contribute strongly to this line and therefore potentially to the rest of the ROSAT R12 band usually associated with 106 K emission from the Local Hot Bubble. The limited statistics of this experiment and systematic uncertainties due to the contamination require only >32% thermal emission for O VII and >20% from charge exchange for C VI at the 90% confidence level. An experimental gold coating on the silicon substrate of the array greatly reduced extraneous signals induced on nearby pixels from cosmic rays passing through the substrate, reducing the triggered event rate by a factor of 15 from a previous flight of the instrument.
Optics Developments for X-Ray Astronomy

NASA Technical Reports Server (NTRS)

Ramsey, Brian

2014-01-01

X-ray optics has revolutionized x-ray astronomy. The degree of background suppression that these afford, have led to a tremendous increase in sensitivity. The current Chandra observatory has the same collecting area (approx. 10(exp 3)sq cm) as the non-imaging UHURU observatory, the first x-ray observatory which launched in 1970, but has 5 orders of magnitude more sensitivity due to its focusing optics. In addition, its 0.5 arcsec angular resolution has revealed a wealth of structure in many cosmic x-ray sources. The Chandra observatory achieved its resolution by using relatively thick pieces of Zerodur glass, which were meticulously figured and polished to form the four-shell nested array. The resulting optical assembly weighed around 1600 kg, and cost approximately $0.5B. The challenge for future x-ray astronomy missions is to greatly increase the collecting area (by one or more orders of magnitude) while maintaining high angular resolution, and all within realistic mass and budget constraints. A review of the current status of US optics for x-ray astronomy will be provided along with the challenges for future developments.
FPGA-Based X-Ray Detection and Measurement for an X-Ray Polarimeter

NASA Technical Reports Server (NTRS)

Gregory, Kyle; Hill, Joanne; Black, Kevin; Baumgartner, Wayne

2013-01-01

This technology enables detection and measurement of x-rays in an x-ray polarimeter using a field-programmable gate array (FPGA). The technology was developed for the Gravitational and Extreme Magnetism Small Explorer (GEMS) mission. It performs precision energy and timing measurements, as well as rejection of non-x-ray events. It enables the GEMS polarimeter to detect precisely when an event has taken place so that additional measurements can be made. The technology also enables this function to be performed in an FPGA using limited resources so that mass and power can be minimized while reliability for a space application is maximized and precise real-time operation is achieved. This design requires a low-noise, charge-sensitive preamplifier; a highspeed analog to digital converter (ADC); and an x-ray detector with a cathode terminal. It functions by computing a sum of differences for time-samples whose difference exceeds a programmable threshold. A state machine advances through states as a programmable number of consecutive samples exceeds or fails to exceed this threshold. The pulse height is recorded as the accumulated sum. The track length is also measured based on the time from the start to the end of accumulation. For track lengths longer than a certain length, the algorithm estimates the barycenter of charge deposit by comparing the accumulator value at the midpoint to the final accumulator value. The design also employs a number of techniques for rejecting background events. This innovation enables the function to be performed in space where it can operate autonomously with a rapid response time. This implementation combines advantages of computing system-based approaches with those of pure analog approaches. The result is an implementation that is highly reliable, performs in real-time, rejects background events, and consumes minimal power.
History of Chandra X-Ray Observatory

NASA Image and Video Library

2004-08-12

NASA’s Chandra X-Ray Observatory (CXO) was launched July 22, 1999 aboard the Space Shuttle Columbia, STS-93 mission. This image was produced by combining a dozen CXO observations made of a 130 light-year region in the center of the Milky Way over the last 5 years. The colors represent low (red), medium (green) and high (blue) energy x-rays. Thanks to Chandra's unique resolving power, astronomers have now been able to identify thousands of point-like x-ray sources due to neutron stars, black holes, white dwarfs, foreground stars, and background galaxies. What remains is a diffuse x-ray glow extending from the upper left to the lower right, along the direction of the disk of the galaxy. NASA’s Marshall Space Flight Center in Huntsville, Alabama manages the Chandra program. (NASA/CXC/UCLA/M. Muno et al.)
Chandra Resolves Cosmic X-ray Glow and Finds Mysterious New Sources

NASA Astrophysics Data System (ADS)

2000-01-01

While taking a giant leap towards solving one of the greatest mysteries of X-ray astronomy, NASA's Chandra X-ray Observatory also may have revealed the most distant objects ever seen in the universe and discovered two puzzling new types of cosmic objects. Not bad for being on the job only five months. Chandra has resolved most of the X-ray background, a pervasive glow of X-rays throughout the universe, first discovered in the early days of space exploration. Before now, scientists have not been able to discern the background's origin, because no X-ray telescope until Chandra has had both the angular resolution and sensitivity to resolve it. "This is a major discovery," said Dr. Alan Bunner, Director of NASA's Structure andEvolution of the universe science theme. "Since it was first observed thirty-seven years ago, understanding the source of the X-ray background has been aHoly Grail of X-ray astronomy. Now, it is within reach." The results of the observation will be discussed today at the 195th national meeting of the American Astronomical Society in Atlanta, Georgia. An article describing this work has been submitted to the journal Nature by Dr. Richard Mushotzky, of NASA Goddard Space Flight Center, Greenbelt, Md., Drs. Lennox Cowie and Amy Barger at the University of Hawaii, Honolulu, and Dr. Keith Arnaud of the University of Maryland, College Park. "We are all very excited by this finding," said Mushotzky. "The resolution of most of the hard X-ray background during the first few months of the Chandra mission is a tribute to the power of this observatory and bodes extremely well for its scientific future," Scientists have known about the X-ray glow, called the X-ray background, since the dawn of X-ray astronomy in the early 1960s. They have been unable to discern its origin, however, for no X-ray telescope until Chandra has had both the angular resolution and sensitivity to resolve it. The German-led ROSAT mission, now completed, resolved much of the lower
X-ray Weak Broad-line Qquasars: Absorption or Intrinsic X-ray Weakness

NASA Technical Reports Server (NTRS)

Mushotzky, Richard (Technical Monitor); Risaliti, Guida

2005-01-01

XMM observations of X-ray weak quasars have been performed during 2003 and 2004. The data for all the observations have become available in 2004 (there has been a delay of several months on the initial schedule, due to high background flares which contaminated the observations: as a consequence, most of them had to be rescheduled). We have reduced and analyzed all the data, and obtained interesting scientific results. Out of the eight sources, 4 are confirmed to be extremely X-ray weak, in agreement with the results of previous Chandra observations. 3 sources are confined to be highly variable both in flux (by factor 20-50) and in spectral properties (dramatic changes in spectral index). For both these groups of objects we are completing a publication: 1) For the X-ray weak sources, a paper is submitted with a complete analysis of the X-ray spectra both from Chandra and XMM-Newton, and a comparison with optical and near-IR photometry obtained from all-sky surveys. Possible models for the unusual spectral energy distribution of these sources are also presented. 2) For the variable sources, a paper is being finalized where the X-ray spectra obtained with XMM-Newton are compared with previous X-ray observations and with observations at other wavelengths. It is shown that these sources are high luminosity and extreme cases of the highly variable class of narrow-line Seyfert Is. In order to further understand the nature of these X-ray weak quasars, we submitted proposals for spectroscopy at optical and infrared telescopes. We obtained time at the TNG 4 meter telescope for near-IR observations and at the Hobby-Eberly Telescope for optical high-resolution spectroscopy. These observations have been performed in early 2004. They will complement the XMM data and will lead to understanding of whether the X-ray weakness of these sources is an intrinsic property or is due to absorption by circum-nuclear material. The infrared spectra of the variable sources have been already
X-ray Obscured AGN in the GOODS-N

NASA Astrophysics Data System (ADS)

Georgantopoulos, I.; Akylas, A.; Rovilos, E.; Xilouris, E.

2010-07-01

We explore the X-ray properties of the Dust Obscured Galaxies (DOGs) i.e. sources with f24μ / fR > 1000. This population has been proposed to contain a significant fraction of Compton-thick sources at high redshift. In particular we study the X-ray spectra of the 14 DOGS detected in the CDFN 2Ms exposure. Their stacked spectrum is flat with Γ=1±0.1 very similar to the stacked spectrum of the undetected DOGs (Γ=0.8±0.2). However, most of our X-ray detected DOGs present only moderate absorption with column densities 1022 < NH < 1024 cm-2. Only three sources (20%) present very flat spectra and are probably associated with reflection dominated Compton-thick sources. Our finding is rather at odds with papers which claim that the vast majority of DOGs are associated with Compton-thick sources. In any case, such sources at high redshift (z > 2) present limited interest for the X-ray background: the population synthesis models predict a contribution, for the z > 2 Compton-thick AGN, to the X-ray background flux at 30 keV, of less than 1 percent.
Blazar Astronomy above 50 GeV

NASA Astrophysics Data System (ADS)

Smith, D. A.

This contribution is dedicated to the memory of Chaman L. Bhat, an atmospheric Cherenkov pioneer and a leader of the Indian gamma-ray community, who died in a road accident on Mt. Abu on December 17, just after the workshop. While few blazars have been detected beyond EGRET energies, these extreme cases may be the ones that 'make or break' some models describing blazars in particular, and therefore AGNs in general. This paper first reviews the status of the various atmospheric Cherenkov gamma-ray telescopes. We then describe the most recent results from these instruments, paying particular attention to the recent detection of 1ES 1426+428 by the Whipple, CAT, and HEGRA imagers. We illustrate the dilemma of target selection using the example of W Com. We then discuss the consequences of the first measurements of Mrk 421 below 100 GeV by the solar heliostat arrays CELESTE and STACEE. This first foray into the energy range linking EGRET with the current imagers requires us to start using functional forms for the spectral energy distributions that are more physical than the simple power laws (or parabolas) used up to now to describe the imager or satellite results. We can hope that HESS, followed by MAGIC and VERITAS, as well as CELESTE and STACEE, will make this a recurring problem in 2002 and 2003.
A Strong X-ray Flare in TeV-detected blazar 1ES 1959+650

NASA Astrophysics Data System (ADS)

Kapanadze, Bidzina

2017-06-01

Since 2015 August, the nearby TeV-detected HBL source 1ES 1959+650 (z=0.048) is in a phase of enhanced X-ray activity compared to the previous years (Kapanadze et al. 2016, MNRAS, 461, L26; ATel #8014, #8289, #8342, #8468, #9121, #9205, #9694, #9949, #10430 and http://www.swift.psu.edu/monitoring/source.php?source=1ES1959+650 for the historical 0.3-10 keV light curve).
Variance analysis of x-ray CT sinograms in the presence of electronic noise background.

PubMed

Ma, Jianhua; Liang, Zhengrong; Fan, Yi; Liu, Yan; Huang, Jing; Chen, Wufan; Lu, Hongbing

2012-07-01

Low-dose x-ray computed tomography (CT) is clinically desired. Accurate noise modeling is a fundamental issue for low-dose CT image reconstruction via statistics-based sinogram restoration or statistical iterative image reconstruction. In this paper, the authors analyzed the statistical moments of low-dose CT data in the presence of electronic noise background. The authors first studied the statistical moment properties of detected signals in CT transmission domain, where the noise of detected signals is considered as quanta fluctuation upon electronic noise background. Then the authors derived, via the Taylor expansion, a new formula for the mean-variance relationship of the detected signals in CT sinogram domain, wherein the image formation becomes a linear operation between the sinogram data and the unknown image, rather than a nonlinear operation in the CT transmission domain. To get insight into the derived new formula by experiments, an anthropomorphic torso phantom was scanned repeatedly by a commercial CT scanner at five different mAs levels from 100 down to 17. The results demonstrated that the electronic noise background is significant when low-mAs (or low-dose) scan is performed. The influence of the electronic noise background should be considered in low-dose CT imaging.
Variance analysis of x-ray CT sinograms in the presence of electronic noise background

PubMed Central

Ma, Jianhua; Liang, Zhengrong; Fan, Yi; Liu, Yan; Huang, Jing; Chen, Wufan; Lu, Hongbing

2012-01-01

Purpose: Low-dose x-ray computed tomography (CT) is clinically desired. Accurate noise modeling is a fundamental issue for low-dose CT image reconstruction via statistics-based sinogram restoration or statistical iterative image reconstruction. In this paper, the authors analyzed the statistical moments of low-dose CT data in the presence of electronic noise background. Methods: The authors first studied the statistical moment properties of detected signals in CT transmission domain, where the noise of detected signals is considered as quanta fluctuation upon electronic noise background. Then the authors derived, via the Taylor expansion, a new formula for the mean–variance relationship of the detected signals in CT sinogram domain, wherein the image formation becomes a linear operation between the sinogram data and the unknown image, rather than a nonlinear operation in the CT transmission domain. To get insight into the derived new formula by experiments, an anthropomorphic torso phantom was scanned repeatedly by a commercial CT scanner at five different mAs levels from 100 down to 17. Results: The results demonstrated that the electronic noise background is significant when low-mAs (or low-dose) scan is performed. Conclusions: The influence of the electronic noise background should be considered in low-dose CT imaging. PMID:22830738
Background and imaging simulations for the hard X-ray camera of the MIRAX mission

NASA Astrophysics Data System (ADS)

Castro, M.; Braga, J.; Penacchioni, A.; D'Amico, F.; Sacahui, R.

2016-07-01

We report the results of detailed Monte Carlo simulations of the performance expected both at balloon altitudes and at the probable satellite orbit of a hard X-ray coded-aperture camera being developed for the Monitor e Imageador de RAios X (MIRAX) mission. Based on a thorough mass model of the instrument and detailed specifications of the spectra and angular dependence of the various relevant radiation fields at both the stratospheric and orbital environments, we have used the well-known package GEANT4 to simulate the instrumental background of the camera. We also show simulated images of source fields to be observed and calculated the detailed sensitivity of the instrument in both situations. The results reported here are especially important to researchers in this field considering that we provide important information, not easily found in the literature, on how to prepare input files and calculate crucial instrumental parameters to perform GEANT4 simulations for high-energy astrophysics space experiments.
Active Galactic Nuclei, Quasars, BL Lac Objects and X-Ray Background

NASA Technical Reports Server (NTRS)

Mushotzky, Richard (Technical Monitor); Elvis, Martin

2005-01-01

The XMM COSMOS survey is producing the large surface density of X-ray sources anticipated. The first batch of approx. 200 sources is being studied in relation to the large scale structure derived from deep optical/near-IR imaging from Subaru and CFHT. The photometric redshifts from the opt/IR imaging program allow a first look at structure vs. redshift, identifying high z clusters. A consortium of SAO, U. Arizona and the Carnegie Institute of Washington (Pasadena) has started a large program using the 6.5meter Magellan telescopes in Chile with the prime objective of identifying the XMM X-ray sources in the COSMOS field. The first series of observing runs using the new IMACS multi-slit spectrograph on Magellan will take place in January and February of 2005. Some 300 spectra per field will be taken, including 70%-80% of the XMM sources in each field. The four first fields cover the center of the COSMOS field. A VLT consortium is set to obtain bulk redshifts of the field galaxies. The added accuracy of the spectroscopic redshifts over the photo-z's will allow much lower density structures to be seen, voids and filaments. The association of X-ray selected AGNs, and quasars with these filaments, is a major motivation for our studies. Comparison to the deep VLA radio data now becoming available is about to begin.

A graphite crystal polarimeter for stellar X-ray astronomy.

NASA Technical Reports Server (NTRS)

Weisskopf, M. C.; Berthelsdorf, R.; Epstein, G.; Linke, R.; Mitchell, D.; Novick, R.; Wolff, R. S.

1972-01-01

The first crystal X-ray polarimeter to be used for X-ray astronomy is described. Polarization is measured by modulation of the X rays diffracted at an average 45 deg glancing angle from large, curved graphite crystal panels as these rotate about an axis parallel to the incident X-ray flux. Arrangement of the crystal panels, the design of the detector, and the signal-processing circuitry were optimized to minimize systematic effects produced by off-axis pointing of the rocket and cosmic ray induced events. The in-flight performance of the instrument in relation to the observed background signal is discussed.
Magnetization of AGN jets as imposed by leptonic models of luminous blazars

NASA Astrophysics Data System (ADS)

Janiak, Mateusz; Sikora, Marek; Moderski, Rafal

2015-03-01

Recent measurements of frequency-dependent shift of radio-core locations indicate that the ratio of the magnetic to kinetic energy flux (the σ parameter) is of the order of unity. These results are consistent with predictions of magnetically-arrested-disk (MAD) models of a jet formation, but contradict the predictions of leptonic models of γ-ray production in luminous blazars. We demonstrate this discrepancy by computing the γ-ray-to-synchrotron luminosity ratio (the q parameter) as a function of a distance from the black hole for different values of σ and using both spherical and planar models for broad-line region and dusty torus. We find that it is impossible to reproduce observed q >> 1 for jets with σ >= 1. This may indicate that blazar radiation is produced in reconnection layers or in spines of magnetically stratified jets.
VizieR Online Data Catalog: Jet kinematics of blazars at 43GHz with the VLBA (Jorstad+, 2017)

NASA Astrophysics Data System (ADS)

Jorstad, S. G.; Marscher, A. P.; Morozova, D. A.; Troitsky, I. S.; Agudo, I.; Casadio, C.; Foord, A.; Gomez, J. L.; MacDonald, N. R.; Molina, S. N.; Lahteenmaki, A.; Tammi, J.; Tornikoski, M.

2018-04-01

The VLBA-BU-BLAZAR monitoring program consists of approximately monthly observations with the VLBA at 43GHz of a sample of AGNs detected as γ-ray sources. In this paper, we present the results of observations from 2007 June to 2013 January. The sample consists of 21 FSRQs, 12 BLLacs, and 3 radio galaxies (RGs). It includes the blazars and radio galaxies detected at γ-ray energies by EGRET with average flux density at 43GHz exceeding 0.5Jy, declination north of -30°, and optical magnitude in the R band brighter than 18.5. (5 data files).
Modeling of proton-induced radioactivation background in hard X-ray telescopes: Geant4-based simulation and its demonstration by Hitomi's measurement in a low Earth orbit

NASA Astrophysics Data System (ADS)

Odaka, Hirokazu; Asai, Makoto; Hagino, Kouichi; Koi, Tatsumi; Madejski, Greg; Mizuno, Tsunefumi; Ohno, Masanori; Saito, Shinya; Sato, Tamotsu; Wright, Dennis H.; Enoto, Teruaki; Fukazawa, Yasushi; Hayashi, Katsuhiro; Kataoka, Jun; Katsuta, Junichiro; Kawaharada, Madoka; Kobayashi, Shogo B.; Kokubun, Motohide; Laurent, Philippe; Lebrun, Francois; Limousin, Olivier; Maier, Daniel; Makishima, Kazuo; Mimura, Taketo; Miyake, Katsuma; Mori, Kunishiro; Murakami, Hiroaki; Nakamori, Takeshi; Nakano, Toshio; Nakazawa, Kazuhiro; Noda, Hirofumi; Ohta, Masayuki; Ozaki, Masanobu; Sato, Goro; Sato, Rie; Tajima, Hiroyasu; Takahashi, Hiromitsu; Takahashi, Tadayuki; Takeda, Shin'ichiro; Tanaka, Takaaki; Tanaka, Yasuyuki; Terada, Yukikatsu; Uchiyama, Hideki; Uchiyama, Yasunobu; Watanabe, Shin; Yamaoka, Kazutaka; Yasuda, Tetsuya; Yatsu, Yoichi; Yuasa, Takayuki; Zoglauer, Andreas

2018-05-01

Hard X-ray astronomical observatories in orbit suffer from a significant amount of background due to radioactivation induced by cosmic-ray protons and/or geomagnetically trapped protons. Within the framework of a full Monte Carlo simulation, we present modeling of in-orbit instrumental background which is dominated by radioactivation. To reduce the computation time required by straightforward simulations of delayed emissions from activated isotopes, we insert a semi-analytical calculation that converts production probabilities of radioactive isotopes by interaction of the primary protons into decay rates at measurement time of all secondary isotopes. Therefore, our simulation method is separated into three steps: (1) simulation of isotope production, (2) semi-analytical conversion to decay rates, and (3) simulation of decays of the isotopes at measurement time. This method is verified by a simple setup that has a CdTe semiconductor detector, and shows a 100-fold improvement in efficiency over the straightforward simulation. To demonstrate its experimental performance, the simulation framework was tested against data measured with a CdTe sensor in the Hard X-ray Imager onboard the Hitomi X-ray Astronomy Satellite, which was put into a low Earth orbit with an altitude of 570 km and an inclination of 31°, and thus experienced a large amount of irradiation from geomagnetically trapped protons during its passages through the South Atlantic Anomaly. The simulation is able to treat full histories of the proton irradiation and multiple measurement windows. The simulation results agree very well with the measured data, showing that the measured background is well described by the combination of proton-induced radioactivation of the CdTe detector itself and thick Bi4Ge3O12 scintillator shields, leakage of cosmic X-ray background and albedo gamma-ray radiation, and emissions from naturally contaminated isotopes in the detector system.
X-Ray Weak Broad-Line Quasars: Absorption or Intrinsic X-Ray Weakness

NASA Technical Reports Server (NTRS)

Risaliti, Guido; Mushotzky, Richard F. (Technical Monitor)

2004-01-01

XMM observations of X-ray weak quasars have been performed during 2003. The data for all but the last observation are now available (there has been a delay of several months on the initial schedule, due to high background flares which contaminated the observations: as a consequence, most of them had to be rescheduled). We have reduced and analyzed these data, and obtained interesting preliminary scientific results. Out of the eight sources, 4 are confirmed to be extrimely X-ray weak, in agreement with the results of previous Chandra observations. 3 sources are confirmed to be highly variable both in flux (by factors 20-50) and in spectral properties (dramatic changes in spectral index). For both these groups of objects, an article is in preparation. Preliminary results have been presented at an international workshop on AGN surveys in December 2003, in Cozumel (Mexico). In order to further understand the nature of these X-ray weak quasars, we submitted proposals for spectroscopy at optical and infrared telescopes. We obtained time at the TNG 4 meter telescope for near-IR observations, and at the Hobby-Eberly Telescope for optical high-resolution spectroscopy. These observations will be performed in early 2004, and will complement the XMM data, in order to understand whether the X-ray weakness of these sources is an intrinsic property or is due to absorption by circumnuclear material.
Stacking Searches for Greater Than 100 MeV Gamma Ray Emission from Radio Galaxies and Seyfert Galaxies

NASA Technical Reports Server (NTRS)

Cillis, A. N.; Hartman, R. C.; Bertsch, D. L.

2003-01-01

The EGRET telescope on CGRO detected more than sixty sources of high-energy gamma radiation associated with active galactic nuclei (AGN). All but one of those belong to the blazar subclass; the only exception is the nearby radio galaxy Centaurus A. Since there is no obvious reason other than proximity to expect Cen A to be the only non-blazar AGN emitting in high-energy gamma rays, we have utilized the "stacking" technique to search for $>100$-MeV emission from two non-blazar AGN subclasses, radio galaxies and Seyfert galaxies. Maps of gamma-ray counts, exposure, and diffuse background have been created, then co-added in varying numbers based on sorts by redshift, 5-GHZ flux density, and optical brightness, and finally tested for gamma-ray emission. No detection significance greater than $2\\sigma$ has been found for any subclass, sorting parameter, or number of objects co-added. Monte Carlo simulations have also been performed, to validate the technique and estimate the significance of the results.
CubeX: The CubeSAT X-ray Telescope for Elemental Abundance Mapping of Airless Bodies and X-ray Pulsar Navigation

NASA Astrophysics Data System (ADS)

Nittler, L. R.; Hong, J.; Kenter, A.; Romaine, S.; Allen, B.; Kraft, R.; Masterson, R.; Elvis, M.; Gendreau, K.; Crawford, I.; Binzel, R.; Boynton, W. V.; Grindlay, J.; Ramsey, B.

2017-12-01

The surface elemental composition of a planetary body provides crucial information about its origin, geological evolution, and surface processing, all of which can in turn provide information about solar system evolution as a whole. Remote sensing X-ray fluorescence (XRF) spectroscopy has been used successfully to probe the major-element compositions of airless bodies in the inner solar system, including the Moon, near-Earth asteroids, and Mercury. The CubeSAT X-ray Telescope (CubeX) is a concept for a 6U planetary X-ray telescope (36U with S/C), which utilizes Miniature Wolter-I X-ray optics (MiXO), monolithic CMOS and SDD X-ray sensors for the focal plane, and a Solar X-ray Monitor (heritage from the REXIS XRF instrument on NASA's OSIRIS-REx mission). CubeX will map the surface elemental composition of diverse airless bodies by spectral measurement of XRF excited by solar X-rays. The lightweight ( 1 kg) MiXO optics provide sub-arcminute resolution with low background, while the inherently rad-hard CMOS detectors provide improved spectral resolution ( 150 eV) at 0 °C. CubeX will also demonstrate X-ray pulsar timing based deep space navigation (XNAV). Successful XNAV will enable autonomous deep navigation with little to no support from the Deep Space Network, hence lowering the operation cost for many more planetary missions. Recently selected by NASA Planetary Science Deep Space SmallSat Studies, the first CubeX concept, designed to rideshare to the Moon as a secondary spacecraft on a primary mission, is under study in collaboration with the Mission Design Center at NASA Ames Research Center. From high altitude ( 6,000 km) frozen polar circular orbits, CubeX will study > 8 regions ( 110 km) of geological interest on the Moon over one year to produce a high resolution ( 2-3 km) elemental abundance map of each region. The novel focal plane design of CubeX also allows us to evaluate the performance of absolute navigation by sequential observations of several
Swift detections of the flaring blazar GAIA 18ayp (PKS 2333-415) in X-rays and the UV

NASA Astrophysics Data System (ADS)

Grupe, Dirk; Komossa, S.; Angioni, R.; Schartel, N.

2018-04-01

We report Swift observations of the z=1.41 QSO GAIA 18ayp (PKS 2333-415) which was detected by GAIA in an optically flaring state on 2018-April-14. Swift observed GAIA 18ayp on 2018 April 23 for a total of 1.4 ks. The QSO is clearly detected in X-rays and the UV. The X-ray position found using the enhanced XRT position (Goad et al. 2007, Evans et al. 2009) is RA-2000 = 23 36 34.1, Dec-2000 = -41 15 21.4 with an uncertainty of 3.0".
The SWIFT Gamma-Ray Burst X-Ray Telescope

NASA Technical Reports Server (NTRS)

Hill, J. E.; Burrows, D. N.; Nousek, J. A.; Wells, A.; Chincarini, G.; Abbey, A. F.; Angelini, L.; Beardmore, A.; Brauninger, H. W.; Chang, W.

2006-01-01

The Swift Gamma-Ray Burst Explorer is designed to make prompt multi-wavelength observations of Gamma-Ray Bursts and GRB afterglows. The X-ray Telescope enables Swift to determine GRB positions with a few arcseconds accuracy within 100 seconds of the burst onset. The XRT utilizes a mirror set built for JET-X and an XMM-Newton/ EPIC MOS CCD detector to provide a sensitive broad-band (0.2-10 keV) X-ray imager with an effective area of more than 120 sq cm at 1.5 keV, a field of view of 23.6 x 23.6 arcminutes, and an angular resolution of 18 arcseconds (HPD). The detection sensitivity is 2x10(exp 14) erg/sq cm/s in 10(exp 4) seconds. The instrument provides automated source detection and position reporting within 5 seconds of target acquisition. It can also measure the redshifts of GRBs with Iron line emission or other spectral features. The XRT operates in an auto-exposure mode, adjusting the CCD readout mode automatically to optimize the science return as the source intensity fades. The XRT measures spectra and lightcurves of the GRB afterglow beginning about a minute after the burst and follows each burst for days or weeks. We provide an overview of the X-ray Telescope scientific background from which the systems engineering requirements were derived, with specific emphasis on the design and qualification aspects from conception through to launch. We describe the impact on cleanliness and vacuum requirements for the instrument low energy response and to maintain the high sensitivity to the fading signal of the Gamma-ray Bursts.
Systematic and Performance Tests of the Hard X-ray Polarimeter X-Calibur

NASA Astrophysics Data System (ADS)

Endsley, Ryan; Beilicke, Matthias; Kislat, Fabian; Krawczynski, Henric; X-Calibur/InFOCuS

2015-01-01

X-ray polarimetry has great potential to reveal new astrophysical information about the emission processes of high energy sources such as black hole environments, X-ray binary systems, and active galactic nuclei. Here we present the results and conclusions of systematic and performance measurements of the hard X-ray polarimeter, X-Calibur. Designed to be flown on a balloon-borne X-ray telescope, X-Calibur will achieve unprecedented sensitivity and makes use of the fact that polarized X-rays preferentially Compton-scatter perpendicular to their E-field vector. Extensive laboratory measurements taken at Washington University and the Cornell High-Energy Synchrotron Source (CHESS) indicate that X-Calibur combines a detection efficiency on the order of unity with a high modulation factor of µ ≈ 0.5 averaged over the whole detector assembly, and with values up to µ ≈ 0.7 for select subsections of the polarimeter. Additionally, we are able to suppress background flux by more than two orders of magnitude by utilizing an active shield and scintillator coincidence. Comparing laboratory data with Monte Carlo simulations of both polarized and unpolarized hard X-ray beams illustrate that we have an exceptional understanding of the detector response.
PKS 0537-441 - A gravitationally lensed blazar?

NASA Astrophysics Data System (ADS)

Stickel, M.; Fried, J. W.; Kuehr, H.

1988-11-01

Deep direct optical imaging data and spectroscopic observations of the southern blazar PKS 0537-441 (z = 0.894) and a neighboring galaxy are reported. The blazar has an extended, spatially resolved appearance. Image decomposition reveals a foreground disk galaxy seen nearly face-on which lies along the line of sight to the blazar. This foreground galaxy is mainly responsible for the extended image of PKS 0537-441, and its morphology is similar to that of a neighboring disk galaxy 11 arcsec to the east and slightly south of the blazar with a redshift of z = 0.186. Both objects presumably form a close pair at the same redshift. It is argued that the observed properties of the blazar are influenced by gravitational lensing in the foreground galaxy.
A magnetic diverter for charged particle background rejection in the SIMBOL-X telescope

NASA Astrophysics Data System (ADS)

Spiga, D.; Fioretti, V.; Bulgarelli, A.; Dell'Orto, E.; Foschini, L.; Malaguti, G.; Pareschi, G.; Tagliaferri, G.; Tiengo, A.

2008-07-01

Minimization of charged particle background in X-ray telescopes is a well known issue. Charged particles (chiefly protons and electrons) naturally present in the cosmic environment constitute an important background source when they collide with the X-ray detector. Even worse, a serious degradation of spectroscopic performances of the X-ray detector was observed in Chandra and Newton-XMM, caused by soft protons with kinetic energies ranging between 100 keV and some MeV being collected by the grazing-incidence mirrors and funneled to the detector. For a focusing telescope like SIMBOL-X, the exposure of the soft X-ray detector to the proton flux can increase significantly the instrumental background, with a consequent loss of sensitivity. In the worst case, it can also seriously compromise the detector duration. A well-known countermeasure that can be adopted is the implementation of a properly-designed magnetic diverter, that should prevent high-energy particles from reaching the focal plane instruments of SIMBOL-X. Although Newton-XMM and Swift-XRT are equipped with magnetic diverters for electrons, the magnetic fields used are insufficient to effectively act on protons. In this paper, we simulate the behavior of a magnetic diverter for SIMBOL-X, consisting of commercially-available permanent magnets. The effects of SIMBOL-X optics is simulated through GEANT4 libraries, whereas the effect of the intense required magnetic fields is simulated along with specifically-written numerical codes in IDL.
The Cosmological Impact of Luminous TeV Blazars. II. Rewriting the Thermal History of the Intergalactic Medium

NASA Astrophysics Data System (ADS)

Chang, Philip; Broderick, Avery E.; Pfrommer, Christoph

2012-06-01

The universe is opaque to extragalactic very high energy gamma rays (VHEGRs, E > 100 GeV) because they annihilate and pair produce on the extragalactic background light. The resulting ultrarelativistic pairs are commonly assumed to lose energy primarily through inverse Compton scattering of cosmic microwave background (CMB) photons, reprocessing the original emission from TeV to GeV energies. In Broderick et al., we argued that this is not the case; powerful plasma instabilities driven by the highly anisotropic nature of the ultrarelativistic pair distribution provide a plausible way to dissipate the kinetic energy of the TeV-generated pairs locally, heating the intergalactic medium (IGM). Here, we explore the effect of this heating on the thermal history of the IGM. We collate the observed extragalactic VHEGR sources to determine a local VHEGR heating rate. Given the pointed nature of VHEGR observations, we estimate the correction for the various selection effects using Fermi observations of high- and intermediate-peaked BL Lac objects. As the extragalactic component of the local VHEGR flux is dominated by TeV blazars, we then estimate the evolution of the TeV blazar luminosity density by tying it to the well-observed quasar luminosity density and producing a VHEGR heating rate as a function of redshift. This heating is relatively homogeneous for z <~ 4, but there is greater spatial variation at higher redshift (order unity at z ~ 6) because of the reduced number of blazars that contribute to local heating. We show that this new heating process dominates photoheating in the low-redshift evolution of the IGM and calculate the effect of this heating in a one-zone model. As a consequence, the inclusion of TeV blazar heating qualitatively and quantitatively changes the structure and history of the IGM. Due to the homogeneous nature of the extragalactic background light, TeV blazars produce a uniform volumetric heating rate. This heating is sufficient to increase the
Cryogenic x-ray diffraction microscopy utilizing high-pressure cryopreservation

NASA Astrophysics Data System (ADS)

Lima, Enju; Chushkin, Yuriy; van der Linden, Peter; Kim, Chae Un; Zontone, Federico; Carpentier, Philippe; Gruner, Sol M.; Pernot, Petra

2014-10-01

We present cryo x-ray diffraction microscopy of high-pressure-cryofixed bacteria and report high-convergence imaging with multiple image reconstructions. Hydrated D. radiodurans cells were cryofixed at 200 MPa pressure into ˜10-μm-thick water layers and their unstained, hydrated cellular environments were imaged by phasing diffraction patterns, reaching sub-30-nm resolutions with hard x-rays. Comparisons were made with conventional ambient-pressure-cryofixed samples, with respect to both coherent small-angle x-ray scattering and the image reconstruction. The results show a correlation between the level of background ice signal and phasing convergence, suggesting that phasing difficulties with frozen-hydrated specimens may be caused by high-background ice scattering.
Improving x-ray fluorescence signal for benchtop polychromatic cone-beam x-ray fluorescence computed tomography by incident x-ray spectrum optimization: A Monte Carlo study

PubMed Central

Manohar, Nivedh; Jones, Bernard L.; Cho, Sang Hyun

2014-01-01

Purpose: To develop an accurate and comprehensive Monte Carlo (MC) model of an experimental benchtop polychromatic cone-beam x-ray fluorescence computed tomography (XFCT) setup and apply this MC model to optimize incident x-ray spectrum for improving production/detection of x-ray fluorescence photons from gold nanoparticles (GNPs). Methods: A detailed MC model, based on an experimental XFCT system, was created using the Monte Carlo N-Particle (MCNP) transport code. The model was validated by comparing MC results including x-ray fluorescence (XRF) and scatter photon spectra with measured data obtained under identical conditions using 105 kVp cone-beam x-rays filtered by either 1 mm of lead (Pb) or 0.9 mm of tin (Sn). After validation, the model was used to investigate the effects of additional filtration of the incident beam with Pb and Sn. Supplementary incident x-ray spectra, representing heavier filtration (Pb: 2 and 3 mm; Sn: 1, 2, and 3 mm) were computationally generated and used with the model to obtain XRF/scatter spectra. Quasimonochromatic incident x-ray spectra (81, 85, 90, 95, and 100 keV with 10 keV full width at half maximum) were also investigated to determine the ideal energy for distinguishing gold XRF signal from the scatter background. Fluorescence signal-to-dose ratio (FSDR) and fluorescence-normalized scan time (FNST) were used as metrics to assess results. Results: Calculated XRF/scatter spectra for 1-mm Pb and 0.9-mm Sn filters matched (r ≥ 0.996) experimental measurements. Calculated spectra representing additional filtration for both filter materials showed that the spectral hardening improved the FSDR at the expense of requiring a much longer FNST. In general, using Sn instead of Pb, at a given filter thickness, allowed an increase of up to 20% in FSDR, more prominent gold XRF peaks, and up to an order of magnitude decrease in FNST. Simulations using quasimonochromatic spectra suggested that increasing source x-ray energy, in the
Improving x-ray fluorescence signal for benchtop polychromatic cone-beam x-ray fluorescence computed tomography by incident x-ray spectrum optimization: a Monte Carlo study.

PubMed

Manohar, Nivedh; Jones, Bernard L; Cho, Sang Hyun

2014-10-01

To develop an accurate and comprehensive Monte Carlo (MC) model of an experimental benchtop polychromatic cone-beam x-ray fluorescence computed tomography (XFCT) setup and apply this MC model to optimize incident x-ray spectrum for improving production/detection of x-ray fluorescence photons from gold nanoparticles (GNPs). A detailed MC model, based on an experimental XFCT system, was created using the Monte Carlo N-Particle (MCNP) transport code. The model was validated by comparing MC results including x-ray fluorescence (XRF) and scatter photon spectra with measured data obtained under identical conditions using 105 kVp cone-beam x-rays filtered by either 1 mm of lead (Pb) or 0.9 mm of tin (Sn). After validation, the model was used to investigate the effects of additional filtration of the incident beam with Pb and Sn. Supplementary incident x-ray spectra, representing heavier filtration (Pb: 2 and 3 mm; Sn: 1, 2, and 3 mm) were computationally generated and used with the model to obtain XRF/scatter spectra. Quasimonochromatic incident x-ray spectra (81, 85, 90, 95, and 100 keV with 10 keV full width at half maximum) were also investigated to determine the ideal energy for distinguishing gold XRF signal from the scatter background. Fluorescence signal-to-dose ratio (FSDR) and fluorescence-normalized scan time (FNST) were used as metrics to assess results. Calculated XRF/scatter spectra for 1-mm Pb and 0.9-mm Sn filters matched (r ≥ 0.996) experimental measurements. Calculated spectra representing additional filtration for both filter materials showed that the spectral hardening improved the FSDR at the expense of requiring a much longer FNST. In general, using Sn instead of Pb, at a given filter thickness, allowed an increase of up to 20% in FSDR, more prominent gold XRF peaks, and up to an order of magnitude decrease in FNST. Simulations using quasimonochromatic spectra suggested that increasing source x-ray energy, in the investigated range of 81-100 ke
The Hard X-ray Imager (HXI) for the ASTRO-H Mission

NASA Astrophysics Data System (ADS)

Sato, Goro; Kokubun, Motohide; Nakazawa, Kazuhiro; Enoto, Teruaki; Fukazawa, Yasushi; Harayama, Atsushi; Hayashi, Katsuhiro; Kataoka, Jun; Katsuta, Junichiro; Kawaharada, Madoka; Laurent, Philippe; Lebrun, François; Limousin, Olivier; Makishima, Kazuo; Mizuno, Tsunefumi; Mori, Kunishiro; Nakamori, Takeshi; Noda, Hirofumi; Odaka, Hirokazu; Ohno, Masanori; Ohta, Masayuki; Saito, Shinya; Sato, Rie; Tajima, Hiroyasu; Takahashi, Hiromitsu; Takahashi, Tadayuki; Takeda, Shinichiro; Terada, Yukikatsu; Uchiyama, Hideki; Uchiyama, Yasunobu; Watanabe, Shin; Yamaoka, Kazutaka; Yatsu, Yoichi; Yuasa, Takayuki

2014-07-01

The 6th Japanese X-ray satellite, ASTRO-H, is scheduled for launch in 2015. The hard X-ray focusing imaging system will observe astronomical objects with the sensitivity for detecting point sources with a brightness of 1/100,000 times fainter than the Crab nebula at > 10 keV. The Hard X-ray Imager (HXI) is a focal plane detector 12 m below the hard X-ray telescope (HXT) covering the energy range from 5 to 80 keV. The HXI is composed of a stacked Si/CdTe semiconductor detector module and surrounding BGO scintillators. The latter work as active shields for efficient reduction of background events caused by cosmic-ray particles, cosmic X-ray background, and in-orbit radiation activation. In this paper, we describe the detector system, and present current status of flight model development, and performance of HXI using an engineering model of HXI.
Infrared-faint radio sources: a cosmological view. AGN number counts, the cosmic X-ray background and SMBH formation

NASA Astrophysics Data System (ADS)

Zinn, P.-C.; Middelberg, E.; Ibar, E.

2011-07-01

Context. Infrared-faint radio sources (IFRS) are extragalactic emitters clearly detected at radio wavelengths but barely detected or undetected at optical and infrared wavelengths, with 5σ sensitivities as low as 1 μJy. Aims: Spectral energy distribution (hereafter SED) modelling and analyses of their radio properties indicate that IFRS are consistent with a population of (potentially extremely obscured) high-redshift AGN at 3 ≤ z ≤ 6. We demonstrate some astrophysical implications of this population and compare them to predictions from models of galaxy evolution and structure formation. Methods: We compiled a list of IFRS from four deep extragalactic surveys and extrapolated the IFRS number density to a survey-independent value of (30.8 ± 15.0) deg-2. We computed the IFRS contribution to the total number of AGN in the Universe to account for the cosmic X-ray background. By estimating the black hole mass contained in IFRS, we present conclusions for the SMBH mass density in the early universe and compare it to relevant simulations of structure formation after the Big Bang. Results: The number density of AGN derived from the IFRS density was found to be ~310 deg-2, which is equivalent to a SMBH mass density of the order of 103 M⊙ Mpc-3 in the redshift range 3 ≤ z ≤ 6. This produces an X-ray flux of 9 × 10-16 W m-2 deg-2 in the 0.5-2.0 keV band and 3 × 10-15 W m-2 deg-2 in the 2.0-10 keV band, in agreement with the missing unresolved components of the Cosmic X-ray Background. To address SMBH formation after the Big Bang we invoke a scenario involving both halo gas accretion and major mergers.
X-Rays

MedlinePlus

X-rays are a type of radiation called electromagnetic waves. X-ray imaging creates pictures of the inside of ... different amounts of radiation. Calcium in bones absorbs x-rays the most, so bones look white. Fat ...
Search for the Identification of 3EG J1835+5918: Evidence for a New Type of High-Energy Gamma-Ray Source?

NASA Technical Reports Server (NTRS)

Mirabal, N.; Halpern, Jules P.; Eracleous, M.; Becker, R. H.; Oliversen, Ronald (Technical Monitor)

2001-01-01

Most of the EGRET high-energy gamma-ray sources remain unidentified. It is highly likely that many of these are fainter blazars or pulsars, but there may also be new types of sources to be discovered. We have focussed our search for novel gamma-ray sources on 3EG 1835+5918, which is the brightest and most accurately positioned of the unidentified EGRET sources at high Galactic latitude (l, b = 89 deg, 25 deg). In this talk, we will summarize the results of X-ray, radio, and optical surveys of this location. In particular, we have made complete optical identifications of all of the ROSAT and ASCA sources in this region to a flux limit of approximately 1 x 10(exp -13) ergs/sq cm s. All of the X-ray sources within the EGRET error circle are radio-quiet quasars or coronally emitting stars. Previous radio pulsar searches have been unsuccessful. We set an upper limit of 3.8 mJy (at 1.4 GHz) on any possible radio counterpart to 3EG 1835+5918. We also find several quasars and white dwarfs using optical color selection, and we have monitored the entire field for variable optical objects on short and long time scales. Since no blazar-like or pulsar-like candidate has been found as a result of these searches, we assert that 3EG 1835+5918 must be lacking in one or more of the physically essential attributes of those classes of gamma-ray emitters. In particular, its radio flux is at least two orders of magnitude fainter than any of the securely identified EGRET blazars, and its soft X-ray flux is at least 30 times fainter than that of Geminga and other EGRET pulsars. If it is an AGN it lacks the beamed radio emission of blazars. If it is an isolated neutron star, it lacks both the thermal X-rays from a cooling surface and the magnetospheric non-thermal X-ray emission that is characteristic of all EGRET pulsars. As such, it is more problematic physically than Geminga, which is an ordinary pulsar that only lacks radio emission. As a pulsar, 3EG 1835+5918 would have to be either

Fermi Large Area Telescope detection of gravitational lens delayed γ-ray flares from Blazar B0218+357

DOE PAGES

Cheung, C. C.; Larsson, S.; Scargle, J. D.; ...

2014-01-30

We report the first clear γ-ray measurement of a delay between flares from the gravitationally lensed images of a blazar, using data from the Fermi Large Area Telescope (LAT). We detected a delay in B0218+357, a known double-image lensed system, during a period of enhanced γ-ray activity with peak fluxes consistently observed to reach >20-50 × its previous average flux. An auto-correlation function analysis identified a delay in the γ-ray data of 11.46 ± 0.16 days (1σ) that is ~1 day greater than previous radio measurements. Considering that it is beyond the capabilities of the LAT to spatially resolve themore » two images, we nevertheless decomposed individual sequences of superposing γ-ray flares/delayed emissions. In three such ~8-10 day-long sequences within a ~4 month span, considering confusion due to overlapping flaring emission and flux measurement uncertainties, we found flux ratios consistent with ~1, thus systematically smaller than those from radio observations. During the first, best-defined flare, the delayed emission was detailed with a Fermi pointing, and we observed flux doubling timescales of ~3-6 hr implying as well extremely compact γ-ray emitting regions.« less
Resolving the Extragalactic γ-Ray Background above 50 GeV with the Fermi Large Area Telescope.

PubMed

Ackermann, M; Ajello, M; Albert, A; Atwood, W B; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Bechtol, K; Bellazzini, R; Bissaldi, E; Blandford, R D; Bloom, E D; Bonino, R; Bregeon, J; Britto, R J; Bruel, P; Buehler, R; Caliandro, G A; Cameron, R A; Caragiulo, M; Caraveo, P A; Cavazzuti, E; Cecchi, C; Charles, E; Chekhtman, A; Chiang, J; Chiaro, G; Ciprini, S; Cohen-Tanugi, J; Cominsky, L R; Costanza, F; Cutini, S; D'Ammando, F; de Angelis, A; de Palma, F; Desiante, R; Digel, S W; Di Mauro, M; Di Venere, L; Domínguez, A; Drell, P S; Favuzzi, C; Fegan, S J; Ferrara, E C; Franckowiak, A; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Giglietto, N; Giommi, P; Giordano, F; Giroletti, M; Godfrey, G; Green, D; Grenier, I A; Guiriec, S; Hays, E; Horan, D; Iafrate, G; Jogler, T; Jóhannesson, G; Kuss, M; La Mura, G; Larsson, S; Latronico, L; Li, J; Li, L; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Magill, J; Maldera, S; Manfreda, A; Mayer, M; Mazziotta, M N; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Negro, M; Nuss, E; Ohsugi, T; Okada, C; Omodei, N; Orlando, E; Ormes, J F; Paneque, D; Perkins, J S; Pesce-Rollins, M; Petrosian, V; Piron, F; Pivato, G; Porter, T A; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Reposeur, T; Romani, R W; Sánchez-Conde, M; Schmid, J; Schulz, A; Sgrò, C; Simone, D; Siskind, E J; Spada, F; Spandre, G; Spinelli, P; Suson, D J; Takahashi, H; Thayer, J B; Tibaldo, L; Torres, D F; Troja, E; Vianello, G; Yassine, M; Zimmer, S

2016-04-15

The Fermi Large Area Telescope (LAT) Collaboration has recently released a catalog of 360 sources detected above 50 GeV (2FHL). This catalog was obtained using 80 months of data re-processed with Pass 8, the newest event-level analysis, which significantly improves the acceptance and angular resolution of the instrument. Most of the 2FHL sources at high Galactic latitude are blazars. Using detailed Monte Carlo simulations, we measure, for the first time, the source count distribution, dN/dS, of extragalactic γ-ray sources at E>50 GeV and find that it is compatible with a Euclidean distribution down to the lowest measured source flux in the 2FHL (∼8×10^{-12} ph cm^{-2} s^{-1}). We employ a one-point photon fluctuation analysis to constrain the behavior of dN/dS below the source detection threshold. Overall, the source count distribution is constrained over three decades in flux and found compatible with a broken power law with a break flux, S_{b}, in the range [8×10^{-12},1.5×10^{-11}] ph cm^{-2} s^{-1} and power-law indices below and above the break of α_{2}∈[1.60,1.75] and α_{1}=2.49±0.12, respectively. Integration of dN/dS shows that point sources account for at least 86_{-14}^{+16}% of the total extragalactic γ-ray background. The simple form of the derived source count distribution is consistent with a single population (i.e., blazars) dominating the source counts to the minimum flux explored by this analysis. We estimate the density of sources detectable in blind surveys that will be performed in the coming years by the Cherenkov Telescope Array.
Multi-Epoch Multiwavelength Spectra and Models for Blazar 3C 279

NASA Technical Reports Server (NTRS)

Hartman, R. C.; Boettcher, M.; Aldering, G.; Aller, H.; Aller, M.; Backman, D. E.; Balonek, T. J.; Bertsch, D. L.; Bloom, S. D.; Bock, H.;

2001-01-01

Of the blazars detected by EGRET in GeV gamma-rays, 3C 279 is not only the best-observed by EGRET, but also one of the best-monitored at lower frequencies. We have assembled eleven spectra, from GHz radio through GeV gamma-rays, from the time intervals of EGRET observations. Although some of the data have appeared in previous publications, most are new, including data taken during the high states in early 1999 and early 2000. All of the spectra show substantial gamma-ray contribution to the total luminosity of the object; in a high state, the gamma-ray luminosity dominates over that at all other frequencies by a factor of more than 10. There is no clear pattern of time correlation; different bands do not always rise and fall together, even in the optical, X-ray, and gamma-ray bands. The spectra are modeled using a leptonic jet, with combined synchrotron self-Compton + external Compton gamma-ray production. Spectral variability of 3C 279 is consistent with variations of the bulk Lorentz factor of the jet, accompanied by changes in the spectral shape of the electron distribution. Our modeling results are consistent with the UV spectrum of 3C 279 being dominated by accretion disk radiation during times of low gamma-ray intensity.

Distributions of Gamma-Ray Bursts and Blazars in the L p-E p-Plane and Possible Implications for their Radiation Physics

NASA Astrophysics Data System (ADS)

Lyu, Fen; Liang, En-Wei; Liang, Yun-Feng; Wu, Xue-Feng; Zhang, Jin; Sun, Xiao-Na; Lu, Rui-Jing; Zhang, Bing

2014-09-01

We present a spectral analysis for a sample of redshift-known gamma-ray bursts (GRBs) observed with Fermi/GBM. Together with the results derived from our systematical spectral energy distribution modeling with the leptonic models for a Fermi/LAT blazar sample, we compare the distributions of the GRBs and the blazars by plotting the synchrotron peak luminosity (L s) and the corresponding peak photon energy E s of blazars in the L p-E p-plane of GRBs, where L p and E p are the peak luminosity and peak photon energy of the GRB time-integrated νf ν spectrum, respectively. The GRBs are in the high-L p, high-E p corner of the plane and a tight L p-E p relation is found, i.e., L_p\\propto E_p2.13^{+0.54-0.46}. Both flat spectrum radio quasars (FSRQs) and low-synchrotron peaking BL Lac objects (LBLs) are clustered in the low-E p, low-L p corner. Intermediate- and high-synchrotron peaking BL Lac objects (IBLs and HBLs) have E s ~ 2 × 10-3-102 keV and L s ~ 1044-1047 erg s-1, but no dependence of L s on E s is found. We show that the tight Lp -Ep relation of GRBs is potentially explained with the synchrotron radiation of fast-cooling electrons in a highly magnetized ejecta, and the weak anti-correlation of L s-E s for FSRQs and LBLs may be attributed to synchrotron radiation of slow-cooling electrons in a moderately magnetized ejecta. The distributions of IBLs and HBLs in the L p-E p-plane may be interpreted with synchrotron radiation of fast-cooling electrons in a matter-dominated ejecta. These results may present a unified picture for the radiation physics of relativistic jets in GRBs and blazars within the framework of the leptonic synchrotron radiation models.
Local ISM 3D Distribution and Soft X-ray Background Inferences for Nearby Hot Gas

NASA Technical Reports Server (NTRS)

Puspitarini, L.; Lallement, R.; Snowden, Steven L.; Vergely, J.-L.; Snowden, S.

2014-01-01

Three-dimensional (3D) interstellar medium (ISM) maps can be used to locate not only interstellar (IS) clouds, but also IS bubbles between the clouds that are blown by stellar winds and supernovae, and are filled by hot gas. To demonstrate this, and to derive a clearer picture of the local ISM, we compare our recent 3D IS dust distribution maps to the ROSAT diffuse Xray background maps after removal of heliospheric emission. In the Galactic plane, there is a good correspondence between the locations and extents of the mapped nearby cavities and the soft (0.25 keV) background emission distribution, showing that most of these nearby cavities contribute to this soft X-ray emission. Assuming a constant dust to gas ratio and homogeneous 106 K hot gas filling the cavities, we modeled in a simple way the 0.25 keV surface brightness along the Galactic plane as seen from the Sun, taking into account the absorption by the mapped clouds. The data-model comparison favors the existence of hot gas in the solar neighborhood, the so-called Local Bubble (LB). The inferred mean pressure in the local cavities is found to be approx.9,400/cu cm K, in agreement with previous studies, providing a validation test for the method. On the other hand, the model overestimates the emission from the huge cavities located in the third quadrant. Using CaII absorption data, we show that the dust to CaII ratio is very small in those regions, implying the presence of a large quantity of lower temperature (non-X-ray emitting) ionized gas and as a consequence a reduction of the volume filled by hot gas, explaining at least part of the discrepancy. In the meridian plane, the two main brightness enhancements coincide well with the LB's most elongated parts and chimneys connecting the LB to the halo, but no particular nearby cavity is found towards the enhancement in the direction of the bright North Polar Spur (NPS) at high latitude. We searched in the 3D maps for the source regions of the higher energy
A peculiar multiwavelength flare in the blazar 3C 454.3

DOE PAGES

Gupta, Alok C.; Mangalam, Arun; Wiita, Paul J.; ...

2017-08-14

The blazar 3C 454.3 exhibited a strong flare seen in γ-rays, X-rays and optical/near-infrared bands during 2009 December 3–12. Emission in the V and J bands rose more gradually than did the γ-rays and soft X-rays, though all peaked at nearly the same time. Optical polarization measurements showed dramatic changes during the flare, with a strong anticorrelation between optical flux and degree of polarization (which rose from ~3 to ~20 percent) during the declining phase of the flare. The flare was accompanied by large rapid swings in polarization angle of ~170°. This combination of behaviours appears to be unique. Wemore » have cm-band radio data during the same period but they show no correlation with variations at higher frequencies. Such peculiar behaviour may be explained using jet models incorporating fully relativistic effects with a dominant source region moving along a helical path or by a shock-in-jet model incorporating three-dimensional radiation transfer if there is a dominant helical magnetic field. We find that spectral energy distributions at different times during the flare can be fit using modified one-zone models where only the magnetic field strength and particle break frequencies and normalizations need change. An optical spectrum taken at nearly the same time provides an estimate for the central black hole mass of ~2.3 × 10 9 M ⊙. Furthermore, we also consider two weaker flares seen during the ~200 d span over which multiband data are available. In one of them, the V and J bands appear to lead the γ-ray and X-ray bands by a few days; in the other, all variations are simultaneous.« less
Multiwavelength observations of the gamma-ray blazar PKS 0528+134 in quiescence

DOE PAGES

Palma, N. I.; Böttcher, M.; de la Calle, I.; ...

2011-06-16

Here, we present multiwavelength observations of the ultraluminous blazar-type radio loud quasar PKS 0528+134 in quiescence during the period July to December 2009. Four Target-of-Opportunity (ToO) observations with the XMM-Newton Satellite in the 0.2 – 10 keV range were supplemented with optical observations.
THE CONTRIBUTION OF FERMI -2LAC BLAZARS TO DIFFUSE TEV–PEV NEUTRINO FLUX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aartsen, M. G.; Abraham, K.; Ackermann, M.

2017-01-20

The recent discovery of a diffuse cosmic neutrino flux extending up to PeV energies raises the question of which astrophysical sources generate this signal. Blazars are one class of extragalactic sources which may produce such high-energy neutrinos. We present a likelihood analysis searching for cumulative neutrino emission from blazars in the 2nd Fermi -LAT AGN catalog (2LAC) using IceCube neutrino data set 2009-12, which was optimized for the detection of individual sources. In contrast to those in previous searches with IceCube, the populations investigated contain up to hundreds of sources, the largest one being the entire blazar sample in themore » 2LAC catalog. No significant excess is observed, and upper limits for the cumulative flux from these populations are obtained. These constrain the maximum contribution of 2LAC blazars to the observed astrophysical neutrino flux to 27% or less between around 10 TeV and 2 PeV, assuming the equipartition of flavors on Earth and a single power-law spectrum with a spectral index of −2.5. We can still exclude the fact that 2LAC blazars (and their subpopulations) emit more than 50% of the observed neutrinos up to a spectral index as hard as −2.2 in the same energy range. Our result takes into account the fact that the neutrino source count distribution is unknown, and it does not assume strict proportionality of the neutrino flux to the measured 2LAC γ -ray signal for each source. Additionally, we constrain recent models for neutrino emission by blazars.« less
Extragalactic gamma-ray background from AGN winds and star-forming galaxies in cosmological galaxy-formation models

NASA Astrophysics Data System (ADS)

Lamastra, A.; Menci, N.; Fiore, F.; Antonelli, L. A.; Colafrancesco, S.; Guetta, D.; Stamerra, A.

2017-10-01

We derive the contribution to the extragalactic gamma-ray background (EGB) from active galactic nuclei (AGN) winds and star-forming galaxies by including a physical model for the γ-ray emission produced by relativistic protons accelerated by AGN-driven and supernova-driven shocks into a state-of-the-art semi-analytic model of galaxy formation. This is based on galaxy interactions as triggers of AGN accretion and starburst activity and on expanding blast waves as the mechanism to communicate outwards the energy injected into the interstellar medium by the active nucleus. We compare the model predictions with the latest measurement of the EGB spectrum performed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) in the range between 100 MeV and 820 GeV. We find that AGN winds can provide 35 ± 15% of the observed EGB in the energy interval Eγ = 0.1-1 GeV, for 73 ± 15% at Eγ = 1-10 GeV, and for 60 ± 20% at Eγ ≳10 GeV. The AGN wind contribution to the EGB is predicted to be larger by a factor of 3-5 than that provided by star-forming galaxies (quiescent plus starburst) in the hierarchical clustering scenario. The cumulative γ-ray emission from AGN winds and blazars can account for the amplitude and spectral shape of the EGB, assuming the standard acceleration theory, and AGN wind parameters that agree with observations. We also compare the model prediction for the cumulative neutrino background from AGN winds with the most recent IceCube data. We find that for AGN winds with accelerated proton spectral index p = 2.2-2.3, and taking into account internal absorption of γ-rays, the Fermi-LAT and IceCube data could be reproduced simultaneously.
The NuSTAR Extragalactic Surveys: The Number Counts Of Active Galactic Nuclei And The Resolved Fraction Of The Cosmic X-ray Background

NASA Technical Reports Server (NTRS)

Harrison, F. A.; Aird, J.; Civano, F.; Lansbury, G.; Mullaney, J. R.; Ballentyne, D. R.; Alexander, D. M.; Stern, D.; Ajello, M.; Barret, D.;

2016-01-01

We present the 3-8 kiloelectronvolts and 8-24 kiloelectronvolts number counts of active galactic nuclei (AGNs) identified in the Nuclear Spectroscopic Telescope Array (NuSTAR) extragalactic surveys. NuSTAR has now resolved 33 percent -39 percent of the X-ray background in the 8-24 kiloelectronvolts band, directly identifying AGNs with obscuring columns up to approximately 10 (exp 25) per square centimeter. In the softer 3-8 kiloelectronvolts band the number counts are in general agreement with those measured by XMM-Newton and Chandra over the flux range 5 times 10 (exp -15) less than or approximately equal to S (3-8 kiloelectronvolts) divided by ergs per second per square centimeter less than or approximately equal to 10 (exp -12) probed by NuSTAR. In the hard 8-24 kiloelectronvolts band NuSTAR probes fluxes over the range 2 times 10 (exp -14) less than or approximately equal to S (8-24 kiloelectronvolts) divided by ergs per second per square centimeter less than or approximately equal to 10 (exp -12), a factor approximately 100 times fainter than previous measurements. The 8-24 kiloelectronvolts number counts match predictions from AGN population synthesis models, directly confirming the existence of a population of obscured and/or hard X-ray sources inferred from the shape of the integrated cosmic X-ray background. The measured NuSTAR counts lie significantly above simple extrapolation with a Euclidian slope to low flux of the Swift/BAT15-55 kiloelectronvolts number counts measured at higher fluxes (S (15-55 kiloelectronvolts) less than or approximately equal to 10 (exp -11) ergs per second per square centimeter), reflecting the evolution of the AGN population between the Swift/BAT local (redshift is less than 0.1) sample and NuSTAR's redshift approximately equal to 1 sample. CXB (Cosmic X-ray Background) synthesis models, which account for AGN evolution, lie above the Swift/BAT measurements, suggesting that they do not fully capture the evolution of obscured

X-ray absorption spectroscopy to determine originating depth of electrons that form an inelastic background of Auger electron spectrum

NASA Astrophysics Data System (ADS)

Isomura, Noritake; Cui, Yi-Tao; Murai, Takaaki; Oji, Hiroshi; Kimoto, Yasuji

2017-07-01

In Auger electron spectroscopy (AES), the spectral background is mainly due to inelastic scattering of Auger electrons that lose their kinetic energy in a sample bulk. To investigate the spectral components within this background for SiO2(19.3 nm)/Si(100) with known layer thickness, X-ray absorption spectroscopy (XAS) was used in the partial-electron-yield (PEY) mode at several electron kinetic energies to probe the background of the Si KLL Auger peak. The Si K-edge PEY-XAS spectra constituted of both Si and SiO2 components at each kinetic energy, and their component fractions were approximately the same as those derived from the simulated AES background for the same sample structure. The contributions of Auger electrons originating from layers at different depths to the inelastic background could thus be identified experimentally.
Search for GeV and X-Ray Flares Associated with the IceCube Track-like Neutrinos

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, Fang-Kun; Wang, Xiang-Yu, E-mail: xywang@nju.edu.cn

Dozens of high-energy neutrinos have been detected by the IceCube neutrino telescope, but no clear association with any classes of astrophysical sources has been identified so far. Recently, Kadler et al. reported that a PeV cascade-like neutrino event occurred in positional and temporal coincidence with a giant gamma-ray flare of the blazar PKS B1424-418. Since IceCube track-like events have much better angular resolution, we here search for possible short-term gamma-ray flares that are associated with the IceCube track-like events with Fermi Large Area Telescope (LAT) observations. Among them, three track-like neutrino events occur within the field of view of Fermimore » -LAT at the time of the detection, so searching for the prompt gamma-ray emission associated with neutrinos is possible. Assuming a point source origin and a single power-law spectrum for the possible gamma-ray sources associated with neutrinos, a likelihood analysis of 0.2–100 GeV photons observed by Fermi -LAT on the timescales of ∼12 hr and one year are performed, and for the three special neutrinos, the analyses are also performed on the timescales of thousands of seconds before and after the neutrino detection. No significant GeV excesses over the background are found and upper limit fluxes at the 95% confidence level are obtained for different timescales. We also search for possible the Swift hard X-ray transient sources associated with the IceCube track-like neutrino events, but the search also yields null results. We discuss the implication of the non-detection of gamma-ray flares for the constraints on the neutrino source density.« less
Properties of Blazar Jets Defined by an Economy of Power

NASA Astrophysics Data System (ADS)

Petropoulou, Maria; Dermer, Charles D.

2016-07-01

The absolute power of a relativistic black hole jet includes the power in the magnetic field, the leptons, the hadrons, and the radiated photons. A power analysis of a relativistic radio/γ-ray blazar jet leads to bifurcated leptonic synchrotron-Compton (LSC) and leptohadronic synchrotron (LHS) solutions that minimize the total jet power. Higher Doppler factors with increasing peak synchrotron frequency are implied in the LSC model. Strong magnetic fields {B}\\prime ≳ 100 {{G}} are found for the LHS model with variability times ≲ {10}3 {{s}}, in accord with highly magnetized, reconnection-driven jet models. Proton synchrotron models of ≳ 100 {GeV} blazar radiation can have sub-Eddington absolute jet powers, but models of dominant GeV radiation in flat spectrum radio quasars require excessive power.
Recent enhancement of the R-band optical flux from the active blazar S5 0716+714

NASA Astrophysics Data System (ADS)

Marchini, Alessandro; Bellizzi, Lorenzo; Bonnoli, Giacomo; Millucci, Vincenzo; Stiaccini, Leonardo; Trefoloni, Bartolomeo

2018-06-01

We report that the blazar S5 0716+714 (RA: 7 21 53.45 Dec: 71 20 36.36 J2000.0) reached last night (May 31.83) the optical magnitude R=12.16(0.01). The blazar is bright in optical since a few months (see ATel #11107,#11339) and we are monitoring it from the Astronomical Observatory of the University of Siena since the unprecedented flare in VHE gamma rays reported by the MAGIC Collaboration in December 2017 (ATel #11100).
Extended adiabatic blast waves and a model of the soft X-ray background. [interstellar matter

NASA Technical Reports Server (NTRS)

Cox, D. P.; Anderson, P. R.

1981-01-01

An analytical approximation is generated which follows the development of an adiabatic spherical blast wave in a homogeneous ambient medium of finite pressure. An analytical approximation is also presented for the electron temperature distribution resulting from coulomb collisional heating. The dynamical, thermal, ionization, and spectral structures are calculated for blast waves of energy E sub 0 = 5 x 10 to the 50th power ergs in a hot low-density interstellar environment. A formula is presented for estimating the luminosity evolution of such explosions. The B and C bands of the soft X-ray background, it is shown, are reproduced by such a model explosion if the ambient density is about .000004 cm, the blast radius is roughly 100 pc, and the solar system is located inside the shocked region. Evolution in a pre-existing cavity with a strong density gradient may, it is suggested, remove both the M band and OVI discrepancies.
PKS 2123-463: A Confirmed Gamma-ray Blazar at High Redshift

NASA Technical Reports Server (NTRS)

DAmmando, F.; Rau, A.; Schady, P.; Finke, J.; Orienti, M.; Greiner, J.; Kann, D. A.; Ojha, R.; Foley, A. R.; Stevens, J.;

2012-01-01

The flat spectrum radio quasar (FSRQ) PKS 2123-463 was associated in the First Fermi-LAT source catalog with the gamma-ray source 1FGL J2126.1-4603, but when considering the full first two years of Fermi observations, no gamma-ray source at a position consistent with this FSRQ was detected, and thus PKS 2123-463 was not reported in the Second Fermi-LAT source catalog. On 2011 December 14 a gamma-ray source positionally consistent with PKS 2123-463 was detected in flaring activity by Fermi-LAT. This activity triggered radio-to-X-ray observations by the Swift, GROND, ATCA, Ceduna, and KAT-7 observatories. Results of the localization of the gamma-ray source over 41 months of Fermi-LAT operation are reported here in conjunction with the results of the analysis of radio, optical, UV and X-ray data collected soon after the gamma-ray flare. The strict spatial association with the lower energy counterpart together with a simultaneous increase of the activity in optical, UV, X-ray and gamma-ray bands led to a firm identification of the gamma-ray source with PKS 2123-463. A new photometric redshift has been estimated as z = 1.46 +/- 0.05 using GROND and Swift/UVOT observations, in rough agreement with the disputed spectroscopic redshift of z = 1.67. We fit the broadband spectral energy distribution with a synchrotron/external Compton model. We find that a thermal disk component is necessary to explain the optical/UV emis- sion detected by Swift/UVOT. This disk has a luminosity of 1.8x1046 erg s-1, and a fit to the disk emission assuming a Schwarzschild (i.e., nonrotating) black hole gives a mass of 2 x 109 M(solar mass). This is the first black hole mass estimate for this source.

An optical view of extragalactic gamma-ray emitters

NASA Astrophysics Data System (ADS)

Paiano, Simona; Falomo, Renato; Landoni, Marco; Treves, Aldo; Scarpa, Riccardo

2017-11-01

The Fermi Gamma-ray Observatory discovered about a thousand extragalactic sources emitting energy from 100 MeV to 100 GeV. The majority of these sources belong to the class of blazars characterized by a quasi-featureless optical spectrum (BL Lac Objects). This hampers the determination of their redshift and therefore hinders the characterization of this class of objects. To investigate the nature of these sources and to determine their redshift, we are carrying out an extensive campaign at the 10m Gran Telescopio Canarias to secure high signal-to-noise ratio optical spectra. These observations allow us to confirm the blazar nature of the targets, to find new redshifts or to set stringent limits on the redshift based on the minimum equivalent width of absorption features expected from their host galaxy, assuming it is a massive elliptical galaxy.These results are of importance for the multi-frequencies emission models of the blazars, to test their extreme physics, to shed light on their cosmic evolution and abundance in the far Universe.These gamma emitters are also of great importance for the characterization of the extragalactic background light through the absorption by the IR-optical background photons.
Broadband study of blazar 1ES 1959+650 during flaring state in 2016

NASA Astrophysics Data System (ADS)

Patel, S. R.; Shukla, A.; Chitnis, V. R.; Dorner, D.; Mannheim, K.; Acharya, B. S.; Nagare, B. J.

2018-03-01

Aims: The nearby TeV blazar 1ES 1959+650 (z = 0.047) was reported to be in flaring state during June-July 2016 by Fermi-LAT, FACT, MAGIC and VERITAS collaborations. We studied the spectral energy distributions (SEDs) in different states of the flare during MJD 57530-57589 using simultaneous multiwaveband data with the aim of understanding the possible broadband emission scenario during the flare. Methods: The UV-optical and X-ray data from UVOT and XRT respectively on board Swift and high energy γ-ray data from Fermi-LAT were used to generate multiwaveband lightcurves as well as to obtain high flux states and quiescent state SEDs. The correlation and lag between different energy bands was quantified using discrete correlation function. The synchrotron self-Compton (SSC) model was used to reproduce the observed SEDs during flaring and quiescent states of the source. Results: A good correlation is seen between X-ray and high energy γ-ray fluxes. The spectral hardening with increase in the flux is seen in X-ray band. The power law index vs. flux plot in γ-ray band indicates the different emission regions for 0.1-3 GeV and 3-300 GeV energy photons. Two zone SSC model satisfactorily fits the observed broadband SEDs. The inner zone is mainly responsible for producing synchrotron peak and high energy γ-ray part of the SED in all states. The second zone is mainly required to produce less variable optical-UV and low energy γ-ray emission. Conclusions: Conventional single zone SSC model does not satisfactorily explain broadband emission during observation period considered. There is an indication of two emission zones in the jet which are responsible for producing broadband emission from optical to high energy γ-rays.
Spectra of black hole accretion models of ultraluminous X-ray sources

NASA Astrophysics Data System (ADS)

Narayan, Ramesh; SaÌ§dowski, Aleksander; Soria, Roberto

2017-08-01

We present general relativistic radiation magnetohydrodynamics simulations of super-Eddington accretion on a 10 M⊙ black hole. We consider a range of mass accretion rates, black hole spins and magnetic field configurations. We compute the spectra and images of the models as a function of viewing angle and compare them with the observed properties of ultraluminous X-ray sources (ULXs). The models easily produce apparent luminosities in excess of 1040 erg s-1 for pole-on observers. However, the angle-integrated radiative luminosities rarely exceed 2.5 × 1039 erg s-1 even for mass accretion rates of tens of Eddington. The systems are thus radiatively inefficient, though they are energetically efficient when the energy output in winds and jets is also counted. The simulated models reproduce the main empirical types of spectra - disc-like, supersoft, soft, hard - observed in ultraluminous X-ray sources (ULXs). The magnetic field configuration, whether 'standard and normal evolution' (SANE) or 'magnetically arrested disc' (MAD), has a strong effect on the results. In SANE models, the X-ray spectral hardness is almost independent of accretion rate, but decreases steeply with increasing inclination. MAD models with non-spinning black holes produce significantly softer spectra at higher values of \\dot{M}, even at low inclinations. MAD models with rapidly spinning black holes are unique. They are radiatively efficient (efficiency factor ˜10-20 per cent), superefficient when the mechanical energy output is also included (70 per cent) and produce hard blazar-like spectra. In all models, the emission shows strong geometrical beaming, which disagrees with the more isotropic illumination favoured by observations of ULX bubbles.
Luminosity of serendipitous x-ray QSOs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Margon, B.; Chanan, G.A.; Downes, R.A.

1982-02-01

We have identified the optical counterparts of 47 serendipitously discovered Einstein Observatory X-ray sources with previously unreported quasi-stellar objects. The mean ratio of X-ray to optical luminosity of this sample agrees reasonably well with that derived from X-ray observations of previously known QSOs. However, despite the fact that our limiting magnitude V = 18.5 should permit detection of typical QSOs (i.e., M/sub c/ = -26) to z = 0.9, the mean redshift of our sample is only z = 0.42 Thus the mean luminosity of these objects, M/sub c/ = -24, differs significantly from that of previous QSO surveys withmore » similar optical thresholds. The existence of large numbers of these lower luminosity QSOs which are difficult to discover by previous selection techniques, provides observational confirmation of the steep luminosity function inferred indirectly from optical counts. However, possible explanations for the lack of higher luminosity QSOs in our sample prove even more interesting. If one accepts the global value of the X-ray to optical luminosity ratio proposed by Zamorani et al, and Ku, Helfand, and Lucy, then reconciliation of this ratio with our observations severely constrains the QSO space density and luminosity functions. Alternatively, the ''typical'' QSO-a radio quiet, high redshift (z>1), optically luminous but not superluminous (M/sub c/> or =-27) object-may not be a strong X-ray source. This inference is not in conflict with existing results from Einstein X-ray surveys of preselected QSOs, which also fail to detect such objects. The contribution of QSOs to the diffuse X-ray background radiation is therefore highly uncertain, but may be quite small. Current X-ray data probably do not place significant constraints on the optical number counts of faint QSOs.« less

Imaging proportional counters for the stellar X-ray polarimeter. [on Soviet Spectrum X-Gamma mission

NASA Technical Reports Server (NTRS)

Watkins, R. B., Jr.; Kaaret, P.

1990-01-01

The xenon-filled IPCs being developed for the Stellar X-ray Polarimeter are described. The requirements placed on the IPCs by the design of the polarimeter are discussed and results on the performance of prototype counters are presented. The design of a prototype of the IPCs is described. Finally, the performance of the prototype is reported. Due to the extremely low count rates encountered in X-ray polarimetry, efficient background rejection is the most critical parameter of the IPCs. Using a background rejection scheme employing anticoincidence and pulse shape discrimination, a rejection efficiency of 99 percent has been achieved for Co-60-induced events over an energy range of 2 to 15 keV while retaining more than 80 percent of the X-ray efficiency.
An investigation of the cosmic diffuse X-ray background

NASA Astrophysics Data System (ADS)

John, Tomykkutty Velliyedathu

2016-03-01

The cosmic diffuse X-ray background (CXB), which is only second to the cosmic microwave background (CMB) in prominence, has challenged astrophysicists ever since its serendipitous discovery in 1962. In the past five decades, we have made considerable progress unraveling its mysterious origins. Nevertheless, precise identification of its various components and their individual contributions still remains a puzzling task. The bulk of the XRB comes from the integrated flux of the most luminous astronomical objects- Active Galactic Nuclei (AGN)- as well as the emission from starburst and normal galaxies and can account for most of the emission above 1 keV. In the energy range below 1 keV, several components can be identified besides the dominant extragalactic component. While two thermal components, one at about one million K and the other at about 2.3 million K adequately account for the emission from hot gas in collisional ionization equilibrium, solar wind charge exchange (SWCX) makes a substantial contribution to the SXRB. One of the biggest challenges is to separate the contributions of individual components. This is made difficult by the fact that the spectral structure of all the Galactic components is similar. Shadow experiments have been used to discriminate the various constituents; however, these have only limited use owing to their dependence on estimates of cloud parameters. The best way to make reliable inferences on the contributions of DXB components is to apply good models to valid data with high statistics. With this in mind, for this work, we selected high quality data, from the well-surveyed sky direction- the Chandra Deep Field South (CDF-S)- with 4 Ms of observing time, analyzed them and using several models, derived the important parameters for the various DXB constituents obtaining very good constraints. In addition, we used the same data, spread over a period of nine years, to make a systematic analysis of the temporal variation of heliospheric
Ghost imaging with paired x-ray photons

NASA Astrophysics Data System (ADS)

Schori, A.; Borodin, D.; Tamasaku, K.; Shwartz, S.

2018-06-01

We report the experimental observation of ghost imaging with paired x-ray photons, which are generated by parametric downconversion. We use the one-to-one relation between the photon energies and the emission angles and the anticorrelation between the k -vectors of the signal and the idler photons to reconstruct the images of slits with nominally zero background levels. Further extension of our procedure can be used for the observation of various quantum phenomena at x-ray wavelengths.
X-ray beamsplitter

DOEpatents

Ceglio, Natale M.; Stearns, Daniel S.; Hawryluk, Andrew M.; Barbee, Jr., Troy W.

1989-01-01

An x-ray beamsplitter which splits an x-ray beam into two coherent parts by reflecting and transmitting some fraction of an incident beam has applications for x-ray interferometry, x-ray holography, x-ray beam manipulation, and x-ray laser cavity output couplers. The beamsplitter is formed of a wavelength selective multilayer thin film supported by a very thin x-ray transparent membrane. The beamsplitter resonantly transmits and reflects x-rays through thin film interference effects. A thin film is formed of 5-50 pairs of alternate Mo/Si layers with a period of 20-250 A. The support membrane is 10-200 nm of silicon nitride or boron nitride. The multilayer/support membrane structure is formed across a window in a substrate by first forming the structure on a solid substrate and then forming a window in the substrate to leave a free-standing structure over the window.
Search for Hard X-Ray Emission from the Soft X-Ray Transient Aquila X-1

NASA Astrophysics Data System (ADS)

Harmon, B. A.; Zhang, S. N.; Paciesas, W. S.; Tavani, M.; Kaaret, P.; Ford, E.

1994-12-01

We are investigating the possibility of hard x-ray emission from the recurrent soft x-ray transient and x-ray burst source Aquila X-1 (Aql X-1). Outbursts of this source are relatively frequent with a spacing of ~ 4-10 months (Kitamoto, S. et al. 1993, ApJ, 403, 315). The recent detections of hard tails (\$>\$20 keV) in low luminosity x-ray bursters (Barret, D. & Vedrenne, G. 1994, ApJ Supp. S. 92, 505) suggest that neutron star transient systems such as Aql X-1 can produce hard x-ray emission which is detectable by BATSE. We are correlating reported optical and soft x-ray observations since 1991 of Aql X-1 with BATSE observations in order to search for hard x-ray emission episodes, and to study their temporal and spectral evolution. We will present preliminary results of this search in the 20-1000 keV band using the Earth occultation technique applied to the large area detectors. If this work is successful, we hope to alert the astronomical community for the next Aql X-1 outburst expected in 1995. Simultaneous x-ray/hard x-ray and optical observations of Aql X-1 during outburst would be of great importance for the modeling of soft x-ray transients and related systems.
Simulation and Laboratory results of the Hard X-ray Polarimeter: X-Calibur

NASA Astrophysics Data System (ADS)

Guo, Qingzhen; Beilicke, M.; Kislat, F.; Krawczynski, H.

2014-01-01

X-ray polarimetry promises to give qualitatively new information about high-energy sources, such as binary black hole (BH) systems, Microquasars, active galactic nuclei (AGN), GRBs, etc. We designed, built and tested a hard X-ray polarimeter 'X-Calibur' to be flown in the focal plane of the InFOCuS grazing incidence hard X-ray telescope in 2014. X-Calibur combines a low-Z Compton scatterer with a CZT detector assembly to measure the polarization of 20- 80 keV X-rays making use of the fact that polarized photons Compton scatter preferentially perpendicular to the E field orientation. X-Calibur achieves a high detection efficiency of order unity. We optimized of the design of the instrument based on Monte Carlo simulations of polarized and unpolarized X-ray beams and of the most important background components. We have calibrated and tested X-Calibur extensively in the laboratory at Washington University and at the Cornell High-Energy Synchrotron Source (CHESS). Measurements using the highly polarized synchrotron beam at CHESS confirm the polarization sensitivity of the instrument. In this talk we report on the optimization of the design of the instrument based on Monte Carlo simulations, as well as results of laboratory calibration measurements characterizing the performance of the instrument.
Cosmic X-ray physics

NASA Technical Reports Server (NTRS)

Mccammon, D.; Cox, D. P.; Kraushaar, W. L.; Sanders, W. T.

1987-01-01

The soft X-ray sky survey data are combined with the results from the UXT sounding rocket payload. Very strong constraints can then be placed on models of the origin of the soft diffuse background. Additional observational constraints force more complicated and realistic models. Significant progress was made in the extraction of more detailed spectral information from the UXT data set. Work was begun on a second generation proportional counter response model. The first flight of the sounding rocket will have a collimator to study the diffuse background.
PKS 2123-463: A Confirmed Gamma-ray Blazar at High Redshift

NASA Technical Reports Server (NTRS)

D'Ammando, F.; Rau, A.; Schady, P.; Finke, J.; Orienti, M.; Greiner, J.; Kann, D. A.; Ojha, R.; Foley, A. R.; Stevens, J.;

2013-01-01

The flat spectrum radio quasar (FSRQ) PKS 2123-463 was associated in the first Fermi- Large Area Telescope (LAT) source catalogue with the gamma-ray source 1FGL J2126.1-4603, but when considering the full first two years of Fermi observations, no gamma-ray source at a position consistent with this FSRQ was detected, and thus PKS 2123-463 was not reported in the second Fermi-LAT source catalogue. On 2011 December 14 a gamma-ray source positionally consistent with PKS 2123-463 was detected in flaring activity by Fermi-LAT. This activity triggered radio-to-X-ray observations by the Swift,Gamma-ray Optical/Near-Infrared Detector (GROND), Australia Telescope Compact Array (ATCA), Ceduna and Seven Dishes Karoo Array Telescope (KAT-7) observatories. Results of the localization of the gamma-ray source over 41 months of Fermi-LAT operation are reported here in conjunction with the results of the analysis of radio, optical, ultraviolet (UV) and X-ray data collected soon after the gamma-ray flare. The strict spatial association with the lower energy counterpart together with a simultaneous increase of the activity in optical, UV, X-ray and gamma-ray bands led to a firm identification of the gamma-ray source with PKS 2123-463. A new photometric redshift has been estimated as z = 1.46 plus or minus 0.05 using GROND and Swift Ultraviolet/Optical Telescope (UVOT) observations, in rough agreement with the disputed spectroscopic redshift of z = 1.67.We fit the broad-band spectral energy distribution with a synchrotron/external Compton model. We find that a thermal disc component is necessary to explain the optical/UV emission detected by Swift/UVOT. This disc has a luminosity of approximately 1.8 x 10(exp 46) erg s(exp -1), and a fit to the disc emission assuming a Schwarzschild (i.e. non-rotating) black hole gives a mass of approximately 2 x 10(exp 9) solar mass. This is the first black hole mass estimate for this source.

Modeling of proton-induced radioactivation background in hard X-ray telescopes: Geant4-based simulation and its demonstration by Hitomi ’s measurement in a low Earth orbit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Odaka, Hirokazu; Asai, Makoto; Hagino, Kouichi

Hard X-ray astronomical observatories in orbit suffer from a significant amount of background due to radioactivation induced by cosmic-ray protons and/or geomagnetically trapped protons. Within the framework of a full Monte Carlo simulation, we present modeling of in-orbit instrumental background which is dominated by radioactivation. To reduce the computation time required by straightforward simulations of delayed emissions from activated isotopes, we insert a semi-analytical calculation that converts production probabilities of radioactive isotopes by interaction of the primary protons into decay rates at measurement time of all secondary isotopes. Therefore, our simulation method is separated into three steps: (1) simulation ofmore » isotope production, (2) semi-analytical conversion to decay rates, and (3) simulation of decays of the isotopes at measurement time. This method is verified by a simple setup that has a CdTe semiconductor detector, and shows a 100-fold improvement in efficiency over the straightforward simulation. To demonstrate its experimental performance, the simulation framework was tested against data measured with a CdTe sensor in the Hard X-ray Imager onboard the Hitomi X-ray Astronomy Satellite, which was put into a low Earth orbit with an altitude of 570 km and an inclination of 31°, and thus experienced a large amount of irradiation from geomagnetically trapped protons during its passages through the South Atlantic Anomaly. The simulation is able to treat full histories of the proton irradiation and multiple measurement windows. As a result, the simulation results agree very well with the measured data, showing that the measured background is well described by the combination of proton-induced radioactivation of the CdTe detector itself and thick Bi 4Ge 3O 12 scintillator shields, leakage of cosmic X-ray background and albedo gamma-ray radiation, and emissions from naturally contaminated isotopes in the detector system.« less
Modeling of proton-induced radioactivation background in hard X-ray telescopes: Geant4-based simulation and its demonstration by Hitomi ’s measurement in a low Earth orbit

DOE PAGES

Odaka, Hirokazu; Asai, Makoto; Hagino, Kouichi; ...

2018-02-19

Hard X-ray astronomical observatories in orbit suffer from a significant amount of background due to radioactivation induced by cosmic-ray protons and/or geomagnetically trapped protons. Within the framework of a full Monte Carlo simulation, we present modeling of in-orbit instrumental background which is dominated by radioactivation. To reduce the computation time required by straightforward simulations of delayed emissions from activated isotopes, we insert a semi-analytical calculation that converts production probabilities of radioactive isotopes by interaction of the primary protons into decay rates at measurement time of all secondary isotopes. Therefore, our simulation method is separated into three steps: (1) simulation ofmore » isotope production, (2) semi-analytical conversion to decay rates, and (3) simulation of decays of the isotopes at measurement time. This method is verified by a simple setup that has a CdTe semiconductor detector, and shows a 100-fold improvement in efficiency over the straightforward simulation. To demonstrate its experimental performance, the simulation framework was tested against data measured with a CdTe sensor in the Hard X-ray Imager onboard the Hitomi X-ray Astronomy Satellite, which was put into a low Earth orbit with an altitude of 570 km and an inclination of 31°, and thus experienced a large amount of irradiation from geomagnetically trapped protons during its passages through the South Atlantic Anomaly. The simulation is able to treat full histories of the proton irradiation and multiple measurement windows. As a result, the simulation results agree very well with the measured data, showing that the measured background is well described by the combination of proton-induced radioactivation of the CdTe detector itself and thick Bi 4Ge 3O 12 scintillator shields, leakage of cosmic X-ray background and albedo gamma-ray radiation, and emissions from naturally contaminated isotopes in the detector system.« less
The hard x-ray imager (HXI) onboard ASTRO-H

NASA Astrophysics Data System (ADS)

Nakazawa, Kazuhiro; Sato, Goro; Kokubun, Motohide; Enoto, Teruaki; Fukazawa, Yasushi; Hagino, Kouichi; Harayama, Atsushi; Hayashi, Katsuhiro; Kataoka, Jun; Katsuta, Junichiro; Laurent, Philippe; Lebrun, François; Limousin, Olivier; Makishima, Kazuo; Mizuno, Tsunefumi; Mori, Kunishiro; Nakamori, Takeshi; Nakano, Toshio; Noda, Hirofumi; Odaka, Hirokazu; Ohno, Masanori; Ohta, Masayuki; Saito, Shinya; Sato, Rie; Tajima, Hiroyasu; Takahashi, Hiromitsu; Takahashi, Tadayuki; Takeda, Shin'ichiro; Terada, Yukikatsu; Uchiyama, Hideki; Uchiyama, Yasunobu; Watanabe, Shin; Yamaoka, Kazutaka; Yatsu, Yoichi; Yuasa, Takayuki

2016-07-01

Hitomi X-ray observatory launched in 17 February 2016 had a hard X-ray imaging spectroscopy system made of two hard X-ray imagers (HXIs) coupled with two hard X-ray telescopes (HXTs). With 12 m focal length, they provide fine (2' half-power diameter; HPD) imaging spectroscopy at 5 to 80 keV. The HXI main imagers are made of 4 layers of Si and a CdTe semiconductor double-sided strip detectors, stacked to enhance detection efficiency as well as to enable photon interaction-depth sensing. Active shield made of 9 BGO scintillators surrounds the imager to provide with low background. Following the deployment of the Extensible Optical Bench (EOB) on 28 February, the HXI was gradually turned on. Two imagers successfully started observation on 14 March, and was operational till the incident lead to Hitomo loss, on 26 March. All detector channels, 1280 ch of imager and 11 channel of active shields and others each, worked well and showed performance consistent with those seen on ground. From the first light observation of G21.5-0.9 and the following Crab observations, 5-80 keV energy coverage and good detection efficiency were confirmed. With blank sky observations, we checked our background level. In some geomagnetic region, strong background continuum, presumably caused by trapped electron with energy 100 keV, is seen. But by cutting the high-background time-intervals, the background became significantly lower, typically with 1-3 x 10-4 counts s-1 keV-1 cm-2 (here cm2 is shown with detector geometrical area). Above 30 keV, line and continuum emission originating from activation of CdTe was significantly seen, though the level of 1-4 x 10-4 counts s-1 keV-1 cm-2 is still comparable to those seen in NuSTAR. By comparing the effective area and background rate, preliminary analysis shows that the HXI had a statistical sensitivity similar to NuSTAR for point sources, and more than twice better for largely extended sources.
Revisiting the incidence of Mg II absorbers along the blazar sightlines

NASA Astrophysics Data System (ADS)

Mishra, Sapna; Chand, Hum; Gopal-Krishna; Joshi, Ravi

2018-04-01

It is believed that the cool gas clouds traced by Mg II absorption, within a velocity offset of 5000 km/s from the background quasar, are associated with the quasar itself, whereas the absorbers seen at larger velocity offsets towards us are intervening systems and hence their existence is completely independent of the background quasar. Recent evidence by Bergeron et al. 2011 (hereafter BBM), however, seriously questions this canonical view, by showing that the number density of intervening Mg II absorbers along the sightlines towards 45 blazars is, on average, 2 times the expectation based on the Mg II absorption systems seen on the sightlines to normal QSOs. Given the serious implications of this finding, it becomes important to revisit this issue by enlarging the source sample and subjecting it to an independent analysis. Here, we first report our results based on a re-analysis of the spectroscopic data for the BBM sample; this has reproduced their factor 2 excess in dN/dz along blazar sightlines, vis-a-vis the normal QSOs. Next, we assemble a 6 times larger sample of blazar sightlines, albeit with lower SNR. Using this enlarged sample together with the BBM sample, our analysis shows that the dN/dz of Mg II absorbers statistically matches that known for normal QSO sightlines.
X-ray beamsplitter

DOEpatents

Ceglio, N.M.; Stearns, D.G.; Hawryluk, A.M.; Barbee, T.W. Jr.

1987-08-07

An x-ray beamsplitter which splits an x-ray beam into two coherent parts by reflecting and transmitting some fraction of an incident beam has applications for x-ray interferometry, x-ray holography, x-ray beam manipulation, and x-ray laser cavity output couplers. The beamsplitter is formed of a wavelength selective multilayer thin film supported by a very thin x-ray transparent membrane. The beamsplitter resonantly transmits and reflects x-rays through thin film interference effects. A thin film is formed of 5--50 pairs of alternate Mo/Si layers with a period of 20--250 A. The support membrane is 10--200 nm of silicon nitride or boron nitride. The multilayer/support membrane structure is formed across a window in a substrate by first forming the structure on a solid substrate and then forming a window in the substrate to leave a free-standing structure over the window. 6 figs.
Deconstructing the Spectrum of the Soft X-ray Background

NASA Technical Reports Server (NTRS)

Kuntz, K. D.; Snowden, S. L.

2000-01-01

The soft X-ray background in the 0.1-1.0 keV band is known to be produced by at least three sources; the Local Hot Bubble (LHB), the extragalactic power law (EPL), and a seemingly galactic component that lies outside the bulk of the absorption that is due to the ISM of the galactic disk. This last component, which we call the Trans-Absorption Emission (TAE), has been modeled by a number of groups who have derived disparate measures of its temperature. The differences have arisen from differing assumptions about the structure of the emitting gas and unrecognized methodological difficulties. In particular, spectral fitting methods do not uniquely separate the TAE from the foreground emission that is due the LHB. This "degeneracy" can be resolved using the angular variation of the absorption of the TAE. We show that the TAE cannot be characterized by a single thermal component; no single-component model can be consistent with both the spectral energy distribution of the TAE emission and the angular variation due to absorption by the galactic disk. We use the angular anticorrelation of the ROSAT All-Sky Survey with the galactic absorption to separate local from distant emission components, and to fit the spectral energy distribution of the resulting distant emission. We find that the emission is best described by a two-thermal-component model with logT(sub S) = 6.06(sup +0.14, sub -0.12) and log T(sub H) = 6.42(sup +0.14, sub -0.12). This two-thermal-component TAE fits the ROSAT spectral energy distribution significantly better than single-component models, and is consistent with both angular variation and spectral constraints.
The X-ray Integral Field Unit (X-IFU) for Athena

NASA Technical Reports Server (NTRS)

Ravera, Laurent; Barret, Didier; Willem den Herder, Jan; Piro, Luigi; Cledassou, Rodolphe; Pointecouteau, Etienne; Peille, Philippe; Pajot, Francois; Arnaud, Monique; Pigot, Claude;

2014-01-01

Athena is designed to implement the Hot and Energetic Universe science theme selected by the European Space Agency for the second large mission of its Cosmic Vision program. The Athena science payload consists of a large aperture high angular resolution X-ray optics (2 m2 at 1 keV) and twelve meters away, two interchangeable focal plane instruments: the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager. The X-IFU is a cryogenic X-ray spectrometer, based on a large array of Transition Edge Sensors (TES), oering 2.5 eV spectral resolution, with approximately 5" pixels, over a field of view of 5' in diameter. In this paper, we present the X-IFU detector and readout electronics principles, some elements of the current design for the focal plane assembly and the cooling chain. We describe the current performance estimates, in terms of spectral resolution, effective area, particle background rejection and count rate capability. Finally, we emphasize on the technology developments necessary to meet the demanding requirements of the X-IFU, both for the sensor, readout electronics and cooling chain.

On the Direct Correlation between Gamma-Rays and PeV Neutrinos from Blazars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Shan; Pohl, Martin; Winter, Walter, E-mail: shan.gao@desy.de

We study the frequently used assumption in multi-messenger astrophysics that the gamma-ray and neutrino fluxes are directly connected because they are assumed to be produced by the same photohadronic production chain. An interesting candidate source for this test is the flat-spectrum radio quasar PKS B1424-418, which recently called attention to a potential correlation between an IceCube PeV neutrino event and its burst phase. We simulate both the multi-waveband photon and the neutrino emission from this source using a self-consistent radiation model. We demonstrate that a simple hadronic model cannot adequately describe the spectral energy distribution for this source, but amore » lepto-hadronic model with a subdominant hadronic component can reproduce the multi-waveband photon spectrum observed during various activity phases of the blazar. As a conclusion, up to about 0.3 neutrino events may coincide with the burst, which implies that the leptonic contribution dominates in the relevant energy band. We also demonstrate that the time-wise correlation between the neutrino event and burst phase is weak.« less
DETECTING RELATIVISTIC X-RAY JETS IN HIGH-REDSHIFT QUASARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

McKeough, Kathryn; Siemiginowska, Aneta; Kashyap, Vinay L.

We analyze Chandra X-ray images of a sample of 11 quasars that are known to contain kiloparsec scale radio jets. The sample consists of five high-redshift ( z ≥ 3.6) flat-spectrum radio quasars, and six intermediate redshift (2.1 < z < 2.9) quasars. The data set includes four sources with integrated steep radio spectra and seven with flat radio spectra. A total of 25 radio jet features are present in this sample. We apply a Bayesian multi-scale image reconstruction method to detect and measure the X-ray emission from the jets. We compute deviations from a baseline model that does not include the jet,more » and compare observed X-ray images with those computed with simulated images where no jet features exist. This allows us to compute p -value upper bounds on the significance that an X-ray jet is detected in a pre-determined region of interest. We detected 12 of the features unambiguously, and an additional six marginally. We also find residual emission in the cores of three quasars and in the background of one quasar that suggest the existence of unresolved X-ray jets. The dependence of the X-ray to radio luminosity ratio on redshift is a potential diagnostic of the emission mechanism, since the inverse Compton scattering of cosmic microwave background photons (IC/CMB) is thought to be redshift dependent, whereas in synchrotron models no clear redshift dependence is expected. We find that the high-redshift jets have X-ray to radio flux ratios that are marginally inconsistent with those from lower redshifts, suggesting that either the X-ray emissions are due to the IC/CMB rather than the synchrotron process, or that high-redshift jets are qualitatively different.« less
FBQS J1644+2619: multiwavelength properties and its place in the class of γ-ray emitting Narrow Line Seyfert 1s

NASA Astrophysics Data System (ADS)

Larsson, J.; D'Ammando, F.; Falocco, S.; Giroletti, M.; Orienti, M.; Piconcelli, E.; Righini, S.

2018-05-01

A small fraction of Narrow Line Seyfert 1s (NLSy1s) are observed to be γ-ray emitters. Understanding the properties of these sources is of interest since the majority of NLSy1s are very different from typical blazars. Here, we present a multifrequency analysis of FBQS J1644+2619, one of the most recently discovered γ-ray emitting NLSy1s. We analyse an ˜80 ks XMM-Newton observation obtained in 2017, as well as quasi-simultaneous multiwavelength observations covering the radio-γ-ray range. The spectral energy distribution of the source is similar to the other γ-ray NLSy1s, confirming its blazar-like nature. The X-ray spectrum is characterized by a hard photon index (Γ = 1.66) above 2 keV and a soft excess at lower energies. The hard photon index provides clear evidence that inverse Compton emission from the jet dominates the spectrum, while the soft excess can be explained by a contribution from the underlying Seyfert emission. This contribution can be fitted by reflection of emission from the base of the jet, as well as by Comptonization in a warm, optically thick corona. We discuss our results in the context of the other γ-ray NLSy1s and note that the majority of them have similar X-ray spectra, with properties intermediate between blazars and radio-quiet NLSy1s.
X-Ray Polarization from High Mass X-Ray Binaries

NASA Technical Reports Server (NTRS)

Kallman, T.; Dorodnitsyn, A.; Blondin, J.

2015-01-01

X-ray astronomy allows study of objects which may be associated with compact objects, i.e. neutron stars or black holes, and also may contain strong magnetic fields. Such objects are categorically non-spherical, and likely non-circular when projected on the sky. Polarization allows study of such geometric effects, and X-ray polarimetry is likely to become feasible for a significant number of sources in the future. A class of potential targets for future X-ray polarization observations is the high mass X-ray binaries (HMXBs), which consist of a compact object in orbit with an early type star. In this paper we show that X-ray polarization from HMXBs has a distinct signature which depends on the source inclination and orbital phase. The presence of the X-ray source displaced from the star creates linear polarization even if the primary wind is spherically symmetric whenever the system is viewed away from conjunction. Direct X-rays dilute this polarization whenever the X-ray source is not eclipsed; at mid-eclipse the net polarization is expected to be small or zero if the wind is circularly symmetric around the line of centers. Resonance line scattering increases the scattering fraction, often by large factors, over the energy band spanned by resonance lines. Real winds are not expected to be spherically symmetric, or circularly symmetric around the line of centers, owing to the combined effects of the compact object gravity and ionization on the wind hydrodynamics. A sample calculation shows that this creates polarization fractions ranging up to tens of percent at mid-eclipse.
Non-variable TeV emission from the extended jet of a blazar in the stochastic acceleration scenario: the case of the hard TeV emission of 1ES 1101-232

NASA Astrophysics Data System (ADS)

Yan, Dahai; Zeng, Houdun; Zhang, Li

2012-08-01

The detections of X-ray emission from the kiloparsec-scale jets of blazars and radio galaxies could imply the existence of high-energy electrons in these extended jets, and these electrons could produce high-energy emission through the inverse Compton (IC) process. In this paper, we study the non-variable hard TeV emission from a blazar. The multiband emission consists of two components: (i) the traditional synchrotron self-Compton (SSC) emission from the inner jet; (ii) the emission produced via SSC and IC scattering of cosmic microwave background (CMB) photons (IC/CMB) and extragalactic background light (EBL) photons by relativistic electrons in the extended jet under the stochastic acceleration scenario. Such a model is applied to 1ES 1101-232. The results indicate the following. (i) The non-variable hard TeV emission of 1ES 1101-232, which is dominated by IC/CMB emission from the extended jet, can be reproduced well by using three characteristic values of the Doppler factor (δD = 5, 10 and 15) for the TeV-emitting region in the extended jet. (ii) In the cases of δD = 15 and 10, the physical parameters can achieve equipartition (or quasi-equipartition) between the relativistic electrons and the magnetic field. In contrast, the physical parameters largely deviate from equipartition for the case of δD = 5. Therefore, we conclude that the TeV emission region of 1ES 1101-232 in the extended jet should be moderately or highly beamed.

EBL constraints with VERITAS gamma-ray observations

NASA Astrophysics Data System (ADS)

Fernandez Alonso, M.; VERITAS Collaboration

2017-10-01

The extragalactic background light (EBL) contains all the radiation emitted by nuclear and accretion processes since the epoch of recombination. Direct measurements of the EBL in the near-IR to mid-IR waveband are extremely difficult due mainly to the zodiacal light foreground. Instead, gamma-ray astronomy offers the possibility to indirectly set limits to the EBL by studying the effects of gamma-ray absorption in the spectra of detected sources in the very high energy range (VHE: 100 GeV). These effects can be generally seen in the spectra of VHE blazars as a softening (steepening) of the spectrum and/or abrupt changes in the spectral index or breaks. In this work, we use recent VERITAS data of a group of blazars and apply two methods to derive constraints for the EBL spectral properties. We present preliminary results that will be completed with new observations in the near future to enhance the calculated restrictions to the EBL.
Development of a mercuric iodide solid state spectrometer for X-ray astronomy

NASA Technical Reports Server (NTRS)

Vallerga, J.

1983-01-01

Mercuric iodide detectors, experimental development for astronomical use, X ray observations of the 1980 Cygnus X-1 High State, astronomical had X ray detectors in current use, detector development, balloon flight of large area (1500 sq cm) Phoswich detectors, had X ray telescope design, shielded mercuric iodide background measurement, Monte Carlo analysis, measurements with a shielded mercuric iodide detector are discussed.
Be/X-ray Binary Science for Future X-ray Timing Missions

NASA Technical Reports Server (NTRS)

Wilson-Hodge, Colleen A.

2011-01-01

For future missions, the Be/X-ray binary community needs to clearly define our science priorities for the future to advocate for their inclusion in future missions. In this talk, I will describe current designs for two potential future missions and Be X-ray binary science enabled by these designs. The Large Observatory For X-ray Timing (LOFT) is an X-ray timing mission selected in February 2011 for the assessment phase from the 2010 ESA M3 call for proposals. The Advanced X-ray Timing ARray (AXTAR) is a NASA explorer concept X-ray timing mission. This talk is intended to initiate discussions of our science priorities for the future.
Abdomen X-Ray (Radiography)

MedlinePlus

... News Physician Resources Professions Site Index A-Z X-ray (Radiography) - Abdomen Abdominal x-ray uses a ... of an abdominal x-ray? What is abdominal x-ray? An x-ray (radiograph) is a noninvasive ...
Neutral particle background in cosmic ray telescopes composed of silicon solid state detectors

NASA Technical Reports Server (NTRS)

Mewaldt, R. A.; Stone, E. C.; Vogt, R. E.

1977-01-01

The energy loss-spectrum of secondary charged particles produced by the interaction of gamma-rays and energetic neutrons in silicon solid state detectors has been measured with a satellite-borne cosmic ray telescope. In the satellite measurements presented here two distinct neutral background effects are identified: secondary protons and alpha particles with energies of about 2 to 100 MeV produced by neutron interactions, and secondary electrons with energies of about 0.2 to 10 MeV produced by X-ray interactions. The implications of this neutral background for satellite measurements of low energy cosmic rays are discussed, and suggestions are given for applying these results to other detector systems in order to estimate background contamination and optimize detector system design.
From the Blazar Sequence to the Blazar Envelope: Revisiting the Relativistic Jet Dichotomy in Radio-Loud AGN

NASA Technical Reports Server (NTRS)

Meyer, Eileen T.; Fossati, Giovanini; Georganopoulos, Markos; Lister, Matthew L.

2012-01-01

We revisit the concept of a blazar sequence that relates the synchrotron peak frequency (Vpeak) in blazars with synchrotron peak luminosity (Lpeak, in vLv) using a large sample of radio-loud AGN. We present observational evidence that the blazar sequence is formed from two populations in the synchrotron Vpeak - Lpeak plane, each forming an upper edge to an envelope of progressively misaligned blazars, and connecting to an adjacent group of radio galaxies having jets viewed at much larger angles to the line of sight. When binned by jet kinetic power (Lkin; as measured through a scaling relationship with extended radio power), we find that radio core dominance decreases with decreasing synchrotron Lpeak, revealing that sources in the envelope are generally more misaligned. We find population-based evidence of velocity gradients in jets at low kinetic powers (approximately 10(exp 42) - 10(exp 44.5) erg s(exp -1)), corresponding to FR I radio galaxies and most BL Lacs. These low jet power 'weak jet' sources, thought to exhibit radiatively inefficient accretion, are distinguished from the population of non-decelerating, low synchrotron-peaking (LSP) blazars and FR II radio galaxies ('strong' jets) which are thought to exhibit radiatively efficient accretion. The two-population interpretation explains the apparent contradiction of the existence of highly core-dominated, low-power blazars at both low and high synchrotron peak frequencies, and further implies that most intermediate synchrotron peak (ISP) sources are not intermediate in intrinsic jet power between LSP and high synchrotron-peaking (HSP) sources, but are more misaligned versions of HSP sources with similar jet powers.
A search for X-ray polarization in cosmic X-ray sources. [binary X-ray sources and supernovae remnants

NASA Technical Reports Server (NTRS)

Hughes, J. P.; Long, K. S.; Novick, R.

1983-01-01

Fifteen strong X-ray sources were observed by the X-ray polarimeters on board the OSO-8 satellite from 1975 to 1978. The final results of this search for X-ray polarization in cosmic sources are presented in the form of upper limits for the ten sources which are discussed elsewhere. These limits in all cases are consistent with a thermal origin for the X-ray emission.
X-Ray Emission from the Soft X-Ray Transient Aquila X-1

NASA Technical Reports Server (NTRS)

Tavani, Marco

1998-01-01

Aquila X-1 is the most prolific of soft X-ray transients. It is believed to contain a rapidly spinning neutron star sporadically accreting near the Eddington limit from a low-mass companion star. The interest in studying the repeated X-ray outbursts from Aquila X-1 is twofold: (1) studying the relation between optical, soft and hard X-ray emission during the outburst onset, development and decay; (2) relating the spectral component to thermal and non-thermal processes occurring near the magnetosphere and in the boundary layer of a time-variable accretion disk. Our investigation is based on the BATSE monitoring of Aquila X-1 performed by our group. We observed Aquila X-1 in 1997 and re-analyzed archival information obtained in April 1994 during a period of extraordinary outbursting activity of the source in the hard X-ray range. Our results allow, for the first time for this important source, to obtain simultaneous spectral information from 2 keV to 200 keV. A black body (T = 0.8 keV) plus a broken power-law spectrum describe accurately the 1994 spectrum. Substantial hard X-ray emission is evident in the data, confirming that the accretion phase during sub-Eddington limit episodes is capable of producing energetic hard emission near 5 x 10(exp 35) ergs(exp -1). A preliminary paper summarizes our results, and a more comprehensive account is being written. We performed a theoretical analysis of possible emission mechanisms, and confirmed that a non-thermal emission mechanism triggered in a highly sheared magnetosphere at the accretion disk inner boundary can explain the hard X-ray emission. An anticorrelation between soft and hard X-ray emission is indeed prominently observed as predicted by this model.
Limits on soft X-ray flux from distant emission regions

NASA Technical Reports Server (NTRS)

Burrows, D. N.; Mccammon, D.; Sanders, W. T.; Kraushaar, W. L.

1984-01-01

The all-sky soft X-ray data of McCammon et al. and the new N sub H survey (Stark et al. was used to place limits on the amount of the soft X-ray diffuse background that can originate beyond the neutral gas of the galactic disk. The X-ray data for two regions of the sky near the galactic poles are shown to be uncorrelated with 21 cm column densities. Most of the observed x-ray flux must therefore originate on the near side of the most distant neutral gas. The results from these regions are consistent with X-ray emission from a locally isotropic, unabsorbed source, but require large variations in the emission of the local region over large angular scales.
Research in X-ray Astronomy

NASA Technical Reports Server (NTRS)

1997-01-01

This research grant supported an active sounding rocket program at Penn State University over a period of over 10 years. During this period, the grant supported at least 8 graduate students in Astronomy & Astrophysics for at least a portion of their research. During the same period, our group was involved in seven sounding rocket flights, launched from White Sands, New Mexico, and from Woomera, Australia. Most of these rocket flights, and most of the work supported by this grant, involved the use of X-ray CCD cameras. The first X-ray CCD camera ever flown in space was our sounding rocket observation of SN1987A (flight 36.030 in 1987). Subsequent flights utilized improved CCD detectors, culminating in the'state-of-the-art EEV detector developed for our CUBIC mission, which was flown on 36.093 last May. Data from the last three flights, which observed the diffuse X-ray background with CCDS, include detection of the OVII He(alpha) line in the high latitude diffuse background and detection of the Mg XI He(alpha) line in the North Polar Spur. These results have been reported at meetings of the American Astronomical Society and the SPIE. The analysis of flights 36.092 and 36.106 is part of Jeff Mendenhall's PhD thesis and will be published in the Astrophysical Journal next year. The 36.093 data are currently being analyzed by PhD student Laura Cawley. From 1990 to 1996 this grant supported our development and launch of the CUBIC instrument on the SAC-B satellite, which was designed to measure the spectrum of the soft X-ray diffuse background with moderate energy resolution and high S/N ratio. Unfortunately, this mission terminated shortly after launch due to a failure of the Pegasus XL launch vehicle. This work resulted in publication of 4 papers in the SPIE Proceedings and four others in refereed journals, in addition to several other conference proceedings and contributed papers. In addition to the CCD flights described above, this grant has supported preliminary
The Hard X-ray Imager (HXI) for the ASTRO-H mission

NASA Astrophysics Data System (ADS)

Kokubun, Motohide; Nakazawa, Kazuhiro; Enoto, Teruaki; Fukazawa, Yasushi; Kataoka, Jun; Kawaharada, Madoka; Laurent, Philippe; Lebrun, François; Limousin, Olivier; Makishima, Kazuo; Mizuno, Tsunefumi; Mori, Kunishiro; Nakamori, Takeshi; Odaka, Hirokazu; Ohno, Masanori; Ohta, Masayuki; Sato, Goro; Sato, Rie; Tajima, Hiroyasu; Takahashi, Hiromitsu; Takahashi, Tadayuki; Tanaka, Takaaki; Terada, Yukikatsu; Uchiyama, Hideki; Uchiyama, Yasunobu; Watanabe, Shin; Yatsu, Yoichi; Yuasa, Takayuki

2012-09-01

The Hard X-ray Imager (HXI) is one of the four detectors on board the ASTRO-H mission (6th Japanese X-ray satellite), which is scheduled to be launched in 2014. Using the hybrid structure composed of double-sided silicon strip detectors and a cadmium telluride double-sided strip detector, both with a high spatial resolution of 250 μm. Combined with the hard X-ray telescope (HXT), it consists a hard X-ray imaging spectroscopic instrument covering the energy range from 5 to 80 keV with an effective area of <300 cm2 in total at 30 keV. An energy resolution of 1-2 keV (FWHM) and lower threshold of 5 keV are both achieved with using a low noise front-end ASICs. In addition, the thick BGO active shields surrounding the main detector package is a heritage of the successful performance of the Hard X-ray Detector on board the Suzaku satellite. This feature enables the instrument to achieve an extremely good reduction of background caused by cosmic-ray particles, cosmic X-ray background, and in-orbit radiation activation. In this paper, we present the detector concept, design, latest results of the detector development, and the current status of the hardware.
"X-Ray Transients in Star-Forming Regions" and "Hard X-Ray Emission from X-Ray Bursters"

NASA Technical Reports Server (NTRS)

Halpern, Jules P.; Kaaret, Philip

1999-01-01

This grant funded work on the analysis of data obtained with the Burst and Transient Experiment (BATSE) on the Compton Gamma-Ray Observatory. The goal of the work was to search for hard x-ray transients in star forming regions using the all-sky hard x-ray monitoring capability of BATSE. Our initial work lead to the discovery of a hard x-ray transient, GRO J1849-03. Follow-up observations of this source made with the Wide Field Camera on BeppoSAX showed that the source should be identified with the previously known x-ray pulsar GS 1843-02 which itself is identified with the x-ray source X1845-024 originally discovered with the SAS-3 satellite. Our identification of the source and measurement of the outburst recurrence time, lead to the identification of the source as a Be/X-ray binary with a spin period of 94.8 s and an orbital period of 241 days. The funding was used primarily for partial salary and travel support for John Tomsick, then a graduate student at Columbia University. John Tomsick, now Dr. Tomsick, received his Ph.D. from Columbia University in July 1999, based partially on results obtained under this investigation. He is now a postdoctoral research scientist at the University of California, San Diego.
Geant4 simulations of a wide-angle x-ray focusing telescope

NASA Astrophysics Data System (ADS)

Zhao, Donghua; Zhang, Chen; Yuan, Weimin; Zhang, Shuangnan; Willingale, Richard; Ling, Zhixing

2017-06-01

The rapid development of X-ray astronomy has been made possible by widely deploying X-ray focusing telescopes on board many X-ray satellites. Geant4 is a very powerful toolkit for Monte Carlo simulations and has remarkable abilities to model complex geometrical configurations. However, the library of physical processes available in Geant4 lacks a description of the reflection of X-ray photons at a grazing incident angle which is the core physical process in the simulation of X-ray focusing telescopes. The scattering of low-energy charged particles from the mirror surfaces is another noteworthy process which is not yet incorporated into Geant4. Here we describe a Monte Carlo model of a simplified wide-angle X-ray focusing telescope adopting lobster-eye optics and a silicon detector using the Geant4 toolkit. With this model, we simulate the X-ray tracing, proton scattering and background detection. We find that: (1) the effective area obtained using Geant4 is in agreement with that obtained using Q software with an average difference of less than 3%; (2) X-rays are the dominant background source below 10 keV; (3) the sensitivity of the telescope is better by at least one order of magnitude than that of a coded mask telescope with the same physical dimensions; (4) the number of protons passing through the optics and reaching the detector by Firsov scattering is about 2.5 times that of multiple scattering for the lobster-eye telescope.
Lumbosacral spine x-ray

MedlinePlus

X-ray - lumbosacral spine; X-ray - lower spine ... The test is done in a hospital x-ray department or your health care provider's office by an x-ray technician. You will be asked to lie on the x-ray ...
X-ray ptychography

NASA Astrophysics Data System (ADS)

Pfeiffer, Franz

2018-01-01

X-ray ptychographic microscopy combines the advantages of raster scanning X-ray microscopy with the more recently developed techniques of coherent diffraction imaging. It is limited neither by the fabricational challenges associated with X-ray optics nor by the requirements of isolated specimen preparation, and offers in principle wavelength-limited resolution, as well as stable access and solution to the phase problem. In this Review, we discuss the basic principles of X-ray ptychography and summarize the main milestones in the evolution of X-ray ptychographic microscopy and tomography over the past ten years, since its first demonstration with X-rays. We also highlight the potential for applications in the life and materials sciences, and discuss the latest advanced concepts and probable future developments.
Discovery of a new TeV gamma-ray source: VER J0521+211

DOE PAGES

Archambault, S.; Arlen, T.; Aune, T.; ...

2013-09-27

Here, we report the detection of a new TeV gamma-ray source, VER J0521+211, based on observations made with the VERITAS imaging atmospheric Cherenkov Telescope Array. These observations were motivated by the discovery of a cluster of >30 GeV photons in the first year of Fermi Large Area Telescope observations. VER J0521+211 is relatively bright at TeV energies, with a mean photon flux of (1.93 ± 0.13 stat ± 0.78 sys) × 10 –11 cm –2 s –1 above 0.2 TeV during the period of the VERITAS observations. The source is strongly variable on a daily timescale across all wavebands, frommore » optical to TeV, with a peak flux corresponding to ~0.3 times the steady Crab Nebula flux at TeV energies. Follow-up observations in the optical and X-ray bands classify the newly discovered TeV source as a BL Lac-type blazar with uncertain redshift, although recent measurements suggest z = 0.108. VER J0521+211 exhibits all the defining properties of blazars in radio, optical, X-ray, and gamma-ray wavelengths.« less
The Athena X-ray Integral Field Unit (X-IFU)

NASA Technical Reports Server (NTRS)

Barret, Didier; Trong, Thein Lam; Den Herder, Jan-Willem; Piro, Luigi; Barcons, Xavier; Huovelin, Juhani; Kelley, Richard; Mas-Hesse, J. Miquel; Mitsuda, Kazuhisa; Paltani, Stephane;

2016-01-01

The X-ray Integral Field Unit (X-IFU) on board the Advanced Telescope for High-ENergy Astrophysics (Athena) will provide spatially resolved high-resolution X-ray spectroscopy from 0.2 to 12 keV, with 5 pixels over a field of view of 5 arc minute equivalent diameter and a spectral resolution of 2.5 eV up to 7 keV. In this paper, we first review the core scientific objectives of Athena, driving the main performance parameters of the X-IFU, namely the spectral resolution, the field of view, the effective area, the count rate capabilities, the instrumental background. We also illustrate the breakthrough potential of the X-IFU for some observatory science goals. Then we brie y describe the X-IFU design as defined at the time of the mission consolidation review concluded in May 2016, and report on its predicted performance. Finally, we discuss some options to improve the instrument performance while not increasing its complexity and resource demands (e.g. count rate capability, spectral resolution). (2016) .

Investigation of Deuterium Loaded Materials Subject to X-Ray Exposure

NASA Technical Reports Server (NTRS)

Benyo, Theresa L.; Steinetz, Bruce M.; Hendricks, Robert C.; Martin, Richard E.; Forsley, Lawrence P.; Daniels, Christopher C.; Chait, Arnon; Pines, Vladimir; Pines, Marianna; Penney, Nicholas;

2017-01-01

Results are presented from an exploratory study involving x-ray irradiation of select deuterated materials. Titanium deuteride plus deuterated polyethylene, deuterated polyethylene alone, and for control, hydrogen-based polyethylene samples and nondeuterated titanium samples were exposed to x-ray irradiation. These samples were exposed to various energy levels from 65 to 280 kV with prescribed electron flux from 500 to 9000 µA impinging on a tungsten braking target, with total exposure times ranging from 55 to 280 min. Gamma activity was measured using a high-purity germanium (HPGe) detector, and for all samples no gamma activity above background was detected. Alpha and beta activities were measured using a gas proportional counter, and for select samples beta activity was measured with a liquid scintillator spectrometer. The majority of the deuterated materials subjected to the microfocus x-ray irradiation exhibited postexposure beta activity above background and several showed short-lived alpha activity. The HPE and nondeuterated titanium control samples exposed to the x-ray irradiation showed no postexposure alpha or beta activities above background. Several of the samples (SL10A, SL16, SL17A) showed beta activity above background with a greater than 4s confidence level, months after exposure. Portions of SL10A, SL16, and SL17A samples were also scanned using a beta scintillator and found to have beta activity in the tritium energy band, continuing without noticeable decay for over 12 months. Beta scintillation investigation of as-received materials (before x-ray exposure) showed no beta activity in the tritium energy band, indicating the beta emitters were not in the starting materials.

A Catalog of Soft X-Ray Shadows, and More Contemplation of the 1/4 KeV Background

NASA Technical Reports Server (NTRS)

Snowden, S. L.; Freyberg, M. J.; Kuntz, K. D.; Sanders, W. T.

1999-01-01

This paper presents a catalog of shadows in the 1/4 keV soft X-ray diffuse background 4 (SXRB) that were identified by a comparison between ROSAT All-Sky Survey maps and DIRB&corrected IRAS 100 micron maps. These "shadows" are the negative correlations between the surface brightness of the SXRB and the column density of the Galactic interstellar medium (ISIM) over limited angular regions (a few degrees in extent). We have compiled an extensive but not exhaustive set of 378 shadows in the polar regions of the Galaxy (Absolute value (beta) > and approximately equal 20 deg.), and determined their foreground and background X-ray intensities (relative to the absorbing features), and the respective hardness ratios of that emission. The portion of the sky that was examined to find these shadows was restricted in general to regions where the minimum column density is less than and approximately equal to 4 x 10(exp 20) H/square cm, i.e., relatively high Galactic latitudes, and to regions away from distinct extended features in the SXRB such as supernova remnants and superbubbles. The results for the foreground intensities agree well with the recent results of a general analysis of the local 1/4 KeV emission while the background intensities show additional. but not unexpected scatter. The results also confirm the existence of a gradient in the hardness of the local 1/4 keV emission along a Galactic center/ anticenter axis with a temperature that varies from 10(exp 6.13) K to 10(exp 6.02) K, respectively. The average temperature of the foreground component from this analysis is 10(exp 6.08) K, compared to 10(exp 6.06) K in the previous analysis. Likewise, the average temperature for the distant component for the current and previous analyses are 10(exp 6.06) K and 10(exp 6.02) K, respectively. Finally, the results for the 1/4 keV halo emission are compared to the observed fluxes at 3/4 keV, where the lack of correlation suggests that the Galactic halo's 1/4 keV and 3/4 ke
Fermi Large Area Telescope Constraints On The Gamma-Ray Opacity Of The Universe

DOE PAGES

Abdo, A. A.

2010-10-19

The extragalactic background light (EBL) includes photons with wavelengths from ultraviolet to infrared, which are effective at attenuating gamma rays with energy above ~10 GeV during propagation from sources at cosmological distances. This results in a redshift- and energy-dependent attenuation of the γ-ray flux of extragalactic sources such as blazars and gamma-ray bursts (GRBs). The Large Area Telescope on board Fermi detects a sample of γ-ray blazars with redshift up to z ~ 3, and GRBs with redshift up to z ~ 4.3. Using photons above 10 GeV collected by Fermi over more than one year of observations for thesemore » sources, we investigate the effect of γ-ray flux attenuation by the EBL. We place upper limits on the γ-ray opacity of the universe at various energies and redshifts and compare this with predictions from well-known EBL models. We find that an EBL intensity in the optical-ultraviolet wavelengths as great as predicted by the "baseline" model of Stecker et al. can be ruled out with high confidence.« less

Time Projection Chamber Polarimeters for X-ray Astrophysics

NASA Astrophysics Data System (ADS)

Hill, Joanne; Black, Kevin; Jahoda, Keith

2015-04-01

Time Projection Chamber (TPC) based X-ray polarimeters achieve the sensitivity required for practical and scientifically significant astronomical observations, both galactic and extragalactic, with a combination of high analyzing power and good quantum efficiency. TPC polarimeters at the focus of an X-ray telescope have low background and large collecting areas providing the ability to measure the polarization properties of faint persistent sources. TPCs based on drifting negative ions rather than electrons permit large detector collecting areas with minimal readout electronics enabling wide field of view polarimeters for observing unpredictable, bright transient sources such as gamma-ray bursts. We described here the design and expected performance of two different TPC polarimeters proposed for small explorer missions: The PRAXyS (Polarimetry of Relativistic X-ray Sources) X-ray Polarimeter Instrument, optimized for observations of faint persistent sources and the POET (Polarimetry of Energetic Transients) Low Energy Polarimeter, designed to detect and measure bright transients. also NASA/GSFC.
UNDERSTANDING X-RAY STARS:. The Discovery of Binary X-ray Sources

NASA Astrophysics Data System (ADS)

Schreier, E. J.; Tananbaum, H.

2000-09-01

The discovery of binary X-ray sources with UHURU introduced many new concepts to astronomy. It provided the canonical model which explained X-ray emission from a large class of galactic X-ray sources: it confirmed the existence of collapsed objects as the source of intense X-ray emission; showed that such collapsed objects existed in binary systems, with mass accretion as the energy source for the X-ray emission; and provided compelling evidence for the existence of black holes. This model also provided the basis for explaining the power source of AGNs and QSOs. The process of discovery and interpretation also established X-ray astronomy as an essential sub-discipline of astronomy, beginning its incorporation into the mainstream of astronomy.
Thoracic spine x-ray

MedlinePlus

Vertebral radiography; X-ray - spine; Thoracic x-ray; Spine x-ray; Thoracic spine films; Back films ... The test is done in a hospital radiology department or in the health care provider's office. You will lie on the x-ray table in different positions. If the x-ray ...
Fluorescence background subtraction technique for hybrid fluorescence molecular tomography/x-ray computed tomography imaging of a mouse model of early stage lung cancer.

PubMed

Ale, Angelique; Ermolayev, Vladimir; Deliolanis, Nikolaos C; Ntziachristos, Vasilis

2013-05-01

The ability to visualize early stage lung cancer is important in the study of biomarkers and targeting agents that could lead to earlier diagnosis. The recent development of hybrid free-space 360-deg fluorescence molecular tomography (FMT) and x-ray computed tomography (XCT) imaging yields a superior optical imaging modality for three-dimensional small animal fluorescence imaging over stand-alone optical systems. Imaging accuracy was improved by using XCT information in the fluorescence reconstruction method. Despite this progress, the detection sensitivity of targeted fluorescence agents remains limited by nonspecific background accumulation of the fluorochrome employed, which complicates early detection of murine cancers. Therefore we examine whether x-ray CT information and bulk fluorescence detection can be combined to increase detection sensitivity. Correspondingly, we research the performance of a data-driven fluorescence background estimator employed for subtraction of background fluorescence from acquisition data. Using mice containing known fluorochromes ex vivo, we demonstrate the reduction of background signals from reconstructed images and sensitivity improvements. Finally, by applying the method to in vivo data from K-ras transgenic mice developing lung cancer, we find small tumors at an early stage compared with reconstructions performed using raw data. We conclude with the benefits of employing fluorescence subtraction in hybrid FMT-XCT for early detection studies.
X-ray binaries

NASA Technical Reports Server (NTRS)

1976-01-01

Satellite X-ray experiments and ground-based programs aimed at observation of X-ray binaries are discussed. Experiments aboard OAO-3, OSO-8, Ariel 5, Uhuru, and Skylab are included along with rocket and ground-based observations. Major topics covered are: Her X-1, Cyg X-3, Cen X-3, Cyg X-1, the transient source A0620-00, other possible X-ray binaries, and plans and prospects for future observational programs.
Constraining dark matter annihilation with the isotropic γ-ray background: Updated limits and future potential

NASA Astrophysics Data System (ADS)

Bringmann, Torsten; Calore, Francesca; Di Mauro, Mattia; Donato, Fiorenza

2014-01-01

The nature of the isotropic γ-ray background (IGRB) measured by the Large Area Telescope (LAT) on the Fermi γ-ray space telescope (Fermi) remains partially unexplained. Non-negligible contributions may originate from extragalactic populations of unresolved sources such as blazars, star-forming galaxies or galactic millisecond pulsars. A recent prediction of the diffuse γ-ray emission from active galactic nuclei (AGN) with a large viewing angle with respect to the line of sight has demonstrated that this faint but numerous population is also expected to contribute significantly to the total IGRB intensity. A more exotic contribution to the IGRB invokes the pair annihilation of dark matter (DM) weakly interacting massive particles (WIMPs) into γ rays. In this work, we evaluate the room left for galactic DM at high latitudes (>10∘) by including photons from both prompt emission and inverse Compton scattering, emphasizing the impact of the newly discovered contribution from misaligned AGN (MAGN) for such an analysis. Summing up all significant galactic and extragalactic components of the IGRB, we find that an improved understanding of the associated astrophysical uncertainties is still mandatory to put stringent bounds on thermally produced DM. On the other hand, we also demonstrate that the IGRB has the potential to be one of the most competitive future ways to test the DM WIMP hypothesis, once the present uncertainties are even slightly reduced. In fact, if MAGN contribute even at 90% of the maximal level consistent with our current understanding, thermally produced WIMPs would be severely constrained as DM candidates for masses up to several TeV.
First broadband characterization and redshift determination of the VHE blazar MAGIC J2001+439

DOE PAGES

Aleksić, J.; Ansoldi, S.; Antonelli, L. A.; ...

2014-12-09

We aim to characterize the broadband emission from 2FGL J2001.1+4352, which has been associated with the unknown-redshift blazar MG4 J200112+4352. Based on its gamma-ray spectral properties, it was identified as a potential very high energy (VHE; E> 100 GeV) gamma-ray emitter. We investigate whether this object is aVHE emitter, characterize its gamma-ray spectrum, and study the broadband emission within the one-zone synchrotron self-Compton (SSC) scenario, which is commonly used to describe the emission in blazars. Moreover, we also intend to determine the redshift of this object, which is a crucial parameter for its scientific interpretation. Here, the source was observedmore » with MAGIC first in 2009 and later in 2010 within a multi-instrument observation campaign. The MAGIC observations yielded 14.8 h of good quality stereoscopic data. Besides MAGIC, the campaign involved, observations with Fermi-LAT, Swift-XRT/UVOT, the optical telescopes KVA, Goddard Robotic Telescope, Galaxy View observatory, Crimean Astrophysical observatory, St. Petersburg observatory, and the Owens Valley Radio Observatory. The object was monitored at radio, optical and gamma-ray energies during the years 2010 and 2011. We characterize the radio to VHE spectral energy distribution and quantify the multiband variability and correlations over short (few days) and long (many months) timescales. We also organized deep imaging optical observations with the Nordic Optical Telescope in 2013 to determine the source redshift. As a result, the source, named MAGIC J2001+439, is detected for the first time at VHE with MAGIC at a statistical significance of 6.3σ (E > 70 GeV) during a 1.3 h long observation on 2010 July 16. The multi-instrument observations show variability in all energy bands with the highest amplitude of variability in the X-ray and VHE bands. Besides the variability on few-day timescales, the long-term monitoring of MAGIC J2001+439 shows that, the gamma-ray, optical, and radio
Skull x-ray

MedlinePlus

X-ray - head; X-ray - skull; Skull radiography; Head x-ray ... Chernecky CC, Berger BJ. Radiography of skull, chest, and cervical spine - diagnostic. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures . 6th ed. ...
Full-field transmission x-ray imaging with confocal polycapillary x-ray optics

PubMed Central

Sun, Tianxi; MacDonald, C. A.

2013-01-01

A transmission x-ray imaging setup based on a confocal combination of a polycapillary focusing x-ray optic followed by a polycapillary collimating x-ray optic was designed and demonstrated to have good resolution, better than the unmagnified pixel size and unlimited by the x-ray tube spot size. This imaging setup has potential application in x-ray imaging for small samples, for example, for histology specimens. PMID:23460760
CHANDRA ACIS SURVEY OF X-RAY POINT SOURCES IN NEARBY GALAXIES. II. X-RAY LUMINOSITY FUNCTIONS AND ULTRALUMINOUS X-RAY SOURCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Song; Qiu, Yanli; Liu, Jifeng

Based on the recently completed Chandra /ACIS survey of X-ray point sources in nearby galaxies, we study the X-ray luminosity functions (XLFs) for X-ray point sources in different types of galaxies and the statistical properties of ultraluminous X-ray sources (ULXs). Uniform procedures are developed to compute the detection threshold, to estimate the foreground/background contamination, and to calculate the XLFs for individual galaxies and groups of galaxies, resulting in an XLF library of 343 galaxies of different types. With the large number of surveyed galaxies, we have studied the XLFs and ULX properties across different host galaxy types, and confirm withmore » good statistics that the XLF slope flattens from lenticular ( α ∼ 1.50 ± 0.07) to elliptical (∼1.21 ± 0.02), to spirals (∼0.80 ± 0.02), to peculiars (∼0.55 ± 0.30), and to irregulars (∼0.26 ± 0.10). The XLF break dividing the neutron star and black hole binaries is also confirmed, albeit at quite different break luminosities for different types of galaxies. A radial dependency is found for ellipticals, with a flatter XLF slope for sources located between D {sub 25} and 2 D {sub 25}, suggesting the XLF slopes in the outer region of early-type galaxies are dominated by low-mass X-ray binaries in globular clusters. This study shows that the ULX rate in early-type galaxies is 0.24 ± 0.05 ULXs per surveyed galaxy, on a 5 σ confidence level. The XLF for ULXs in late-type galaxies extends smoothly until it drops abruptly around 4 × 10{sup 40} erg s{sup −1}, and this break may suggest a mild boundary between the stellar black hole population possibly including 30 M {sub ⊙} black holes with super-Eddington radiation and intermediate mass black holes.« less
X-ray generator

DOEpatents

Dawson, John M.

1976-01-01

Apparatus and method for producing coherent secondary x-rays that are controlled as to direction by illuminating a mixture of high z and low z gases with an intense burst of primary x-rays. The primary x-rays are produced with a laser activated plasma, and these x-rays strip off the electrons of the high z atoms in the lasing medium, while the low z atoms retain their electrons. The neutral atoms transfer electrons to highly excited states of the highly striped high z ions giving an inverted population which produces the desired coherent x-rays. In one embodiment, a laser, light beam provides a laser spark that produces the intense burst of coherent x-rays that illuminates the mixture of high z and low z gases, whereby the high z atoms are stripped while the low z ones are not, giving the desired mixture of highly ionized and neutral atoms. To this end, the laser spark is produced by injecting a laser light beam, or a plurality of beams, into a first gas in a cylindrical container having an adjacent second gas layer co-axial therewith, the laser producing a plasma and the intense primary x-rays in the first gas, and the second gas containing the high and low atomic number elements for receiving the primary x-rays, whereupon the secondary x-rays are produced therein by stripping desired ions in a neutral gas and transfer of electrons to highly excited states of the stripped ions from the unionized atoms. Means for magnetically confining and stabilizing the plasma are disclosed for controlling the direction of the x-rays.
The X-Ray Binary Population of the Nearby Dwarf Starburst Galaxy IC 10: Variable and Transient X-Ray Sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laycock, Silas; Cappallo, Rigel; Williams, Benjamin F.

We have monitored the Cassiopeia dwarf galaxy (IC 10) in a series of 10 Chandra ACIS-S observations to capture its variable and transient X-ray source population, which is expected to be dominated by High Mass X-ray Binaries (HMXBs). We present a sample of 21 X-ray sources that are variable between observations at the 3 σ level, from a catalog of 110 unique point sources. We find four transients (flux variability ratio greater than 10) and a further eight objects with ratios >5. The observations span the years 2003–2010 and reach a limiting luminosity of >10{sup 35} erg s{sup −1}, providingmore » sensitivity to X-ray binaries in IC 10 as well as flare stars in the foreground Milky Way. The nature of the variable sources is investigated from light curves, X-ray spectra, energy quantiles, and optical counterparts. The purpose of this study is to discover the composition of the X-ray binary population in a young starburst environment. IC 10 provides a sharp contrast in stellar population age (<10 My) when compared to the Magellanic Clouds (40–200 My) where most of the known HMXBs reside. We find 10 strong HMXB candidates, 2 probable background Active Galactic Nuclei, 4 foreground flare-stars or active binaries, and 5 not yet classifiable sources. Complete classification of the sample requires optical spectroscopy for radial velocity analysis and deeper X-ray observations to obtain higher S/N spectra and search for pulsations. A catalog and supporting data set are provided.« less
Upper Limits from Five Years of Blazar Observations with the VERITAS Cherenkov Telescopes

NASA Astrophysics Data System (ADS)

Archambault, S.; Archer, A.; Benbow, W.; Bird, R.; Biteau, J.; Buchovecky, M.; Buckley, J. H.; Bugaev, V.; Byrum, K.; Cerruti, M.; Chen, X.; Ciupik, L.; Connolly, M. P.; Cui, W.; Eisch, J. D.; Errando, M.; Falcone, A.; Feng, Q.; Finley, J. P.; Fleischhack, H.; Fortin, P.; Fortson, L.; Furniss, A.; Gillanders, G. H.; Griffin, S.; Grube, J.; Gyuk, G.; Hütten, M.; Håkansson, N.; Hanna, D.; Holder, J.; Humensky, T. B.; Johnson, C. A.; Kaaret, P.; Kar, P.; Kelley-Hoskins, N.; Kertzman, M.; Kieda, D.; Krause, M.; Krennrich, F.; Kumar, S.; Lang, M. J.; Maier, G.; McArthur, S.; McCann, A.; Meagher, K.; Moriarty, P.; Mukherjee, R.; Nguyen, T.; Nieto, D.; O'Faoláin de Bhróithe, A.; Ong, R. A.; Otte, A. N.; Park, N.; Perkins, J. S.; Pichel, A.; Pohl, M.; Popkow, A.; Pueschel, E.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Rovero, A. C.; Santander, M.; Sembroski, G. H.; Shahinyan, K.; Smith, A. W.; Staszak, D.; Telezhinsky, I.; Tucci, J. V.; Tyler, J.; Vincent, S.; Wakely, S. P.; Weiner, O. M.; Weinstein, A.; Williams, D. A.; Zitzer, B.; VERITAS Collaboration; Fumagalli, M.; Prochaska, J. X.

2016-06-01

Between the beginning of its full-scale scientific operations in 2007 and 2012, the VERITAS Cherenkov telescope array observed more than 130 blazars; of these, 26 were detected as very-high-energy (VHE; E > 100 GeV) γ-ray sources. In this work, we present the analysis results of a sample of 114 undetected objects. The observations constitute a total live-time of ˜570 hr. The sample includes several unidentified Fermi-Large Area Telescope (LAT) sources (located at high Galactic latitude) as well as all the sources from the second Fermi-LAT catalog that are contained within the field of view of the VERITAS observations. We have also performed optical spectroscopy measurements in order to estimate the redshift of some of these blazars that do not have spectroscopic distance estimates. We present new optical spectra from the Kast instrument on the Shane telescope at the Lick observatory for 18 blazars included in this work, which allowed for the successful measurement or constraint on the redshift of four of them. For each of the blazars included in our sample, we provide the flux upper limit in the VERITAS energy band. We also study the properties of the significance distributions and we present the result of a stacked analysis of the data set, which shows a 4σ excess.
UPPER LIMITS FROM FIVE YEARS OF BLAZAR OBSERVATIONS WITH THE VERITAS CHERENKOV TELESCOPES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Archambault, S.; Archer, A.; Buckley, J. H.

2016-06-01

Between the beginning of its full-scale scientific operations in 2007 and 2012, the VERITAS Cherenkov telescope array observed more than 130 blazars; of these, 26 were detected as very-high-energy (VHE; E > 100 GeV) γ -ray sources. In this work, we present the analysis results of a sample of 114 undetected objects. The observations constitute a total live-time of ∼570 hr. The sample includes several unidentified Fermi -Large Area Telescope (LAT) sources (located at high Galactic latitude) as well as all the sources from the second Fermi -LAT catalog that are contained within the field of view of the VERITASmore » observations. We have also performed optical spectroscopy measurements in order to estimate the redshift of some of these blazars that do not have spectroscopic distance estimates. We present new optical spectra from the Kast instrument on the Shane telescope at the Lick observatory for 18 blazars included in this work, which allowed for the successful measurement or constraint on the redshift of four of them. For each of the blazars included in our sample, we provide the flux upper limit in the VERITAS energy band. We also study the properties of the significance distributions and we present the result of a stacked analysis of the data set, which shows a 4 σ excess.« less
X-ray lithography masking

NASA Technical Reports Server (NTRS)

Smith, Henry I. (Inventor); Lim, Michael (Inventor); Carter, James (Inventor); Schattenburg, Mark (Inventor)

1998-01-01

X-ray masking apparatus includes a frame having a supporting rim surrounding an x-ray transparent region, a thin membrane of hard inorganic x-ray transparent material attached at its periphery to the supporting rim covering the x-ray transparent region and a layer of x-ray opaque material on the thin membrane inside the x-ray transparent region arranged in a pattern to selectively transmit x-ray energy entering the x-ray transparent region through the membrane to a predetermined image plane separated from the layer by the thin membrane. A method of making the masking apparatus includes depositing back and front layers of hard inorganic x-ray transparent material on front and back surfaces of a substrate, depositing back and front layers of reinforcing material on the back and front layers, respectively, of the hard inorganic x-ray transparent material, removing the material including at least a portion of the substrate and the back layers of an inside region adjacent to the front layer of hard inorganic x-ray transparent material, removing a portion of the front layer of reinforcing material opposite the inside region to expose the surface of the front layer of hard inorganic x-ray transparent material separated from the inside region by the latter front layer, and depositing a layer of x-ray opaque material on the surface of the latter front layer adjacent to the inside region.
Internal absorption of gamma-rays in relativistic blobs of active galactic nuclei

NASA Astrophysics Data System (ADS)

Sitarek, Julian; Bednarek, Wlodek

2007-06-01

We investigate the production of gamma-rays in the inverse Compton (IC) scattering process by leptons accelerated inside relativistic blobs in jets of active galactic nuclei. Leptons are injected homogeneously inside the spherical blob and initiate IC e ± pair cascade in the synchrotron radiation (produced by the same population of leptons, SSC model), provided that the optical depth for gamma-rays is larger than unity. It is shown that for likely parameters internal absorption of gamma-rays has to be important. We suggest that new type of blazars might be discovered by the future simultaneous X-ray and γ-ray observations, showing peak emissions in the hard X-rays, and in the GeV γ-rays. Moreover, the considered scenario might be also responsible for the orphan X-ray flares recently reported from BL Lac type active galaxies.
Sinus x-ray

MedlinePlus

Paranasal sinus radiography; X-ray - sinuses ... sinus x-ray is taken in a hospital radiology department. Or the x-ray may be taken ... Brown J, Rout J. ENT, neck, and dental radiology. In: Adam A, Dixon AK, Gillard JH, Schaefer- ...
X-Ray Data Booklet

Science.gov Websites

X-RAY DATA BOOKLET Center for X-ray Optics and Advanced Light Source Lawrence Berkeley National Laboratory Introduction X-Ray Properties of Elements Electron Binding Energies X-Ray Energy Emission Energies Table of X-Ray Properties Synchrotron Radiation Characteristics of Synchrotron Radiation History of X
Lone Blazar

NASA Image and Video Library

2012-04-12

This image from NASA WISE spacecraft shows a blazar, a voracious supermassive black hole inside a galaxy with a jet that happens to be pointed right toward Earth. Active black holes are often found at the hearts of elliptical galaxies.
Recent X-ray Variability of Eta Car Approaching The X-ray Eclipse

NASA Technical Reports Server (NTRS)

Corcoran, M.; Swank, J. H.; Ishibashi, K.; Gull, T.; Humphreys, R.; Damineli, A.; Walborn, N.; Hillier, D. J.; Davidson, K.; White, S. M.

2002-01-01

We discuss recent X-ray spectral variability of the supermassive star Eta Car in the interval since the last X-ray eclipse in 1998. We concentrate on the interval just prior to the next X-ray eclipse which is expected to occur in June 2003. We compare the X-ray behavior during the 2001-2003 cycle with the previous cycle (1996-1998) and note similarities and differences in the temporal X-ray behavior. We also compare a recent X-ray observation of Eta Car obtained with the Chandra high energy transmission grating in October 2002 with an earlier observation from Nov 2002, and interpret these results in terms of the proposed colliding wind binary model for the star. In addition we discuss planned observations for the upcoming X-ray eclipse.

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