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Sample records for gamma-ray blazar pg

  1. Evidence for quasi-periodic modulation in the gamma-ray blazar PG 1553+113

    NASA Astrophysics Data System (ADS)

    Cutini, Sara; Ciprini, Stefano; Larsson, Stefan; Thompson, David John; Stamerra, Antonio; Fermi LAT Collaboration

    2016-01-01

    For the first time a gamma-ray and multiwavelength nearly-periodic oscillation in an active galactic nucleus is reported using the Fermi Large Area Telescope (LAT). A quasi-periodicity in the gamma-ray flux (E>100 MeV and E>1 GeV) is observed from the well-known GeV/TeV BL Lac object PG 1553+113 (Ackermann et al. submitted). The significance of the 2.18 +/- 0.08 year-period gamma-ray modulation, seen in 3.5 oscillation maxima observed, is supported by significant cross-correlated variations observed in radio and optical flux light curves, through data collected in the OVRO, Tuorla, KAIT, and CSS monitoring programs and Swift UVOT. The optical cycle, appearing in about 10 years of data, has a similar period, while the radio-band oscillation observed at 15 GHz is less regular and coherent. The available X-ray flux data obtained by Swift XRT appears also to be linearly correlated with the gamma-ray flux. Further long-term multi-wavelength monitoring of this blazar may discriminate among the possible explanations for this first evidence of periodicity.

  2. UNIDENTIFIED {gamma}-RAY SOURCES: HUNTING {gamma}-RAY BLAZARS

    SciTech Connect

    Massaro, F.; Ajello, M.; D'Abrusco, R.; Paggi, A.; Tosti, G.; Gasparrini, D.

    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, 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 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.

  3. Unidentified Gamma-Ray Sources: Hunting Gamma-Ray Blazars

    SciTech Connect

    Massaro, F.; D'Abrusco, R.; Tosti, G.; Ajello, M.; Gasparrini, A.Paggi.D.

    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. Based 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.

  4. Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-Ray Blazar PG 1553+113

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Ajello, M.; Albert, A.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Becerra Gonzalez, J.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonino, R.; Bottacini, E.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caputo, R.; Caragiulo, M.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Chekhtman, A.; Chiang, J.; Chiaro, G.; Ciprini, S.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; D'Ammando, F.; de Angelis, A.; de Palma, F.; Desiante, R.; Di Venere, L.; D´nguez, A.; Drell, P. S.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fuhrmann, L.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Godfrey, G.; Green, D.; Grenier, I. A.; Grove, J. E.; Guiriec, S.; Harding, A. K.; Hays, E.; Hewitt, J. W.; Hill, A. B.; Horan, D.; Jogler, T.; Jóhannesson, G.; Johnson, A. S.; Kamae, T.; Kuss, M.; Larsson, S.; Latronico, L.; Li, J.; Li, L.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Magill, J.; Maldera, S.; Manfreda, A.; Max-Moerbeck, W.; Mayer, M.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nuss, E.; Ohno, M.; Ohsugi, T.; Ojha, R.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Pearson, T. J.; Perkins, J. S.; Perri, M.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Readhead, A.; Reimer, A.; Reimer, O.; Schulz, A.; Sgrò, C.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Suson, D. J.; Takahashi, H.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Vianello, G.; Wood, K. S.; Wood, M.; Zimmer, S.; Berdyugin, A.; Corbet, R. H. D.; Hovatta, T.; Lindfors, E.; Nilsson, K.; Reinthal, R.; Sillanpää, A.; Stamerra, A.; Takalo, L. O.; Valtonen, M. J.

    2015-11-01

    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 data 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.

  5. Hard gamma ray emission from blazars

    NASA Technical Reports Server (NTRS)

    Marscher, Alan P.; Bloom, Steven D.

    1992-01-01

    The gamma-ray emission expected from compact extragalactic sources of nonthermal radiation is examined. The highly variable objects in this class should produce copious amounts of self-Compton gamma-rays in the compact relativistic jet. This is shown to be a likely interpretation of the hard gamma-ray emission recently detected from the quasar 3C 279 during a period of strong nonthermal flaring at lower frequencies. Ways of discriminating between the self-Compton model and other possible gamma-ray emission mechanisms are discussed.

  6. Elevated Optical Luminosity for Gamma-ray Blazar BL Lacertae

    NASA Astrophysics Data System (ADS)

    Furniss, A.; Fumagalli, M.; Hogan, M.; Kaplan, K.; Prochaska, P. X.; Williams, D. A.

    2012-06-01

    We report on the increased optical luminosity of BL Lacertae (RA=22h02m43.29s, dec=42d16m39.98s), a low-frequency-peaked gamma-ray emitting blazar at a redshift of 0.068 (3EG J2202+4225, 2FGL J2202.8+4216). We have collected regular R-band exposures for BL Lacertae as part of a larger optical monitoring program of gamma-ray-bright blazars using the Super-LOTIS (Livermore Optical Transient Imaging System) robotic telescope at the Steward Observatory on Kitt Peak, near Tucson Arizona.

  7. 15 GHz Radio Variability of Gamma-Ray Blazars

    NASA Astrophysics Data System (ADS)

    Richards, Joseph; Max-Moerbeck, W.; Pavlidou, V.; Pearson, T. J.; Readhead, A. C. S.; Stevenson, M. A.; King, O. G.; Reeves, R.; Angelakis, E.; Fuhrmann, L.; Zensus, J. A.; Healey, S. E.; Romani, R. W.; Shaw, M. S.; Grainge, K.; Taylor, G. B.; Cotter, G.

    2011-01-01

    Since 2007, the Owens Valley Radio Observatory (OVRO) 40 meter telescope has been engaged in an intensive fast-cadence gamma-ray blazar monitoring program, observing about 1500 objects twice per week. Using our intrinsic modulation index method and careful likelihood analyses, we find that gamma-ray loud objects associated with Fermi 1LAC sources in our sample demonstrate radio variability amplitudes significantly larger than do gamma-ray quiet objects. We also find significant differences in variability amplitude between flat spectrum radio quasars and BL Lacertae objects within our sample as well as possible evidence for cosmological evolution of variability amplitude.

  8. 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

  9. Triggered Observations of a new VHE Gamma-ray Blazar

    NASA Astrophysics Data System (ADS)

    Boettcher, Markus

    2011-10-01

    We propose triggered observations of a new VHE blazar. Observations will be triggered following the detection of a flaring state by VERITAS. Simultaneous radio, near-IR, and optical coverage by the GLAST-AGILE Support Program (GASP) will be arranged, and we will include Fermi MeV -- GeV gamma-ray data. The proposed campaign aims at the study of new TeV blazars with data to allow meaningful studies of their broadband spectral and variability properties, and ultimately understand the mechanisms of particle acceleration and emission of radiation in TeV blazars. This proposal follows the same strategy as a predecessor proposal in AO-6 which was triggered and led to a highly successful multiwavelength campaign on W~Comae in June 2008.

  10. Studying Gamma-Ray Blazars With the GLAST-LAT

    SciTech Connect

    Lott, B.; Carson, J.; Madejski, G.; Ciprini, S.; Dermer, C.D.; Giommi, P.; Lonjou, V.; Reimer, A.; /Stanford U., HEPL /KIPAC, Menlo Park

    2007-11-13

    Thanks to its sensitivity (4 10{sup -9} ph (E> 100 MeV) cm{sup -2} s{sup -1} for one year of observation), the GLAST LAT should detect many more (over a thousand) gamma-ray blazars than currently known. This large blazar sample will enable detailed population studies to be carried out. Moreover, the LAT large field-of-view combined with the scanning mode will provide a very uniform exposure over the sky, allowing a constant monitoring of several tens of blazars and flare alerts to be issued. This poster presents the LAT performance relevant to blazar studies, more particularly related to timing and spectral properties. Major specific issues regarding the blazar phenomenon that the LAT data should shed light on thanks to these capabilities will be discussed, as well as the different approaches foreseen to address them. The associated data required in other bands, to be collected in contemporaneous/simultaneous multiwavelength campaigns are mentioned as well.

  11. The Gamma-Ray Blazar Quest: state of the art and future perspectives

    NASA Astrophysics Data System (ADS)

    Massaro, Francesco; Alvarez Crespo, Nuria; D'Abrusco, Raffaele; Landoni, Marco; Masetti, Nicola; Ricci, Federica; Milisavljevic, Dan; Paggi, Alessandro; Smith, Howard Alan

    2016-04-01

    In 2011 we discovered that gamma-ray blazars detected by Fermi show extremely peculiar infrared colors. On the basis of this discovery we developed a procedure that allowed us to recognize gamma-ray blazar candidates within the sources associated in the Fermi catalogs with an uncertain classification. We also built a method to search for blazar-like sources as potential counterpart of the unidentified gamma-ray sources (UGSs). However, to confirm the real nature of the selected candidates, optical spectroscopy is necessary. Thus, we started an optical spectroscopic campaign to observe the selected gamma-ray blazar candidates and unveil their origin. In this work we present the state-of-art of our observational campaign that allowed us to discover previously unknown gamma-ray blazars and a review of the results achieved to date. Future perspectives of our observing strategy developed to ''resolve the gamma-ray sky`` having all Fermi objects associated will be also discussed.

  12. The Radio Variability of Gamma-Ray Blazars

    NASA Astrophysics Data System (ADS)

    Richards, Joseph

    2012-01-01

    Since late 2007, we have regularly monitored over 1100 systematically-selected blazars at 15 GHz using the Owens Valley Radio Observatory 40m radio telescope. The number of sources in the program has grown to nearly 1600, including all the active galactic nuclei associated with Fermi Large Area Telescope (LAT) gamma-ray point source detections north of our declination limit of -20°. Here, we describe the first 42 months of this program, including the automated data reduction pipeline and MySQL database system for storing the reduced data and intermediate data products. Using the "intrinsic modulation index," a maximum-likelihood method, we estimate the variability amplitudes for 1413 sources from their radio light curves and compare the properties of physically-defined subpopulations of the sample. We find that, among our preselected sample, gamma-ray-loud blazars detected by the LAT are significantly more variable at 15 GHz, attributable to a difference in variability between the gamma-ray-loud and gamma-ray-quiet flat spectrum radio quasars. The BL Lacertae objects in the samples do not show this division in variability amplitudes. In the first two years of our program, a 3σ-significant difference between variability amplitudes for sources at redshift z≥1 and for sources at z<1 was found. This difference is found no longer to be significant in the full 42-month data set, particularly after we apply an analysis method to account for the effect of cosmological time dilation. This work was supported in part by NASA grants NNX08AW31G and NNG06GG1G and NSF grant AST-0808050.

  13. The Radio Variability of Gamma-Ray Blazars

    NASA Astrophysics Data System (ADS)

    Richards, Joseph Lee

    2012-05-01

    Since late 2007, we have regularly monitored over 1100 systematically selected blazars at 15 GHz using the Owens Valley Radio Observatory 40 m radio telescope. The number of sources in the program has grown to nearly 1600, including all the active galactic nuclei associated with Fermi Large Area Telescope (LAT) gamma-ray point source detections north of our declination limit of -20°. Here, we describe the first 42 months of this program, including the design and implementation of an automated data reduction pipeline and a MySQL database system for storing the reduced data and intermediate data products. Using the "intrinsic modulation index," a maximum-likelihood method, we estimate the variability amplitudes for 1413 sources from their radio light curves and compare the properties of physically defined subpopulations of the sample. We find that, among our preselected sample, gamma-ray--loud blazars detected by the LAT are significantly more variable at 15 GHz, attributable to a difference in variability between the gamma-ray--loud and gamma-ray--quiet flat spectrum radio quasars. The BL Lacertae objects in the samples do not show this division in variability amplitudes. In the first two years of our program, a 3sigma-significant difference between variability amplitudes for sources at redshift z ≥ 1 and for sources at z < 1 was found. This difference is found no longer to be significant in the full 42-month data set, particularly after we apply an analysis method to account for the effect of cosmological time dilation.

  14. Blazars and gamma-ray cosmology: recent and prospective results

    NASA Astrophysics Data System (ADS)

    Biteau, Jonathan; Williams, David A.

    2016-01-01

    Blazars are dazzling gamma-ray beacons shedding light on some of the darkest mysteries of modern-day astroparticle physics. Some of these mysteries include the light content of the universe, including the UV-IR background, the emission of first stars and of organic molecules; large-scale magnetic fields and their potential primordial origin; spacetime structure, with the potential for Lorentz-invariance violations near the Planck scale; and the search for new interaction channels with photons, e.g. in the form of axion-like particles. These crucial scientific topics can be studied through the signatures of billion-year propagation of GeV-TeV gamma rays that reach Earth from astrophysical sources. We discuss how spectral imprints in data from ground-based and satellite experiments are beginning to answer some of the fundamental questions of gamma-ray cosmology. Recent results, obtained with increased datasets and advanced analysis techniques, are opening the path for future observatories. We examine the areas that remain to be explored, in particular by the proposed Cherenkov Telescope Array, CTA.

  15. Gamma-ray blazars: The view from AGILE

    NASA Astrophysics Data System (ADS)

    D'Ammando, F.; Bulgarelli, A.; Chen, A. W.; Donnarumma, I.; Giuliani, A.; Longo, F.; Pacciani, L.; Pucella, G.; Striani, E.; Tavani, M.; Vercellone, S.; Vittorini, V.; Covino, S.; Krimm, H. A.; Raiteri, C. M.; Romano, P.; Villata, M.

    2011-07-01

    During the first 3 years of operation the Gamma-Ray Imaging Detector onboard the AGILE satellite detected several blazars in a high γ-ray activity: 3C 279, 3C 454.3, PKS 1510-089, S5 0716+714, 3C 273, W Comae, Mrk 421, PKS 0537-441 and 4C +21.35. Thanks to the rapid dissemination of our alerts, we were able to obtain multiwavelength data from other observatories such as Spitzer, Swift, RXTE, Suzaku, INTEGRAL, MAGIC, VERITAS, and ARGO as well as radio-to-optical coverage by means of the GASP Project of the WEBT and the REM Telescope. This large multifrequency coverage gave us the opportunity to study the variability correlations between the emission at different frequencies and to obtain simultaneous Spectral Energy Distributions of these sources from radio to γ-ray energy bands, investigating the different mechanisms responsible for their emission and uncovering in some cases a more complex behavior with respect to the standard models. We present a review of the most interesting AGILE results on these γ-ray blazars and their multifrequency data.

  16. 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.

    2016-09-01

    We present average R-band optopolarimetric data, as well as variability parameters, from the first and second RoboPolobserving 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.

  17. Renewed Gamma-Ray Emission from the blazar PKS 1510-089 Detected by AGILE

    NASA Astrophysics Data System (ADS)

    Munar-Adrover, P.; Pittori, C.; Bulgarelli, A.; Lucarelli, F.; Verrecchia, F.; Piano, G.; Fioretti, V.; Zoli, A.; Tavani, M.; Vercellone, S.; Minervini, G.; 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.; Donnarumma, I.; 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.; Parmiggiani, N.; Ferrari, A.; Antonelli, A.; Giommi, P.; Salotti, L.; Valentini, G.; D'Amico, F.

    2016-09-01

    AGILE is currently detecting enhanced gamma-ray emission above 100 MeV from a source which position is consistent with the blazar PKS 1510-089. (the last activity of this source was reported in ATel #9350).

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

    SciTech Connect

    Singal, J.; Ko, A.; Petrosian, V.

    2014-05-10

    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 accounted 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.

  19. 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.

  20. SEARCHING FOR {gamma}-RAY BLAZAR CANDIDATES AMONG THE UNIDENTIFIED INTEGRAL SOURCES

    SciTech Connect

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

    2012-05-10

    The identification of low-energy counterparts for {gamma}-ray sources is one of the biggest challenges in modern {gamma}-ray astronomy. Recently, we developed and successfully applied a new association method to recognize {gamma}-ray blazar candidates that could be possible counterparts for the unidentified {gamma}-ray sources above 100 MeV in the second Fermi Large Area Telescope Catalog. This method is based on the infrared colors of the recent Wide-Field Infrared Survey Explorer (WISE) all-sky survey. In this Letter, we applied our new association method to the case of unidentified INTEGRAL sources (UISs) listed in the fourth soft gamma-ray source catalog. Only 86 UISs out of the 113 can be analyzed due to the sky coverage of the WISE Preliminary Data Release. Among these 86 UISs, we found that 18 appear to have a {gamma}-ray blazar candidate within their positional error region. Finally, we analyzed Swift archival data available for 10 out of these 18 {gamma}-ray blazar candidates, and we found that 7 out of 10 are clearly detected in soft X-rays and/or in the optical-ultraviolet band. We cannot confirm the associations between the UISs and the selected {gamma}-ray blazar candidates due to the discrepancies between the INTEGRAL and the soft X-ray spectra. However, the discovery of the soft X-ray counterparts for the selected {gamma}-ray blazar candidates adds an important clue to help us understand their origin and to confirm their blazar nature.

  1. Searching for Gamma-Ray Blazar Candidates Among the Unidentified INTEGRAL Sources

    SciTech Connect

    Massaro, F.; Paggi, A.; D'Abrusco, R.; Tosti, G.; /Perugia U.

    2012-04-02

    The identification of low-energy counterparts for {gamma}-ray sources is one of the biggest challenge in modern {gamma}-ray astronomy. Recently, we developed and successfully applied a new association method to recognize {gamma}-ray blazar candidates that could be possible counterparts for the unidentified {gamma}-ray sources above 100 MeV in the second Fermi Large Area Telescope (LAT) catalog (2FGL). This method is based on the Infrared (IR) colors of the recent Wide-Field Infrared Survey Explorer (WISE) all-sky survey. In this letter we applied our new association method to the case of unidentified INTEGRAL sources (UISs) listed in the fourth soft gamma-ray source catalog (4IC). Only 86 UISs out of the 113 can be analyzed, due to the sky coverage of the WISE Preliminary data release. Among these 86 UISs, we found that 18 appear to have a {gamma}-ray blazar candidate within their positional error region. Finally, we analyzed the Swift archival data available for 10 out these 18 {gamma}-ray blazar candidates, and we found that 7 out of 10 are clearly detected in soft X-rays and/or in the optical-ultraviolet band. We cannot confirm the associations between the UISs and the selected {gamma}-ray blazar candidates due to the discrepancies between the INTEGRAL and the soft X-ray spectra. However, the discovery of the soft X-ray counterparts for the selected {gamma}-ray blazar candidates adds an important clue to help understand their origin and to confirm their blazar nature.

  2. IDENTIFICATION OF NEW GAMMA-RAY BLAZAR CANDIDATES WITH MULTIFREQUENCY ARCHIVAL OBSERVATIONS

    SciTech Connect

    Cowperthwaite, Philip S.; Massaro, F.; D'Abrusco, R.; Paggi, A.; Smith, Howard A.; Tosti, G.

    2013-11-01

    Blazars are a highly variable, radio-loud subclass of active galactic nuclei. In order to better understand such objects we must be able to easily identify candidate blazars from the growing population of unidentified sources. Working toward this goal, we attempt to identify new gamma-ray blazar candidates from a sample of 102 previously unidentified sources. These sources are selected from The Astronomer's Telegram and the literature on the basis of non-periodic variability and multi-wavelength behavior. We then attempt to associate these objects to an IR counterpart in the Wide-field Infrared Survey Explorer all-sky survey. We are able to identify 16 candidate sources whose IR colors are consistent with those of the blazar population. Of those, 13 sources have IR colors indicative of being gamma-ray emitting blazar candidates. These sources all possess archival multi-wavelength observations that support their blazar-like nature.

  3. Identification of New Gamma-Ray Blazar Candidates with Multifrequency Archival Observations

    NASA Astrophysics Data System (ADS)

    Cowperthwaite, Philip S.; Massaro, F.; D'Abrusco, R.; Paggi, A.; Tosti, G.; Smith, Howard A.

    2013-11-01

    Blazars are a highly variable, radio-loud subclass of active galactic nuclei. In order to better understand such objects we must be able to easily identify candidate blazars from the growing population of unidentified sources. Working toward this goal, we attempt to identify new gamma-ray blazar candidates from a sample of 102 previously unidentified sources. These sources are selected from The Astronomer's Telegram and the literature on the basis of non-periodic variability and multi-wavelength behavior. We then attempt to associate these objects to an IR counterpart in the Wide-field Infrared Survey Explorer all-sky survey. We are able to identify 16 candidate sources whose IR colors are consistent with those of the blazar population. Of those, 13 sources have IR colors indicative of being gamma-ray emitting blazar candidates. These sources all possess archival multi-wavelength observations that support their blazar-like nature.

  4. TEMPORAL CORRELATIONS BETWEEN OPTICAL AND GAMMA-RAY ACTIVITY IN BLAZARS

    SciTech Connect

    Cohen, Daniel P.; Filippenko, Alexei V.; Zheng, WeiKang; Li, Weidong; Romani, Roger W.; Cenko, S. Bradley

    2014-12-20

    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. 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. It is clear that long-term monitoring at high cadence is necessary to reveal the underlying physical correlation.

  5. Temporal Correlations between Optical and Gamma-Ray Activity in Blazars

    NASA Astrophysics Data System (ADS)

    Cohen, Daniel P.; Romani, Roger W.; Filippenko, Alexei V.; Cenko, S. Bradley; Lott, Benoit; Zheng, WeiKang; Li, Weidong

    2014-12-01

    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. 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. It is clear that long-term monitoring at high cadence is necessary to reveal the underlying physical correlation.

  6. 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.

  7. X-RAY AND GAMMA-RAY POLARIZATION IN LEPTONIC AND HADRONIC JET MODELS OF BLAZARS

    SciTech Connect

    Zhang, H.; Boettcher, M.

    2013-09-01

    We present a theoretical analysis of the expected X-ray and {gamma}-ray polarization signatures resulting from synchrotron self-Compton emission in leptonic models compared to the polarization signatures from proton synchrotron and cascade synchrotron emission in hadronic models for blazars. Source parameters resulting from detailed spectral-energy-distribution modeling are used to calculate photon-energy-dependent upper limits on the degree of polarization, assuming a perfectly organized mono-directional magnetic field. In low-synchrotron-peaked blazars, hadronic models exhibit substantially higher maximum degrees of X-ray and gamma-ray polarization than leptonic models, which may be within reach of existing X-ray and {gamma}-ray polarimeters. In high-synchrotron-peaked blazars (with electron-synchrotron-dominated X-ray emission), leptonic and hadronic models predict the same degree of X-ray polarization but substantially higher maximum {gamma}-ray polarization in hadronic models than leptonic ones. These predictions are particularly relevant in view of the new generation of balloon-borne X-ray polarimeters (and possibly GEMS, if revived), and the ability of Fermi-LAT to measure {gamma}-ray polarization at <200 MeV. We suggest observational strategies combining optical, X-ray, and {gamma}-ray polarimetry to determine the degree of ordering of the magnetic field and to distinguish between leptonic and hadronic high-energy emissions.

  8. VARIABILITY OF GAMMA-RAY EMISSION FROM BLAZARS ON BLACK HOLE TIMESCALES

    SciTech Connect

    Vovk, Ie.; Neronov, A.

    2013-04-20

    We investigate the variability properties of blazars in the GeV band using data from the Fermi/Large Area Telescope (LAT) telescope. We find that blazars exhibit variability down to the minimum timescale resolvable by Fermi; this variability is a function of the peak photon count rate in the LAT. This implies that the real minimum variability timescales for the majority of blazars are typically shorter than those resolvable by the LAT. We find that for several blazars these minimum variability timescales reach those associated with the blazar central engine, the supermassive black hole. At the same time, none of the blazars exhibits variability on a timescale shorter than the black hole horizon light-crossing time and/or the period of rotation around the last stable circular orbit. Based on this fact, we argue that the timing properties of the {gamma}-ray signal could be determined by the processes in the direct vicinity of the supermassive black hole.

  9. Probing the Disk-Jet Connection in Fermi Gamma-Ray Bright Blazars

    NASA Astrophysics Data System (ADS)

    Isler, Jedidah; Urry, C. M.; Coppi, P. S.; Bailyn, C. D.; Chatterjee, R.; Fossati, G.; Bonning, E. W.; Maraschi, L.; Buxton, M.; SMARTS

    2014-01-01

    Relativistic jets in blazars produce radio through gamma-ray emission, via synchrotron radiation at long wavelengths and inverse Compton scattering at gamma-ray energies. Variability across these wavelengths allows us to estimate the densities and energies of the radiating particles. Yet, the physics of blazar jets is still uncertain; e.g., it is not clear whether the gamma-rays come from sub- or kilo-parsec scales. The unprecedented temporal and spectral sensitivity of the Fermi Space Telescope has ushered in a new era of discovery and over the past 5 years I have obtained queue-scheduled, nightly optical-infrared (OIR) photometry and bi-weekly optical spectroscopy using the Small and Medium Aperture Research Telescope System (SMARTS) 1.3m+Andicam and 1.5m+RCSpec, in Cerro Tololo, Chile; totaling ~70 gamma-ray bright blazars that are detected nightly with Fermi. In my dissertation, I analyze 5 years of bi-monthly spectroscopy of 6 blazars. I find that the broad lines - which are presumably photoionized by the accretion disk - vary substantially less than the OIR continuum, which is dominated by the Doppler-beamed jet. However, during the largest gamma-ray flares in 3C 454.3 and PKS 1510-089, I see significant broad emission line variations, with lags on the order days and infer that the jet, in its brightest state, contributes significantly to photoionizing the broad-line clouds, meaning the gamma-emitting region is within the broad line region at sub-parsec scales. These variations are not seen at lower gamma-ray fluxes or in any other blazars we observed. I also describe inferences about the jet physics obtained from the SMARTS OIR photometry, which is well correlated with the gamma-ray flux for 11 blazars, with lags of less than one day, strongly supporting the inverse Compton model for gamma-ray production. In addition, color changes in the OIR constrain the ratio of thermal disk to non-thermal jet emission. The color evolution differs by source and also in a

  10. AGILE confirmation of enhanced gamma-ray activity from the Blazar 1ES 1959+650

    NASA Astrophysics Data System (ADS)

    Lucarelli, F.; Pittori, C.; Verrecchia, F.; Bulgarelli, A.; Fioretti, V.; Zoli, A.; Piano, G.; Munar-Adrover, P.; Tavani, M.; 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.; Parmiggiani, N.; Ferrari, A.; Antonelli, A.; Giommi, P.; Salotti, L.; Valentini, G.; D'Amico, F.

    2016-06-01

    Following ATel #9148, reporting multi-wavelength activity from the BL Lac type blazar 1ES 1959+650, AGILE also detects increased gamma-ray emission above 100 MeV from a position compatible with this BL Lac source.

  11. Rapid Gamma-Ray and Optical Variability in Bright Fermi Blazars

    NASA Astrophysics Data System (ADS)

    Coppi, Paolo S.; Saitoh, Shinya; Stawarz, Lukasz

    2016-04-01

    Using an "aperture photometry" technique to generate Fermi lightcurves on minute timescales, we have searched the brightest blazar flares for variability down to ~10 minute timescales. We find evidence for strong gamma-ray variability down to ~1 - 2 hour timescales, but not on ~10-30 minute timescales even though the photon statistics are sufficient to detect it. Using SMARTS optical/NIR, we then search for correlated rapid optical variability on similar timescales. While variability on these very short timescales is detected in a few cases, the optical variability amplitude is typically much smaller than the gamma-ray one. Interestingly, on ~1-3 daytimescales the optical and gamma-ray variability are instead well-correlated and of similar amplitude. We discuss the implications of this variability behavior for blazar modeling.

  12. ON WEAK REDSHIFT DEPENDENCE OF GAMMA-RAY SPECTRA OF DISTANT BLAZARS

    SciTech Connect

    Essey, Warren; Kusenko, Alexander

    2012-05-20

    Line-of-sight interactions of cosmic rays provide a natural explanation of the hard gamma-ray spectra of distant blazars, which are believed to be capable of producing both gamma rays and cosmic rays. For sources with redshifts z {approx}> 0.1, secondary gamma rays produced in cosmic-ray interactions with background photons close to an observer can dominate over primary gamma rays originating at the source. The transition from one component to another is accompanied by a change in the spectral index depending on the source redshift. We present theoretical predictions and show that they agree with the data from Fermi Large Area Telescope. This agreement, combined with the spectral data from Atmospheric Cherenkov Telescopes, provides evidence of cosmic-ray acceleration by active galactic nuclei and opens new opportunities for studying photon backgrounds and intergalactic magnetic fields.

  13. THE REMARKABLE {gamma}-RAY ACTIVITY IN THE GRAVITATIONALLY LENSED BLAZAR PKS 1830-211

    SciTech Connect

    Donnarumma, I.; De Rosa, A.; Vittorini, V.; Tavani, M.; Striani, E.; Pacciani, L.; Popovic, L. C.; Simic, S.; Kuulkers, E.; Vercellone, S.; Verrecchia, F.; Pittori, C.; Giommi, P.; Barbiellini, G.; Bulgarelli, A.

    2011-08-01

    We report the extraordinary {gamma}-ray activity (E > 100 MeV) of the gravitationally lensed blazar PKS 1830-211 (z = 2.507) detected by AGILE between 2010 October and November. On October 14, the source experienced a factor of {approx}12 flux increase with respect to its average value and remained brightest at this flux level ({approx}500 x 10{sup -8} photons cm{sup -2} s{sup -1}) for about four days. The one-month {gamma}-ray light curve across the flare showed a mean flux F(E > 100 MeV) = 200 x 10{sup -8} photons cm{sup -2} s{sup -1}, which resulted in a factor of four enhancement with respect to the average value. Following the {gamma}-ray flare, the source was observed in near-IR (NIR)-optical energy bands at the Cerro Tololo Inter-American Observatory and in X-Rays by Swift/X-Ray Telescope and INTEGRAL/IBIS. The main result of these multifrequency observations is that the large variability observed in {gamma}-rays does not have a significant counterpart at lower frequencies: no variation greater than a factor of {approx}1.5 appeared in the NIR and X-Ray energy bands. PKS 1830-211 is then a good '{gamma}-ray only flaring' blazar showing substantial variability only above 10-100 MeV. We discuss the theoretical implications of our findings.

  14. The connection between the 15 GHz radio and gamma-ray emission in blazars

    NASA Astrophysics Data System (ADS)

    Max-Moerbeck, W.; Richards, J. L.; Hovatta, T.; Pavlidou, V.; Pearson, T. J.; Readhead, A. C. S.; King, O. G.; Reeves, R.

    2015-03-01

    Since mid-2007 we have carried out a dedicated long-term monitoring programme at 15 GHz using the Owens Valley Radio Observatory 40 meter telescope (OVRO 40m). One of the main goals of this programme is to study the relation between the radio and gamma-ray emission in blazars and to use it as a tool to locate the site of high energy emission. Using this large sample of objects we are able to characterize the radio variability, and study the significance of correlations between the radio and gamma-ray bands. We find that the radio variability of many sources can be described using a simple power law power spectral density, and that when taking into account the red-noise characteristics of the light curves, cases with significant correlation are rare. We note that while significant correlations are found in few individual objects, radio variations are most often delayed with respect to the gamma-ray variations. This suggests that the gamma-ray emission originates upstream of the radio emission. Because strong flares in most known gamma-ray-loud blazars are infrequent, longer light curves are required to settle the issue of the strength of radio-gamma cross-correlations and establish confidently possible delays between the two. For this reason continuous multiwavelength monitoring over a longer time period is essential for statistical tests of jet emission models.

  15. The high-energy diffuse cosmic gamma-ray background radiation from blazars

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.; Salamon, M. H.; Malkan, M. A.

    1993-01-01

    We predict the spectrum and flux of the high-energy diffuse cosmic gamma-ray background radiation produced by blazars. Our calculations are based on the Compton Observatory EGRET observations of high-energy gamma-rays from these objects, the Whipple observation of TeV gamma-rays from Mrk 421, and radio population studies of flat-spectrum radio sources. Our statistical analysis gives a result consistent with a linear correlation. We then use the radio luminosity function and redshift evolution to calculate the gamma-ray background. We find that blazars cannot account for the flux level or steep spectrum of the background observed by SAS 2 in the sub-GeV range, but could likely provide the dominant background component in the multi-GeV energy range and above. We predict a differential photon spectral index for this component of about 2 up to about 10 GeV. Above that energy, the spectrum should gradually steepen owing to pair production by interactions of the gamma-rays with intergalactic infrared photons. Using the calculations of this effect by Stecker et al. (1992), we estimate a spectral index of about 3.5 for energies above a TeV.

  16. Optical Photometry of the flaring gamma-ray blazar AO 0235+164

    NASA Astrophysics Data System (ADS)

    Pursimo, Tapio; Losada, Illa R.; Messa, Matteo; Gafton, Emanuel; Ojha, Roopesh

    2016-03-01

    We report optical photometry of the blazar AO 0235+164 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 seen in the public lightcurve of the Fermi/LAT instrument: http://fermi.gsfc.nasa.gov/FTP/glast/data/lat/catalogs/asp/current/lightcurves/0235+164_86400.png Fermi/LAT first reported a detection of gamma-ray activity from this source in Sep, 2008 (ATel#1744) and a short timescale flare in Oct 14, 2008 (ATel#1784).

  17. UNVEILING THE NATURE OF THE UNIDENTIFIED GAMMA-RAY SOURCES. III. GAMMA-RAY BLAZAR-LIKE COUNTERPARTS AT LOW RADIO FREQUENCIES

    SciTech Connect

    Massaro, F.; Funk, S.; D'Abrusco, R.; Paggi, A.; Giroletti, M.; Masetti, N.; Tosti, G.; Nori, M.

    2013-07-01

    About one-third of the {gamma}-ray sources listed in the second Fermi Large Area Telescope catalog (2FGL) have no firmly established counterpart at lower energies and so are classified as unidentified gamma-ray sources (UGSs). Here, we propose a new approach to find candidate counterparts for the UGSs based on the 325 MHz radio survey performed with the Westerbork Synthesis Radio Telescope in the northern hemisphere. First, we investigate the low-frequency radio properties of blazars, the largest known population of {gamma}-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS) with those of the NRAO Very Large Array Sky Survey. We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in the literature to look for infrared and optical counterparts of the {gamma}-ray blazar candidates selected using the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research, we identify 23 new {gamma}-ray blazar candidates out of the 32 UGSs investigated. Comparison with previous results on the UGSs is also presented. Finally, we speculate on the advantages of using low-frequency radio observations to associate UGSs and to search for {gamma}-ray pulsar candidates.

  18. Rapid millimeter and centimeter band flux density increase in the gamma-ray blazar BL Lacertae

    NASA Astrophysics Data System (ADS)

    Hovatta, Talvikki; Richards, Joseph L.; Max-Moerbeck, Walter; Pearson, Timothy J.; Readhead, Anthony C. S.

    2012-11-01

    We have observed a rapid flux density increase of BL Lacertae (2200+420) at 15 GHz (2 cm) and 95 GHz (3 mm) following the report on highest millimeter flux density ever observed at the SMA (ATel #4557). Since 2009, BL Lacertae has been observed approximately twice per week at 15 GHz with the Owens Valley Radio Observatory (OVRO) 40m Telescope as part of our gamma-ray blazar monitoring program (Richards et al....

  19. The High-energy Continuum Emission of the Gamma-Ray Blazar PKS 0528+134

    NASA Technical Reports Server (NTRS)

    Sambruna, Rita M.; Urry, C. Megan; Maraschi, L.; Ghisellini, G.; Mukherjee, R.; Pesce, Joseph E.; Wagner, S. J.; Wehrle, A. E.; Hartman, R. C.; Lin, Y. C.; VonMintigny, C.

    1997-01-01

    We present Advanced Satellite for Cosmology and Astrophysics (ASCA) observations of the gamma-ray blazar PKS 0528 + 134, obtained at two separate epochs in 1994 August and 1995 March. These data represent the first measurement of the X-ray continuum emission of this source in the medium-hard X-ray band. Both ASCA spectra are consistent with a single power law with photon index GAMMA approx. = 1.7-1.8 and column density N(sub H) approx. = 5 x 10(exp 21)/ sq cm, higher than Galactic. The X-ray flux increased by a factor of 4 in approx. 7 months without appreciable change of the spectral shape. During the lower state of 1994 August, PKS 0528 + 134 was observed simultaneously in the optical, X-rays, and at gamma-ray energies with Energetic Gamma Ray Experiment Telescope (EGRET). The gamma-ray intensity is the faintest detected thus far in the source, with a steep spectrum (GAMMA approx. = 2.7). The extrapolation of the X-ray continuum to the gamma-ray range requires a sharp spectral break at approx. 10(exp 22) Hz. We discuss the radio through gamma-ray spectral energy distribution of PKS 0528 + 134, comparing the low state of 1994 August with the flare state of 1993 March. We show that in PKS 0528 + 134, a non-negligible contribution from the external radiation field is present and that, although synchrotron self-Compton scenarios cannot be ruled out, inverse Compton upscattering of thermal seed photons may be the dominant cooling process for the production of the high-energy continuum in this blazar.

  20. GAMMA-RAY OBSERVATIONAL PROPERTIES OF TeV-DETECTED BLAZARS

    SciTech Connect

    Sentuerk, G. D.; Errando, M.; Mukherjee, R.; Boettcher, M.

    2013-02-20

    The synergy between the Fermi-LAT and ground-based Cherenkov telescope arrays gives us the opportunity for the first time to characterize the high-energy emission from blazars over 5 decades in energy, from 100 MeV to 10 TeV. In this study, we perform a Fermi-LAT spectral analysis for TeV-detected blazars and combine it with archival TeV data. We examine the observational properties in the {gamma}-ray band of our sample of TeV-detected blazars and compare the results with X-ray and GeV-selected populations. The spectral energy distributions (SEDs) that result from combining Fermi-LAT and ground-based spectra are studied in detail. Simple parameterizations such as a power-law function do not always reproduce the high-energy SEDs, where spectral features that could indicate intrinsic absorption are observed.

  1. SIMILAR RADIATION MECHANISM IN GAMMA-RAY BURSTS AND BLAZARS: EVIDENCE FROM TWO LUMINOSITY CORRELATIONS

    SciTech Connect

    Wang, F. Y.; Yi, S. X.; Dai, Z. G.

    2014-05-01

    Active galactic nuclei and gamma-ray bursts (GRBs) are powerful astrophysical events with relativistic jets. In this Letter, the broadband spectral properties of GRBs and well-observed blazars are compared. The distribution of GRBs is consistent with the well-known blazar sequence including the νL {sub ν}(5 GHz) – α{sub RX} and νL {sub ν}(5 GHz) – ν{sub peak} correlations, where α{sub RX} is defined as the broadband spectral slope in radio-to-X-ray bands, and ν{sub peak} is defined as the spectral peak frequency. Moreover, GRBs occupy the low radio luminosity end of these sequences. These two correlations suggest that GRBs could have a radiation process, i.e., synchrotron radiation, similar to blazars both in the prompt emission and afterglow phases.

  2. Location and origin of gamma-rays in blazars

    NASA Astrophysics Data System (ADS)

    Rani, B.; Krichbaum, T. P.; Hodgson, J. A.; Zensus, J. A.

    2016-05-01

    One of the most intriguing and challenging quests of current astrophysics is to understand the physical conditions and processes responsible for production of high-energy particles, and emission of γ-rays. A combination of high-resolution Very Long Baseline Interferometry (VLBI) images with broadband flux variability measurements is a unique way to probe the emission mechanisms at the bases of jets. Our analysis of γ-ray flux variability observed by the Fermi-LAT (Large Area Telescope) along with the parsec-scale jet kinematics suggests that the γ-ray emission in blazar S5 0716+714 has a significant correlation with the mm-VLBI core flux and the orientation of jet outflow on parsec scales. These results indicate that the inner jet morphology has a tight connection with the observed γ-ray flares. An overview of our current understanding on high-energy radiation processes, their origin, and location is presented here.

  3. Constraining the Location of Gamma-Ray Flares in Luminous Blazars

    NASA Astrophysics Data System (ADS)

    Nalewajko, Krzysztof; Begelman, Mitchell C.; Sikora, Marek

    2014-07-01

    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) luminosity L SSC <~ L X, and from an upper limit on the efficient cooling photon energy E cool, obs <~ 100 MeV. These three constraints are particularly strong for sources with low accretion disk luminosity L 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 var, obs. Alternative scenarios motivated by the observed gamma-ray/millimeter connection, in which gamma-ray flares of t 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 could be provided by determination of the

  4. Constraining the location of gamma-ray flares in luminous blazars

    SciTech Connect

    Nalewajko, Krzysztof; Begelman, Mitchell C.; Sikora, Marek

    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) 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 could be

  5. The High-Energy Continuum Emission of the Gamma-Ray Blazar PKS 0528+134

    NASA Technical Reports Server (NTRS)

    Sambruna, Rita M.; Urry, C. Megan; Maraschi, L.; Ghisellini, G.; Mukherjee, R.; Pesce, Joseph E.; Wagner, S. J.; Wehrle, A. E.; Hartman, R. C.; Lin, Y. C.

    1997-01-01

    We present Advanced Satellite for Cosmology and Astrophysics (ASCA) observations of the gamma-ray blazar PKS 0528 + 134, obtained at two separate epochs in 1994 August and 1995 March. These data represent the first measurement of the X-ray continuum emission of this source in the medium-hard X-ray band. Both ASCA spectra are consistent with a single power law with photon index GAMMA approximate 1.7-1.8 and column density N(sub H) approximately 5 x 10(exp 21) /sq cm, higher than Galactic. The X-ray flux increased by a factor of 4 in approximately 7 months without appreciable change of the spectral shape. During the lower state of 1994 August, PKS 0528 + 134 was observed simultaneously in the optical, X-rays, and at gamma-ray energies with EGRET. The gamma-ray intensity is the faintest detected thus far in the source, with a steep spectrum (GAMMA approximately 2.7). The extrapolation of the X-ray continuum to the gamma-ray range requires a sharp spectral break at approximately 10(exp 22) Hz. We discuss the radio through gamma-ray spectral energy distribution of PKS 0528 + 134, comparing the low state of 1994 August with the flare state of 1993 March. We show that in PKS 0528 + 134, a non-negligible contribution from the external radiation field is present and that, although synchrotron self-Compton scenarios cannot be ruled out, inverse Compton upscattering of thermal seed photons may be the dominant cooling process for the production of the high-energy continuum in this blazar.

  6. 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.; Mazziotta, M. N.; Monte, C.; Perri, M.; Raino, S.; Tosti, G.; Tramacere, A.; Verracchia, F.; Aller, H. D.; Aller, MF.; Angelakis, E.; Bastieri, D.; Berdyugin, A.; Bonaldi, A.; Bonavera, L.; Lawrence, C. R.

    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

  7. Intergalactic magnetic fields and gamma-ray observations of extreme TeV blazars

    SciTech Connect

    Arlen, Timothy C.; Vassilev, Vladimir V.; Weisgarber, Thomas; Wakely, Scott P.; Shafi, S. Yusef

    2014-11-20

    The intergalactic magnetic field (IGMF) in cosmic voids can be indirectly probed through its effect on electromagnetic cascades initiated by a source of teraelectronvolt (TeV) gamma-rays, such as active galactic nuclei (AGNs). AGNs that are sufficiently luminous at TeV energies, 'extreme TeV blazars', can produce detectable levels of secondary radiation from inverse Compton scattering of the electrons in the cascade, provided that the IGMF is not too large. We review recent work in the literature that utilizes this idea to derive constraints on the IGMF for three TeV-detected blazars, 1ES 0229+200, 1ES 1218+304, and RGB J0710+591, and we also investigate four other hard-spectrum TeV blazars in the same framework. Through a recently developed, detailed, three-dimensional particle-tracking Monte Carlo code, incorporating all major effects of QED and cosmological expansion, we research the effects of major uncertainties, such as the spectral properties of the source, uncertainty in the ultraviolet and far-infrared extragalactic background light, undersampled very high energy (energy ≥100 GeV) coverage, past history of gamma-ray emission, source versus observer geometry, and the jet AGN Doppler factor. The implications of these effects on the recently reported lower limits of the IGMF are thoroughly examined to conclude that the presently available data are compatible with a zero-IGMF hypothesis.

  8. Intergalactic Magnetic Fields and Gamma-Ray Observations of Extreme TeV Blazars

    NASA Astrophysics Data System (ADS)

    Arlen, Timothy C.; Vassilev, Vladimir V.; Weisgarber, Thomas; Wakely, Scott P.; Yusef Shafi, S.

    2014-11-01

    The intergalactic magnetic field (IGMF) in cosmic voids can be indirectly probed through its effect on electromagnetic cascades initiated by a source of teraelectronvolt (TeV) gamma-rays, such as active galactic nuclei (AGNs). AGNs that are sufficiently luminous at TeV energies, "extreme TeV blazars", can produce detectable levels of secondary radiation from inverse Compton scattering of the electrons in the cascade, provided that the IGMF is not too large. We review recent work in the literature that utilizes this idea to derive constraints on the IGMF for three TeV-detected blazars, 1ES 0229+200, 1ES 1218+304, and RGB J0710+591, and we also investigate four other hard-spectrum TeV blazars in the same framework. Through a recently developed, detailed, three-dimensional particle-tracking Monte Carlo code, incorporating all major effects of QED and cosmological expansion, we research the effects of major uncertainties, such as the spectral properties of the source, uncertainty in the ultraviolet and far-infrared extragalactic background light, undersampled very high energy (energy >=100 GeV) coverage, past history of gamma-ray emission, source versus observer geometry, and the jet AGN Doppler factor. The implications of these effects on the recently reported lower limits of the IGMF are thoroughly examined to conclude that the presently available data are compatible with a zero-IGMF hypothesis.

  9. A figure of merit for blazar-like source identification in the gamma-ray energy band

    SciTech Connect

    Cavazzuti, Elisabetta; Pittori, Carlotta; Giommi, Paolo; Colafrancesco, Sergio

    2007-07-12

    The microwave to gamma-ray slope {alpha}{mu}{gamma} can be used as a viable figure of merit for blazar-like source identification in gamma-rays. Taking into account the constraints from the observed extragalactic gamma-ray background, one can estimate the maximum duty cycle allowed for a selected sample of low energy peaked (LBL) blazars, in order to be detectable for the nominal sensitivity values of AGILE and GLAST gamma-ray experiments. This work is based on the results of a recently derived blazar radio LogN-LogS obtained by combining several multi-frequency surveys. We present our estimates of duty cycle constraints applied on a sample composed by 146 high latitude and 74 medium latitude LBL blazars from the new WMAP3 yr catalog. Our results can be used as an indicator to identify good gamma-ray blazar candidates: sources with high values of duty cycle can in principle be detectable also in a ''steady'' state by AGILE and GLAST without over-predicting the extragalactic background.

  10. The Population of Gamma-Ray Loud NLSy1 Galaxies With Blazar-Like Properties

    NASA Astrophysics Data System (ADS)

    Miller, Hugh R.; Eggen, Joseph R.; Maune, Jeremy

    2016-04-01

    We report an investigation of the blazar-like properties for a subset of a sample of radio-loud NLSy1 galaxies. Using the properties of rapid and large amplitude optical and radio variability, rapid and large amplitude variations in the optical polarization and position angle, and choosing a sample that is very radio loud (R > 100), we find that that one can identify a sample of NLSy1 galaxies which exhibit properties, such as gamma ray emission, that are thought to be characteristic of the presence of relativistic jets oriented near the line-of-sight to the observer. As a result, we report the identification a number of newly discovered gamma-ray loud NLSy1 galaxies found in the Fermi database.

  11. The imprint of the extragalactic background light in the gamma-ray spectra of blazars.

    PubMed

    Ackermann, M; Ajello, M; Allafort, A; Schady, P; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Bellazzini, R; Blandford, R D; Bloom, E D; Borgland, A W; Bottacini, E; Bouvier, A; Bregeon, J; Brigida, M; Bruel, P; Buehler, R; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Cavazzuti, E; Cecchi, C; Charles, E; Chaves, R C G; Chekhtman, A; Cheung, C C; Chiang, J; Chiaro, G; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Cutini, S; D'Ammando, F; de Palma, F; Dermer, C D; Digel, S W; do Couto e Silva, E; Domínguez, A; Drell, P S; Drlica-Wagner, A; Favuzzi, C; Fegan, S J; Focke, W B; Franckowiak, A; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Germani, S; Giglietto, N; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grenier, I A; Grove, J E; Guiriec, S; Gustafsson, M; Hadasch, D; Hayashida, M; Hays, E; Jackson, M S; Jogler, T; Kataoka, J; Knödlseder, J; Kuss, M; Lande, J; Larsson, S; Latronico, L; Longo, F; Loparco, F; Lovellette, M N; Lubrano, P; Mazziotta, M N; McEnery, J E; Mehault, J; Michelson, P F; Mizuno, T; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Tramacere, A; Nuss, E; Greiner, J; Ohno, M; Ohsugi, T; Omodei, N; Orienti, M; Orlando, E; Ormes, J F; Paneque, D; Perkins, J S; Pesce-Rollins, M; Piron, F; Pivato, G; Porter, T A; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Reyes, L C; Ritz, S; Rau, A; Romoli, C; Roth, M; Sánchez-Conde, M; Sanchez, D A; Scargle, J D; Sgrò, C; Siskind, E J; Spandre, G; Spinelli, P; Stawarz, Łukasz; Suson, D J; Takahashi, H; Tanaka, T; Thayer, J G; Thompson, D J; Tibaldo, L; 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; Wood, M

    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. Here, 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. 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. PMID:23118013

  12. 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.; Bloom, E. D.; Borgland, A. W.; Bottacini, E.; Bouvier, A.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Gehrels, N.; Guirec, S.; Hays, E.; McEnery, J. E.; Perkins, J. S.; Scargle, J. D.; Troja, E.

    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.

  13. Comprehensive Multi-waveband Monitoring of Gamma-ray Bright Blazars

    NASA Astrophysics Data System (ADS)

    Marscher, Alan P.; Jorstad, S. G.; Larionov, V. M.; Chatterjee, R.; D'Arcangelo, F.; Manne-Nicholas, E.; Olmstead, A. R.; McHardy, I. M.; Agudo, I.; Gomez, J. L.; Aller, M. F.; Hagen-Thorn, V. A.; Gear, W. K.; Porter, D.

    2009-01-01

    We are monitoring 29 blazars with monthly VLBA polarimetric imaging at 43 GHz, occasional VLBA imaging at 86 GHz, and polarimetry at 90 GHz with the IRAM 30 m telescope and at optical wavelengths with the Lowell Observatory Perkins Telescope, the Calar Alto 2.2 m telescope, the Crimean Astrophysical Observatory 0.7 m telescope, and the St. Petersburg State U. 0.4 m telescope; optical and near-IR photometry with the robotic 2 m Liverpool Telescope. We observe 5 of the objects 2-7 times per week at 2.4-10 keV X-ray energies with RXTE. All but two blazars in our sample were detected as gamma-ray sources by EGRET. We will present our light curves, sequences of VLBI images, and polarization data alongside data from the first 5 months of gamma-ray observations with the Fermi LAT detector for the 15 blazars from our program for which Fermi data are publicly available. These include, for example, the August-September 2008 gamma-ray outbursts of the quasars PKS 1510-089 and 3C 454.3 and the BL Lac object 0235+164. Relative timing of flares, polarization events, and motions of superluminal knots allow us to determine where the high-energy emission occurs relative to the core seen on the VLBA images. The research at Boston U. was supported by NSF grant AST-0406865 and NASA grants NNX06AG86G (RXTE), NNX08AJ64G (ADP), and NNX08AV65G (Fermi).

  14. The Extragalactic Background Light Absorption Feature in the Blazar Component of the Extragalactic Gamma-ray Background

    NASA Astrophysics Data System (ADS)

    Venters, Tonia M.; Pavlidou, Vasiliki; Reyes, Luis C.

    2009-10-01

    High-energy photons from cosmological emitters suffer attenuation due to pair production interactions with the extragalactic background light (EBL). The collective emission of any high-energy emitting cosmological population will exhibit an absorption feature at the highest energies. We calculate this absorption feature in the collective emission of blazars for various models of the blazar gamma-ray luminosity function (GLF) and the EBL. We find that models of the blazar GLF that predict higher relative contributions of high-redshift blazars to the blazar collective spectrum result in emission that is more susceptible to attenuation by the EBL, and hence result in more prominent absorption features, allowing for better differentiation amongst EBL models. We thus demonstrate that observations of such an absorption feature will contain information regarding both the blazar GLF and the EBL, and we discuss tests for EBL models and the blazar GLF that will become possible with upcoming Fermi observations.

  15. 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.; Mazziotta, M. N.; Monte, C.; Perri, M.; Raino, S.; Tosti, G.; Tramacere, A.; Verrecchia, F.; Aller, H. D.; Aller, M. F.; Angelakis, E.; Bastieri, D.; Berdyugin, A.; Bonaldi, A.; Bonavera, L.; Burigana, C.

    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

  16. Multiwavelength Observations of the Gamma-ray Blazars Detected by AGILE

    NASA Astrophysics Data System (ADS)

    D'Ammando, F.; Vercellone, S.; Donnarumma, I.; Pacciani, L.; Pucella, G.; Tavani, M.; Vittorini, V.; Bulgarelli, A.; Chen, A. W.; Giuliani, A.; Longo, F.; AGILE Team

    2011-02-01

    Since its launch in April 2007, the AGILE satellite detected with the Gamma-Ray Imaging Detector several blazars in high γ-ray activity: 3C 279, 3C 454.3, PKS 1510-089, S5 0716+714, 3C 273, W Comae and Mrk 421. Thanks to the rapid dissemination of our alerts, we were able to obtain multiwavelength ToO data from other observatories such as Spitzer, Swift, RXTE, Suzaku, INTEGRAL, MAGIC, VERITAS, as well as radio-to-optical coverage by means of the GASP Project of the WEBT and the REM Telescope. This large multifrequency coverage gave us the opportunity to study truly simultaneous spectral energy distributions of these sources from radio to γ-ray energy bands and to investigate the different mechanisms responsible for their emission. We present an overview of the AGILE results on these γ-ray blazars and the relative multifrequency data.

  17. The extension of variability properties in gamma-ray bursts to blazars

    NASA Astrophysics Data System (ADS)

    Wu, Qingwen; Zhang, Bing; Lei, Wei-Hua; Zou, Yuan-Chuan; Liang, En-Wei; Cao, Xinwu

    2016-01-01

    Both gamma-ray bursts (GRBs) and blazars have relativistic jets pointing at a small angle from our line of sight. Several recent studies suggested that these two kinds of sources may share similar jet physics. In this work, we explore the variability properties for GRBs and blazars as a whole. We find that the correlation between minimum variability time-scale (MTS) and Lorentz factor, Γ, as found only in GRBs by Sonbas et al. can be extended to blazars with a joint correlation of MTS∝Γ-4.7±0.3. The same applies to the MTS∝ L_{γ }^{-1.0± 0.1} correlation as found in GRBs, which can be well extended into blazars as well. These results provide further evidence that the jets in these two kinds of sources are similar despite of the very different mass scale of their central engines. Further investigations of the physical origin of these correlations are needed, which can shed light on the nature of the jet physics.

  18. A blazar candidate counterpart of the new gamma-ray flare in the region of PKS 1451-375

    NASA Astrophysics Data System (ADS)

    Massaro, F.; Cowperthwaite, P. C.; D'Abrusco, R.; Paggi, A.

    2012-11-01

    Following the Fermi LAT detection of a new gamma-ray flare from a region near the flat spectrum radio quasar: PKS 1451-375 (ATEL #4534), we searched in the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010 AJ, 140, 1868) catalog at the position of the Fermi source for a gamma-ray blazar candidate....

  19. A WISE blazar candidate counterpart of the gamma-ray flaring source nearby NRAO 676 (TXS 2159+505)

    NASA Astrophysics Data System (ADS)

    Massaro, F.; Paggi, A.; D'Abrusco, R.

    2012-06-01

    Following the Fermi LAT detection of a new gamma-ray flaring source in the vicinity of the the flat spectrum radio quasar NRAO 676 (TXS 2159+505) (ATEL #4182), we searched in the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010 AJ, 140, 1868) catalog at the position of the Fermi source for a gamma-ray blazar candidate using the association procedure outlined in Massaro, F.......

  20. SEARCHING FOR NEW {gamma}-RAY BLAZAR CANDIDATES IN THE THIRD PALERMO BAT HARD X-RAY CATALOG WITH WISE

    SciTech Connect

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

    2013-06-01

    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 and 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.

  1. Gamma-ray flares in blazars accompanied by synchrotron polarization angle swings

    NASA Astrophysics Data System (ADS)

    Zhang, Haocheng; Boettcher, Markus; Chen, Xuhui

    2014-08-01

    We present a detailed analysis of time- and energy-dependent synchrotron polarization signatures in a shock-in-jet model for gamma-ray blazars. Our calculations employ a full 3D radiation transfer code, considering synchrotron emission from a helical magnetic field, and taking into account all light-travel-time and other relevant geometric effects, while the relevant synchrotron self-Compton and external Compton effects are handled with a 2D Monte-Carlo/Fokker-Planck code. We find that a scenario in which a relativistic shock propagating through the jet leads to a compression of the magnetic field, increasing the toroidal field component, can lead to correlated synchrotron + SSC flaring, associated with substantial variability in the synchrotron polarization percentage and position angle (PA). Most importantly, this scenario naturally explains large PA rotations by ≥180 deg, as observed in connection with gamma-ray flares in several blazars, without the need for bent or helical jet trajectories or other non-axisymmetric jet features.

  2. Radio and Gamma-Ray Monitoring of Strongly Lensed Quasars and Blazars

    NASA Astrophysics Data System (ADS)

    Rumbaugh, Nick; Fassnacht, Chris; McKean, John; Koopmans, Leon; Auger, Matthew; Suyu, Sherry; Marshall, Philip J.

    2015-01-01

    We observed six strongly lensed, radio-loud quasars (MG 0414+0534, CLASS B0712+472, JVAS B1030+074, CLASS B1127+385, CLASS B1152+199, and JVAS B1938+666) in order to identify systems suitable for measuring cosmological parameters using time delays between their multiple images. Two separate monitoring campaigns were carried out using the VLA. We found evidence for variability in a majority of the lightcurves. B0712 and B1030 had particularly strong variations, exhibiting linear flux trends. These results show that most of these systems should be targeted with followup monitoring campaigns, especially B0712 and B1030. In additional to these follow-up campaigns, future work will involve searching for and performing time delay measurements on lensed blazars using the Fermi gamma-ray telescope, following the proof of concept by Cheung et al. 2014. Discrepancies between gamma-ray and radio time delays of B0218 suggest physically separated emissions sources. We plan to extend study of emission regions to other lensed blazars.

  3. Spectacular variability of gamma-ray emission in blazar 3C279 during the large outburst in June 2015

    NASA Astrophysics Data System (ADS)

    Madejski, Grzegorz; Hayashida, Masaaki; Asano, Katsuaki; Thompson, David; Nalewajko, Krzysztof; Sikora, Marek; Fermi-LAT Collaboration

    2016-03-01

    The most luminous celestial extragalactic sources of persistent gamma-ray emission are active galaxies with relativistic jets pointing towards the observer. Those are commonly called blazars, and Flat Spectrum Radio Quasar 3C 279 has been one of the brightest gamma-ray blazars in the sky. In Dec. 2013, April 2014, and June 2015 it showed powerful outbursts with the gamma-ray flux at E > 100 MeV higher than 1e-5 ph/cm2/s, measured by the Fermi-LAT gamma-ray detector. The Dec. 2013 outburst showed an unusually hard power-law gamma-ray spectrum (photon index ~1.7), and an asymmetric light curve profile with a few-hour time scale variability. The June 2015 outburst was extreme, with a record-breaking E > 100 MeV flux of 4e-5 ph/cm2/s, more than 10 × higher than the average gamma-ray flux of the Crab Nebula. The high flux prompted a Fermi-LAT Target of Opportunity pointing observation. The increase of exposure and the very high flux state of the source allowed us to resolve the gamma-ray flux on a sub-orbital time scales, revealing variability on time scales of tens of minutes. Here, we present the observational results of those outbursts from 3C279 with a focus on detailed analysis of the 2015 June outburst.

  4. TIME STRUCTURE OF GAMMA-RAY SIGNALS GENERATED IN LINE-OF-SIGHT INTERACTIONS OF COSMIC RAYS FROM DISTANT BLAZARS

    SciTech Connect

    Prosekin, Anton; Aharonian, Felix; Essey, Warren; Kusenko, Alexander

    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 are 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.

  5. AGILE detection of intense gamma-ray emission from the blazar PKS 1510-089

    NASA Astrophysics Data System (ADS)

    Pucella, G.; Vittorini, V.; D'Ammando, F.; Tavani, M.; Raiteri, C. M.; Villata, M.; Argan, A.; Barbiellini, G.; Boffelli, F.; Bulgarelli, A.; Caraveo, P.; Cattaneo, P. W.; Chen, A. W.; Cocco, V.; Costa, E.; Del Monte, E.; de Paris, G.; Di Cocco, G.; Donnarumma, I.; Evangelista, Y.; Feroci, M.; Fiorini, M.; Froysland, T.; Fuschino, F.; Galli, M.; Gianotti, F.; Giuliani, A.; Labanti, C.; Lapshov, I.; Lazzarotto, F.; Lipari, P.; Longo, F.; Marisaldi, M.; Mereghetti, S.; Morselli, A.; Pacciani, L.; Pellizzoni, A.; Perotti, F.; Picozza, P.; Prest, M.; Rapisarda, M.; Rappoldi, A.; Soffitta, P.; Trifoglio, M.; Trois, A.; Vallazza, E.; Vercellone, S.; Zambra, A.; Zanello, D.; Antonelli, L. A.; Colafrancesco, S.; Cutini, S.; Gasparrini, D.; Giommi, P.; Pittori, C.; Verrecchia, F.; Salotti, L.; Aller, M. F.; Aller, H. D.; Carosati, D.; Larionov, V. M.; Ligustri, R.

    2008-11-01

    Context: We report the detection by the AGILE (Astro-rivelatore Gamma a Immagini LEggero) satellite of an intense gamma-ray flare from the source AGL J1511-0909, associated with the powerful quasar PKS 1510-089, during ten days of observations from 23 August to 1 September 2007. Aims: During the observation period, the source was in optical decrease following a flaring event monitored by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT). The simultaneous gamma-ray, optical, and radio coverage allows us to study the spectral energy distribution and the theoretical models based on the synchrotron and inverse Compton (IC) emission mechanisms. Methods: AGILE observed the source with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the hard X-ray imager Super-AGILE sensitive in the 30 MeV div 50 GeV and 18 div 60 keV bands, respectively. Results: Between 23 and 27 August 2007, AGILE detected gamma-ray emission from PKS 1510-089 when this source was located 50° off-axis, with an average flux of (270 ± 65) × 10-8 photons cm-2 s-1 for photon energy above 100 MeV. In the following period, 28 August-1 September, after a satellite re-pointing, AGILE detected the source at 35° off-axis, with an average flux (E > 100 MeV) of (195 ± 30) × 10-8 photons cm-2 s-1. No emission was detected by Super-AGILE, with a 3-σ upper limit of 45 mCrab in 200 ks. Conclusions: The spectral energy distribution is modelled with a homogeneous one-zone synchrotron self Compton (SSC) emission plus contributions by external photons: the SSC emission contributes primarily to the X-ray band, whereas the contribution of the IC from the external disc and the broad line region match the hard gamma-ray spectrum observed.

  6. FLUX AND PHOTON SPECTRAL INDEX DISTRIBUTIONS OF FERMI-LAT BLAZARS AND CONTRIBUTION TO THE EXTRAGALACTIC GAMMA-RAY BACKGROUND

    SciTech Connect

    Singal, J.; Petrosian, V.; Ajello, M.

    2012-07-01

    We present a determination of the distributions of the photon spectral index and gamma-ray flux-the so-called log N-log S relation-for the 352 blazars detected with a greater than approximately 7{sigma} detection threshold and located above {+-}20 Degree-Sign Galactic latitude by the Large Area Telescope of the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true log N-log S counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation between the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law with high and low indices of -2.37 {+-} 0.13 and -1.70 {+-} 0.26, respectively, and the intrinsic photon index distribution can be represented by a Gaussian with mean of 2.41 {+-} 0.13 and width of 0.25 {+-} 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and flat spectrum radio quasar type blazars separately. We then calculate the contribution of Fermi blazars to the diffuse extragalactic gamma-ray background radiation. Under the assumption that the flux distribution of blazars continues to arbitrarily low fluxes, we calculate the best-fit contribution of all blazars to the total extragalactic gamma-ray output to be 60%, with a large uncertainty.

  7. DEEP BROADBAND OBSERVATIONS OF THE DISTANT GAMMA-RAY BLAZAR PKS 1424+240

    SciTech Connect

    Archambault, S.; Aune, T.; Behera, B.; Chen, X.; Federici, S.; Beilicke, M.; Bugaev, V.; Benbow, W.; Cerruti, M.; Berger, K.; Bird, R.; Biteau, J.; Byrum, K.; Cardenzana, J. V; Ciupik, L.; Connolly, M. P.; Cui, W.; Dumm, J.; Errando, M.; Falcone, A.; Collaboration: VERITAS Collaboration; Fermi LAT Collaboration; and others

    2014-04-10

    We present deep VERITAS observations of the blazar PKS 1424+240, along with contemporaneous Fermi Large Area Telescope, Swift X-ray Telescope, and Swift UV Optical Telescope data between 2009 February 19 and 2013 June 8. This blazar resides at a redshift of z ≥ 0.6035, displaying a significantly attenuated gamma-ray flux above 100 GeV due to photon absorption via pair-production with the extragalactic background light. We present more than 100 hr of VERITAS observations over three years, a multiwavelength light curve, and the contemporaneous spectral energy distributions. The source shows a higher flux of (2.1 ± 0.3) × 10{sup –7} photons m{sup –2} s{sup –1} above 120 GeV in 2009 and 2011 as compared to the flux measured in 2013, corresponding to (1.02 ± 0.08) × 10{sup –7} photons m{sup –2} s{sup –1} above 120 GeV. The measured differential very high energy (VHE; E ≥ 100 GeV) spectral indices are Γ = 3.8 ± 0.3, 4.3 ± 0.6 and 4.5 ± 0.2 in 2009, 2011, and 2013, respectively. No significant spectral change across the observation epochs is detected. We find no evidence for variability at gamma-ray opacities of greater than τ = 2, where it is postulated that any variability would be small and occur on timescales longer than a year if hadronic cosmic-ray interactions with extragalactic photon fields provide a secondary VHE photon flux. The data cannot rule out such variability due to low statistics.

  8. EXPLORING THE RELATION BETWEEN (SUB-)MILLIMETER RADIATION AND {gamma}-RAY EMISSION IN BLAZARS WITH PLANCK AND FERMI

    SciTech Connect

    Leon-Tavares, J.; Tornikoski, M.; Laehteenmaeki, A.; Valtaoja, E.; Giommi, P.; Polenta, G.; Gasparrini, D.; Cutini, S.

    2012-07-20

    The coexistence of Planck and Fermi satellites in orbit has enabled the exploration of the connection between the (sub-)millimeter and {gamma}-ray emission in a large sample of blazars. We find that the {gamma}-ray emission and the (sub-)mm luminosities are correlated over five orders of magnitude, L{sub {gamma}}{proportional_to}L{sub (sub-)mm}. However, this correlation is not significant at some frequency bands when simultaneous observations are considered. The most significant statistical correlations, on the other hand, arise when observations are quasi-simultaneous within two months. Moreover, we find that sources with an approximate spectral turnover in the middle of the mm-wave regime are more likely to be strong {gamma}-ray emitters. These results suggest a physical relation between the newly injected plasma components in the jet and the high levels of {gamma}-ray emission.

  9. Connection of Very High Energy Gamma-ray Flares in Blazars to Activity at Lower Frequencies

    NASA Astrophysics Data System (ADS)

    Marscher, Alan P.; Jorstad, Svetlana G.

    2016-04-01

    The author will briefly review the results of multi-wavelength observations of blazars that emit very high-energy (VHE) gamma rays. The VHE gamma-ray emission is generally episodic, including flares that are often very short-lived. While many of these flares have counterparts only at X-ray energies, or no counterparts at all, some events are seen also at optical wavelengths, and a number are associated with the passage of new superluminal knots passing through the core in mm-wave VLBA images. Two explanations for the short-term VHE flares in the relativistic jets are supersonic turbulence and ultra-fast plasma jets resulting from magnetic reconnections. Observations of frequency-dependent linear polarization during flares can potentially decide between these models. VLBA images can help to locate VHE events that are seen at millimeter wavelengths. In some cases, the flares take place near the parsec-scale core, while in others they occur closer to the black hole.This research is supported in part by NASA through Swift Guest Investigator grants NNX15AR45G and NNX15AR34G.

  10. Exploring Blazar Jet Dynamics with Optical and Gamma Ray Cross-Correlations Using the Fermi Gamma Ray Space Telescope Public Data

    NASA Astrophysics Data System (ADS)

    Cook, Kyle; Carini, M. T.

    2010-01-01

    For the past 9 years Western Kentucky University has been monitoring approximately 50 Blazar sources at the R-band optical wavelengths. The Fermi Gamma Ray Space Telescope provides a source of gamma-ray data publicly available for cross correlation analysis, and the recent release of the data has made this possible. Such an analysis will prove useful in understanding the processes present in the jets producing the observed emission in these AGN. This type of analysis is being conducted at Western Kentucky University, pulling together the optical data from the WKU telescope network as well as other public databases and comparing them to the released FGST data. Here we present the initial results from the cross-correlation analysis and apply it to sources of interest. This research is funded by the NASA Kentucky Space Grant Consortium.

  11. Gamma-ray blazars and active galactic nuclei seen by the Fermi-LAT

    NASA Astrophysics Data System (ADS)

    Lott, B.; Cavazzuti, E.; Ciprini, S.; Cutini, S.; Gasparrini, D.

    2015-03-01

    The third catalog of active galactic nuclei (AGNs) detected by the Fermi-LAT (3LAC) is presented. It is based on the third Fermi-LAT catalog (3FGL) of sources detected with a test statistic (TS) greater than 25 using the first 4 years of data. The 3LAC includes 1591 AGNs located at high Galactic latitudes, |b| > 10 (with 28 duplicate associations, thus corresponding to 1563 gamma-ray sources among 2192 sources in the 3FGL catalog), a 71% increase over the second catalog based on 2 years of data. A very large majority of these AGNs (98%) are blazars. About half of the newly detected blazars are of unknown type, i.e., they lack spectroscopic information of sufficient quality to determine the strength of their emission lines. The general properties of the 3LAC sample confirm previous findings from earlier catalogs, but some new subclasses (e.g., intermediate- and high-synchrotron-peaked FSRQs) have now been significantly detected.

  12. 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.

  13. A possible WISE blazar counterpart of the New Gamma-ray Transient Fermi J1717-5156

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    Following the Fermi LAT Detection of a new gamma-ray transient near the Galactic plane: Fermi J1717-5156 (ATEL #4023), we searched in the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010 AJ, 140, 1868) catalog at the position of the Fermi source for a gamma-ray blazar candidate using the association procedure outlined in Massaro, F. et al. 2011 ApJ, 740L, 48 and in Massaro, F. et al. 2012 ApJ in press (http://arxiv.org/abs/1203.3801).

  14. Implications of plasma beam instabilities for the statistics of the Fermi hard gamma-ray blazars and the origin of the extragalactic gamma-ray background

    SciTech Connect

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

    2014-08-01

    Fermi has been instrumental in constraining the luminosity function and redshift evolution of gamma-ray bright BL Lac objects, a subpopulation of blazars with almost featureless optical spectra. This includes limits on the spectrum and anisotropy of the extragalactic gamma-ray background (EGRB), redshift distribution of nearby Fermi active galactic nuclei (AGNs), and the construction of a logN-log S relation. Based on these, it has been argued that the evolution of the gamma-ray bright BL Lac population must be much less dramatic than that of other AGNs. However, critical to such claims is the assumption that inverse Compton cascades reprocess emission above a TeV into the Fermi energy range, substantially enhancing the strength of the observed limits. Here we demonstrate that in the absence of such a process, due, e.g., to the presence of virulent plasma beam instabilities that preempt the cascade, a population of TeV-bright BL Lac objects that evolve similarly to quasars is consistent with the population of hard gamma-ray BL Lac objects observed by Fermi. Specifically, we show that a simple model for the properties and luminosity function is simultaneously able to reproduce their logN-log S relation, local redshift distribution, and contribution to the EGRB and its anisotropy without any free parameters. Insofar as the naturalness of a picture in which the hard gamma-ray BL Lac population exhibits the strong redshift evolution observed in other tracers of the cosmological history of accretion onto halos is desirable, this lends support for the absence of the inverse Compton cascades and the existence of the beam plasma instabilities.

  15. {gamma}-RAY AND PARSEC-SCALE JET PROPERTIES OF A COMPLETE SAMPLE OF BLAZARS FROM THE MOJAVE PROGRAM

    SciTech Connect

    Lister, M. L.; Hovatta, T.; Aller, M.; Aller, H.; Kellermann, K. I.; Kovalev, Y. Y.; Pushkarev, A. B.; Ros, E.; Ackermann, M.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Antolini, E.; Baldini, L.; Bellazzini, R.; Ballet, J.; Bastieri, D. E-mail: moritz.boeck@sternwarte.uni-erlangen.de

    2011-11-20

    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) 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.

  16. 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.; McEnery, Julie E.

    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.

  17. MULTIWAVELENGTH OBSERVATIONS OF THE GAMMA-RAY BLAZAR PKS 0528+134 IN QUIESCENCE

    SciTech Connect

    Palma, N. I.; Boettcher, M.; Li, Y.; De la Calle, I.; Agudo, I.; Jorstad, S. G.; Joshi, M.; Aller, M.; Aller, H.; Bach, U.; BenItez, E.; Buemi, C. S.; Leto, P.; Escande, L.; Gurwell, M. A.; Heidt, J.; Hiriart, D.; Laehteenmaeki, A.; Larionov, V. M. E-mail: marscher@bu.edu E-mail: jlgomez@iaa.es

    2011-07-01

    We present multiwavelength observations of the ultraluminous blazar-type radio loud quasar PKS 0528+134 in quiescence during the period 2009 July-December. Four Target-of-Opportunity observations with the XMM-Newton satellite in the 0.2-10 keV range were supplemented with optical observations at the MDM Observatory, radio and optical data from the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope and the Very Long Baseline Array, additional X-ray data from the Rossi X-ray Timing Explorer (2-10 keV) and from Suzaku (0.5-10 keV) as well as {gamma}-ray data from the Fermi Large Area Telescope in the 100 MeV-200 GeV range. In addition, publicly available data from the SMARTS blazar monitoring program and the University of Arizona/Steward Observatory Fermi Support program were included in our analysis. We found no evidence of significant flux or spectral variability in {gamma}-rays and most radio bands. However, significant flux variability on a timescale of several hours was found in the optical regime, accompanied by a weak trend of spectral softening with increasing flux. We suggest that this might be the signature of a contribution of unbeamed emission, possibly from the accretion disk, at the blue end of the optical spectrum. The optical flux is weakly polarized with rapid variations of the degree and direction of polarization, while the polarization of the 43 GHz radio core remains steady, perpendicular to the jet direction. Optical spectropolarimetry of the object in the quiescent state suggests a trend of increasing degree of polarization with increasing wavelength, providing additional evidence for an unpolarized emission component, possibly thermal emission from the accretion disk, contributing toward the blue end of the optical spectrum. Over an extended period of several months, PKS 0528+134 shows moderate (amplitude {approx}< 50%) flux variability in the X-rays and most radio frequencies on {approx}1-2 week timescales. We constructed four

  18. GAMMA-RAY LIGHT CURVES AND VARIABILITY OF BRIGHT FERMI-DETECTED BLAZARS

    SciTech Connect

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Borgland, A. W.; Bouvier, A.; Antolini, E.; Bonamente, E.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Brez, A.; Ballet, J.; Bastieri, D.; Brigida, M.; Bruel, P. E-mail: stefano.ciprini@pg.infn.i E-mail: stefan@astro.su.s E-mail: stefan@astro.su.s E-mail: sarac@slac.stanford.ed

    2010-10-10

    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% of 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 {sup {alpha}} 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

  19. The observed radio/gamma-ray emission correlation for blazars with the Fermi-LAT and the RATAN-600 data

    NASA Astrophysics Data System (ADS)

    Mufakharov, T.; Mingaliev, M.; Sotnikova, Yu.; Naiden, Ya.; Erkenov, A.

    2015-07-01

    We study the correlation between gamma-ray and radio band radiation for 123 blazars, using the Fermi-LAT first source catalogue (1FGL) and the RATAN-600 data obtained at the same period of time (within a few months). We found an apparent positive correlation for BL Lac and flat-spectrum radio quasar (FSRQ) sources from our sample through testing the value of the Pearson product-moment correlation coefficient. The BL Lac objects show higher values of the correlation coefficient than FSRQs at all frequencies, except 21.7 GHz, and at all bands, except 10-100 GeV, typically at high confidence level (>99 per cent). At higher gamma-ray energies the correlation weakens and even becomes negative for BL Lacs and FSRQs. For BL Lac blazars, the correlation of the fluxes appeared to be more sensitive to the considered gamma-ray energy band, than to the frequency, while for FSRQ sources the correlation changed notably both with the considered radio frequency and gamma-ray energy band. We used a data randomization method to quantify the significance of the computed correlation coefficients. We find that the statistical significance of the correlations we obtained between the flux densities at all frequencies and the photon flux in all gamma-ray bands below 3 GeV is high for BL Lacs (chance probability ˜10-3-10-7). The correlation coefficient is high and significant for the 0.1-0.3 GeV band and low and insignificant for the 10-100 GeV band for both types of blazars for all considered frequencies.

  20. Breaks in gamma-ray spectra of distant blazars and transparency of the Universe

    NASA Astrophysics Data System (ADS)

    Rubtsov, G. I.; Troitsky, S. V.

    2014-11-01

    Energetic gamma rays scatter on soft background radiation when propagating through the Universe, producing electron-positron pairs (A.I. Nikishov, Sov. Phys. JETP 14, 393 (1962)). Gamma rays with energies between 100 GeV and a few TeV interact mostly with infrared background photons whose amount is poorly known experimentally but safely constrained from below by account of the contribution of observed light from known galaxies (R.C. Keenan, A.J. Barger, L.L. Cowie, and W.-H. Wang, Astrophys. J. 723, 40 (2010); arXiv: 1102.2428). The expected opacity of the intergalactic space limits the mean free path of TeV gamma rays to dozens of Megaparsecs. However, TeV photons from numerous more distant sources have been detected (S.P. Wakely and D. Horan, http://tevcat.uchicago.edu/). This might be interpreted, in each particular case, in terms of hardening of the emitted spectrum caused by presently unknown mechanisms at work in the sources (S. Archambault et al. (VERITAS and Fermi LAT Collaborations), Astrophys. J. 785, L16 (2014); arXiv: 1403.4308). Here we show that this interpretation is not supported by the analysis of the ensemble of all observed sources. In the frameworks of an infrared-background model with the lowest opacity (R.C. Gilmore, R.S. Somerville, J.R. Primack, and A. Dominguez, Mon. Not. Roy. Astron. Soc. 422, 3189 (2012); arXiv: 1104.0671), we reconstruct the emitted spectra of distant blazars and find that upward spectral breaks appear precisely at those energies where absorption effects are essential. Since these energies are very different for similar sources located at various distances, we conclude that the breaks are artefacts of the incorrect account of absorption and, therefore, the opacity of the Universe for gamma rays is overestimated even in the most conservative model. This implies that some novel physical or astrophysical phenomena should affect long-distance propagation of gamma rays. A scenario in which a part of energetic photons is

  1. ON THE ORIGIN OF THE {gamma}-RAY/OPTICAL LAGS IN LUMINOUS BLAZARS

    SciTech Connect

    Janiak, Mateusz; Sikora, Marek; Moderski, Rafal; Nalewajko, Krzysztof; Madejski, Greg M. E-mail: sikora@camk.edu.pl

    2012-12-01

    Blazars are strongly variable sources that occasionally show spectacular flares visible in various energy bands. These flares are often, but not always, correlated. In a number of cases, the peaks of optical flares are found to be somewhat delayed with respect to the {gamma}-ray peaks. One notable example of such a delay was found in 3C 279 by Hayashida et al. and interpreted as a result of steeper drop with a distance of the energy density of an external radiation field than of the magnetic energy density. In this paper, we demonstrate that, in general, depending on the respective energy density profile along the jet, such lags can have both signs and that they can take place for any ratio of these energy densities. We study the dependence of such lags on the ratio of these energy densities at a distance of a maximal energy dissipation in a jet, on their gradients, as well as on the time profile of the relativistic electron injection within the moving source. We show how prominent such lags can be, and their expected timescales. We suggest that studies of such lags can provide a powerful tool to resolve the structure of relativistic jets and their radiative environment. As an example we model the lag observed in 3C 279, showing that in this object the flare is produced at a distance of a few parsecs from the central black hole, consistent with our previous inferences based on the spectra and optical polarization properties.

  2. Spectacular variability of gamma-ray emission in blazar 3C279 during the large outburst in June 2015

    NASA Astrophysics Data System (ADS)

    Madejski, Grzegorz Maria; Hayashida, Masaaki; Asano, Katsuaki; Thompson, David John; Nalewajko, Krzysztof; Sikora, Marek; Fermi-LAT Team

    2016-01-01

    The Flat Spectrum Radio Quasar 3C 279 has been one of the brightest gamma-ray blazars in the sky. In Dec. 2013, April 2014, and June 2015 it showed powerful outbursts with the gamma-ray flux higher than 1x10^{-5} ph/cm^2/s (above 100 MeV). The December 2013 outburst showed an unusually hard power-law gamma-ray spectrum (index~1.7), and an asymmetric light curve profile with a few-hour time scale variability. The outburst in June 2015 was extreme, revealing a record-breaking integral flux above 100 MeV of 4x10^{-5} ph/cm^2/s, more than an order of magnitude higher than the average gamma-ray flux of the Crab. At the same time, the X-ray flux also showed the highest level of soft X-ray flux ever measured by Swift-XRT. The high flux prompted a Fermi-LAT ToO pointing observation. The increase of exposure and the very high flux state of the source allowed us to resolve the gamma-ray flux on a sub-orbital time scales. Our analysis of the LAT data revealed variability on time scales of tens of minutes. In this contribution, we will present the observational results of those outbursts from 3C279 together with multi-wavelength observations, with a focus on detailed analysis of the 2015 June outburst.

  3. 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.; Marshall, P. J.; Wood, D. L.; Ajello, M.; Bastieri, D.; Chekhtman, A.; D'Ammando, F.; Giroletti, M.; Grove, J. E.; Lott, B.; Ohja, R.; Orienti, M.; Perkins, J. S.; Razzano, M.; Smith, A. W.; Thompson, D. J.; Wood, K. S.

    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.

  4. Equipartition Gamma-Ray Blazars and the Location of the Gamma-Ray Emission Site in 3C 279

    NASA Astrophysics Data System (ADS)

    Dermer, Charles D.; Cerruti, Matteo; Lott, Benoit; Boisson, Catherine; Zech, Andreas

    2014-02-01

    Blazar spectral models generally have numerous unconstrained parameters, leading to ambiguous values for physical properties like Doppler factor δD or fluid magnetic field B'. To help remedy this problem, a few modifications of the standard leptonic blazar jet scenario are considered. First, a log-parabola function for the electron distribution is used. Second, analytic expressions relating energy loss and kinematics to blazar luminosity and variability, written in terms of equipartition parameters, imply δD, B', and the peak electron Lorentz factor \\gamma _{pk}^\\prime. The external radiation field in a blazar is approximated by Lyα radiation from the broad-line region (BLR) and ≈0.1 eV infrared radiation from a dusty torus. When used to model 3C 279 spectral energy distributions from 2008 and 2009 reported by Hayashida et al., we derive δD ~ 20-30, B' ~ few G, and total (IR + BLR) external radiation field energy densities u ~ 10-2-10-3 erg cm-3, implying an origin of the γ-ray emission site in 3C 279 at the outer edges of the BLR. This is consistent with the γ-ray emission site being located at a distance R <~ Γ2 ct var ~ 0.1(Γ/30)2(t var/104 s) pc from the black hole powering 3C 279's jets, where t var is the variability timescale of the radiation in the source frame, and at farther distances for narrow-jet and magnetic-reconnection models. Excess >~ 5 GeV γ-ray emission observed with Fermi LAT from 3C 279 challenges the model, opening the possibility of a second leptonic component or a hadronic origin of the emission. For low hadronic content, absolute jet powers of ≈10% of the Eddington luminosity are calculated.

  5. Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars and Contribution to the Extragalactic Gamma-ray Background

    SciTech Connect

    Singal, J.; Petrosian, V.; Ajello, M.; /KIPAC, Menlo Park /SLAC /Stanford U.

    2011-12-09

    We present a determination of the distributions of gamma-ray flux - the so called LogN-LogS relation - and photon spectral index for the 352 blazars detected with a greater than approximately seven sigma detection threshold and located above {+-} 20{sup o} Galactic latitude by the Large Area Telescope of the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true LogN-LogS counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation among the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law of slopes -2.37 {+-} 0.13 and -1.70 {+-} 0.26, and the intrinsic photon index distribution can be represented by a Gaussian with mean 2.41 {+-} 0.13 and 1{sigma} width of 0.25 {+-} 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and FSRQs type blazars separately. We then calculate the contribution of blazars to the diffuse cosmic gamma-ray background radiation to be 28% {+-} 19%.

  6. Equipartition gamma-ray blazars and the location of the gamma-ray emission site in 3C 279

    SciTech Connect

    Dermer, Charles D.; Cerruti, Matteo; Lott, Benoit

    2014-02-20

    Blazar spectral models generally have numerous unconstrained parameters, leading to ambiguous values for physical properties like Doppler factor δ{sub D} or fluid magnetic field B'. To help remedy this problem, a few modifications of the standard leptonic blazar jet scenario are considered. First, a log-parabola function for the electron distribution is used. Second, analytic expressions relating energy loss and kinematics to blazar luminosity and variability, written in terms of equipartition parameters, imply δ{sub D}, B', and the peak electron Lorentz factor γ{sub pk}{sup ′}. The external radiation field in a blazar is approximated by Lyα radiation from the broad-line region (BLR) and ≈0.1 eV infrared radiation from a dusty torus. When used to model 3C 279 spectral energy distributions from 2008 and 2009 reported by Hayashida et al., we derive δ{sub D} ∼ 20-30, B' ∼ few G, and total (IR + BLR) external radiation field energy densities u ∼ 10{sup –2}-10{sup –3} erg cm{sup –3}, implying an origin of the γ-ray emission site in 3C 279 at the outer edges of the BLR. This is consistent with the γ-ray emission site being located at a distance R ≲ Γ{sup 2} ct {sub var} ∼ 0.1(Γ/30){sup 2}(t {sub var}/10{sup 4} s) pc from the black hole powering 3C 279's jets, where t {sub var} is the variability timescale of the radiation in the source frame, and at farther distances for narrow-jet and magnetic-reconnection models. Excess ≳ 5 GeV γ-ray emission observed with Fermi LAT from 3C 279 challenges the model, opening the possibility of a second leptonic component or a hadronic origin of the emission. For low hadronic content, absolute jet powers of ≈10% of the Eddington luminosity are calculated.

  7. Optical Spectroscopic Observations of Gamma-Ray Blazar Candidates. VI. Further Observations from TNG, WHT, OAN, SOAR, and Magellan Telescopes

    NASA Astrophysics Data System (ADS)

    Álvarez Crespo, N.; Massaro, F.; Milisavljevic, D.; Landoni, M.; Chavushyan, V.; Patiño-Álvarez, V.; Masetti, N.; Jiménez-Bailón, E.; Strader, J.; Chomiuk, L.; Katagiri, H.; Kagaya, M.; Cheung, C. C.; Paggi, A.; D'Abrusco, R.; Ricci, F.; La Franca, F.; Smith, Howard A.; Tosti, G.

    2016-04-01

    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 we 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.

  8. Why Have Many of the Brightest Radio-loud Blazars Not Been Detected in Gamma-Rays by Fermi?

    NASA Astrophysics Data System (ADS)

    Lister, M. L.; Aller, M. F.; Aller, H. D.; Hovatta, T.; Max-Moerbeck, W.; Readhead, A. C. S.; Richards, J. L.; Ros, E.

    2015-09-01

    We use the complete MOJAVE 1.5 Jy sample of active galactic nuclei (AGNs) to examine the gamma-ray detection statistics of the brightest radio-loud blazars in the northern sky. We find that 23% of these AGNs were not detected above 0.1 GeV by the Fermi-LAT during the four-year 3FGL catalog period partly because of an instrumental selection effect and partly due to their lower Doppler boosting factors. Blazars with synchrotron peaks in their spectral energy distributions located below {10}13.4 Hz also tend to have high-energy peaks that lie below the 0.1 GeV threshold of the LAT, and are thus less likely to be detected by Fermi. The non-detected AGNs in the 1.5 Jy sample also have significantly lower 15 GHz radio modulation indices and apparent jet speeds, indicating that they have lower than average Doppler factors. Since the effective amount of relativistic Doppler boosting is enhanced in gamma-rays (particularly in the case of external inverse-Compton scattering), this makes them less likely to appear in the 3FGL catalog. Based on their observed properties, we have identified several bright radio-selected blazars that are strong candidates for future detection by Fermi.

  9. 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

  10. Chandra And HST Observations of Gamma-Ray Blazars: Comparing Jet Emission at Small And Large Scales

    SciTech Connect

    Tavecchio, Fabrizio; Maraschi, L.; Wolter, A.; Cheung, C.C.; Sambruna, R.M.; Urry, C.M.; /Yale U., Dept. Astron.

    2007-03-20

    We present new Chandra and HST data for four gamma-ray blazars selected on the basis of radio morphology with the aim of revealing X-ray and optical emission from their jets at large scales. All the sources have been detected. Spectral Energy Distributions of the large scale jets are obtained as well as new X-ray spectra for the blazar cores. Modeling for each object the core (sub-pc scale) and large-scale ({approx}> 100 kpc) jet SEDs, we derive the properties of the same jet at the two scales. The comparison of speeds and powers at different scales supports a simple scenario for the dynamics and propagation of high power relativistic jets.

  11. Derivation of a Relation for the Steepening of TeV Selected Blazar Gamma-Ray Spectra with Energy and Redshift

    NASA Technical Reports Server (NTRS)

    Stecker, F.

    2010-01-01

    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 SED of TeV Selected BL Lacs, the redshift evolution 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.

  12. The VHE gamma-ray spectra of several hard-spectrum blazars from long-term observations with the VERITAS telescope array

    NASA Astrophysics Data System (ADS)

    Madhavan, Arun

    2013-08-01

    Analysis is presented on VERITAS observations of the very high energy gamma-ray spectra of five high frequency peaked BL Lac objects over a range of redshifts. Each object has an unusually hard intrinsic GeV spectrum, and is expected to produce TeV gamma-ray emission into the optically- thick regime of the universe's diffuse extragalactic background light (EBL). Hard spectrum HBLs have recently emerged as an effective tool for measurement of the EBL spectrum, due to extinction of gamma-ray signals from blazars via the pair production interaction gamma-TeVgamma EBL → e+e -. The VERITAS collaboration has approved long term observations on several of these sources, with the specific intent of studying their spectra to probe for absorption features resulting from these interactions. An introduction to the field of particle astrophysics is presented, followed by an overview of the EBL and its relation to the evolution of the universe. The VERITAS gamma-ray telescope is described in detail, followed by a full overview of the analysis techniques used to derive gamma-ray spectra from VERITAS data. The analyses of the blazars themselves are presented, followed by a discussion of their application to further constraints of the EBL. Each blazar is de-absorbed with an assumed EBL spectrum. In each case the intrinsic TeV spectrum is consistent with lower-energy gamma-ray emission in the optically-thin regime of the EBL.

  13. Comprehensive Monitoring of Gamma-Ray Bright Blazars. I. Statistical Study of Optical, X-Ray, and Gamma-Ray Spectral Slopes

    NASA Astrophysics Data System (ADS)

    Williamson, Karen E.; Jorstad, Svetlana G.; Marscher, Alan P.; Larionov, Valeri M.; Smith, Paul S.; Agudo, Iván; Arkharov, Arkady A.; Blinov, Dmitry A.; Casadio, Carolina; Efimova, Natalia V.; Gómez, José L.; Hagen-Thorn, Vladimir A.; Joshi, Manasvita; Konstantinova, Tatiana S.; Kopatskaya, Evgenia N.; Larionova, Elena G.; Larionova, Liudmilla V.; Malmrose, Michael P.; McHardy, Ian M.; Molina, Sol N.; Morozova, Daria A.; Schmidt, Gary D.; Taylor, Brian W.; Troitsky, Ivan S.

    2014-07-01

    We present γ-ray, X-ray, ultraviolet, optical, and near-infrared light curves of 33 γ-ray bright blazars over 4 years that we have been monitoring since 2008 August with multiple optical, ground-based telescopes and the Swift satellite, and augmented by data from the Fermi Gamma-ray Space Telescope and other publicly available data from Swift. The sample consists of 21 flat-spectrum radio quasars (FSRQs) and 12 BL Lac objects (BL Lacs). We identify quiescent and active states of the sources based on their γ-ray behavior. We derive γ-ray, X-ray, and optical spectral indices, αγ, α X , and α o , respectively (F νvpropνα), and construct spectral energy distributions during quiescent and active states. We analyze the relationships between different spectral indices, blazar classes, and activity states. We find (1) significantly steeper γ-ray spectra of FSRQs than for BL Lacs during quiescent states, but a flattening of the spectra for FSRQs during active states while the BL Lacs show no significant change; (2) a small difference of α X within each class between states, with BL Lac X-ray spectra significantly steeper than in FSRQs; (3) a highly peaked distribution of X-ray spectral slopes of FSRQs at ~ -0.60, but a very broad distribution of α X of BL Lacs during active states; (4) flattening of the optical spectra of FSRQs during quiescent states, but no statistically significant change of α o of BL Lacs between states; and (5) a positive correlation between optical and γ-ray spectral slopes of BL Lacs, with similar values of the slopes. We discuss the findings with respect to the relative prominence of different components of high-energy and optical emission as the flux state changes.

  14. 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.; White, Nicholas E. (Technical Monitor)

    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.

  15. Statistical Analysis of the Long Baseline Variability Properties of a Large Gamma-Ray Selected Blazar AGN Sample

    NASA Astrophysics Data System (ADS)

    Shrader, Chris R.

    2013-06-01

    The Fermi Gamma-Ray Space Telescope has cataloged over 1800 gamma-ray (>100 MeV) point sources of which more than 1100 are identified with AGN. These AGN, and a large number of unidentified high-latitude objects of which a large fraction are also likely AGN, are predominantly representative of the radio-loud “blazar” subclass. The emission from these objects is well known to be beaming dominated and is almost always variable, often exhibiting high-amplitude flaring. To date there have been numerous studies of individual objects including multi-wavelength campaigns in some cases including parsec-scale radio jet morphological study. Collectively, this has led to new insight in to our understanding of the blazar phenomena and jet propagation in general. However, there remains a dearth of information on the collective variability characteristics of the population as a statistical ensemble. What, for example, are the distributions of flare amplitudes, durations, temporal profiles and recurrence histories among the gamma-ray blazar subclasses? Given the unprecedented sky coverage of Fermi - the full sky is observed approximately every two orbits leading to an approximate one part in 6 monitoring duty cycle for any point on the sky - we have begun to explore this issue. A light curve database compiled and maintained (weekly) by the Fermi Science Support Center contains flux histories for every source in the Fermi 2FGL catalog. In this contribution, we present our analysis of the statistical properties of the high-latitude component of this light curve database.

  16. The Redshift-Dependence of Gamma-Ray Absorption in the Environments of Blazars

    SciTech Connect

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

    2011-11-21

    One of the key scientific objectives of the new generation high energy instruments is the quest for signatures from the extragalactic background light (EBL) at UV/optical/IR energies and its evolution by means of photon-photon absorption over extragalactic distances.I will discuss the various methods proposed, and biases that may be introduced when studying the evolution of the EBL with capable {gamma}-ray observatories like e.g. GLAST or CTA, where the {gamma}-ray horizon is probed by means of statistical analysis of absorption features in AGN spectra at various redshifts. In particular, the effect of the redshift-dependence of 'local opacity' in {gamma}-ray loud quasars due to possible {gamma}-ray absorption through photon-photon pair production of jet photons in the external photon environments (accretion disk, broad-line region radiation field) on evolutionary studies of the EBL is highlighted.

  17. 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.; Blanchard, J. M.; Edwards, P. G.; Kadler, M.; Lovell, J. E. 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.

  18. ROLE OF LINE-OF-SIGHT COSMIC-RAY INTERACTIONS IN FORMING THE SPECTRA OF DISTANT BLAZARS IN TeV GAMMA RAYS AND HIGH-ENERGY NEUTRINOS

    SciTech Connect

    Essey, Warren; Kusenko, Alexander; Kalashev, Oleg; Beacom, John F.

    2011-04-10

    Active galactic nuclei (AGNs) can produce both gamma rays and cosmic rays. The observed high-energy gamma-ray signals from distant blazars may be dominated by secondary gamma rays produced along the line of sight by the interactions of cosmic-ray protons with background photons. This explains the surprisingly low attenuation observed for distant blazars, because the production of secondary gamma rays occurs, on average, much closer to Earth than the distance to the source. Thus, the observed spectrum in the TeV range does not depend on the intrinsic gamma-ray spectrum, while it depends on the output of the source in cosmic rays. We apply this hypothesis to a number of sources and, in every case, we obtain an excellent fit, strengthening the interpretation of the observed spectra as being due to secondary gamma rays. We explore the ramifications of this interpretation for limits on the extragalactic background light and for the production of cosmic rays in AGNs. We also make predictions for the neutrino signals, which can help probe the acceleration of cosmic rays in AGNs.

  19. AGILE observation of a gamma-ray flare from the blazar 3C 279

    NASA Astrophysics Data System (ADS)

    Giuliani, A.; D'Ammando, F.; Vercellone, S.; Vittorini, V.; Chen, A. W.; Donnarumma, I.; Pacciani, L.; Pucella, G.; Trois, A.; Bulgarelli, A.; Longo, F.; Tavani, M.; Tosti, G.; Impiombato, D.; Argan, A.; Barbiellini, G.; Boffelli, F.; Caraveo, P. A.; Cattaneo, P. W.; Cocco, V.; Costa, E.; Del Monte, E.; de Paris, G.; Di Cocco, G.; Evangelista, Y.; Feroci, M.; Fiorini, M.; Fornari, F.; Froysland, T.; Fuschino, F.; Galli, M.; Gianotti, F.; Labanti, C.; Lapshov, Y.; Lazzarotto, F.; Lipari, P.; Marisaldi, M.; Mereghetti, S.; Morselli, A.; Pellizzoni, A.; Perotti, F.; Picozza, P.; Prest, M.; Rapisarda, M.; Rappoldi, A.; Soffitta, P.; Trifoglio, M.; Vallazza, E.; Zambra, A.; Zanello, D.; Cutini, S.; Gasparrini, D.; Pittori, C.; Preger, B.; Santolamazza, P.; Verrecchia, F.; Giommi, P.; Colafrancesco, S.; Salotti, L.

    2009-02-01

    Context: We report the detection by the AGILE satellite of an intense gamma-ray flare from the gamma-ray source 3EG J1255-0549, associated with the Flat Spectrum Radio Quasar 3C 279, during the AGILE pointings towards the Virgo Region on 2007 July 9-13. Aims: The simultaneous optical, X-ray and gamma-ray covering allows us to study the spectral energy distribution (SED) and the theoretical models relative to the mid-July flaring episode. Methods: AGILE observed the source during its Science Performance Verification Phase with its two co-aligned imagers: the Gamma-Ray Imaging Detector (GRID) and the hard X-ray imager (Super-AGILE) sensitive in the 30 MeV-50 GeV and 18-60 keV respectively. During the AGILE observation the source was monitored simultaneously in the optical band by the REM telescope and in the X-ray band by the Swift satellite through 4 target of opportunity observations. Results: During 2007 July 9-13, AGILE-GRID detected gamma-ray emission from 3C 279, with the source at ~2° from the center of the field of view, with an average flux of (210 ± 38) × 10-8 ph cm-2 s-1 for energy above 100 MeV. No emission was detected by Super-AGILE, with a 3-σ upper limit of 10 mCrab. During the observation, which lasted about 4 days, no significative gamma-ray flux variation was observed. Conclusions: The Spectral Energy Distribution is modelled with a homogeneous one-zone Synchrotron Self Compton emission plus the contributions by external Compton scattering of the direct disk radiation and, to a lesser extent, by external Compton scattering of photons from the Broad Line Region.

  20. 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.; Blanchard, J. M.; Edwards, P. G.; Kadler, M.; Lovell, J. E.

    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.

  1. Hints of an axion-like particle mixing in the GeV gamma-ray blazar data?

    SciTech Connect

    Mena, Olga; Razzaque, Soebur E-mail: srazzaque@uj.ac.za

    2013-11-01

    Axion-Like Particles (ALPs), if exist in nature, are expected to mix with photons in the presence of an external magnetic field. The energy range of photons which undergo strong mixing with ALPs depends on the ALP mass, on its coupling with photons as well as on the external magnetic field and particle density configurations. Recent observations of blazars by the Fermi Gamma-Ray Space Telescope in the 0.1–300 GeV energy range show a break in their spectra in the 1–10 GeV range. We have modeled this spectral feature for the flat-spectrum radio quasar 3C454.3 during its November 2010 outburst, assuming that a significant fraction of the gamma rays convert to ALPs in the large scale jet of this blazar. Using theoretically motivated models for the magnetic field and particle density configurations in the kiloparsec scale jet, outside the broad-line region, we find an ALP mass m{sub a} ∼ (1−3)⋅10{sup −7} eV and coupling g{sub aγ} ∼ (1−3)⋅10{sup −10} GeV{sup −1} after performing an illustrative statistical analysis of spectral data in four different epochs of emission. The precise values of m{sub a} and g{sub aγ} depend weakly on the assumed particle density configuration and are consistent with the current experimental bounds on these quantities. We apply this method and ALP parameters found from fitting 3C454.3 data to another flat-spectrum radio quasar PKS1222+216 (4C+21.35) data up to 400 GeV, as a consistency check, and found good fit. We find that the ALP-photon mixing effect on the GeV spectra may not be washed out for any reasonable estimate of the magnetic field in the intergalactic media.

  2. Renewed gamma-ray activity of the Blazar 3C 454.3 detected by AGILE

    NASA Astrophysics Data System (ADS)

    Bulgarelli, A.; Parmiggiani, N.; Fioretti, V.; Zoli, A.; Lucarelli, F.; Verrecchia, F.; Pittori, C.; Vercellone, S.; Piano, G.; Munar-Adrover, P.; Tavani, M.; Donnarumma, I.; 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.; Antonelli, A.; Giommi, P.; Salotti, L.; Valentini, G.; D'Amico, F.

    2016-06-01

    The AGILE satellite is detecting a significant enhancement in gamma-ray activity from the FSRQ 3C 454.3 (known as 1AGLR J2254+1609) since the recent AGILE ATel #9157, and the optical activity reported in ATel #9150.

  3. High Energy Observations of X-Ray Binaries and Gamma-Ray Blazars

    NASA Technical Reports Server (NTRS)

    Vestrand, W. Thomas

    1999-01-01

    The report discusses the CGRO observation of X-ray binary systems and studies of gamma-ray blasars. Numerous authors have suggested mechanisms for particle acceleration within X-Ray Binary (XRB) systems. Among the acceleration mechanisms that have been applied are pulsar acceleration, shock acceleration at an accretion shock front, shock acceleration at a pulsar wind termination shock, plasma turbulence excited by the accretion flow, and a number of electrodynamic mechanisms. There are therefore many mechanisms which are capable of generating very energetic particles in the XRB environment. If the reports of TeV/PeV gamma-ray generation in XRBs are correct, then one can show that the accelerated particles must be hadrons and that the most likely gamma-ray production mechanism is the decay of collisionally-produced (or photoproduced) neutral pions. At these ultra-high energies, the emission is so strongly beamed that the target conditions are constrained by the requirement that the column depth be large enough to efficiently generate gamma-rays, but not so large that the gamma-rays are absorbed. These constraints naturally lead to models that explain the periodic, narrow duty-cycle pulses observed at TeV/PeV energies as arising from interactions with, either, the atmosphere of the binary companion, an accretion column, or an accretion disk. The production of these TeV/PeV gamma-rays by the decay of pions from "leading isobars" must also be accompanied by a more isotropic emission component in the EGRET energy band from the decay of slower pions (i.e. the "pionization" component). Since the attenuation of 35 MeV-1 GeV photons by photon-photon pair production is not likely to be significant in most XRBs, the TeV/PeV reports therefore strongly suggest sporadic emission in the EGRET energy band. One of the key unresolved issues for understanding AGN is the relationship between XBLs and RBLs.To test the "reunification" hypothesis, authors conducted a multiwavelength

  4. Fermi LAT detection of Increased Flux from new gamma-ray blazar PKS 0250-225

    NASA Astrophysics Data System (ADS)

    Corbel, Stephane; Reyes, Luis C.

    2009-02-01

    The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope (formerly GLAST, launched June 11, 2008), has observed an increasing gamma-ray flux from a source positionally consistent with PKS 0250-225 (RA: 02h52m47.9s, Dec:-22d19m25s, J2000). Preliminary analysis indicates that PKS 0250-225 (z=1.427 ; as CGRaBS J0252-2219 in Healey S. et al. 2007, ApJS, 175, 97) has been in a high state since Feb 17 with a gamma-ray flux (E>100MeV) of (0.5 +/- 0.1) x 10-6 ph cm-2 s-1, which represents a > 3-fold increase in flux with respect to the average preliminary flux observed during the first 6 months of data of the Fermi mission and about an 8-fold increase with respect to the first 3 months, suggesting thus a long-term trend of increasing flux.

  5. Fermi-LAT Detection of a Hard Spectrum and Enhanced Gamma-ray Emission from the Blazar PMN J2052-5533

    NASA Astrophysics Data System (ADS)

    Carpenter, Bryce; Magill, Jeff; Ojha, Roopesh

    2015-09-01

    The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has observed an unusually hard spectrum gamma-ray flare from a source positionally consistent with the blazar PMN J2052-5533 (3FGL J2051.8-5535; Acero et al. 2015, ApJS 218, 23), with coordinates RA: 20h52m13.68s, Dec: -55d33m10.0s, J2000, (Healey et al. 2007, ApJS, 171, 61). There is no redshift reported for this source in the literature.

  6. Fermi-LAT detection of hard spectrum and highest-level gamma-ray outburst from the distant blazar PKS 1502+106

    NASA Astrophysics Data System (ADS)

    Ciprini, Stefano; Fermi Large Area Telescope Collaboration

    2015-07-01

    The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed flaring gamma rays from a source positionally consistent with the flat spectrum radio quasar PKS 1502+106 (also known as OR 103, S3 1502+10 and 3FGL J1504.4+1029, Acero et al. 2015, ApJS 218, 23), with radio coordinates, (J2000.0), R.A.: 226.10408 deg, Dec: 10.49422 deg (Johnston et al. 1995, AJ, 110, 880). This blazar has a redshift of z=1.8383 (Hewett & Wild 2010, MNRAS, 405, 2302).

  7. Optical polarization plane rotation for the blazar PG 1553+113

    NASA Astrophysics Data System (ADS)

    Blinov, D.; Casadi, C.

    2016-09-01

    We report about RoboPol observations of the ongoing rotation of the optical polarization angle for the blazar PG 1553+113 (RA=15h55m43s; Dec=+11d11m24s). The rotation began around August, 19. So far the total amplitude of the rotation is ~130 degrees with an average rate of ~8 deg/day.

  8. AGILE detection of increasing gamma-ray activity from the Blazar 3C 454.3

    NASA Astrophysics Data System (ADS)

    Lucarelli, F.; Pittori, C.; Verrecchia, F.; Bulgarelli, A.; Fioretti, V.; Zoli, A.; Piano, G.; Munar-Adrover, P.; Tavani, M.; 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.; Parmiggiani, N.; Ferrari, A.; Antonelli, A.; Giommi, P.; Salotti, L.; Valentini, G.; D'Amico, F.

    2016-06-01

    The AGILE satellite is detecting an enhancement of gamma-ray emission above 100 MeV from the FSRQ 3C 454.3. Integrating from 2016-06-11 01:00 UT to 2016-06-15 01:00 UT, a maximum likelihood analysis yields the detection of the source with a flux of (2.7 +/- 0.7) x 10^-6 ph/cm2/s (E > 100 MeV), at a significance level above 5 sigma.

  9. Swift follow-up of the gamma-ray flaring blazar PKS 0727-11

    NASA Astrophysics Data System (ADS)

    D'Ammando, F.; Sokolovsky, K. V.

    2010-10-01

    Following the gamma-ray flare of the high redshift flat spectrum radio quasar PKS 0727-11 (also known as PKS J0730-1141 and 1FGL J0730.3-1141, Abdo et al. 2010, ApJS, 188, 405; z = 1.59, Zensus et al. 2002) detected by Fermi LAT on September 21, 2010 (ATel #2860), we performed two Swift target of opportunity observations on September 26 and 29. Swift/XRT data were taken in Photon Counting mode for a total exposure of about 9.0 ksec.

  10. BLAZARS AS ULTRA-HIGH-ENERGY COSMIC-RAY SOURCES: IMPLICATIONS FOR TeV GAMMA-RAY OBSERVATIONS

    SciTech Connect

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

    2012-04-10

    The spectra of BL Lac objects and Fanaroff-Riley I radio galaxies are commonly explained by the one-zone leptonic synchrotron self-Compton (SSC) model. Spectral modeling of correlated multiwavelength data gives the comoving magnetic field strength, the bulk outflow Lorentz factor, and the emission region size. Assuming the validity of the SSC model, the Hillas condition shows that only in rare cases such sources accelerate protons to much above 10{sup 19} eV, so {approx}> 10{sup 20} eV ultra-high-energy cosmic rays (UHECRs) are likely to be heavy ions if powered by this type of radio-loud active galactic nuclei (AGNs). Survival of nuclei is shown to be possible in TeV BL Lacs and misaligned counterparts with weak photohadronic emissions. Another signature of hadronic production is intergalactic UHECR-induced cascade emission, which is an alternative explanation of the TeV spectra of some extreme non-variable blazars such as 1ES 0229+200 or 1ES 1101-232. We study this kind of cascade signal, taking into account effects of the structured extragalactic magnetic fields in which the sources should be embedded. We demonstrate the importance of cosmic-ray deflections on the {gamma}-ray flux, and show that required absolute cosmic-ray luminosities are larger than the average UHECR luminosity inferred from UHECR observations and can even be comparable to the Eddington luminosity of supermassive black holes. Future TeV {gamma}-ray observations using the Cerenkov Telescope Array and the High Altitude Water Cerenkov detector array can test for UHECR acceleration by observing >25 TeV photons from relatively low redshift sources such as 1ES 0229+200, and {approx}>TeV photons from more distant radio-loud AGNs.

  11. Search for muon-neutrino emission from GeV and TeV gamma-ray flaring blazars using five years of data of the ANTARES telescope

    NASA Astrophysics Data System (ADS)

    The ANTARES Collaboration

    2015-12-01

    The ANTARES telescope is well-suited for detecting astrophysical transient neutrino sources as it can observe a full hemisphere of the sky at all times with a high duty cycle. The background due to atmospheric particles can be drastically reduced, and the point-source sensitivity improved, by selecting a narrow time window around possible neutrino production periods. Blazars, being radio-loud active galactic nuclei with their jets pointing almost directly towards the observer, are particularly attractive potential neutrino point sources, since they are among the most likely sources of the very high-energy cosmic rays. Neutrinos and gamma rays may be produced in hadronic interactions with the surrounding medium. Moreover, blazars generally show high time variability in their light curves at different wavelengths and on various time scales. This paper presents a time-dependent analysis applied to a selection of flaring gamma-ray blazars observed by the FERMI/LAT experiment and by TeV Cherenkov telescopes using five years of ANTARES data taken from 2008 to 2012. The results are compatible with fluctuations of the background. Upper limits on the neutrino fluence have been produced and compared to the measured gamma-ray spectral energy distribution.

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

    SciTech Connect

    Vercellone, S.; Romano, P.; Vittorini, V.; Donnarumma, I.; Pacciani, L.; Fiocchi, M.; Bazzano, A.; Ubertini, P.; Raiteri, C. M.; Villata, M.; Bianchin, V.; Bulgarelli, A.; Maraschi, L.; Pian, E.; Chen, A. W.

    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{sup -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.

  13. TIME SERIES ANALYSIS OF GAMMA-RAY BLAZARS AND IMPLICATIONS FOR THE CENTRAL BLACK-HOLE MASS

    SciTech Connect

    Nakagawa, Kenji; Mori, Masaki

    2013-08-20

    Radiation from the blazar class of active galactic nuclei (AGNs) exhibits fast time variability which is usually ascribed to instabilities in the emission region near the central supermassive black hole. The variability time scale is generally faster in higher energy region, and data recently provided by the Fermi Gamma-ray Space Telescope in the GeV energy band enable a detailed study of the temporal behavior of AGN. Due to its wide field-of-view in the scanning mode, most sky regions are observed for several hours per day and daily light curves of many AGNs have been accumulated for more than 4 yr. In this paper we investigate the time variability of 15 well-detected AGNs by studying the normalized power spectrum density of their light curves in the GeV energy band. One source, 3C 454.3, shows a specific time scale of 6.8 Multiplication-Sign 10{sup 5} s, and this value suggests, assuming the internal shock model, a mass for the central black hole of (10{sup 8}-10{sup 10}) M{sub Sun} which is consistent with other estimates. It also indicates the typical time interval of ejected blobs is (7-70) times the light crossing time of the Schwarzschild radius.

  14. Time Series Analysis of Gamma-Ray Blazars and Implications for the Central Black-hole Mass

    NASA Astrophysics Data System (ADS)

    Nakagawa, Kenji; Mori, Masaki

    2013-08-01

    Radiation from the blazar class of active galactic nuclei (AGNs) exhibits fast time variability which is usually ascribed to instabilities in the emission region near the central supermassive black hole. The variability time scale is generally faster in higher energy region, and data recently provided by the Fermi Gamma-ray Space Telescope in the GeV energy band enable a detailed study of the temporal behavior of AGN. Due to its wide field-of-view in the scanning mode, most sky regions are observed for several hours per day and daily light curves of many AGNs have been accumulated for more than 4 yr. In this paper we investigate the time variability of 15 well-detected AGNs by studying the normalized power spectrum density of their light curves in the GeV energy band. One source, 3C 454.3, shows a specific time scale of 6.8 × 105 s, and this value suggests, assuming the internal shock model, a mass for the central black hole of (108-1010) M ⊙ which is consistent with other estimates. It also indicates the typical time interval of ejected blobs is (7-70) times the light crossing time of the Schwarzschild radius.

  15. Time-dependent Modeling of Gamma-Ray Flares in Blazar PKS1510--089

    NASA Astrophysics Data System (ADS)

    Saito, S.; Stawarz, Ł.; Tanaka, Y. T.; Takahashi, T.; Sikora, M.; Moderski, R.

    2015-08-01

    Here we present a new approach for constraining luminous blazars, incorporating fully time-dependent and self-consistent modeling of bright γ-ray flares of PKS 1510-089, resolved with Fermi-LAT, in the framework of the internal shock scenario. The results of our modeling imply the location of the γ-ray flaring zone to be outside of the broad-line region, namely around ≃ 0.3 pc from the core for a free-expanding jet with the opening angle {{Γ }} {θ }{jet}≃ 1 (where Γ is the jet bulk Lorentz factor), up to ≃ 3 pc for a collimated outflow with {{Γ }} {θ }{jet}≃ 0.1. Moreover, under the {{Γ }} {θ }{jet}≃ 1 condition, our modeling indicates the maximum efficiency of the jet production during the flares, with the total jet energy flux strongly dominated by protons and exceeding the available accretion power in the source. This is in contrast to the quiescence states of the blazar, characterized by lower jet kinetic power and an approximate energy equipartition between different plasma constituents. We demostrate how strictly simultaneous observations of flaring PKS 1510-089 at optical, X-ray, and GeV photon energies, on hourly timescales, augmented by extensive simulations as presented in this paper, may help to impose further precise constraints on the magnetization and opening angle of the emitting region. In addition, our detailed modeling implies that a non-uniformity of the Doppler factor across the jet, caused by the radial expansion of the outflow, may lead to a pronounced time distortion in the observed γ-ray light curves, resulting, in particular, in asymmetric flux profiles with substantially extended decay phases.

  16. GAMMA-RAY LOUDNESS, SYNCHROTRON PEAK FREQUENCY, AND PARSEC-SCALE PROPERTIES OF BLAZARS DETECTED BY THE FERMI LARGE AREA TELESCOPE

    SciTech Connect

    Linford, J. D.; Taylor, G. B.; Schinzel, F. K.

    2012-09-20

    The parsec-scale radio properties of 232 active galactic nuclei, most of which are blazars, detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA) at 5 GHz. Data from both the first 11 months (1FGL) and the first 2 years (2FGL) of the Fermi mission were used to investigate these sources' {gamma}-ray properties. We use the ratio of the {gamma}-ray-to-radio luminosity as a measure of {gamma}-ray loudness. We investigate the relationship of several radio properties to {gamma}-ray loudness and to the synchrotron peak frequency. There is a tentative correlation between {gamma}-ray loudness and synchrotron peak frequency for BL Lac objects in both 1FGL and 2FGL, and for flat-spectrum radio quasars (FSRQs) in 2FGL. We find that the apparent opening angle tentatively correlates with {gamma}-ray loudness for FSRQs, but only when we use the 2FGL data. We also find that the total VLBA flux density correlates with the synchrotron peak frequency for BL Lac objects and FSRQs. The core brightness temperature also correlates with synchrotron peak frequency, but only for the BL Lac objects. The low-synchrotron-peaked (LSP) BL Lac object sample shows indications of contamination by FSRQs which happen to have undetectable emission lines. There is evidence that the LSP BL Lac objects are more strongly beamed than the rest of the BL Lac object population.

  17. A determination of the gamma-ray flux and photon spectral index distributions of blazars from the Fermi-LAT 3LAC

    NASA Astrophysics Data System (ADS)

    Singal, J.

    2015-11-01

    We present a determination of the distributions of gamma-ray photon flux - the so-called LogN-LogS relation - and photon spectral index for blazars, based on the third extragalactic source catalogue of the Fermi Gamma-ray Space Telescope's Large Area Telescope, and considering the photon energy range from 100 MeV to 100 GeV. The data set consists of the 774 blazars in the so-called Clean sample detected with a greater than approximately 7σ detection threshold and located above ±20° Galactic latitude. We use non-parametric methods verified in previous works to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation between the flux and photon index. The intrinsic flux distribution can be represented by a broken power law with a high-flux power-law index of -2.43 ± 0.08 and a low-flux power-law index of -1.87 ± 0.10. The intrinsic photon index distribution can be represented by a Gaussian with mean of 2.62 ± 0.05 and width of 0.17 ± 0.02. We also report the intrinsic distributions for the subpopulations of BL Lac and FSRQ (Flat Spectrum Radio Quasar)-type blazars separately and these differ substantially. We then estimate the contribution of FSRQs and BL Lacs to the diffuse extragalactic gamma-ray background radiation. Under the simplistic assumption that the flux distributions probed in this analysis continue to arbitrary low flux, we calculate that the best-fitting contribution of FSRQs is 35 per cent and BL Lacs 17 per cent of the total gamma-ray output of the Universe in this energy range.

  18. The Cosmological Impact of Luminous TeV Blazars. I. Implications of Plasma Instabilities for the Intergalactic Magnetic Field and Extragalactic Gamma-Ray Background

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

    Inverse Compton cascades (ICCs) initiated by energetic gamma rays (E >~ 100 GeV) enhance the GeV emission from bright, extragalactic TeV sources. The absence of this emission from bright TeV blazars has been used to constrain the intergalactic magnetic field (IGMF), and the stringent limits placed on the unresolved extragalactic gamma-ray background (EGRB) by Fermi have been used to argue against a large number of such objects at high redshifts. However, these are predicated on the assumption that inverse Compton scattering is the primary energy-loss mechanism for the ultrarelativistic pairs produced by the annihilation of the energetic gamma rays on extragalactic background light photons. Here, we show that for sufficiently bright TeV sources (isotropic-equivalent luminosities >~ 1042 erg s-1) plasma beam instabilities, specifically the "oblique" instability, present a plausible mechanism by which the energy of these pairs can be dissipated locally, heating the intergalactic medium. Since these instabilities typically grow on timescales short in comparison to the inverse Compton cooling rate, they necessarily suppress the ICCs. As a consequence, this places a severe constraint on efforts to limit the IGMF from the lack of a discernible GeV bump in TeV sources. Similarly, it considerably weakens the Fermi limits on the evolution of blazar populations. Specifically, we construct a TeV-blazar luminosity function from those objects currently observed and find that it is very well described by the quasar luminosity function at z ~ 0.1, shifted to lower luminosities and number densities, suggesting that both classes of sources are regulated by similar processes. Extending this relationship to higher redshifts, we show that the magnitude and shape of the EGRB above ~10 GeV are naturally reproduced with this particular example of a rapidly evolving TeV-blazar luminosity function.

  19. Four Years of EUVE Observations of the Bursting Gamma-Ray Emitting Blazar Markarian 421

    NASA Technical Reports Server (NTRS)

    Cagnoni, Ilaria; Fruscione, Antonella; Papadakis, Iossif

    1998-01-01

    We present spectral and timing analysis of all the data collected by the Extreme Ultraviolet Explorer Satellite (EUVE) for the bright, nearby BL Lacertae object, Markarian 421, during the four-year period 1994-1997. During these years Mrk 421 has been observed by EUVE 4 times with the Deep-Survey/Spectrograph and 2 times with the imaging telescopes for a total of approximately 1.4 7nillions seconds. From 1993 to 1996 three very bright gamma ray flares were also detected by the Whipple observatory. In 1994 Mrk 421 was observed simultaneously by EUVE (Apr 2-12) and IUE one month before the TeV flare; of the 2 EUVF, observations (Feb 4-7 and Apr 25-May 13) of 1995, the second was part of a multiwavelength campaign that mapped the evolution of the TeV flare. In 1996 we observed Mrk 421 twice simultaneously with XTE: one immediately before (Apr 17-30) and another one (May 10-11) right after the May 7 1996 TeV flare. And finally in 1997 from Feb. 7 to Feb. ll. The total light curve seems to be smoothly varying on the long time-scale while on a shorter time-scale there is evidence of an EUVE flare well correlated to the TeV energy 1995 flare. We have analysed the three spectral data set in an homogenous way using the appropriate calibration data for the off-axis observations and our analysis confirms the presence of the absorption features around approximately 70A, in the entire 1995 dataset and possibly in the 1996 data set. We also show the first power spectrum analysis of the Mrk 421 EUVE lightcurves and a comparison with the power spectra predicted by current theoretical models.

  20. GAMMA-RAY FLARING ACTIVITY FROM THE GRAVITATIONALLY LENSED BLAZAR PKS 1830–211 OBSERVED BY Fermi LAT

    SciTech Connect

    Abdo, A. A.; Ackermann, M.; Buehler, R.; Ajello, M.; Allafort, A.; Bechtol, K.; Blandford, R. D.; Borgland, A. W.; Caliandro, G. A.; Cameron, R. A.; Amin, M. A.; Baldini, L.; Bellazzini, R.; Barbiellini, G.; Bastieri, D.; Buson, S.; Bonamente, E.; Bregeon, J.; Bulmash, D. E-mail: stefano.ciprini@asdc.asi.it E-mail: dammando@ira.inaf.it E-mail: sara.buson@pd.infn.it E-mail: dammando@ira.inaf.it; and others

    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 × 10{sup 50} erg s{sup –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.

  1. 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.

  2. A UNIFORM CORRELATION BETWEEN SYNCHROTRON LUMINOSITY AND DOPPLER FACTOR IN GAMMA-RAY BURSTS AND BLAZARS: A HINT OF SIMILAR INTRINSIC LUMINOSITIES?

    SciTech Connect

    Wu Qingwen; Zou Yuanchuan; Wang Dingxiong; Cao Xinwu; Chen Liang E-mail: zouyc@hust.edu.cn E-mail: cxw@shao.ac.cn

    2011-10-10

    We compile 23 gamma-ray bursts (GRBs) and 21 blazars with estimated Doppler factors, and the Doppler factors of GRBs are estimated from their Lorentz factors by assuming their jet viewing angles {theta} {yields} 0{sup 0}. Using the conventional assumption that the prompt emission of GRBs is dominated by the synchrotron radiation, we calculate the synchrotron luminosity of GRBs from their total isotropic energy and burst duration. Intriguingly, we discover a uniform correlation between the synchrotron luminosity and Doppler factor, L{sub syn}{proportional_to}D{sup 3.1}, for GRBs and blazars, which suggests that they may share some similar jet physics. One possible reason is that GRBs and blazars have, more or less, similar intrinsic synchrotron luminosities and both of them are strongly enhanced by the beaming effect. After Doppler and redshift correction, we find that the intrinsic peak energy of the GRBs ranges from 0.1 to 3 keV with a typical value of 1 keV. We further correct the beaming effect for the observed luminosity of GRBs and find that a positive correlation exists between the intrinsic synchrotron luminosity and peak energy for GRBs, which is similar to that of blazars. Our results suggest that both the intrinsic positive correlation and the beaming effect may be responsible for the observed tight correlation between the isotropic energy and the peak energy in GRBs (the so-called Amati relation).

  3. The BL-Lacertae gamma-ray blazar PKS 1424+240 associated with a group of galaxies at z = 0.6010

    NASA Astrophysics Data System (ADS)

    Rovero, A. C.; Muriel, H.; Donzelli, C.; Pichel, A.

    2016-04-01

    Context. PKS 1424+240 is a BL-Lac blazar with unknown redshift that was detected at high-energy gamma rays by Fermi-LAT with a hard spectrum. At very high energy (VHE), it was first detected by VERITAS and later confirmed by MAGIC. Its spectral energy distribution is highly attenuated at VHE gamma rays, which is coherent with distant sources. Several estimations enabled the redshift to be constrained to the range 0.6 blazar that has been detected at VHE. The ambiguity in the redshift is still large enough to prevent precise studies of the extragalatic background light and the intrinsic blazar spectrum. Aims: Given the difficulty of measuring spectroscopic redshifts for BL-Lac objects directly, we aim to establish a reliable redshift value for this blazar by finding its host group of galaxies. Methods: Elliptical galaxies are associated with groups, and BL-Lac objects are typically hosted by them, so we decided to search for the host group of the blazar. For this, we performed optical spectroscopic observations of thirty objects in the field of view of PKS 1424+240 using the Gemini Multi-Object Spectrograph. After analysing the data for groups, we evaluated the probability of finding groups of galaxies by chance around the position of PKS 1424+240, using a deep catalogue of groups. We also used photometric data from the SDSS catalogue to analyse the red sequence of the proposed blazar host group Results: We found a new group of galaxies with eight members at z = 0.6010 ± 0.003, a virial radius of Rvir = 1.53 Mpc, and a velocity dispersion of σv = 813 ± 187 km s-1. The photometric study indicates that more members are probably populating this previously uncatalogued group of galaxies. The probability of PKS 1424+240 being a member of this group was found to be ≳98%. Conclusions: The new group of galaxies found at z = 0.6010 ± 0.003 is very likely

  4. VERY RAPID HIGH-AMPLITUDE GAMMA-RAY VARIABILITY IN LUMINOUS BLAZAR PKS 1510-089 STUDIED WITH FERMI-LAT

    SciTech Connect

    Saito, S.; Stawarz, L.; Takahashi, T.; Tanaka, Y. T.; Madejski, G.; D'Ammando, F.

    2013-03-20

    Here we report on the detailed analysis of the {gamma}-ray light curve of a luminous blazar PKS 1510-089 observed in the GeV range with the Large Area Telescope (LAT) on board the Fermi satellite during the period 2011 September-December. By investigating the properties of the detected three major flares with the shortest possible time binning allowed by the photon statistics, we find a variety of temporal characteristics and variability patterns. This includes a clearly asymmetric profile (with a faster flux rise and a slower decay) of the flare resolved on sub-daily timescales, a superposition of many short uncorrelated flaring events forming the apparently coherent longer-duration outburst, and a huge single isolated outburst unresolved down to the timescale of 3 hr. In the latter case we estimate the corresponding {gamma}-ray flux doubling timescale to be below 1 hr, which is extreme and never previously reported for any active galaxy in the GeV range. The other unique finding is that the total power released during the studied rapid and high-amplitude flares constitutes the bulk of the power radiatively dissipated in the source and a significant fraction of the total kinetic luminosity of the underlying relativistic outflow. Our analysis allows us to access directly the characteristic timescales involved in shaping the energy dissipation processes in the source, and to provide constraints on the location and the structure of the blazar emission zone in PKS 1510-089.

  5. DISENTANGLING HADRONIC AND LEPTONIC CASCADE SCENARIOS FROM THE VERY-HIGH-ENERGY GAMMA-RAY EMISSION OF DISTANT HARD-SPECTRUM BLAZARS

    SciTech Connect

    Takami, Hajime; Murase, Kohta; Dermer, Charles D. E-mail: murase@ias.edu

    2013-07-10

    Recent data from the Fermi Large Area Telescope have revealed about a dozen distant hard-spectrum blazars that have very-high-energy (VHE; {approx}> 100 GeV) 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 planned Cherenkov Telescope Array (CTA) and show how it can distinguish the two scenarios by measuring the integrated flux above {approx}500 GeV (depending on source redshift) for several luminous sources with z {approx}< 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. Accurate redshift measurements of hard-spectrum blazars are essential for this study.

  6. Fermi-LAT detection of increased gamma-ray activity from the blazar PKS 0727-115

    NASA Astrophysics Data System (ADS)

    Horan, D.; Hays, E. Gurwell, Mark A.

    2009-01-01

    The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope (formerly GLAST, launched June 11, 2008), has observed an increasing gamma-ray flux from a source positionally consistent with PKS 0727-115 (RA: 07h30m19.1s, Dec: -11d41m13s, J2000, z=1.59 ( Zensus et al. 2002)). Preliminary analysis indicates that over the past month the source has become, on average, brighter with a gamma-ray flux (E>100MeV) of approximately 5.0+/- 0.8 x 10^-7 photons cm^-2 s^-1 on weekly timescales and occasional day-scale detections at the level of approximately 4.0 +/- 1.0 x 10^-7 photons cm^-2 s^-1.

  7. Gamma-ray flares from the blazars TXS 2241+406, Ton 599, and 4C +01.02

    NASA Astrophysics Data System (ADS)

    Ojha, Roopesh; Carpen, Bryce

    2015-11-01

    The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has observed a gamma-ray flare from a source positionally consistent with the BL Lac object TXS 2241+406 (3FGL J2244.1+4057, Acero et al. 2015, ApJS 218, 23) with coordinates RA=22h 44m 12.7311s, Dec=40d 57m 13.62s (J2000, Beasley et al. 2002, ApJS, 141, 13) with redshift z=1.171 (Shaw et al. 2012, ApJ, 748, 49). Preliminary analysis indicates that on 20 November 2015 this source was in a high-flux state, with a daily averaged gamma-ray flux (E > 100MeV) of (1.2+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) and photon spectral index of 2.2+/-0.1 (errors are statistical only).

  8. A Comprehensive Statistical Description of Radio-through-Gamma-Ray Spectral Energy Distributions of All Known Blazars

    NASA Astrophysics Data System (ADS)

    Mao, Peiyuan; Urry, C. Megan; Massaro, Francesco; Paggi, Alessandro; Cauteruccio, Joe; Künzel, Soren R.

    2016-06-01

    We combined multi-wavelength data for blazars from the Roma-BZCAT catalog and analyzed hundreds of X-ray spectra. We present the fluxes and spectral energy distributions (SEDs), in 12 frequency bands from radio to γ-rays, for a final sample of 2214 blazars. Using a model-independent statistical approach, we looked for systematic trends in the SEDs; the most significant trends involved the radio luminosities and X-ray spectral indices of the blazars. We used a principal component analysis (PCA) to determine the basis vectors of the blazar SEDs and, in order to maximize the size of the sample, imputed missing fluxes using the K-nearest neighbors method. Using more than an order of magnitude more data than was available when Fossati et al. first reported trends of SED shape with blazar luminosity, we confirmed the anti-correlation between radio luminosity and synchrotron peak frequency, although with greater scatter than was seen in the smaller sample. The same trend can be seen between bolometric luminosity and synchrotron peak frequency. Finally, we used all of the available blazar data to determine an empirical SED description that depends only on the radio luminosity at 1.4 GHz and the redshift. We verified that this statistically significant relation was not a result of the luminosity–luminosity correlations that are natural in flux-limited samples (i.e., where the correlation is actually caused by the redshift rather than the luminosity).

  9. Fermi-LAT detection of a GeV gamma-ray flare from the blazar PKS 0514-459

    NASA Astrophysics Data System (ADS)

    Ciprini, Stefano

    2016-01-01

    The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar PKS 0514-459 (also known as RX J0515.7-4556 and 3FGL J0515.3-4557), with radio counterpart position R.A.: 78.938767 deg, Dec.: -45.945369 deg (J2000.0, Costa & Loyola 1996, A & AS, 115, 75) and with redshift z=0.194 (Stickel, Kuehr, & Fried 1993, A & AS, 97, 483).

  10. Fermi-LAT detection of a GeV gamma-ray flare from the blazar PKS 1313-333

    NASA Astrophysics Data System (ADS)

    Ciprini, Stefano

    2016-01-01

    The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar PKS 1313-333 (also known as TXS 1313-333, OP -322, 2EG J1314-3430 and 3FGL J1316.0-3338), with radio counterpart position R.A.: 199.033275 deg, Dec.: -33.64977 deg, (J2000.0, Johnston et al. 1995, AJ, 110, 880) and with redshift z=1.210 (Jauncey et al. 1982, AJ, 87, 763).

  11. An Investigation of the Optical Microvariability of the Blazar PG 0735+178

    NASA Astrophysics Data System (ADS)

    McFarland, J. P.; Miller, H. R.; Carini, M. T.; Jang, M.; Noble, J. C.

    2003-05-01

    The blazar PG 0735+178 was monitored for more than 20 nights for microvariability on multiple timescales. We present this data which shows variations of amplitude several hundredths to several tenths of a magnitude on timescales of hours to days. The object also has exhibited variations with an amplitude as large as 2 magnitudes on the timescale of years. This microvariability will be investigated as a function of outburst and quiescent states of the object over the course of these timescales. These variations place severe limits on the size of the emitting region, and provide constraints for the physical processes responsible for these variations. JPM and HRM are grateful for support of a grant from the Research Corporation and the PEGA-RPE program at Georgia State University.

  12. PKS 1502+106: A NEW AND DISTANT GAMMA-RAY BLAZAR IN OUTBURST DISCOVERED BY THE FERMI LARGE AREA TELESCOPE

    SciTech Connect

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Bechtol, K.; Berenji, B.; Bloom, E. D.; Borgland, A. W.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Brez, A.; Ballet, J.; Bastieri, D.; Baughman, B. M.; Bogaert, G.; Brigida, M. E-mail: stefano.ciprini@pg.infn.i

    2010-02-10

    The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope discovered a rapid ({approx}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 ({approx}23 UTC, MJD 54683.95), and followed by bright and variable flux over the next few months. 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 one 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, Metsaehovi-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{sub g}amma, is about 1.1 x 10{sup 49} erg s{sup -1}, and black hole mass likely close to 10{sup 9} M{sub sun}), exhibiting marked gamma-ray bolometric dominance, in particular during the asymmetric outburst (L{sub g}amma/L{sub opt} {approx} 100, and 5 day averaged flux F{sub E>100MeV} = 2.91 +- 1.4 x 10{sup -6} ph cm{sup -2} s{sup -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{sub 0.3-10{sub keV}} = 2.18{sup +0.15}{sub -0.12} x 10{sup -12} erg cm{sup -2} s{sup -1}, and hard photon index {approx}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

  13. Optical Spectroscopic Observations of Gamma-ray Blazar Candidates. IV. Results of the 2014 Follow-up Campaign

    NASA Astrophysics Data System (ADS)

    Ricci, F.; Massaro, F.; Landoni, M.; D'Abrusco, R.; Milisavljevic, D.; Stern, D.; Masetti, N.; Paggi, A.; Smith, Howard A.; Tosti, G.

    2015-05-01

    The extragalactic γ-ray sky is dominated by the emission arising from blazars, one of the most peculiar classes of radio-loud active galaxies. Since the launch of Fermi several methods were developed to search for blazars as potential counterparts of unidentified γ-ray sources (UGSs). To confirm the nature of the selected candidates, optical spectroscopic observations are necessary. In 2013 we started a spectroscopic campaign to investigate γ-ray blazar candidates selected according to different procedures. The main goals of our campaign are: (1) to confirm the nature of these candidates, and (2) whenever possible, determine their redshifts. Optical spectroscopic observations will also permit us to verify the robustness of the proposed associations and check for the presence of possible source class contaminants to our counterpart selection. This paper reports the results of observations carried out in 2014 in the northern hemisphere with Kitt Peak National Observatory and in the southern hemisphere with the Southern Astrophysical Research telescopes. We also report three sources observed with the Magellan and Palomar telescopes. Our selection of blazar-like sources that could be potential counterparts of UGSs is based on their peculiar infrared colors and on their combination with radio observations both at high and low frequencies (i.e., above and below ˜1 GHz) in publicly available large radio surveys. We present the optical spectra of 27 objects. We confirm the blazar-like nature of nine sources that appear to be potential low-energy counterparts of UGSs. Then we present new spectroscopic observations of 10 active galaxies of uncertain type associated with Fermi sources, classifying all of them as blazars. In addition, we present the spectra for five known γ-ray blazars with uncertain redshift estimates and three BL Lac candidates that were observed during our campaign. We also report the case for WISE J173052.85-035247.2, candidate counterpart of the

  14. MULTI-WAVELENGTH OBSERVATIONS OF THE FLARING GAMMA-RAY BLAZAR 3C 66A IN 2008 OCTOBER

    SciTech Connect

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Borgland, A. W.; Bouvier, A.; Buehler, R.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Brez, A.; Ballet, J.; Bastieri, D.; Buson, S.; Bonamente, E.; Brigida, M.; Bruel, P.

    2011-01-01

    The BL Lacertae object 3C 66A was detected in a flaring state by the Fermi Large Area Telescope (LAT) and VERITAS in 2008 October. In addition to these gamma-ray observations, F-GAMMA, GASP-WEBT, PAIRITEL, MDM, ATOM, Swift, and Chandra provided radio to X-ray coverage. The available light curves show variability and, in particular, correlated flares are observed in the optical and Fermi-LAT gamma-ray band. The resulting spectral energy distribution can be well fitted using standard leptonic models with and without an external radiation field for inverse Compton scattering. It is found, however, that only the model with an external radiation field can accommodate the intra-night variability observed at optical wavelengths.

  15. A Change in the Optical Polarization Associated with a Gamma-Ray Flare in the Blazar 3C 279

    SciTech Connect

    Abdo, A.A.

    2011-08-19

    It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our line of sight. The size of the emitting zone and the location of this region relative to the central supermassive black hole are, however, poorly known, with estimates ranging from light-hours to a light-year or more. Here we report the coincidence of a gamma ({gamma})-ray flare with a dramatic change of optical polarization angle. This provides evidence for co-spatiality of optical and {gamma}-ray emission regions and indicates a highly ordered jet magnetic field. The results also require a non-axisymmetric structure of the emission zone, implying a curved trajectory for the emitting material within the jet, with the dissipation region located at a considerable distance from the black hole, at about 10{sup 5} gravitational radii.

  16. A change in the optical polarization associated with a gamma-ray flare in the blazar 3C 279.

    PubMed

    2010-02-18

    It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our line of sight. The size of the emitting zone and the location of this region relative to the central supermassive black hole are, however, poorly known, with estimates ranging from light-hours to a light-year or more. Here we report the coincidence of a gamma (gamma)-ray flare with a dramatic change of optical polarization angle. This provides evidence for co-spatiality of optical and gamma-ray emission regions and indicates a highly ordered jet magnetic field. The results also require a non-axisymmetric structure of the emission zone, implying a curved trajectory for the emitting material within the jet, with the dissipation region located at a considerable distance from the black hole, at about 10(5) gravitational radii. PMID:20164923

  17. First Fermi LAT detection of a strong GeV gamma-ray flare from blazar PKS 0403-13

    NASA Astrophysics Data System (ADS)

    Ciprini, Stefano

    2016-07-01

    The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar PKS 0403-13 (also known as TXS 0403-132, OF -105, RX J0405.5-1308, and 3FGL J0405.5-1307), with radio counterpart position R.A.: 61.391680 deg, Dec.: -13.137136 deg (J2000.0, Fey et al. 2004, AJ, 127, 3587) and with redshift z=0.5706+/-0.0001 (Marziani et al. 1996, ApJS, 104, 37). Preliminary analysis indicates that on 2016 July 11, PKS 0403-13 was in a high state with a daily averaged gamma-ray flux (E > 100 MeV) of (1.6+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 140 times greater than its four-year average flux reported in the third Fermi-LAT source catalog (3FGL, Acero et al. 2015, ApJS, 218, 23). The corresponding daily averaged spectral photon index (E > 100 MeV) of 2.3+/-0.2 (statistical uncertainty only) is compatible with the 3FGL catalog value of 2.35+/-0.11.

  18. Fermi-LAT detection of a GeV gamma-ray flare from the blazar PKS 2023-07

    NASA Astrophysics Data System (ADS)

    Ciprini, Stefano; Fermi Large Area Telescope Collaboration

    2016-04-01

    The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar PKS 2023-07 (also known as NRAO 629, TXS 2022-077, 3EG J2025-0744, 1AGLR J2027-0747 and 3FGL J2025.6-0736), with radio counterpart position R.A.: 306.419418 deg, Dec.: -7.597969 deg (J2000.0, Beasley et al. 2002, ApJS, 141, 13) and with redshift z=1.388 (Drinkwater et al. 1997, MNRAS, 284, 85). Preliminary analysis indicates that on 2016 April 9, PKS 2023-07 was in a high state with a daily averaged gamma-ray flux (E > 100 MeV) of (2.0+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 16 times greater than its four-year average flux reported in the third Fermi-LAT source catalog (3FGL, Acero et al. 2015, ApJS, 218, 23). The corresponding daily averaged spectral photon index (E > 100 MeV) of 2.4+/-0.2 (statistical uncertainty only) is compatible with the 3FGL catalog value of 2.18+/-0.03.

  19. Optical Spectroscopic Observations of Gamma-ray Blazar Candidates. V. TNG, KPNO, and OAN Observations of Blazar Candidates of Uncertain Type in the Northern Hemisphere

    NASA Astrophysics Data System (ADS)

    Álvarez Crespo, N.; Masetti, N.; Ricci, F.; Landoni, M.; Patiño-Álvarez, V.; Massaro, F.; D'Abrusco, R.; Paggi, A.; Chavushyan, V.; Jiménez-Bailón, E.; Torrealba, J.; Latronico, L.; La Franca, F.; Smith, Howard A.; Tosti, G.

    2016-02-01

    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 in 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.

  20. Distributions of gamma-ray bursts and blazars in the L {sub p}-E {sub p}-plane and possible implications for their radiation physics

    SciTech Connect

    Lyu, Fen; Liang, En-Wei; Liang, Yun-Feng; Sun, Xiao-Na; Lu, Rui-Jing; Zhang, Bing; Wu, Xue-Feng; Zhang, Jin E-mail: xfwu@pmo.ac.cn

    2014-09-20

    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 {sub s}) and the corresponding peak photon energy E {sub s} of blazars in the L {sub p}-E {sub p}-plane of GRBs, where L {sub p} and E {sub p} are the peak luminosity and peak photon energy of the GRB time-integrated νf {sub ν} spectrum, respectively. The GRBs are in the high-L {sub p}, high-E {sub p} corner of the plane and a tight L {sub p}-E {sub p} relation is found, i.e., L{sub p}∝E{sub p}{sup 2.13{sub −}{sub 0}{sub .}{sub 4}{sub 6}{sup +{sup 0{sup .{sup 5{sup 4}}}}}}. Both flat spectrum radio quasars (FSRQs) and low-synchrotron peaking BL Lac objects (LBLs) are clustered in the low-E {sub p}, low-L {sub p} corner. Intermediate- and high-synchrotron peaking BL Lac objects (IBLs and HBLs) have E {sub s} ∼ 2 × 10{sup –3}-10{sup 2} keV and L {sub s} ∼ 10{sup 44}-10{sup 47} erg s{sup –1}, but no dependence of L {sub s} on E {sub s} is found. We show that the tight L{sub p} -E{sub p} 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 {sub s}-E {sub 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 {sub p}-E {sub 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.

  1. 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.

  2. 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.

  3. The hadronic origin of the hard gamma-ray spectrum from blazar 1ES 1101-232

    SciTech Connect

    Cao, Gang; Wang, Jiancheng E-mail: jcwang@ynao.ac.cn

    2014-03-10

    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.

  4. Time Dependent Multi Zone Modeling of X-ray and Gamma-ray Variability of the TeV Blazar Mrk 421.

    NASA Astrophysics Data System (ADS)

    Fossati, Giovanni; Chen, X.

    2010-02-01

    We present a new time-dependent multi-zone code and its first application to study the SSC emission of Blazar Mrk 421. The code couples Fokker-Planck and Monte Carlo methods. All the light travel time effects are fully considered, internal and external. It has long been realized that simple one-zone homogeneous models are not adequate to describe several aspects of the phenomenology, in particular those pertaining to the complex multiwavelength variability. Progress has been made by several groups but important trade-offs have always been necessary, such as neglecting internal light travel time or the inclusion of IC losses in the electron evolution. Our code fully accounts for all the relevant effects, and it also affords us significant freedom w.r.t. geometry and "variability". This latter is implemented as a shock traveling along the jet, with electrons being injected as it sweeps the blob. Results are compared with the 2001 observations of Mrk 421. We also analyzed cases including a pre-existing cospatial electron population contributing to the SED, and external radiation field. It seems to be possible to achieve adequate fits to the observations, but a there remain several open issues, such as a systematic soft X-ray intraband lag, and a delay of the gamma-ray flare with respect to the X-ray flare. The two principal challenges are: 1. The simulated VHE spectrum is always softer than the observed one. 2. The correlation between the TeV gamma-ray and X-ray does not reproduce the (super)quadratic relationship observed in multiple occasions. In fact we have not been able to reproduce anything close to it in this first suite of models. We will report also on the extension of the code, and case studies, to jet-in-jet and spine-layer configurations, as well as to the study of red blazars. We acknowledge support from Chandra Award AR9-0016X

  5. Fermi/LAT detection of extraordinary variability in the gamma-ray emission of the blazar PKS 1510-089

    NASA Astrophysics Data System (ADS)

    Foschini, L.; Bonnoli, G.; Ghisellini, G.; Tagliaferri, G.; Tavecchio, F.; Stamerra, A.

    2013-07-01

    We have reanalyzed the giant outburst of the blazar PKS 1510-089 (z = 0.36) that occurred on 2011 October-November. The γ-ray flux in the 0.1-100 GeV energy range exceeded the value of 10-5 ph cm-2 s-1 for several days. The peak flux was reached on 2011 October 19, with a value of ~4.4 × 10-5 ph cm-2 s-1, which in turn corresponds to a luminosity of ~2 × 1049 erg s-1. A very short timescale variability was measured. Particularly on 2011 October 18, the flux-doubling time was as short as ~20 min. This is the shortest variability ever detected in the MeV-GeV energy band. We compared our analysis with two other outbursts observed in 2009 March and 2012 February-March, when the blazar was also detected by H.E.S.S. and MAGIC to infer information about the emission at hundreds of GeV.

  6. Very-long-baseline radio interferometry (VLBI) observations of gamma-ray blazars: results from millimeter-VLBI observations.

    PubMed Central

    Krichbaum, T P; Britzen, S; Standke, K J; Witzel, A; Schalinski, C J; Zensus, J A

    1995-01-01

    VLBI observations of the extremely gamma-bright blazar PKS 0528+134 at 8, 22, 43, and 86 GHz reveal a strongly bent one-sided-core jet structure with at least three moving and two apparently stationary jet components. At the highest observing frequencies the brightest and most compact jet component (the VLBI core) is unresolved with an upper limit to its size of approximately 50 microarcsec corresponding to approximately 0.2 parsec [H0 = 100 km.s-1.Mpc-1 (megaparsec-1), q0 = 0.5, where H0 is Hubble constant and q0 is the deceleration parameter]. Two 86-GHz VLBI observations performed in 1993.3 and 1994.0 reveal a new jet component emerging with superluminal speed from the core. Linear back-extrapolation of its motion yields strong evidence that the ejection of this component is related to an outburst in the millimeter regime and a preceding intense flare of the gamma-flux density observed in early 1993. This and the radio/optical "light curves" and VLBI data for two other sources (S5 0836+710 and 3C 454.3) suggest that the observed gamma-radiation might be Doppler-boosted and perhaps is closely related to the physical processes acting near the "base" of the highly relativistic jets observed in quasars. PMID:11607602

  7. Very-long-baseline radio interferometry (VLBI) observations of gamma-ray blazars: results from millimeter-VLBI observations.

    PubMed

    Krichbaum, T P; Britzen, S; Standke, K J; Witzel, A; Schalinski, C J; Zensus, J A

    1995-12-01

    VLBI observations of the extremely gamma-bright blazar PKS 0528+134 at 8, 22, 43, and 86 GHz reveal a strongly bent one-sided-core jet structure with at least three moving and two apparently stationary jet components. At the highest observing frequencies the brightest and most compact jet component (the VLBI core) is unresolved with an upper limit to its size of approximately 50 microarcsec corresponding to approximately 0.2 parsec [H0 = 100 km.s-1.Mpc-1 (megaparsec-1), q0 = 0.5, where H0 is Hubble constant and q0 is the deceleration parameter]. Two 86-GHz VLBI observations performed in 1993.3 and 1994.0 reveal a new jet component emerging with superluminal speed from the core. Linear back-extrapolation of its motion yields strong evidence that the ejection of this component is related to an outburst in the millimeter regime and a preceding intense flare of the gamma-flux density observed in early 1993. This and the radio/optical "light curves" and VLBI data for two other sources (S5 0836+710 and 3C 454.3) suggest that the observed gamma-radiation might be Doppler-boosted and perhaps is closely related to the physical processes acting near the "base" of the highly relativistic jets observed in quasars. PMID:11607602

  8. Blazars as Ultra-high-energy Cosmic-ray Sources: Implications for TeV Gamma-Ray Observations

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    The spectra of BL Lac objects and Fanaroff-Riley I radio galaxies are commonly explained by the one-zone leptonic synchrotron self-Compton (SSC) model. Spectral modeling of correlated multiwavelength data gives the comoving magnetic field strength, the bulk outflow Lorentz factor, and the emission region size. Assuming the validity of the SSC model, the Hillas condition shows that only in rare cases such sources accelerate protons to much above 1019 eV, so >~ 1020 eV ultra-high-energy cosmic rays (UHECRs) are likely to be heavy ions if powered by this type of radio-loud active galactic nuclei (AGNs). Survival of nuclei is shown to be possible in TeV BL Lacs and misaligned counterparts with weak photohadronic emissions. Another signature of hadronic production is intergalactic UHECR-induced cascade emission, which is an alternative explanation of the TeV spectra of some extreme non-variable blazars such as 1ES 0229+200 or 1ES 1101-232. We study this kind of cascade signal, taking into account effects of the structured extragalactic magnetic fields in which the sources should be embedded. We demonstrate the importance of cosmic-ray deflections on the γ-ray flux, and show that required absolute cosmic-ray luminosities are larger than the average UHECR luminosity inferred from UHECR observations and can even be comparable to the Eddington luminosity of supermassive black holes. Future TeV γ-ray observations using the Cerenkov Telescope Array and the High Altitude Water Cerenkov detector array can test for UHECR acceleration by observing >25 TeV photons from relatively low redshift sources such as 1ES 0229+200, and gsimTeV photons from more distant radio-loud AGNs.

  9. Gamma-Ray Telescopes: 400 Years of Astronomical Telescopes

    NASA Technical Reports Server (NTRS)

    Gehrels, Neil; Cannizzo, John K.

    2010-01-01

    The last half-century has seen dramatic developments in gamma-ray telescopes, from their initial conception and development through to their blossoming into full maturity as a potent research tool in astronomy. Gamma-ray telescopes are leading research in diverse areas such as gamma-ray bursts, blazars, Galactic transients, and the Galactic distribution of Al-26.

  10. Fermi-LAT detection of hard spectrum and high-level gamma-ray flare from the blazar PKS 1954-388

    NASA Astrophysics Data System (ADS)

    Cutini, Sara; Ciprini, Stefano; Fermi Large Area Telescope Collaboration

    2015-09-01

    The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed flaring gamma rays from a source positionally consistent with the flat spectrum radio quasar PKS 1954-388 (also known as MRC 1954-388, RX J1958.0-3845, and 3FGL J1958.0-3847, Acero et al. 2015, ApJS 218, 23), with radio coordinates, (J2000.0), R.A.: 299.499247 deg, Dec.: -38.751766 deg, (Ma et. al. 1998, AJ, 116, 516).

  11. MAGIC detects very high energy gamma-ray emission from the blazar OT 081 (PKS 1749+096, 4C +09.57)

    NASA Astrophysics Data System (ADS)

    Mirzoyan, Razmik

    2016-07-01

    The MAGIC collaboration reports on the detection of very high energy (VHE; E > 150 GeV) gamma-ray emission from OT 081 (RA=17 51 32.82, dec=+09 39 00.73, J2000.0; also known as PKS 1749+096 and 4C +09.57).

  12. Cascaded Gamma Rays as a Probe of Cosmic Rays

    NASA Astrophysics Data System (ADS)

    Murase, Kohta

    2014-06-01

    Very-high-energy (VHE) and ultra-high-energy (UHE) gamma rays from extragalactic sources experience electromagnetic cascades during their propagation in intergalactic space. Recent gamma-ray data on TeV blazars and the diffuse gamma-ray background may have hints of the cascade emission, which are especially interesting if it comes from UHE cosmic rays. I show that cosmic-ray-induced cascades can be discriminated from gamma-ray-induced cascades with detailed gamma-ray spectra. I also discuss roles of structured magnetic fields, which suppress inverse-Compton pair halos/echoes but lead to guaranteed signals - synchrotron pair halos/echoes.

  13. 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.

  14. Characterizing the environment of the blazars PG1553+113 and 3C66A from GEMINI-GMOS data in the i' and g' bands

    NASA Astrophysics Data System (ADS)

    Torres Zafra, T.; Scellone, S. A.; Andruchow, I.

    2014-10-01

    Blazars are active galactic nuclei (AGNs) which, because of their particular orientation with respect to the observer, are characterized by beamed electromagnetic emission from a relativistic jet. It is thus challenging to detect either continuum or line radiation from the nucleus or from the host galaxy; in many cases this prevents the measurement of a spectroscopic redshift. However, the analysis of their environments may give valuable information, considering that galaxies in the blazar's field could share physical and chemical properties with the host galaxy, besides having a similar redshift. We have thus undertaken a photometric study of the galaxies in the fields of the blazars PG1553+113 and 3C66A, based on g' and i' images taken with the GMOS instrument (multi-object spectrograph and camera) at Gemini North 8m telescope. Our goal is to look for concentrations of galaxies around both blazars in order to have a first knowledge of the general characteristics of their immediate environments.

  15. The Role of Multiple Shocks in the Production of GeV Gamma-ray Flaring in the Blazar 1156+295

    NASA Astrophysics Data System (ADS)

    Aller, Margo F.; Hughes, Philip A.; Aller, Hugh D.; Hovatta, Talvikki; Jorstad, Svetlana G.; Marscher, Alan P.; Ramakrishnan, Venkatessh

    2014-06-01

    As part of work to identify jet conditions during GeV flaring detected by the Fermi-LAT, we have carried out radiative transfer modeling of a pair of centimeter-band, total and polarized flux outbursts in the FSRQ 1156+295 from the UMRAO data archive. The modeling incorporates propagating shocks and uses the observed spectral evolution between 14.5 and 4.8 GHz as constraints. The two outbursts are nearly identical in amplitude, spectrum and duration. However, the centimeter-band outburst peaking in 2010.75 is temporally associated with a series of GeV flares extending over nearly 300 days with peak photon flux exceeding 10^{-6} photons/cm^2/s, while the centimeter-band outburst which commenced in early August 2008 is temporally associated with a well-defined gamma-ray quiescent state. Our analysis reveals that the shocks in the parsec-scale jet during the two events have a similar sense (forward), orientation (transverse) and compression, but in the case of the orphan radio-band flare only 2 shocks were required to reproduce the light curves, while in the event with a paired gamma-ray flare, 4 shocks were required. VLBA imaging of the inner jet at 43 GHz identifies a single jet component during the orphan flare and complex structure in the later event. This suggests that differences in shock structure, and associated shock interactions, play a role in the production of gamma-ray flares. This work was supported in part by Fermi GI grants NNX11AO13G, and NNX13AP18G (U. Michigan) and NNX11AQ03G (Boston U.). T. H. was supported in part by a grant from the Jenny and Antti Wihuri foundation and by the Academy of Finland project number 267324.

  16. Confirming the gamma-ray blazar nature of the low energy counterpart QSO PKS1725+123 of 2FGL J1727.9+1220 with WISE

    NASA Astrophysics Data System (ADS)

    Massaro, F.; Paggi, A.; D'Abrusco, R.

    2012-06-01

    Following the near infrared NIR brightening of the QSO PKS1725+123 (=BZQJ1728+1215) (ATEL #4201), associated to the gamma-ray source 2FGL J1727.9+1220 in Nolan et al. (2012 ApJS, 199, 31), we searched in the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010 AJ, 140, 1868) catalog at the VLBI position of the QSO PKS1725+123 (R.A.(J2000): 17h28m07.0512s, Dec.(J2000): +12d15m39.485s) reported in Beasley et al.

  17. X-ray and gamma-ray polarization signatures of 3D multi-zone time-dependent hadronic model of blazar emission

    NASA Astrophysics Data System (ADS)

    Zhang, Haocheng; Diltz, Chris Scott; Boettcher, Markus

    2016-04-01

    The origin of the high-energy spectral component of blazar emission is still controversial. Polarization signatures can provide additional diagnostics on the leptonic and the hadronic models. We have developed a 3D multi-zone, time-dependent hadronic model based on Fokker-Planck equations. Coupled with a polarization-dependent radiation transfer code 3DPol, we derive the snap-shot spectral energy distributions and frequency-dependent polarization signatures, as well as multi-wavelength light curves and polarization variations. These findings can be confronted with future high-energy polarization observations to distinguish between the leptonic and the hadronic models.

  18. Gamma-Rays from Radio Galaxies

    NASA Astrophysics Data System (ADS)

    Madejski, Greg

    2016-07-01

    In this presentation, I will overview the properties of radio galaxies gleaned from observations of their gamma-ray emission, including that arising from the nuclear, and extended components. The gamma-ray spectra of radio galaxies measured by the Fermi-LAT and ground based Air Cerenkov telescopes will be considered in the context of their broad-band emission. The presentation will cover the most compelling models for emission processes, and will attempt to constrain the location of the nuclear gamma-ray emission. This will be compared to the observational properties of blazars, which are believed to be radio galaxies with jets pointing along our line of sight. Finally, I will discuss our best estimates for the contribution of unresolved radio galaxies to the diffuse gamma-ray emission.

  19. Gamma ray generator

    DOEpatents

    Firestone, Richard B; Reijonen, Jani

    2014-05-27

    An embodiment of a gamma ray generator includes a neutron generator and a moderator. The moderator is coupled to the neutron generator. The moderator includes a neutron capture material. In operation, the neutron generator produces neutrons and the neutron capture material captures at least some of the neutrons to produces gamma rays. An application of the gamma ray generator is as a source of gamma rays for calibration of gamma ray detectors.

  20. Doubling the Sample of Jet Speed Measurements for the TeV Blazars

    NASA Astrophysics Data System (ADS)

    Piner, B. Glenn; Tiet, V. C.; Edwards, P. G.

    2011-05-01

    We report on our observations of the parsec-scale radio jet structures of five blazars that have been detected by ground-based TeV gamma-ray telescopes. These five blazars all belong to the class of High-frequency peaked BL Lac objects (HBLs), which are the most common blazar type detected at the TeV energy range. Because of their relative faintness in the radio, these HBLs are not well represented in other radio blazar surveys. Our observations consist of five epochs of Very Long Baseline Array (VLBA) imaging from 2006 to 2009, of each of the five blazars 1ES 1101-232, Markarian 180, 1ES 1218+304, PG 1553+113, and H 2356-309, at frequencies from 5 to 22 GHz. Fundamental jet properties, including the apparent jet speeds, that can be measured from these multi-epoch series of VLBA images are presented and compared with other gamma-ray blazars. This study approximately doubles the number of TeV blazars with multi-epoch parsec-scale structural measurements. This work was supported by the National Science Foundation under Grant 0707523.

  1. GAMMA-RAY BLAZARS NEAR EQUIPARTITION AND THE ORIGIN OF THE GeV SPECTRAL BREAK IN 3C 454.3

    SciTech Connect

    Cerruti, Matteo; Dermer, Charles D.; Lott, Benoit

    2013-07-01

    Observations performed with the Fermi-LAT telescope have revealed the presence of a spectral break in the GeV spectrum of flat-spectrum radio quasars (FSRQs) and other low- and intermediate-synchrotron peaked blazars. We propose that this feature can be explained by Compton scattering of broad-line region photons by a non-thermal population of electrons described by a log-parabolic function. We consider in particular a scenario in which the energy densities of particles, magnetic field, and soft photons in the emitting region are close to equipartition. We show that this model can satisfactorily account for the overall spectral energy distribution of the FSRQ 3C 454.3, reproducing the GeV spectral cutoff due to Klein-Nishina effects and a curving electron distribution.

  2. Very Rapid High-amplitude Gamma-Ray Variability in Luminous Blazar PKS 1510-089 Studied with Fermi-LAT

    SciTech Connect

    Saito, S.; Stawarz, L.; Tanaka, Y.T.; Takahashi, T.; Madejski, G.; D'Ammando, F.

    2013-03-20

    Here we report on the detailed analysis of the γ-ray light curve of a luminous blazar PKS 1510-089 observed in the GeV range with the Large Area Telescope (LAT) onboard the Fermi satellite during the period 2011 September - December. By investigating the properties of the detected three major flares with the shortest possible time binning allowed by the photon statistics, we find a variety of temporal characteristics and variability patterns. This includes a clearly asymmetric profile (with a faster flux rise and a slower decay) of the flare resolved on sub-daily timescales, a superposition of many short uncorrelated flaring events forming the apparently coherent longer-duration outburst, and a huge single isolated outburst unresolved down to the timescale of three-hours. In the latter case we estimate the corresponding γ-ray flux doubling timescale to be below one hour, which is extreme and never previously reported for any active galaxy

  3. The Brightest Gamma-Ray Flaring Blazar in the Sky: AGILE and Multi-wavelength Observations of 3C 454.3 During 2010 November

    NASA Astrophysics Data System (ADS)

    Vercellone, S.; Striani, E.; Vittorini, V.; Donnarumma, I.; Pacciani, L.; Pucella, G.; Tavani, M.; Raiteri, C. M.; Villata, M.; Romano, P.; Fiocchi, M.; Bazzano, A.; Bianchin, V.; Ferrigno, C.; Maraschi, L.; Pian, E.; Türler, M.; Ubertini, P.; Bulgarelli, A.; Chen, A. W.; Giuliani, A.; Longo, F.; Barbiellini, G.; Cardillo, M.; Cattaneo, P. W.; Del Monte, E.; Evangelista, Y.; Feroci, M.; Ferrari, A.; Fuschino, F.; Gianotti, F.; Giusti, M.; Lazzarotto, F.; Pellizzoni, A.; Piano, G.; Pilia, M.; Rapisarda, M.; Rappoldi, A.; Sabatini, S.; Soffitta, P.; Trifoglio, M.; Trois, A.; Giommi, P.; Lucarelli, F.; Pittori, C.; Santolamazza, P.; Verrecchia, F.; Agudo, I.; Aller, H. D.; Aller, M. F.; Arkharov, A. A.; Bach, U.; Berdyugin, A.; Borman, G. A.; Chigladze, R.; Efimov, Yu. S.; Efimova, N. V.; Gómez, J. L.; Gurwell, M. A.; McHardy, I. M.; Joshi, M.; Kimeridze, G. N.; Krajci, T.; Kurtanidze, O. M.; Kurtanidze, S. O.; Larionov, V. M.; Lindfors, E.; Molina, S. N.; Morozova, D. A.; Nazarov, S. V.; Nikolashvili, M. G.; Nilsson, K.; Pasanen, M.; Reinthal, R.; Ros, J. A.; Sadun, A. C.; Sakamoto, T.; Sallum, S.; Sergeev, S. G.; Schwartz, R. D.; Sigua, L. A.; Sillanpää, A.; Sokolovsky, K. V.; Strelnitski, V.; Takalo, L.; Taylor, B.; Walker, G.

    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 γ-ray flare per year, becoming the most active γ-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 γ-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 Fp γ = (6.8 ± 1.0) × 10-5 photons cm-2 s-1 on a timescale of about 12 hr, more than a factor of six higher than the flux of the brightest steady γ-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 γ-ray flare, we find that the radio, optical, and X-ray emission varies within a factor of 2-3, whereas the γ-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.

  4. The WISE Gamma-Ray Strip Parametrization: The Nature of the Gamma-Ray Active Galactic Nuclei of Uncertain Type

    SciTech Connect

    Massaro, F.; D'Abrusco, R.; Tosti, G.; Ajello, M.; Gasparrini, D.; Grindlay, J.E.; Smith, Howard A.; /Harvard-Smithsonian Ctr. Astrophys.

    2012-04-02

    Despite the large number of discoveries made recently by Fermi, the origins of the so called unidentified {gamma}-ray sources remain unknown. The large number of these sources suggests that among them there could be a population that significantly contributes to the isotropic gamma-ray background and is therefore crucial to understand their nature. The first step toward a complete comprehension of the unidentified {gamma}-ray source population is to identify those that can be associated with blazars, the most numerous class of extragalactic sources in the {gamma}-ray sky. Recently, we discovered that blazars can be recognized and separated from other extragalactic sources using the infrared (IR) WISE satellite colors. The blazar population delineates a remarkable and distinctive region of the IR color-color space, the WISE blazar strip. In particular, the subregion delineated by the {gamma}-ray emitting blazars is even narrower and we named it as the WISE Gamma-ray Strip (WGS). In this paper we parametrize the WGS on the basis of a single parameter s that we then use to determine if {gamma}-ray Active Galactic Nuclei of the uncertain type (AGUs) detected by Fermi are consistent with the WGS and so can be considered blazar candidates. We find that 54 AGUs out of a set 60 analyzed have IR colors consistent with the WGS; only 6 AGUs are outliers. This result implies that a very high percentage (i.e., in this sample about 90%) of the AGUs detected by Fermi are indeed blazar candidates.

  5. Discovery of very high energy gamma-ray emission from the blazar 1ES 1727+502 with the MAGIC Telescopes

    NASA Astrophysics Data System (ADS)

    Aleksić, J.; Antonelli, L. A.; Antoranz, P.; Asensio, M.; Backes, M.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bock, R. K.; Boller, A.; Bonnefoy, S.; Bonnoli, G.; Borla Tridon, D.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; Carreto Fidalgo, D.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Cossio, L.; 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.; Eisenacher, D.; Elsaesser, D.; Farina, E.; Ferenc, D.; Fonseca, M. V.; Font, L.; Fruck, C.; García López, R. J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Giavitto, G.; Godinović, N.; González Muñoz, A.; Gozzini, S. R.; Hadamek, A.; Hadasch, D.; Häfner, D.; Herrero, A.; Hose, J.; Hrupec, D.; Idec, W.; Jankowski, F.; Kadenius, V.; Klepser, S.; Knoetig, M. L.; Krähenbühl, T.; Krause, J.; 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.; Masbou, J.; Mazin, D.; Meucci, M.; Miranda, J. M.; Mirzoyan, R.; Moldón, J.; Moralejo, A.; Munar-Adrover, P.; Nakajima, D.; Niedzwiecki, A.; Nilsson, K.; Nowak, N.; Orito, R.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Partini, S.; Persic, M.; Prada, F.; Prada Moroni, P. G.; Prandini, E.; Puljak, I.; Reichardt, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rügamer, S.; Saggion, A.; Saito, K.; Saito, T. Y.; Salvati, M.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shore, S. N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Spanier, F.; Spiro, S.; Stamatescu, V.; Stamerra, A.; Steinke, B.; Storz, J.; Sun, S.; Surić, T.; Takalo, L.; Takami, H.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Tibolla, O.; Torres, D. F.; Toyama, T.; Treves, A.; Uellenbeck, M.; Vogler, P.; Wagner, R. M.; Weitzel, Q.; Zandanel, F.; Zanin, R.; MAGIC Collaboration

    2014-03-01

    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. 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 used simultaneous optical R-band data from the KVA telescope, archival UV/optical and X-ray observations from instruments UVOT and XRT on board of the 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). No significant short-term variability was 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.

  6. Blazar Continuum Variability II: Entering the GLAST Era

    NASA Technical Reports Server (NTRS)

    Thompson, D. J.

    2005-01-01

    Intense, highly-variable gamma-ray emission from blazars was a principal discovery made with EGRET on the Compton Gamma Ray Observatory. The EGRET data remain a valuable resource for modeling of blazar astrophysics and for planning of future gamma-ray missions such as AGILE and GLAST. This presentation will review a bit of history and summarize the EGRET blazar legacy, with emphasis on work done since the end of the Compton Observatory mission.

  7. Studying the High Energy Gamma Ray Sky with Gamma Ray Large Area Space Telescope (GLAST)

    NASA Technical Reports Server (NTRS)

    Kamae, T.; Ohsugi, T.; Thompson, D. J.; Watanabe, K.

    1998-01-01

    Building on the success of the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory, the Gamma Ray Large Area Space Telescope (GLAST) will make a major step in the study of such subjects as blazars, gamma Ray bursts, the search for dark matter, supernova remnants, pulsars, diffuse radiation, and unidentified high energy sources. The instrument will be built on new and mature detector technologies such as silicon strip detectors, low-power low-noise LSI, and a multilevel data acquisition system. GLAST is in the research and development phase, and one full tower (of 25 total) is now being built in collaborating institutes. The prototype tower will be tested thoroughly at Stanford Linear Accelerator Center (SLAC) in the fall of 1999.

  8. Gamma ray transients

    NASA Technical Reports Server (NTRS)

    Cline, Thomas L.

    1987-01-01

    The discovery of cosmic gamma ray bursts was made with systems designed at Los Alamos Laboratory for the detection of nuclear explosions beyond the atmosphere. HELIOS-2 was the first gamma ray burst instrument launched; its initial results in 1976, seemed to deepen the mystery around gamma ray transients. Interplanetary spacecraft data were reviewed in terms of explaining the behavior and source of the transients.

  9. Exploring the Extreme Universe with the Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    Thompson, D. J.

    2010-01-01

    Because high-energy gamma rays are produced by powerful sources, the Fermi Gamma-ray Space Telescope provides a window on extreme conditions in the Universe. Some key observations of the constantly changing gamma-ray sky include: (1) Gamma-rays from pulsars appear to come from a region well above the surface of the neutron star; (2) Multiwavelength studies of blazars show that simple models of jet emission are not always adequate to explain what is seen; (3) Gamma-ray bursts can constrain models of quantum gravity; (4) Cosmic-ray electrons at energies approaching 1 TeV suggest a local source for some of these particles.

  10. Gamma-ray astrophysics

    NASA Technical Reports Server (NTRS)

    Stecker, F. W. (Editor); Trombka, J. I. (Editor)

    1973-01-01

    Conference papers on gamma ray astrophysics are summarized. Data cover the energy region from about 0.3 MeV to a few hundred GeV and theoretical models of production mechanisms that give rise to both galactic and extragalactic gamma rays.

  11. Gamma-Ray Pulsars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2011-01-01

    The Fermi Gamma-Ray Space Telescope has revolutionized the study of pulsar physics with the detection of over 80 gamma-ray pulsars. Several new populations have been discovered, including 24 radio quiet pulsars found through gamma-ray pulsations alone and about 20 millisecond gamma-ray pulsars. The gamma-ray pulsations from millisecond pulsars were discovered by both folding at periods of known radio millisecond pulsars or by detecting them as gamma-ray sources that are followed up by radio pulsar searches. The second method has resulted in a phenomenally successful synergy, with -35 new radio MSPs (to date) having been discovered at Fermi unidentified source locations and the gamma-ray pulsations having then been detected in a number of these using the radio timing solutions. The higher sensitivity and larger energy range of the Fermi Large Area Telescope has produced detailed energy-dependent light curves and phase-resolved spectroscopy on brighter pulsars, that have ruled out polar cap models as the major source of the emission in favor of outer magnetosphere accelerators. The large number of gamma-ray pulsars now allows for the first time meaningful population and sub-population studies that are revealing surprising properties of these fascinating sources.

  12. Gamma ray detector shield

    DOEpatents

    Ohlinger, R.D.; Humphrey, H.W.

    1985-08-26

    A gamma ray detector shield comprised of a rigid, lead, cylindrical-shaped vessel having upper and lower portions with an pneumatically driven, sliding top assembly. Disposed inside the lead shield is a gamma ray scintillation crystal detector. Access to the gamma detector is through the sliding top assembly.

  13. Fermi Gamma-Ray Space Telescope: Science Highlights for the First 8 Months

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2010-01-01

    The Fermi Gamma-ray Space Telescope was launched on June 11, 2008 and since August 2008 has successfully been conducting routine science observations of high energy phenomena in the gamma-ray sky. A number of exciting discoveries have been made during its first year of operation, including blazar flares, high-energy gamma-ray bursts, and numerous new,gamma-ray sources of different types, among them pulsars and Active Galactic Nuclei (AGN). fermi-LAT also performed accurate mea.<;urement of the diffuse gamma-radiation which clarifies the Ge V excess reported by EGRET almost 10 years ago, high precision measurement of the high energy electron spectrum, and other observations. An overview of the observatory status and recent results as of April 30, 2009, are presented. Key words: gamma-ray astronomy, cosmic rays, gamma-ray burst, pulsar, blazar. diffuse gamma-radiation

  14. Gamma ray astronomy

    NASA Technical Reports Server (NTRS)

    Paciesas, William S.

    1991-01-01

    Miscellaneous tasks related to the development of the Bursts and Transient Source Experiment on the Gamma Ray Observatory and to analysis of archival data from balloon flight experiments were performed. The results are summarized and relevant references are included.

  15. Gamma-ray astronomy

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Lingenfelter, R. E.

    1982-01-01

    Cosmic gamma rays, the physical processes responsible for their production and the astrophysical sites from which they were seen are reported. The bulk of the observed gamma ray emission is in the photon energy range from about 0.1 MeV to 1 GeV, where observations are carried out above the atmosphere. There are also, however, gamma ray observations at higher energies obtained by detecting the Cerenkov light produced by the high energy photons in the atmosphere. Gamma ray emission was observed from sources as close as the Sun and the Moon and as distant as the quasar 3C273, as well as from various other galactic and extragalactic sites. The radiation processes also range from the well understood, e.g. energetic particle interactions with matter, to the still incompletely researched, such as radiation transfer in optically thick electron positron plasmas in intense neutron star magnetic fields.

  16. Gamma ray line astronomy

    NASA Technical Reports Server (NTRS)

    Ramaty, R.

    1984-01-01

    The interpretations and implications of the astrophysical observations of gamma-ray lines are reviewed. At the Galactic Center e(+)-e(-) pairs from a compact object produce an annihilation line that shows no redshift, indicating an annihilation site far removed from this object. In the jets of SS433, gamma-ray lines are produced by inelastic excitations, probably in dust grains, although line emission from fusion reactions has also been considered. Observations of diffuse galactic line emission reveal recently synthesized radioactive aluminum in the interstellar medium. In gamma-ray bursts, redshifted pair annihilation lines are consistent with a neutron star origin for the bursts. In solar flares, gamma-ray line emission reveals the prompt acceleration of protons and nuclei, in close association with the flare energy release mechanism.

  17. Gamma Ray Pulsars: Observations

    NASA Technical Reports Server (NTRS)

    Thompson, David J.; White, Nicholas E. (Technical Monitor)

    2000-01-01

    High-energy gamma rays are a valuable tool for studying particle acceleration and radiation in the magnetospheres of energetic pulsars. The six or more pulsars seen by CGRO/EGRET show that: the light curves usually have double-peak structures (suggesting a broad cone of emission); gamma rays are frequently the dominant component of the radiated power; and all the spectra show evidence of a high-energy turnover. Unless a new pulsed component appears at higher energies, progress in gamma-ray pulsar studies will be greatest in the 1-20 GeV range. Ground-based telescopes whose energy ranges extend downward toward 10 GeV should make important measurements of the spectral cutoffs. The Gamma-ray Large Area Space Telescope (GLAST), now in planning for a launch in 2005, will provide a major advance in sensitivity, energy range, and sky coverage.

  18. Gamma ray camera

    SciTech Connect

    Robbins, C.D.; Wang, S.

    1980-09-09

    An anger gamma ray camera is improved by the substitution of a gamma ray sensitive, proximity type image intensifier tube for the scintillator screen in the anger camera, the image intensifier tube having a negatively charged flat scintillator screen and a flat photocathode layer and a grounded, flat output phosphor display screen all of the same dimension (Unity image magnification) and all within a grounded metallic tube envelope and having a metallic, inwardly concaved input window between the scintillator screen and the collimator.

  19. Gamma ray optics

    SciTech Connect

    Jentschel, M.; Guenther, M. M.; Habs, D.; Thirolf, P. G.

    2012-07-09

    Via refractive or diffractive scattering one can shape {gamma} ray beams in terms of beam divergence, spot size and monochromaticity. These concepts might be particular important in combination with future highly brilliant gamma ray sources and might push the sensibility of planned experiments by several orders of magnitude. We will demonstrate the experimental feasibility of gamma ray monochromatization on a ppm level and the creation of a gamma ray beam with nanoradian divergence. The results are obtained using the inpile target position of the High Flux Reactor of the ILL Grenoble and the crystal spectrometer GAMS. Since the refractive index is believed to vanish to zero with 1/E{sup 2}, the concept of refractive optics has never been considered for gamma rays. The combination of refractive optics with monochromator crystals is proposed to be a promising design. Using the crystal spectrometer GAMS, we have measured for the first time the refractive index at energies in the energy range of 180 - 2000 keV. The results indicate a deviation from simple 1/E{sup 2} extrapolation of X-ray results towards higher energies. A first interpretation of these new results will be presented. We will discuss the consequences of these results on the construction of refractive optics such as lenses or refracting prisms for gamma rays and their combination with single crystal monochromators.

  20. Prospects for gamma ray astronomy

    NASA Technical Reports Server (NTRS)

    1981-01-01

    The Solar Maximum Mission and the Gamma Ray Experiment aboard the SMM spacecraft are discussed. Mission plans for interplanetary probes are also discussed. The Gamma Ray observatory and its role in future gamma ray astronomy is highlighted. It is concluded that gamma ray astronomy will be of major importance in the development of astronomical models and in the development of comsological theory.

  1. The gamma-ray observatory

    NASA Technical Reports Server (NTRS)

    1991-01-01

    An overview is given of the Gamma Ray Observatory (GRO) mission. Detection of gamma rays and gamma ray sources, operations using the Space Shuttle, and instruments aboard the GRO, including the Burst and Transient Source Experiment (BATSE), the Oriented Scintillation Spectrometer Experiment (OSSE), the Imaging Compton Telescope (COMPTEL), and the Energetic Gamma Ray Experiment Telescope (EGRET) are among the topics surveyed.

  2. VizieR Online Data Catalog: Dynamic SEDs of southern blazars - DSSB (Krauss+, 2016)

    NASA Astrophysics Data System (ADS)

    Krauss, F.; Wilms, J.; Kadler, M.; Ojha, R.; Schulz, R.; Trustedt, J.; Edwards, P. G.; Stevens, J.; Ros, E.; Baumgartner, W.; Beuchert, T.; Blanchard, J.; Buson, S.; Carpenter, B.; Dauser, T.; Falkner, S.; Gehrels, N.; Grafe, C.; Gulyaev, S.; Hase, H.; Horiuchi, S.; Kreikenbohm, A.; Kreykenbohm, I.; Langejahn, M.; Leiter, K.; Lovell, J. E. J.; Muller, C.; Natusch, T.; Nesci, R.; Pursimo, T.; Phillips, C.; Plotz, C.; Quick, J.; Tzioumis, A. K.; Weston, S.

    2016-05-01

    The Dynamic SEDs of southern blazars catalog is based on a TANAMI multiwavelength project that has been monitoring a sample of 22 radio-loud blazars of the southern sky from radio to gamma-ray wavelengths. (4 data files).

  3. Gamma ray camera

    DOEpatents

    Perez-Mendez, Victor

    1997-01-01

    A gamma ray camera for detecting rays emanating from a radiation source such as an isotope. The gamma ray camera includes a sensor array formed of a visible light crystal for converting incident gamma rays to a plurality of corresponding visible light photons, and a photosensor array responsive to the visible light photons in order to form an electronic image of the radiation therefrom. The photosensor array is adapted to record an integrated amount of charge proportional to the incident gamma rays closest to it, and includes a transparent metallic layer, photodiode consisting of a p-i-n structure formed on one side of the transparent metallic layer, and comprising an upper p-type layer, an intermediate layer and a lower n-type layer. In the preferred mode, the scintillator crystal is composed essentially of a cesium iodide (CsI) crystal preferably doped with a predetermined amount impurity, and the p-type upper intermediate layers and said n-type layer are essentially composed of hydrogenated amorphous silicon (a-Si:H). The gamma ray camera further includes a collimator interposed between the radiation source and the sensor array, and a readout circuit formed on one side of the photosensor array.

  4. Gamma ray camera

    DOEpatents

    Perez-Mendez, V.

    1997-01-21

    A gamma ray camera is disclosed for detecting rays emanating from a radiation source such as an isotope. The gamma ray camera includes a sensor array formed of a visible light crystal for converting incident gamma rays to a plurality of corresponding visible light photons, and a photosensor array responsive to the visible light photons in order to form an electronic image of the radiation therefrom. The photosensor array is adapted to record an integrated amount of charge proportional to the incident gamma rays closest to it, and includes a transparent metallic layer, photodiode consisting of a p-i-n structure formed on one side of the transparent metallic layer, and comprising an upper p-type layer, an intermediate layer and a lower n-type layer. In the preferred mode, the scintillator crystal is composed essentially of a cesium iodide (CsI) crystal preferably doped with a predetermined amount impurity, and the p-type upper intermediate layers and said n-type layer are essentially composed of hydrogenated amorphous silicon (a-Si:H). The gamma ray camera further includes a collimator interposed between the radiation source and the sensor array, and a readout circuit formed on one side of the photosensor array. 6 figs.

  5. Pushing the Limits: High Redshift Fermi-LAT Blazars

    NASA Astrophysics Data System (ADS)

    Ojha, Roopesh; Gasparrini, Dario; Lott, Benoit; Cutini, Sara; Fermi-LAT Collaboration

    2016-01-01

    High-redshift blazars detected by the Fermi Large Area Telescope (LAT) are of great astrophysical import as they are extreme objects whose energetics remain a mystery. Such blazars are intrinsically interesting since they inform us about the evolution of gamma-ray blazars and are, by definition, some of the more luminous blazars in the LAT sample. They are also an excellent tool to study the EBL and thus the gamma-ray horizon. We present the latest high redshift blazar detections in the LAT and discuss some of their implications.

  6. Gamma-ray bursts.

    PubMed

    Gehrels, Neil; Mészáros, Péter

    2012-08-24

    Gamma-ray bursts (GRBs) are bright flashes of gamma rays coming from the cosmos. They occur roughly once per day, typically last for tens of seconds, and are the most luminous events in the universe. More than three decades after their discovery, and after pioneering advances from space and ground experiments, they still remain mysterious. The launch of the Swift and Fermi satellites in 2004 and 2008 brought in a trove of qualitatively new data. In this Review, we survey the interplay between these recent observations and the theoretical models of the prompt GRB emission and the subsequent afterglow. PMID:22923573

  7. Gamma Ray Bursts

    NASA Technical Reports Server (NTRS)

    Gehrels, Neil; Meszaros, Peter

    2012-01-01

    Gamma-ray bursts (GRBs) are bright flashes of gamma-rays coming from the cosmos. They occur roughly once per day ,last typically lOs of seconds and are the most luminous events in the universe. More than three decades after their discovery, and after pioneering advances from space and ground experiments, they still remain mysterious. The launch of the Swift and Fermi satellites in 2004 and 2008 brought in a trove of qualitatively new data. In this review we survey the interplay between these recent observations and the theoretical models of the prompt GRB emission and the subsequent afterglows.

  8. Gamma-Ray Bursts

    NASA Astrophysics Data System (ADS)

    Gehrels, Neil; Mészáros, Péter

    2012-08-01

    Gamma-ray bursts (GRBs) are bright flashes of gamma rays coming from the cosmos. They occur roughly once per day, typically last for tens of seconds, and are the most luminous events in the universe. More than three decades after their discovery, and after pioneering advances from space and ground experiments, they still remain mysterious. The launch of the Swift and Fermi satellites in 2004 and 2008 brought in a trove of qualitatively new data. In this Review, we survey the interplay between these recent observations and the theoretical models of the prompt GRB emission and the subsequent afterglow.

  9. Contemporaneous Multiwaveband Observations of Blazars

    NASA Technical Reports Server (NTRS)

    Marscher, Alan P.; Bloom, Steven D.; Zhang, Yun Fei; Gear, Walter K.

    1994-01-01

    We have observed a number of blazars at wavebands ranging from radio to gamma-ray. We find bright gamma-ray emission to be associated with strong synchrotron flares observed at lower frequencies. The x-ray flux and entire radio spectrum of 4C 39.25 have each increased in strength by 30% over a 2-year period, in agreement with the prediction of the bent relativistic jet model.

  10. Gamma Ray Astronomy

    NASA Technical Reports Server (NTRS)

    Wu, S. T.

    2000-01-01

    The project has progressed successfully during this period of performance. The highlights of the Gamma Ray Astronomy teams efforts are: (1) Support daily BATSE data operations, including receipt, archival and dissemination of data, quick-look science analysis, rapid gamma-ray burst and transient monitoring and response efforts, instrument state-of-health monitoring, and instrument commanding and configuration; (2) On-going scientific analysis, including production and maintenance of gamma-ray burst, pulsed source and occultation source catalogs, gamma-ray burst spectroscopy, studies of the properties of pulsars and black holes, and long-term monitoring of hard x-ray sources; (3) Maintenance and continuous improvement of BATSE instrument response and calibration data bases; (4) Investigation of the use of solid state detectors for eventual application and instrument to perform all sky monitoring of X-Ray and Gamma sources with high sensitivity; and (5) Support of BATSE outreach activities, including seminars, colloquia and World Wide Web pages. The highlights of this efforts can be summarized in the publications and presentation list.

  11. Gamma ray astronomy

    NASA Technical Reports Server (NTRS)

    Paciesas, William S.

    1991-01-01

    Miscellaneous tasks related to the development of the Burst and Transient Source Experiment on the Gamma Ray Observatory and to collection, analysis, and interpretation of data from the MSFC Very Low Frequency transient monitoring program were performed. The results are summarized and relevant references are included.

  12. Gamma ray astronomy

    NASA Technical Reports Server (NTRS)

    Paciesas, William S.

    1992-01-01

    Miscellaneous tasks related to mission operations and data analysis for the Burst and Transient Source Experiment on the Gamma Ray Observatory, to collection, analysis, and interpretation of data from the Marshall Space Flight Center Very Low Frequency transient monitoring program, and to compilation and analysis of induced radioactivity data were performed. The results are summarized and relevant references are included.

  13. Celestial gamma ray study

    NASA Technical Reports Server (NTRS)

    Michelson, Peter F.

    1995-01-01

    This report documents the research activities performed by Stanford University investigators as part of the data reduction effort and overall support of the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Observatory. This report is arranged chronologically, with each subsection detailing activities during roughly a one year period of time, beginning in June 1991.

  14. Probes of the Inner Jets of Blazars

    NASA Technical Reports Server (NTRS)

    Marscher, Alan P.

    1996-01-01

    I review models for the 'inner jet" in blazars, the section that connects the central engine with the radio jet. I discuss how the structure and physics of the inner jet can he explored using millimeter-wave VLBI as well as multiwaveband observations of blazars. Flares at radio to gamma-ray frequencies should exhibit time delays at different wavebands that can test models for both the high-energy emission mechanisms and the nature of the inner jet in blazars.

  15. Gamma ray astronomy in perspective

    NASA Technical Reports Server (NTRS)

    1981-01-01

    A brief overview of the development of gamma ray astronomy is presented. Gamma ray telescopes and other optical measuring instruments are highlighted. Emphasis is placed on findings that were unobtainable before gamma ray astronomy. Information on evolution of the solar system, the relationship of the solar system to the galaxy, and the composition of interstellar matter is discussed.

  16. Gamma ray astronomy

    NASA Technical Reports Server (NTRS)

    Paciesas, William S.

    1994-01-01

    The Burst and Transient Source Experiment (BATSE) is one of four instruments on the Compton observatory which was launched by the space shuttle Atlantis on April 5, 1991. As of mid-March, 1994, BATSE detected more than 925 cosmic gamma-ray bursts and more than 725 solar flares. Pulsed gamma rays have been detected from at least 16 sources and emission from at least 28 sources (including most of the pulsed sources) has been detected by the earth occultation technique. UAH participation in BATSE is extensive but can be divided into two main areas, operations and data analysis. The daily BATSE operations tasks represent a substantial level of effort and involve a large team composed of MSFC personnel as well as contractors such as UAH. The scientific data reduction and analysis of BATSE data is also a substantial level of effort in which UAH personnel have made significant contributions.

  17. Topics in gamma ray astronomy

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Lingenfelter, R. E.

    1986-01-01

    Observations of gamma rays from solar flares, gamma ray bursts, the Galactic center, galactic nucleosynthesis, SS433, and Cygnus X-3, and their effects on astrophysical problems are discussed. It is observed that gamma ray spectra from solar flares are applicable to the study of particle acceleration and confinement and the determination of chemical abundances in the solar atmosphere. The gamma ray lines from the compact galactic object SS433 are utilized to examine the acceleration of jets, and analysis of the gamma ray lines of Cygnus X-3 reveal that particles can be accelerated in compact sources to ultrahigh energies.

  18. Topics in gamma ray astronomy

    NASA Astrophysics Data System (ADS)

    Ramaty, R.; Lingenfelter, R. E.

    Observations of gamma rays from solar flares, gamma ray bursts, the Galactic center, galactic nucleosynthesis, SS433, and Cygnus X-3, and their effects on astrophysical problems are discussed. It is observed that gamma ray spectra from solar flares are applicable to the study of particle acceleration and confinement and the determination of chemical abundances in the solar atmosphere. The gamma ray lines from the compact galactic object SS433 are utilized to examine the acceleration of jets, and analysis of the gamma ray lines of Cygnus X-3 reveal that particles can be accelerated in compact sources to ultrahigh energies.

  19. Gamma ray collimator

    NASA Technical Reports Server (NTRS)

    Casanova, Edgar J. (Inventor)

    1991-01-01

    A gamma ray collimator including a housing having first and second sections is disclosed. The first section encloses a first section of depleted uranium which is disposed for receiving and supporting a radiation emitting component such as cobalt 60. The second section encloses a depleted uranium member which is provided with a conical cut out focusing portion disposed in communication with the radiation emitting element for focusing the emitted radiation to the target.

  20. Gamma ray collimator

    NASA Technical Reports Server (NTRS)

    Casanova, Edgar J. (Inventor)

    1993-01-01

    A gamma ray collimator including a housing having first and second sections. The first section encloses a first section of depleted uranium which is disposed for receiving and supporting a radiation emitting component such as cobalt 60. The second section encloses a depleted uranium member which is provided with a conical cut-out focusing portion disposed in communication with the radiation emitting element for focusing the emitted radiation to the target.

  1. 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.

  2. Rapid Tev Gamma-ray Variability Of Bl Lac

    NASA Astrophysics Data System (ADS)

    Feng, Qi

    2011-09-01

    Recent VERITAS observations of BL Lacertae revealed rapid gamma-ray flaring of the object at TeV energies (Ong, 2011, ATel #3459). Here, we present preliminary results from the observations. The flaring activity was observed during a 20-minute exposure, when the flux above 200 GeV reached a peak of about 3x10^-6 m^-2s^-1 (roughly one and a half times the Crab Nebula flux). The light curve shows that the observations missed the rising phase of the flare but covered the decaying phase almost in its entirety. The decay time of the flare is about 4 minutes, making it one of the most rapid gamma-ray flares seen for any TeV blazars. Compared to several other blazars that are known to produce gamma-ray flares on a timescale of minutes, BL Lacertae produces the bulk of its radiation at much lower frequencies. The measured gamma-ray spectrum appears to be as soft as that of the non-flaring state, when compared with the published MAGIC spectrum of the source. We will discuss the implications of the results. VERITAS research is supported by grants from the U.S. Department of Energy, the U.S. National Science Foundation, the Smithsonian Institution, by NSERC in Canada, by STFC in the U.K. and by Science Foundation Ireland.

  3. AGN Winds and Blazar Phenomenology

    NASA Technical Reports Server (NTRS)

    Kazanas, Demos

    2012-01-01

    The launch of {\\em Fermi} produced a significant number of AGN detections to allow statistical treatment of their properties. One of the first such systematics was the "Blazar Divide" in FSRQs and BL Lacs according to their gamma-ray spectral index and luminosity. Further data accumulation indicated this separation to be less clear than thought before. An MHD wind model which can model successfully the Seyfert X-ray absorber properties provides the vestiges of an account of the observed blazar classification. We propose to employ this model to model in detail the broad band blazar spectra and their statistical properties in terms of the physical parameters of these MHD winds.

  4. The WISE Gamma-Ray Strip Parameterization: The Nature of the Gamma-Ray Active Galactic Nuclei of Uncertain Type

    NASA Astrophysics Data System (ADS)

    Massaro, F.; D'Abrusco, R.; Tosti, G.; Ajello, M.; Gasparrini, D.; Grindlay, J. E.; Smith, Howard A.

    2012-05-01

    Despite the large number of discoveries made recently by Fermi, the origins of the so-called unidentified γ-ray sources remain unknown. The large number of these sources suggests that there could be a population among them that significantly contributes to the isotropic gamma-ray background and it is therefore crucial to understand their nature. The first step toward a complete comprehension of the unidentified γ-ray source population is to identify those that can be associated with blazars, the most numerous class of extragalactic sources in the γ-ray sky. Recently, we discovered that blazars can be recognized and separated from other extragalactic sources using the infrared (IR) WISE satellite colors. The blazar population delineates a remarkable and distinctive region of the IR color-color space, the WISE blazar strip. In particular, the subregion delineated by the γ-ray emitting blazars is even narrower and we named it the WISE Gamma-ray Strip (WGS). In this paper, we parameterize the WGS on the basis of a single parameter s that we then use to determine if γ-ray active galactic nuclei of the uncertain type (AGUs) detected by Fermi are consistent with the WGS and can be considered blazar candidates. We find that 54 AGUs out of a set of 60 analyzed have IR colors consistent with the WGS; only 6 AGUs are outliers. This result implies that a very high percentage (i.e., in this sample about 90%) of the AGUs detected by Fermi are indeed blazar candidates.

  5. Lower Bound on the Cosmic TeV Gamma-Ray Background Radiation

    NASA Astrophysics Data System (ADS)

    Inoue, Yoshiyuki; Tanaka, Yasuyuki T.

    2016-02-01

    The Fermi gamma-ray space telescope has revolutionized our understanding of the cosmic gamma-ray background radiation in the GeV band. However, investigation on the cosmic TeV gamma-ray background radiation still remains sparse. Here, we report the lower bound on the cosmic TeV gamma-ray background spectrum placed by the cumulative flux of individual detected extragalactic TeV sources including blazars, radio galaxies, and starburst galaxies. The current limit on the cosmic TeV gamma-ray background above 0.1 TeV is obtained as 2.8 × 10-8(E/100 GeV)-0.55 exp(-E/2100GeV)[GeV cm-2 s-1 sr-1] < E2dN/dE < 1.1 × 10-7(E/100 GeV)-0.49 [GeV cm-2 s-1 sr-1], where the upper bound is set by requirement that the cascade flux from the cosmic TeV gamma-ray background radiation can not exceed the measured cosmic GeV gamma-ray background spectrum. Two nearby blazars, Mrk 421 and Mrk 501, explain ˜70% of the cumulative background flux at 0.8-4 TeV, while extreme blazars start to dominate at higher energies. We also provide the cumulative background flux from each population, i.e., blazars, radio galaxies, and starburst galaxies which will be the minimum requirement for their contribution to the cosmic TeV gamma-ray background radiation.

  6. A NEW RESULT ON THE ORIGIN OF THE EXTRAGALACTIC GAMMA-RAY BACKGROUND

    SciTech Connect

    Zhou Ming; Wang Jiancheng

    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.

  7. SYNTH - Gamma Ray Spectrum Synthesizer

    Energy Science and Technology Software Center (ESTSC)

    2009-05-18

    SYNTH was designed to synthesize the results of typical gamma-ray spectroscopy experiments. The code allows a user to specify the physical characteristics of a gamma-ray source, the quantity of radionuclides emitting gamma radiation, the source-to-detector distance and the presence and type of any intervening absorbers, the size and type of the gamma-ray detector, and the electronic set-up used to gather the data.

  8. Polarization structure of six gamma-ray quasars at 5 and 15 GHz

    NASA Astrophysics Data System (ADS)

    Vetukhnovskaya, Yu. N.; Gabuzda, D. C.; Yakimov, V. E.

    2011-05-01

    The results of 5 and 15 GHz polarization observations of the six blazars 1222+216, 1406-076, 1606+106, 1611+343, 17415-038, and 2022-077 obtained on the American Very Long Baseline Array are presented. The degrees of polarization in the cores and jets of these six gamma-ray quasars do not differ from those for other blazars.

  9. Confirming the gamma-ray blazar nature of the low energy counterpart QSO GB6 J1604+5714 of 2FGL J1604.6+5710 with WISE

    NASA Astrophysics Data System (ADS)

    Massaro, F.; D'Abrusco, R.; Paggi, A.

    2012-06-01

    Following the rapid optical variability detected in the QSO GB6 J1604+5714 (=BZQJ1604+5714) (ATEL #4184), associated to the gamma-ray source 2FGL J1604.6+5710 (=1FGL J1604.3+5710) in Nolan et al. (2012 ApJS, 199, 31), we searched in the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010 AJ, 140, 1868) catalog at the VLBI position of the QSO GB6 J1604+5714 (R.A.(J2000): 16h04m37.3546s, Dec.(J2000): +57d14m36.660s) reported in Beasley et al......

  10. Blazar Demographics Using Multiwavelength Data

    NASA Astrophysics Data System (ADS)

    Mao, Peiyuan; Massaro, F.; Urry, C. Megan

    2016-01-01

    Blazars are ideal laboratories to study relativistic jets in AGN, which are thought to be an important channel for feeding energy into galaxies and clusters. We present multi-wavelength SEDs of 2214 blazars with known redshifts, based on the Roma-BZCAT data across 12 frequency bands ranging from radio to gamma-ray. We confirm the anti-correlation between radio luminosity and synchrotron peak frequency, (part of what defines the "blazar sequence"), although with greater scatter than seen previously in studies of far fewer blazars. We describe an empirical estimator of luminosities in those 12 frequency bands using only the radio luminosity at 1.4 GHz and the redshift as inputs. Using this estimator, we study the demographics of blazars by comparing Monte-Carlo simulations to blazar surveys at several different frequencies and flux limits. We recover the observed evolutionary parameter for both low-frequency peaked (V/Vmax≈0.6) and high-frequency peaked (V/Vmax≈0.4) blazars, proving that selection effects cause the high-frequency-peaked sources to appear to anti-evolve even though the same underlying evolution was assumed in the simulation. We also show that the if instead we randomly assign fluxes independent of radio luminosity, the simulated blazar samples disagree strongly with the observed ones. These simulations confirm that luminosity and SED shape must indeed be linked in a physical blazar sequence.

  11. Gamma Ray Bursts - Observations

    NASA Technical Reports Server (NTRS)

    Gehrels, N.; Cannizzo, J. K.

    2010-01-01

    We are in an exciting period of discovery for gamma-ray bursts. The Swift observatory is detecting 100 bursts per year, providing arcsecond localizations and sensitive observations of the prompt and afterglow emission. The Fermi observatory is observing 250 bursts per year with its medium-energy GRB instrument and about 10 bursts per year with its high-energy LAT instrument. In addition, rapid-response telescopes on the ground are providing new capabilities to study optical emission during the prompt phase and spectral signatures of the host galaxies. The combined data set is enabling great advances in our understanding of GRBs including afterglow physics, short burst origin, and high energy emission.

  12. The Compton Gamma Ray Observatory

    NASA Astrophysics Data System (ADS)

    Gehrels, N.; Chipman, E.; Kniffen, D.

    1994-06-01

    The Arthur Holly Compton Gamma Ray Observatory Compton) is the second in NASA's series of great Observatories. Launched on 1991 April 5, Compton represents a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made. We describe the capabilities of the four scientific instruments, and the observing program of the first 2 years of the mission. Examples of early discoveries by Compton are enumerated, including the discovery that gamma-ray bursts are isotropic but spatially inhomogeneous in their distribution; the discovery of a new class of high-energy extragalacatic gamma-ray sources, the gamma-ray AGNs; the discovery of emission from SN 1987A in the nuclear line of Co-57; and the mapping of emission from Al-26 in the interstellar medium (ISM) near the Galactic center. Future observations will include deep surveys of selected regions of the sky, long-tem studies of individual objects, correlative studies of objects at gamma-ray and other energies, a Galactic plane survey at intermediate gamma-ray energies, and improved statistics on gamma-ray bursts to search for small anisotropies. After completion of the all-sky survey, a Guest Investigator program is in progress with guest observers' time share increasing from 30% upward for the late mission phases.

  13. The Compton Gamma Ray Observatory

    NASA Technical Reports Server (NTRS)

    Gehrels, N.; Chipman, E.; Kniffen, D.

    1994-01-01

    The Arthur Holly Compton Gamma Ray Observatory Compton) is the second in NASA's series of great Observatories. Launched on 1991 April 5, Compton represents a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made. We describe the capabilities of the four scientific instruments, and the observing program of the first 2 years of the mission. Examples of early discoveries by Compton are enumerated, including the discovery that gamma-ray bursts are isotropic but spatially inhomogeneous in their distribution; the discovery of a new class of high-energy extragalacatic gamma-ray sources, the gamma-ray AGNs; the discovery of emission from SN 1987A in the nuclear line of Co-57; and the mapping of emission from Al-26 in the interstellar medium (ISM) near the Galactic center. Future observations will include deep surveys of selected regions of the sky, long-tem studies of individual objects, correlative studies of objects at gamma-ray and other energies, a Galactic plane survey at intermediate gamma-ray energies, and improved statistics on gamma-ray bursts to search for small anisotropies. After completion of the all-sky survey, a Guest Investigator program is in progress with guest observers' time share increasing from 30% upward for the late mission phases.

  14. Astrophysical gamma-ray spectroscopy

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Lingenfelter, R. E.; Kozlovsky, B.

    1979-01-01

    Observations of gamma-ray lines from solar flares, the Galactic Center, and transient celestial events are reviewed. The lines observed in each case are identified, and possible emission sources are considered. Future prospects for gamma-ray line astronomy are briefly discussed.

  15. Gamma-ray line astrophysics

    NASA Technical Reports Server (NTRS)

    Lingenfelter, R. E.; Ramaty, R.

    1986-01-01

    Recent observations of gamma-ray line emission from solar flares, gamma-ray bursts, the galactic center, the interstellar medium and the jets of SS433 are reviewed. The implications of these observations on high energy processes in these sources are discussed.

  16. Gamma Ray Pulsars: Multiwavelength Observations

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2004-01-01

    High-energy gamma rays are a valuable tool for studying particle acceleration and radiation in the magnetospheres of energetic pulsars. The seven or more pulsars seen by instruments on the Compton Gamma Ray Observatory (CGRO) show that: the light curves usually have double-peak structures (suggesting a broad cone of emission); gamma rays are frequently the dominant component of the radiated power; and all the spectra show evidence of a high-energy turnover. For all the known gamma-ray pulsars, multiwavelength observations and theoretical models based on such observations offer the prospect of gaining a broad understanding of these rotating neutron stars. The Gamma-ray Large Area Space Telescope (GLAST), now in planning for a launch in 2006, will provide a major advance in sensitivity, energy range, and sky coverage.

  17. Planetary gamma-ray spectroscopy

    NASA Technical Reports Server (NTRS)

    Reedy, R. C.

    1978-01-01

    The measured intensities of certain gamma rays of specific energies escaping from a planetary surface can be used to determine the abundances of a number of elements. The fluxes of the more intense gamma-ray lines emitted from 32 elements were calculated using current nuclear data and existing models for the source processes. The source strengths for neutron-capture reactions were modified from those previously used. The fluxes emitted form a surface of average lunar composition are reported for 292 gamma-ray lines. These theoretical fluxes were used elsewhere to convert the data from the Apollo gamma-ray spectrometers to elemental abundances and can be used with measurements from future missions to map the concentrations of a number of elements over a planet's surface. Detection sensitivities for these elements are examined and applications of gamma-ray spectroscopy for future orbiters to Mars and other solar-system objects are discussed.

  18. Gamma rays from Centaurus A

    SciTech Connect

    Gupta, Nayantara

    2008-06-15

    Centaurus A, the cosmic ray accelerator a few Mpc away from us, is possibly one of the nearest sources of extremely high energy cosmic rays. We investigate whether the gamma ray data currently available from Centaurus A in the GeV-TeV energy band can be explained with only proton-proton interactions. We show that for a single power law proton spectrum, mechanisms of {gamma}-ray production other than proton-proton interactions are needed inside this radio-galaxy to explain the gamma ray flux observed by EGRET, upper limits from HESS/CANGAROO-III and the correlated extremely energetic cosmic ray events observed by the Pierre Auger experiment. In future, with better {gamma}-ray data, and simultaneous observation with {gamma}-ray and cosmic ray detectors, it will be possible to carry out such studies on different sources in more detail.

  19. THE FIRM REDSHIFT LOWER LIMIT OF THE MOST DISTANT TeV-DETECTED BLAZAR PKS 1424+240

    SciTech Connect

    Furniss, A.; Williams, D. A.; Primack, J.; Danforth, C.; Stocke, J.; Fumagalli, M.; Prochaska, J. X.; Filippenko, A. V.; Neely, W.

    2013-05-10

    We present the redshift lower limit of z {>=} 0.6035 for the very high energy (VHE; E {>=} 100 GeV) emitting blazar PKS 1424+240 (PG 1424+240). This limit is inferred from Ly{beta} and Ly{gamma} absorption observed in the far-ultraviolet spectra from the Hubble Space Telescope/Cosmic Origins Spectrograph. No VHE-detected blazar has shown solid spectroscopic evidence of being more distant. At this distance, VHE observations by VERITAS are shown to sample historically large gamma-ray opacity values at 500 GeV, extending beyond {tau} = 4 for low-level models of the extragalactic background light (EBL) and beyond {tau} = 5 for high levels. The majority of the z = 0.6035 absorption-corrected VHE spectrum appears to exhibit a lower flux than an extrapolation of the contemporaneous Large Area Telescope power-law fit beyond 100 GeV. However, the highest energy VERITAS point is the only point showing agreement with this extrapolation, possibly implying the overestimation of the gamma-ray opacity or the onset of an unexpected VHE spectral feature. A curved log parabola is favored when fitting the full range of gamma-ray data (0.5-500 GeV). While fitting the absorption-corrected VHE data alone results in a harder differential power law than that from the full range, the indices derived using three EBL models are consistent with the physically motivated limit set by Fermi acceleration processes.

  20. Gamma ray astronomy; E2 Symposium of COSPAR Scientific Commission E, COSPAR Scientific Assembly, 30th, Hamburg, Germany, July 11-21, 1994

    NASA Technical Reports Server (NTRS)

    Gehrels, N. (Editor)

    1995-01-01

    This issue on gamma ray astronomy presents many results from observations made with the Compton Gamma Ray Observatory (CGRO) and other spaceborne experiments and includes studies of Seyfert galaxies, X-ray binaries, neutron stars, diffuse cosmic background radiation, pulsars, blazars, gamma ray bursts, the galactic center, and the distribution of Aluminum-26 in the galaxy. The issue begins with a survey of Compton Telescope (COMPTEL) results and concludes with future prospects for the field.

  1. High energy gamma ray astronomy

    NASA Technical Reports Server (NTRS)

    Fichtel, Carl E.

    1987-01-01

    High energy gamma ray astronomy has evolved with the space age. Nonexistent twenty-five years ago, there is now a general sketch of the gamma ray sky which should develop into a detailed picture with the results expected to be forthcoming over the next decade. The galactic plane is the dominant feature of the gamma ray sky, the longitude and latitude distribution being generally correlated with galactic structural features including the spiral arms. Two molecular clouds were already seen. Two of the three strongest gamma ray sources are pulsars. The highly variable X-ray source Cygnus X-3 was seen at one time, but not another in the 100 MeV region, and it was also observed at very high energies. Beyond the Milky Way Galaxy, there is seen a diffuse radiation, whose origin remains uncertain, as well as at least one quasar, 3C 273. Looking to the future, the satellite opportunities for high energy gamma ray astronomy in the near term are the GAMMA-I planned to be launched in late 1987 and the Gamma Ray Observatory, scheduled for launch in 1990. The Gamma Ray Observatory will carry a total of four instruments covering the entire energy range from 30,000 eV to 3 x 10 to the 10th eV with over an order of magnitude increase in sensitivity relative to previous satellite instruments.

  2. ON THE NATURE OF THE GAMMA-RAY SOURCE 2FGL J1823.8+4312: THE DISCOVERY OF A NEW CLASS OF EXTRAGALACTIC X-RAY SOURCES

    SciTech Connect

    Massaro, F.; Digel, S. W.; Funk, S.; Paggi, A.; D'Abrusco, R.; Grindlay, J. E.; Smith, Howard A.; Tosti, G.

    2012-10-01

    One of the unsolved mysteries of gamma-ray astronomy concerns the nature of unidentified gamma-ray sources. Recently, using the Second Fermi LAT source catalog (2FGL) and the Wide-field Infrared Survey Explorer (WISE) archive, we discovered that the WISE counterparts of gamma-ray blazars, a class of active galactic nuclei, delineate a region (the WISE Gamma-ray Strip) in three-dimensional infrared color space well separated from the locus of other astronomical objects. Based on this result, we built an association procedure to recognize if there are WISE blazar candidates within the positional uncertainty region of the unidentified gamma-ray sources. Here we report on our analysis of 2FGL J1823.8+4312, a gamma-ray active galactic nucleus of uncertain type associated with the X-ray source 1RXS J182418.7+430954 according to the 2FGL, to verify whether it is a blazar. Applying our association method we found two sources with IR colors typical of gamma-ray blazars, located within the 99.9% confidence region of 2FGL J1823.8+4312: WISE J182352.33+431452.5 and WISE J182409.25+431404.7. We then searched in the Chandra, NVSS, and SDSS archival observations for their counterparts. We discovered that WISE J182352.33+431452.5, our preferred gamma-ray blazar candidate according to our WISE association procedure, is detected in the optical and in the X-rays but not in the radio, making it extremely unusual if it is a blazar. Given its enigmatic spectral energy distribution, we considered the possibility that it is a 'radio-faint blazar' or the prototype of a new class of extragalactic sources; our conclusion is independent of whether WISE J182352.33+431452.5 is the actual counterpart of 2FGL J1823.8+4312.

  3. On the Nature of the Gamma-ray Source 2FGL J1823.8 4312: The Discovery of a New Class of Extragalactic X-ray Sources

    SciTech Connect

    Massaro, Francesco

    2012-08-03

    One of the unsolved mysteries of gamma-ray astronomy concerns the nature of the unidentified gamma-ray sources. Recently, using the Second Fermi LAT source catalog (2FGL) and the Wide-field Infrared Survey Explorer (WISE) archive, we discovered that the WISE counterparts of gamma-ray blazars, a class of active galactic nuclei, delineate a region (the WISE Gamma-ray Strip) in the 3-dimensional infrared color space well separated from the locus of the other astronomical objects. Based on this result, we built an association procedure to recognize if there areWISE blazar candidates within the positional uncertainty region of the unidentified gamma-ray sources. Here we report on our analysis of 2FGL J1823.8+4312, a gamma-ray active galactic nucleus of uncertain type associated with the X-ray source 1RXS J182418.7+430954 according to the 2FGL, to verify whether it is a blazar. Applying our association method we found two sources with IR colors typical of gamma-ray blazars, located within the 99.9% confidence region of 2FGL J1823.8+4312: WISE J182352.33+431452.5 and WISE J182409.25+431404.7. Then we searched in the Chandra, NVSS and SDSS archival observations for their counterparts. We discovered that WISE J182352.33+431452.5, our preferred gamma-ray blazar candidate according to our WISE association procedure, is detected in the optical and in the X-rays but not in the radio, making it extremely unusual if it is a blazar. Given its enigmatic spectral energy distribution, we considered the possibility that it is a 'radio faint blazar' or the prototype of a new class of extragalactic sources, our conclusion is independent of whether WISE J182352.33+431452.5 is the actual counterpart of 2FGL J1823.8+4312.

  4. HIGH ENERGY POLARIZATION OF BLAZARS: DETECTION PROSPECTS

    SciTech Connect

    Chakraborty, N.; Pavlidou, V.; Fields, B. D.

    2015-01-01

    Emission from blazar jets in the ultraviolet, optical, and infrared is polarized. If these low-energy photons were inverse-Compton scattered, the upscattered high-energy photons retain a fraction of the polarization. Current and future X-ray and gamma-ray polarimeters such as INTEGRAL-SPI, PoGOLITE, X-Calibur, Gamma-Ray Burst Polarimeter, GEMS-like missions, ASTRO-H, and POLARIX have the potential to discover polarized X-rays and gamma-rays from blazar jets for the first time. Detection of such polarization will open a qualitatively new window into high-energy blazar emission; actual measurements of polarization degree and angle will quantitatively test theories of jet emission mechanisms. We examine the detection prospects of blazars by these polarimetry missions using examples of 3C 279, PKS 1510-089, and 3C 454.3, bright sources with relatively high degrees of low-energy polarization. We conclude that while balloon polarimeters will be challenged to detect blazars within reasonable observational times (with X-Calibur offering the most promising prospects), space-based missions should detect the brightest blazars for polarization fractions down to a few percent. Typical flaring activity of blazars could boost the overall number of polarimetric detections by nearly a factor of five to six purely accounting for flux increase of the brightest of the comprehensive, all-sky, Fermi-LAT blazar distribution. The instantaneous increase in the number of detections is approximately a factor of two, assuming a duty cycle of 20% for every source. The detectability of particular blazars may be reduced if variations in the flux and polarization fraction are anticorrelated. Simultaneous use of variability and polarization trends could guide the selection of blazars for high-energy polarimetric observations.

  5. High Energy Polarization of Blazars: Detection Prospects

    NASA Astrophysics Data System (ADS)

    Chakraborty, N.; Pavlidou, V.; Fields, B. D.

    2015-01-01

    Emission from blazar jets in the ultraviolet, optical, and infrared is polarized. If these low-energy photons were inverse-Compton scattered, the upscattered high-energy photons retain a fraction of the polarization. Current and future X-ray and gamma-ray polarimeters such as INTEGRAL-SPI, PoGOLITE, X-Calibur, Gamma-Ray Burst Polarimeter, GEMS-like missions, ASTRO-H, and POLARIX have the potential to discover polarized X-rays and gamma-rays from blazar jets for the first time. Detection of such polarization will open a qualitatively new window into high-energy blazar emission; actual measurements of polarization degree and angle will quantitatively test theories of jet emission mechanisms. We examine the detection prospects of blazars by these polarimetry missions using examples of 3C 279, PKS 1510-089, and 3C 454.3, bright sources with relatively high degrees of low-energy polarization. We conclude that while balloon polarimeters will be challenged to detect blazars within reasonable observational times (with X-Calibur offering the most promising prospects), space-based missions should detect the brightest blazars for polarization fractions down to a few percent. Typical flaring activity of blazars could boost the overall number of polarimetric detections by nearly a factor of five to six purely accounting for flux increase of the brightest of the comprehensive, all-sky, Fermi-LAT blazar distribution. The instantaneous increase in the number of detections is approximately a factor of two, assuming a duty cycle of 20% for every source. The detectability of particular blazars may be reduced if variations in the flux and polarization fraction are anticorrelated. Simultaneous use of variability and polarization trends could guide the selection of blazars for high-energy polarimetric observations.

  6. Gamma-Ray Astrophysics: New Insight Into the Universe

    NASA Technical Reports Server (NTRS)

    Fichtel, Carl E.; Trombka, Jacob I.

    1997-01-01

    During the 15 years that have passed since the first edition of this book was published, there has been a major increase in our knowledge of gamma-ray astronomy. Much of this advance arises from the extensive results that have been forthcoming from the Compton Gamma-Ray Observatory. There has been the discovery of a new class of gamma-ray objects, namely high-energy gamma- ray-emitting blazars, a special class of Active Galactic Nuclei, whose basic high-energy properties now seem to be understood. A much improved picture of our galaxy now exists in the frequency range of gamma rays. The question of whether cosmic rays are galactic or metagalactic now seems settled with certainty. Significant new information exists on the gamma-ray properties of neutron star pulsars, Seyfert galaxies, and gamma-ray bursts. Substantial new insight has been obtained on solar phenomena through gamma-ray observations. Hence, this seemed to be an appropriate time to write a new edition of this book to add the important scientific implications of these many new findings. The special importance of gamma-ray astrophysics had long been recognized by many physicists and astronomers, and theorists had pursued many aspects of the subject well before the experimental results began to become available. The slower development of the experimental side was not because of a lack of incentive, but due to the substantial experimental difficulties that had to be overcome. Thus, as the gamma-ray results became available in much greater number and detail, it was possible to build upon the theoretical work that already existed and to make substantial progress in the study of many of the phenomena involved. Consequently, a much better understanding of many of the astrophysical phenomena mentioned here and others is now possible. Our principal aims in writing this book are the same as they were for the first edition: to provide a text which describes the significance of gamma-ray astrophysics and to assemble

  7. FERMI LARGE AREA TELESCOPE CONSTRAINTS ON THE GAMMA-RAY OPACITY OF THE UNIVERSE

    SciTech Connect

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Allafort, A.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Borgland, A. W.; Bouvier, A.; Atwood, W. B.; Baldini, L.; Bellazzini, R.; Ballet, J.; Baring, M. G.; Bastieri, D.; Baughman, B. M.; Bhat, P. N.; Bonamente, E. E-mail: bouvier@stanford.ed E-mail: silvia.raino@ba.infn.i E-mail: lreyes@kicp.uchicago.ed

    2010-11-10

    The extragalactic background light (EBL) includes photons with wavelengths from ultraviolet to infrared, which are effective at attenuating gamma rays with energy above {approx}10 GeV during propagation from sources at cosmological distances. This results in a redshift- and energy-dependent attenuation of the {gamma}-ray flux of extragalactic sources such as blazars and gamma-ray bursts (GRBs). The Large Area Telescope on board Fermi detects a sample of {gamma}-ray blazars with redshift up to z {approx} 3, and GRBs with redshift up to z {approx} 4.3. Using photons above 10 GeV collected by Fermi over more than one year of observations for these sources, we investigate the effect of {gamma}-ray flux attenuation by the EBL. We place upper limits on the {gamma}-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.

  8. Jet Shockwaves Produce Gamma Rays

    NASA Video Gallery

    Theorists believe that GRB jets produce gamma rays by two processes involving shock waves. Shells of material within the jet move at different speeds and collide, generating internal shock waves th...

  9. Gamma rays at airplane altitudes

    SciTech Connect

    Iwai, J.; Koss, T.; Lord, J.; Strausz, S.; Wilkes, J.; Woosley, J. )

    1990-03-20

    An examination of the gamma ray flux above 1 TeV in the atmosphere is needed to better understand the anomalous showers from point sources. Suggestions are made for future experiments on board airplanes.

  10. Gamma-ray line astronomy

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Lingenfelter, R. E.

    1979-01-01

    Gamma-ray astronomy is a valuable source of information on solar activity, supernovae, and nucleosynthesis. Cosmic gamma-ray lines were first observed from solar flares and more recently from the galactic center and a transient event. The latter may give an important insight into nuclear reactions taking place near neutron stars and black holes and a measure of the gravitational redshifts of such objects.

  11. Gamma-ray spectrometer experiment

    NASA Technical Reports Server (NTRS)

    Arnold, J. R.; Peterson, L. E.; Metzger, A. E.; Trombka, J. I.

    1972-01-01

    The experiments in gamma-ray spectrometry to determine the geochemical composition of the lunar surface are reported. The theory is discussed of discrete energy lines of natural radioactivity, and the lines resulting from the bombardment of the lunar surface by high energy cosmic rays. The gamma-ray spectrometer used in lunar orbit and during transearth coast is described, and a preliminary analysis of the results is presented.

  12. Directional detector of gamma rays

    DOEpatents

    Cox, Samson A.; Levert, Francis E.

    1979-01-01

    A directional detector of gamma rays comprises a strip of an electrical cuctor of high atomic number backed with a strip of a second electrical conductor of low atomic number. These elements are enclosed within an electrical conductor that establishes an electrical ground, maintains a vacuum enclosure and screens out low-energy gamma rays. The detector exhibits a directional sensitivity marked by an increased output in the favored direction by a factor of ten over the output in the unfavored direction.

  13. The Compton Gamma Ray Observatory

    NASA Astrophysics Data System (ADS)

    Gehrels, N.; Chipman, E.; Kniffen, D. A.

    1993-01-01

    The Arthur Holly Compton Gamma Ray Observatory (Compton) was launched by the Space Shuttle Atlantis on 5 April 1991. The spacecraft and instruments are in good health and returning exciting results. The mission provides nearly six orders of magnitude in spectral coverage, from 30 keV to 30 GeV, with sensitivity over the entire range an order of magnitude better than that of previous observations. The 16,000 kilogram observatory contains four instruments on a stabilized platform. The mission began normal operations on 16 May 1991 and is now over half-way through a full-sky survey. The mission duration is expected to be from six to ten years. A Science Support Center has been established at Goddard Space Flight Center for the purpose of supporting a vigorous Guest Investigator Program. New scientific results to date include: (1) the establishment of the isotropy, combined with spatial inhomogeneity, of the distribution of gamma-ray bursts in the sky; (2) the discovery of intense high energy (100 MeV) gamma-ray emission from 3C 279 and other quasars and BL Lac objects, making these the most distant and luminous gamma-ray sources ever detected; (3) one of the first images of a gamma-ray burst; (4) the observation of intense nuclear and position-annihilation gamma-ray lines and neutrons from several large solar flares; and (5) the detection of a third gamma-ray pulsar, plus several other transient and pulsing hard X-ray sources.

  14. Two Active States of the Narrow-Line Gamma-Ray-Loud AGN GB 1310 + 487

    NASA Technical Reports Server (NTRS)

    Sokolovsky, K. V.; Schinzel, F. K.; Tanaka, Y. T.; Abolmasov, P. K.; Angelakis, E.; Bulgarelli, A.; Carrasco, L.; Cenko, S. B.; Cheung, C. C.; Clubb, K. I.; D'Ammando, F.; Escande, L.; Fegan, S. J.; Filippenko, A. V.; Finke, J. D.; Fuhrmann, L.; Fukazawa, Y.; Hays, E.; Healey, S. E.; Ikejiri, Y.; Itoh, R.; Kawabata, K. S.; Komatsu, T.; Kovalev, Yu. A.; Kovalev, Y. Y.; Krichbaum, T. P.

    2014-01-01

    Context. Previously unremarkable, the extragalactic radio source GB1310 487 showed gamma-ray flare on 2009 November 18, reaching a daily flux of approximately 10(exp -6) photons cm(exp -2) s(exp -1) at energies E greater than 100MeV and became one of the brightest GeV sources for about two weeks. Its optical spectrum shows strong forbidden-line emission while lacking broad permitted lines, which is not typical for a blazar. Instead, the spectrum resembles those of narrow emission-line galaxies. Aims. We investigate changes in the object's radio-to-GeV spectral energy distribution (SED) during and after the prominent gamma-ray flare with the aim of determining the nature of the object and of constraining the origin of the variable high-energy emission. Methods. The data collected by the Fermi and AGILE satellites at gamma-ray energies; Swift at X-ray and ultraviolet (UV); the Kanata, NOT, and Keck telescopes at optical; OAGH and WISE at infrared (IR); and IRAM30m, OVRO 40m, Effelsberg 100m, RATAN-600, and VLBA at radio are analyzed together to trace the SED evolution on timescales of months. Results. The gamma-ray radio-loud narrow-line active galactic nucleus (AGN) is located at redshift z = 0.638. It shines through an unrelated foreground galaxy at z = 0.500. The AGN light is probably amplified by gravitational lensing. The AGN SED shows a two-humped structure typical of blazars and gamma-ray-loud narrow-line Seyfert 1 galaxies, with the high-energy (inverse-Compton) emission dominating by more than an order of magnitude over the low-energy (synchrotron) emission during gamma-ray flares. The difference between the two SED humps is smaller during the low-activity state. Fermi observations reveal a strong correlation between the gamma-ray flux and spectral index, with the hardest spectrum observed during the brightest gamma-ray state. The gamma-ray flares occurred before and during a slow rising trend in the radio, but no direct association between gamma-ray and

  15. Probes of the inner jets of blazars.

    PubMed Central

    Marscher, A P

    1995-01-01

    I review models for the "inner jet" in blazars, the section that connects the central engine with the radio jet. I discuss how the structure and physics of the inner jet can be explored using millimeter-wave VLBI (very-long-baseline radio interferometry) as well as multiwaveband observations of blazars. Flares at radio to gamma-ray frequencies should exhibit time delays at different wavebands that can test models for both the high-energy emission mechanisms and the nature of the inner jet in blazars. PMID:11607614

  16. Multifrequency Catalogue of Blazars - 5th Edition

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The 5th Edition of the Multifrequency Catalogue of Blazars is one of the most complete lists of Active Galactic Nuclei whose emission properties are recognised as typical of blazars. It includes the list of sources and an essential compilation of multifrequency data from radio to gamma rays. The source list for the entire sky is also available online at the ASDC web site (http://www.asdc.asi.it/bzcat/) where it is frequently updated to add new blazars and to improve the database.

  17. Dissecting the gamma-ray background in search of dark matter

    SciTech Connect

    Cholis, Ilias; Hooper, Dan; McDermott, Samuel D. E-mail: dhooper@fnal.gov

    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 competitive 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.

  18. Dissecting the Gamma-Ray Background in Search of Dark Matter

    SciTech Connect

    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 competitive 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.

  19. PG 1553+113: FIVE YEARS OF OBSERVATIONS WITH MAGIC

    SciTech Connect

    Aleksic, J.; Blanch, O.; Alvarez, E. A.; Asensio, M.; Barrio, J. A.; Antonelli, L. A.; Bonnoli, G.; Antoranz, P.; Backes, M.; Bastieri, D.; Gonzalez, J. Becerra; Berger, K.; Bednarek, W.; Berdyugin, A.; Bernardini, E.; Biland, A.; Boller, A.; Braun, I.; Bock, R. K.; Tridon, D. Borla E-mail: elisa.prandini@pd.infn.it; and others

    2012-03-20

    We present the results of five years (2005-2009) of MAGIC observations of the BL Lac object PG 1553+113 at very high energies (VHEs; E > 100 GeV). Power-law fits of the individual years are compatible with a steady mean photon index {Gamma} = 4.27 {+-} 0.14. In the last three years of data, the flux level above 150 GeV shows a clear variability (probability of constant flux < 0.001%). The flux variations are modest, lying in the range from 4% to 11% of the Crab Nebula flux. Simultaneous optical data also show only modest variability that seems to be correlated with VHE gamma-ray variability. We also performed a temporal analysis of (all available) simultaneous Fermi/Large Area Telescope data of PG 1553+113 above 1 GeV, which reveals hints of variability in the 2008-2009 sample. Finally, we present a combination of the mean spectrum measured at VHEs with archival data available for other wavelengths. The mean spectral energy distribution can be modeled with a one-zone synchrotron self-Compton model, which gives the main physical parameters governing the VHE emission in the blazar jet.

  20. Gamma Ray Astronomy with LHAASO

    NASA Astrophysics Data System (ADS)

    Vernetto, S.; LHAASO Collaboration

    2016-05-01

    The aim of LHAASO is the development of an air shower experiment able to monitor with unprecedented sensitivity the gamma ray sky at energies from ~200 GeV to 1 PeV, and at the same time be an instrument able to measure the cosmic ray spectrum, composition and anisotropy in a wide energy range (~1 TeV to 1 EeV). LHAASO, thanks to the large area and the high capability of background rejection, can reach sensitivities to gamma ray fluxes above 30 TeV that are about 100 times higher than that of current instruments, offering the possibility to monitor for the first time the gamma ray sky up to PeV energies and to discover the long sought “Pevatrons”.

  1. 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.

  2. The Gamma-ray Sky with Fermi

    NASA Technical Reports Server (NTRS)

    Thompson, David

    2012-01-01

    Gamma rays reveal extreme, nonthermal conditions in the Universe. The Fermi Gamma-ray Space Telescope has been exploring the gamma-ray sky for more than four years, enabling a search for powerful transients like gamma-ray bursts, novae, solar flares, and flaring active galactic nuclei, as well as long-term studies including pulsars, binary systems, supernova remnants, and searches for predicted sources of gamma rays such as dark matter annihilation. Some results include a stringent limit on Lorentz invariance derived from a gamma-ray burst, unexpected gamma-ray variability from the Crab Nebula, a huge gamma-ray structure associated with the center of our galaxy, surprising behavior from some gamma-ray binary systems, and a possible constraint on some WIMP models for dark matter.

  3. 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.; Readhead, A. C. S.; Richards, J. L.; Stawarz, L.; Donato, D.

    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.

  4. Probing the very high energy γ-ray spectral curvature in the blazar PG 1553+113 with the MAGIC telescopes

    NASA Astrophysics Data System (ADS)

    Aleksić, J.; Ansoldi, S.; Antonelli, L. A.; Antoranz, P.; Babic, A.; Bangale, P.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Biasuzzi, B.; Biland, A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; 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.; de Oña Wilhelmi, E.; Delgado Mendez, C.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher, D.; Elsaesser, D.; Fidalgo, D.; Fonseca, M. V.; Font, L.; Frantzen, K.; Fruck, C.; Galindo, D.; García López, R. J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Godinović, N.; González Muñoz, A.; Gozzini, S. R.; Hadasch, D.; Hanabata, Y.; Hayashida, M.; Herrera, J.; Hildebrand, D.; Hose, J.; Hrupec, D.; Idec, W.; Kadenius, V.; Kellermann, H.; Knoetig, M. L.; Kodani, K.; Konno, Y.; Krause, J.; Kubo, H.; Kushida, J.; La Barbera, A.; Lelas, D.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Lozano, I.; Makariev, M.; Mallot, K.; Maneva, G.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Miranda, J. M.; Mirzoyan, R.; Moralejo, A.; Munar-Adrover, P.; Nakajima, D.; Neustroev, V.; Niedzwiecki, A.; Nilsson, K.; Nishijima, K.; Noda, K.; Orito, R.; Overkemping, A.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Paredes-Fortuny, X.; Persic, M.; Poutanen, J.; Prada Moroni, P. G.; Prandini, E.; Puljak, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rodriguez Garcia, J.; Rügamer, S.; Saito, T.; Saito, K.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Spanier, F.; Stamerra, A.; Steinbring, T.; Storz, J.; Strzys, M.; 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.; Vogler, P.; Will, M.; Zanin, R.; MAGIC Collaboration; D'Ammando, F.; Buson, S.; Lähteenmäki, A.; Tornikoski, M.; Hovatta, T.; Readhead, A. C. S.; Max-Moerbeck, W.; Richards, J. L.

    2015-07-01

    PG 1553+113 is a very high energy (VHE, E > 100 GeV) γ-ray emitter classified as a BL Lac object. Its redshift is constrained by intergalactic absorption lines in the range 0.4 < z < 0.58. The MAGIC telescopes have monitored the source's activity since 2005. In early 2012, PG 1553+113 was found in a high state, and later, in April of the same year, the source reached its highest VHE flux state detected so far. Simultaneous observations carried out in X-rays during 2012 April show similar flaring behaviour. In contrast, the γ-ray flux at E < 100 GeV observed by Fermi-LAT is compatible with steady emission. In this paper, a detailed study of the flaring state is presented. The VHE spectrum shows clear curvature, being well fitted either by a power law with an exponential cut-off or by a log-parabola. A simple power-law fit hypothesis for the observed shape of the PG 1553+113 VHE γ-ray spectrum is rejected with a high significance (fit probability P = 2.6 × 10-6). The observed curvature is compatible with the extragalactic background light (EBL) imprint predicted by current generation EBL models assuming a redshift z ˜ 0.4. New constraints on the redshift are derived from the VHE spectrum. These constraints are compatible with previous limits and suggest that the source is most likely located around the optical lower limit, z = 0.4, based on the detection of Lyα absorption. Finally, we find that the synchrotron self-Compton model gives a satisfactory description of the observed multiwavelength spectral energy distribution during the flare.

  5. The Spectral Index Distribution of EGRET Blazars: Prospects for GLAST

    SciTech Connect

    Venters, Tonia M.; Pavlidou, Vasiliki; /SLAC

    2011-11-29

    The intrinsic distribution of spectral indices in GeV energies of gamma-ray-loud blazars is a critical input in determining the spectral shape of the unresolved blazar contribution to the diffuse extragalactic gamma-ray background, as well as an important test of blazar emission theories. We present a maximum-likelihood method of determining the intrinsic spectral index distribution (ISID) of a population of {gamma}-ray emitters which accounts for error in measurement of individual spectral indices, and we apply it to EGRET blazars. We find that the most likely Gaussian ISID for EGRET blazars has a mean of 2.27 and a standard deviation of 0.20. We additionally find some indication that FSRQs and BL Lacs may have different ISIDs (with BL Lacs being harder). We also test for spectral index hardening associated with blazar variability for which we find no evidence. Finally, we produce simulated GLAST spectral index datasets and perform the same analyses. With improved statistics due to the much larger number of resolvable blazars, GLAST data will help us determine the ISIDs with much improved accuracy. Should any difference exist between the ISIDs of BL Lacs and FSRQs or between the ISIDs of blazars in the quiescent and flaring states, GLAST data will be adequate to separate these ISIDs at a significance better than 3{sigma}.

  6. Gamma-ray Imaging Methods

    SciTech Connect

    Vetter, K; Mihailescu, L; Nelson, K; Valentine, J; Wright, D

    2006-10-05

    In this document we discuss specific implementations for gamma-ray imaging instruments including the principle of operation and describe systems which have been built and demonstrated as well as systems currently under development. There are several fundamentally different technologies each with specific operational requirements and performance trade offs. We provide an overview of the different gamma-ray imaging techniques and briefly discuss challenges and limitations associated with each modality (in the appendix we give detailed descriptions of specific implementations for many of these technologies). In Section 3 we summarize the performance and operational aspects in tabular form as an aid for comparing technologies and mapping technologies to potential applications.

  7. Towed seabed gamma ray spectrometer

    SciTech Connect

    Jones, D.G. )

    1994-08-01

    For more than 50 years, the measurement of radioactivity has been used for onshore geological surveys and in laboratories. The British Geological Survey (BGS) has extended the use of this type of equipment to the marine environment with the development of seabed gamma ray spectrometer systems. The present seabed gamma ray spectrometer, known as the Eel, has been successfully used for sediment and solid rock mapping, mineral exploration, and radioactive pollution studies. The range of applications for the system continues to expand. This paper examines the technological aspects of the Eel and some of the applications for which it has been used.

  8. 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.

  9. Polarization structure of 12 gamma-ray quasars at 5 and 15 GHz

    NASA Astrophysics Data System (ADS)

    Vetukhnovskaya, Yu. N.; Gabuzda, D. C.

    2012-12-01

    The results of dual-frequency polarization observations of 12 gamma-ray quasars are presented (as a continuation of a study of six blazars carried out earlier). The observations were obtained with the American Very Long Baseline Array. The distributions of intensity and polarization were obtained at 5 and 15 GHz. The degrees of polarization in the cores and jets of the 18 gamma-ray quasars do not stand out from those of other quasars. The brightness temperatures of the core components do not strongly exceed 1012 K.

  10. High-energy gamma-ray observations of active galaxies

    NASA Technical Reports Server (NTRS)

    Fichtel, Carl E.

    1994-01-01

    During the period from 1992 May to early 1992 November, the Energetic Gamma-Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory obtained high-energy gamma-ray data for most of the sky. A total of 18 active galaxies have been seen with high certainty, and it is expected that more will be found in the data when a more thorough analysis is complete. All of those that have been seen are radio-loud quasars or BL Lacertae objects; most have already been identified as blazars. No Seyfert galaxies have been found thus far. If the spectra are represented as a power law in energy, spectral slopes ranging from approximately -1.7 to -2.4 are found. A wide range of z-values exits in the observed sample, eight having values in excess of 1.0. Time variations have been seen, with the timescale for a significant change being as short as days in at least one case. These results imply the existence of very large numbers of relativistic particles, probably close to the central object. Although a large extrapolation is required, their existence also suggests that these active galactic nuclei may be the source of the extragalactic cosmic rays.