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Sample records for bright late-time fermi

  1. Broad band spectral energy distribution studies of Fermi bright blazars

    NASA Astrophysics Data System (ADS)

    Monte, C.; Giommi, P.; Cavazzuti, E.; Gasparrini, D.; Rainò, S.; Fuhrmann, L.; Angelakis, E.; Villata, M.; Raiteri, C. M.; Perri, M.; Richards, J.

    2011-02-01

    The Fermi Gamma-ray Space Telescope was successfully launched on June 11, 2008 and has already opened a new era for gamma-ray astronomy. The Large Area Telescope (LAT), the main instrument on board Fermi, presents a significant improvement in sensitivity over its predecessor EGRET, due to its large field of view and effective area, combined with its excellent timing capabilities. The preliminary results of the Spectral Energy Distribution Analysis performed on a sample of bright blazars are presented. For this study, the data from the first three months of data collection of Fermi have been used. The analysis is extended down to radio, mm, near-IR, optical, UV and X-ray bands and up to TeV energies based on unprecedented sample of simultaneous multi-wavelength observations by GASP-WEBT.

  2. Three Millisecond Pulsars in Fermi LAT Unassociated Bright Sources

    NASA Technical Reports Server (NTRS)

    Ransom, S. M.; Ray, P. S.; Camilo, F.; Roberts, M. S. E.; Celik, O.; Wolff, M. T.; Cheung, C. C.; Kerr, M.; Pennucci, T.; DeCesar, M. E.; Cognard, I.; Lyne, A. G.; Stappers, B. W.; Freire, P. C. C.; Grove, J. E.; Abdo, A. A.; Desvignes, G.; Donato, D.; Ferrara, E. C.; Gehrels, N.; Guillemot, L.; Gwon, C.; Johnston, S.; Harding, A. K.; Thompson, D. J.

    2010-01-01

    We searched for radio pulsars in 25 of the non-variable, unassociated sources in the Fermi LAT Bright Source List with the Green Bank Telescope at 820 MHz. We report the discovery of three radio and gamma-ray millisecond pulsar (MSPs) from a high Galactic latitude subset of these sources. All of the pulsars are in binary systems, which would have made them virtually impossible to detect in blind gamma-ray pulsation searches. They seem to be relatively normal, nearby (<= 2 kpc) MSPs. These observations, in combination with the Fermi detection of gamma-rays from other known radio MSPs, imply that most, if not all, radio MSPs are efficient gamma-ray producers. The gamma-ray spectra of the pulsars are power law in nature with exponential cutoffs at a few Ge V, as has been found with most other pulsars. The MSPs have all been detected as X-ray point sources. Their soft X-ray luminosities of approx 10(exp 30) - 10(exp 31) erg/s are typical of the rare radio MSPs seen in X-rays.

  3. The Spectral Energy Distribution of Fermi Bright Blazars

    NASA Technical Reports Server (NTRS)

    Abdo, A. A.; Ackermann, M.; Agudo, I.; Ajello, M.; Aller, H. D.; Aller, M. F.; Angelakis, E.; Arkharov, A. A.; Axelsson, M.; Bach, U.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B. M.; Bechtol, K.; Bellazzini, R.; Benitiez, E.; Berdyugin, A.; Gehrels, N.; Harding, A. K.; Hays, E.; Marshall, F.; Scargle, J. D.; Thompson, D. J.

    2010-01-01

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

  4. Fermi Large Area Telescope Bright Gamma-ray Source List

    SciTech Connect

    Abdo, Aous A.; Ackermann, M.; Ajello, M.; Atwood, W.B.; Axelsson, M.; Baldini, L.; Ballet, J.; Band, D.L.; Barbiellini, Guido; Bastieri, Denis; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bignami, G.F.; Bloom, Elliott D.; Bonamente, E.; Borgland, A.W.; Bregeon, J.; Brigida, M.; Bruel, P.; Burnett, Thompson H.; /more authors..

    2009-05-15

    Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the {gamma}-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than {approx}10{sigma}) {gamma}-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) {gamma}-ray sources in the early mission data.

  5. Fermi view of the bright long GRB 090926A

    SciTech Connect

    Uehara, Takeshi

    2010-10-15

    GRB 090926A is one of the brightest long burst detected by the GBM and LAT instruments on Fermi. More than 200 photons above 100 MeV and more than 30 photons above 1 GeV with the highest energy events up to {approx}20 GeV are observed after the GBM trigger (T0). The GeV emission delayed by 3 s from the onset against the low energy emission, as seen in other LAT GRBs. A sharp pulse around T0+10 s was coincidently observed by both GBM and LAT, and thus the pulse should not be due to the external shock. The spectrum exhibits an extra component against a canonical Band function from T0+3.3 to T0+21.6 s.

  6. GRB090510: a short bright and hard GRB detected by Fermi

    SciTech Connect

    Palma, F. de

    2010-03-26

    On 2009 May 10, 00:22:59 UT (T{sub 0}) the Fermi Gamma-ray Burst Monitor (GBM) triggered and located the short and very bright GRB090510. For the first time, this hard GRB, with an Epeak of few MeV, also triggered independently the Fermi Large Area Telescope (LAT). Swift detected this GRB and the accurate position provided by the Swift/UVOT made possible a spectroscopic redshift measurement of z = 0.903 with VLT/FORS2. This short GRB exhibits new features for this kind of events such an extra component (power-law) at high energies and a long lasting (few minutes) emission observed by the LAT. These observations allow the derivation of very important physical parameters such as the minimum value of the bulk Lorentz factor and they put some unprecedent limits on the dependence of the speed of photons on their energy.

  7. VERITAS Observations of Six Bright, Hard-Spectrum Fermi-LAT Blazars

    NASA Technical Reports Server (NTRS)

    E. Aliu; Archambault, S.; Arlen, T.; Aune, T.; Beilicke, M.; Benbow, W.; Boettcher, M.; Bouvier, A.; Buckley, J. H.; Bugaev, V.; Cesarini, A.; Ciupick, L.; Collins-Hughes, E.; Connolly, M. P.; Cui, W.; Dickherber, R.; Duke, C.; Dumm, J.; Erando, M.; Falcone, A.; Federici, S.; Feng, Q.; Finley, J. P.; Finnegan, G.; Perkins, J. S.

    2012-01-01

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

  8. Propagation of sound and supersonic bright solitons in superfluid Fermi gases in BCS-BEC crossover

    NASA Astrophysics Data System (ADS)

    Wen, Wen; Shen, Shun-Qing; Huang, Guoxiang

    2010-01-01

    We investigate the linear and nonlinear sound propagations in a cigar-shaped superfluid Fermi gas with a large particle number. We first solve analytically the eigenvalue problem of linear collective excitations and provide explicit expressions of all eigenvalues and eigenfunctions, which are valid for all superfluid regimes in the Bardeen-Cooper-Schrieffer-Bose-Einstein condensation (BCS-BEC) crossover. The linear sound speed obtained agrees well with that of a recent experimental measurement. We then consider a weak nonlinear excitation and show that the time evolution of the excitation obeys a Korteweg de Vries equation. Different from the result obtained in quasi-one-dimensional case studied previously, where subsonic dark solitons are obtained via the balance between quantum pressure and nonlinear effect, we demonstrate that bright solitons with supersonic propagating velocity can be generated in the present three-dimensional system through the balance between a waveguidelike dispersion and the interparticle interaction. The supersonic bright solitons obtained display different physical properties in different superfluid regimes and hence can be used to characterize superfluid features of the BCS-BEC crossover.

  9. IDENTIFYING BREAKS AND CURVATURE IN THE FERMI SPECTRA OF BRIGHT FLAT SPECTRUM RADIO QUASARS

    SciTech Connect

    Harris, J.; Daniel, M. K.; Chadwick, P. M.

    2012-12-10

    Knowing the site of {gamma}-ray emission in active galactic nucleus jets will do much for our understanding of the physics of the source. In particular, if the emission region is close to the black hole then absorption of {gamma}-rays with photons from the broad-line region could become significant. Such absorption is predicted to produce two specific spectral breaks in the {gamma}-ray spectra of Flat Spectrum Radio Quasars (FSRQs). We test this hypothesis using three years of Fermi observations of nine bright FSRQs. A simple power-law fit to the spectrum of each source can be significantly improved by introducing a break, but the break energies are inconsistent with those predicted by the double-absorber model. In some cases the fit can be further improved by a log-parabola. In addition, by dividing the data from each source into two equal epochs we find that the best description of an object's spectrum often varies between a log-parabola and a broken power law.

  10. 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

  11. 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

  12. Late-time Spectroscopy of Type Iax Supernovae

    NASA Astrophysics Data System (ADS)

    Foley, Ryan J.; Jha, Saurabh W.; Pan, Yen-Chen; Zheng, WeiKang; Bildsten, Lars; Filippenko, Alexei V.; Kasen, Daniel

    2016-06-01

    We examine the late-time (t ≳ 200 days after peak brightness) spectra of Type Iax supernovae (SNe Iax), a low-luminosity, low-energy class of thermonuclear stellar explosions observationally similar to, but distinct from, Type Ia supernovae. We present new spectra of SN 2014dt, resulting in the most complete late-time spectral sequence of a SN Iax. At late times, SNe Iax have generally similar spectra, all with a similar continuum shape and strong forbidden-line emission. However, there is also significant diversity where some SN Iax spectra display narrow P-Cygni features from permitted lines and a continuum indicative of a photosphere at late times in addition to strong narrow (FWHM < 3500 km s-1) forbidden lines, others have no obvious P-Cygni features, strong broad (FWHM > 6000 km s-1) forbidden lines, and weak narrow forbidden lines, and some SNe Iax have spectra intermediate to these two varieties. We find that SNe Iax with strong broad forbidden lines are more luminous and have higher-velocity ejecta at peak brightness. We estimate blackbody and kinematic radii of the late-time photosphere, finding the latter significantly larger than the former. We propose a two-component model that solves this discrepancy and explains the diversity of the late-time spectra of SNe Iax. In this model, the broad forbidden lines originate from the SN ejecta, while the photosphere, P-Cygni lines, and narrow forbidden lines originate from a wind launched from the remnant of the progenitor white dwarf and is driven by the radioactive decay of newly synthesised material left in the remnant. The relative strength of the two components accounts for the diversity of late-time SN Iax spectra. This model also solves the puzzle of a long-lived photosphere and the slow late-time decline of SNe Iax.

  13. Late-time spectroscopy of Type Iax Supernovae

    NASA Astrophysics Data System (ADS)

    Foley, Ryan J.; Jha, Saurabh W.; Pan, Yen-Chen; Zheng, Wei Kang; Bildsten, Lars; Filippenko, Alexei V.; Kasen, Daniel

    2016-09-01

    We examine the late-time (t ≳ 200 d after peak brightness) spectra of Type Iax supernovae (SNe Iax), a low-luminosity, low-energy class of thermonuclear stellar explosions observationally similar to, but distinct from, Type Ia supernovae. We present new spectra of SN 2014dt, resulting in the most complete late-time spectral sequence of an SN Iax. At late times, SNe Iax have generally similar spectra, all with a similar continuum shape and strong forbidden-line emission. However, there is also significant diversity where some SN Iax spectra display narrow P-Cygni features from permitted lines and a continuum indicative of a photosphere at late times in addition to strong narrow (FWHM < 3500 km s-1) forbidden lines, others have no obvious P-Cygni features, strong broad (FWHM > 6000 km s-1) forbidden lines, and weak narrow forbidden lines, and some SNe Iax have spectra intermediate to these two varieties. We find that SNe Iax with strong broad forbidden lines are more luminous and have higher velocity ejecta at peak brightness. We estimate blackbody and kinematic radii of the late-time photosphere, finding the latter significantly larger than the former. We propose a two-component model that solves this discrepancy and explains the diversity of the late-time spectra of SNe Iax. In this model, the broad forbidden lines originate from the SN ejecta, while the photosphere, P-Cygni lines, and narrow forbidden lines originate from a wind launched from the remnant of the progenitor white dwarf and is driven by the radioactive decay of newly synthesized material left in the remnant. The relative strength of the two components accounts for the diversity of late-time SN Iax spectra. This model also solves the puzzle of a long-lived photosphere and the slow late-time decline of SNe Iax.

  14. 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.

  15. FERMI LARGE AREA TELESCOPE DETECTION OF BRIGHT {gamma}-RAY OUTBURSTS FROM THE PECULIAR QUASAR 4C +21.35

    SciTech Connect

    Tanaka, Y. T.; Stawarz, L.; Saito, S.; Ohno, M.; Takahashi, T.; Thompson, D. J.; D'Ammando, F.; Fegan, S. J.; Cheung, C. C.; Buson, S.; Donato, D.; Chiang, J.; Giroletti, M.; Schinzel, F. K.; Iafrate, G.; Longo, F.

    2011-05-20

    In this paper, we report on the two-year-long Fermi-Large Area Telescope observation of the peculiar blazar 4C +21.35 (PKS 1222+216). This source was in a quiescent state from the start of the science operations of the Fermi Gamma-ray Space Telescope in 2008 August until 2009 September, and then became more active, with gradually increasing flux and some moderately bright flares. In 2010 April and June, 4C +21.35 underwent a very strong GeV outburst composed of several major flares characterized by rise and decay timescales of the order of a day. During the outburst, the GeV spectra of 4C +21.35 displayed a broken power-law form with spectral breaks observed near 1-3 GeV photon energies. We demonstrate that, at least during the major flares, the jet in 4C +21.35 carried a total kinetic luminosity comparable to the total accretion power available to feed the outflow. We also discuss the origin of the break observed in the flaring spectra of 4C +21.35. We show that, in principle, a model involving annihilation of the GeV photons on the He II Lyman recombination continuum and line emission of 'broad-line region' clouds may account for such. However, we also discuss the additional constraint provided by the detection of 4C +21.35 at 0.07-0.4 TeV energies by the MAGIC telescope, which coincided with one of the GeV flares of the source. We argue that there are reasons to believe that the {approx}< TeV emission of 4C +21.35 (as well as the GeV emission of the source, if co-spatial) is not likely to be produced inside the broad-line region zone of highest ionization ({approx}10{sup 17} cm from the nucleus), but instead originates further away from the active center, namely, around the characteristic scale of the hot dusty torus surrounding the 4C +21.35 nucleus ({approx}10{sup 19} cm).

  16. High brightness InP micropillars grown on silicon with Fermi level splitting larger than 1 eV.

    PubMed

    Tran, Thai-Truong D; Sun, Hao; Ng, Kar Wei; Ren, Fan; Li, Kun; Lu, Fanglu; Yablonovitch, Eli; Chang-Hasnain, Constance J

    2014-06-11

    The growth of III-V nanowires on silicon is a promising approach for low-cost, large-scale III-V photovoltaics. However, performances of III-V nanowire solar cells have not yet been as good as their bulk counterparts, as nanostructured light absorbers are fundamentally challenged by enhanced minority carriers surface recombination rates. The resulting nonradiative losses lead to significant reductions in the external spontaneous emission quantum yield, which, in turn, manifest as penalties in the open-circuit voltage. In this work, calibrated photoluminescence measurements are utilized to construct equivalent voltage-current characteristics relating illumination intensities to Fermi level splitting ΔF inside InP microillars. Under 1 sun, we show that splitting can exceed ΔF ∼ 0.90 eV in undoped pillars. This value can be increased to values of ΔF ∼ 0.95 eV by cleaning pillar surfaces in acidic etchants. Pillars with nanotextured surfaces can yield splitting of ΔF ∼ 0.90 eV, even though they exhibit high densities of stacking faults. Finally, by introducing n-dopants, ΔF of 1.07 eV can be achieved due to a wider bandgap energy in n-doped wurzite InP, the higher brightness of doped materials, and the extraordinarily low surface recombination velocity of InP. This is the highest reported value for InP materials grown on a silicon substrate. These results provide further evidence that InP micropillars on silicon could be a promising material for low-cost, large-scale solar cells with high efficiency. PMID:24841253

  17. Fermi LAT Detection of a Bright GeV Flare from the FSRQ PKS 1622-253

    NASA Astrophysics Data System (ADS)

    Carpenter, Bryce; Ojha, Roopesh

    2013-10-01

    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 1622-253 (RA=16h25m46.8916s, Dec=-25d27m38.326s, J2000; Beasley et al. 2002, ApJS, 141, 13) at z= 0.786 (di Serego Alighieri et al. 1994, MNRAS, 269, 998).

  18. The mystery of spectral breaks: Lyman continuum absorption by photon-photon pair production in the Fermi GeV spectra of bright blazars

    SciTech Connect

    Stern, Boris E.; Poutanen, Juri E-mail: juri.poutanen@utu.fi

    2014-10-10

    We re-analyze Fermi/LAT γ-ray spectra of bright blazars using the new Pass 7 version of the detector response files and detect breaks at ∼5 GeV in the rest-frame spectra of 3C 454.3 and possibly also 4C +21.35, associated with the photon-photon pair production absorption by the He II Lyman continuum (LyC). We also detect significant breaks at ∼20 GeV associated with hydrogen LyC in both the individual spectra and the stacked redshift-corrected spectrum of several bright blazars. The detected breaks in the stacked spectra univocally prove that they are associated with atomic ultraviolet emission features of the quasar broad-line region (BLR). The dominance of the absorption by the hydrogen Ly complex over He II, a small detected optical depth, and break energy consistent with head-on collisions with LyC photons imply that the γ-ray emission site is located within the BLR, but most of the BLR emission comes from a flat disk-like structure producing little opacity. Alternatively, the LyC emission region size might be larger than the BLR size measured from reverberation mapping, and/or the γ-ray emitting region is extended. These solutions would resolve the long-standing issue of how the multi-hundred GeV photons can escape from the emission zone without being absorbed by softer photons.

  19. Late-time cosmological phase transitions

    NASA Technical Reports Server (NTRS)

    Schramm, David N.

    1991-01-01

    It is shown that the potential galaxy formation and large scale structure problems of objects existing at high redshifts (Z approx. greater than 5), structures existing on scales of 100 M pc as well as velocity flows on such scales, and minimal microwave anisotropies ((Delta)T/T) (approx. less than 10(exp -5)) can be solved if the seeds needed to generate structure form in a vacuum phase transition after decoupling. It is argued that the basic physics of such a phase transition is no more exotic than that utilized in the more traditional GUT scale phase transitions, and that, just as in the GUT case, significant random Gaussian fluctuations and/or topological defects can form. Scale lengths of approx. 100 M pc for large scale structure as well as approx. 1 M pc for galaxy formation occur naturally. Possible support for new physics that might be associated with such a late-time transition comes from the preliminary results of the SAGE solar neutrino experiment, implying neutrino flavor mixing with values similar to those required for a late-time transition. It is also noted that a see-saw model for the neutrino masses might also imply a tau neutrino mass that is an ideal hot dark matter candidate. However, in general either hot or cold dark matter can be consistent with a late-time transition.

  20. Late-time cosmological phase transitions

    SciTech Connect

    Schramm, D.N. Fermi National Accelerator Lab., Batavia, IL )

    1990-11-01

    It is shown that the potential galaxy formation and large-scale structure problems of objects existing at high redshifts (Z {approx gt} 5), structures existing on scales of 100M pc as well as velocity flows on such scales, and minimal microwave anisotropies ({Delta}T/T) {approx lt} 10{sup {minus}5} can be solved if the seeds needed to generate structure form in a vacuum phase transition after decoupling. It is argued that the basic physics of such a phase transition is no more exotic than that utilized in the more traditional GUT scale phase transitions, and that, just as in the GUT case, significant random gaussian fluctuations and/or topological defects can form. Scale lengths of {approximately}100M pc for large-scale structure as well as {approximately}1 M pc for galaxy formation occur naturally. Possible support for new physics that might be associated with such a late-time transition comes from the preliminary results of the SAGE solar neutrino experiment, implying neutrino flavor mixing with values similar to those required for a late-time transition. It is also noted that a see-saw model for the neutrino masses might also imply a tau neutrino mass that is an ideal hot dark matter candidate. However, in general either hot or cold dark matter can be consistent with a late-time transition. 47 refs., 2 figs.

  1. Impact vaporization: Late time phenomena from experiments

    NASA Technical Reports Server (NTRS)

    Schultz, P. H.; Gault, D. E.

    1987-01-01

    While simple airflow produced by the outward movement of the ejecta curtain can be scaled to large dimensions, the interaction between an impact-vaporized component and the ejecta curtain is more complicated. The goal of these experiments was to examine such interaction in a real system involving crater growth, ejection of material, two phased mixtures of gas and dust, and strong pressure gradients. The results will be complemented by theoretical studies at laboratory scales in order to separate the various parameters for planetary scale processes. These experiments prompt, however, the following conclusions that may have relevance at broader scales. First, under near vacuum or low atmospheric pressures, an expanding vapor cloud scours the surrounding surface in advance of arriving ejecta. Second, the effect of early-time vaporization is relatively unimportant at late-times. Third, the overpressure created within the crater cavity by significant vaporization results in increased cratering efficiency and larger aspect ratios.

  2. Unveiling Unidentified Fermi Sources

    NASA Astrophysics Data System (ADS)

    Zhang, Lizhong; South Pole Telescope

    2016-01-01

    The Fermi γ-ray Space Telescope (Fermi) has surveyed the entire sky at the highest-energy band of the electromagnetic spectrum. The majority of Fermi sources have counterpart identifications from multi-wavelength large-area surveys, particularly in the radio and x-ray bands. However, around 35% of Fermi sources remain unidentified, a problem exasperated by the low resolution of the telescope. Understanding the nature of unidentified Fermi sources is one of the most pressing problems in γ-ray astronomy. The South Pole Telescope (SPT) has completed a survey covering a 2500 square degrees of the southern extragalactic sky with arcminute resolution at millimeter wavelengths. The mm wavelength is the most efficient means to identify blazars and unidentified Fermi sources. Our analysis shows that the SPT point source catalog provides candidate associations for 40% of the unidentified Fermi sources, showing them to be flat-spectrum radio quasars which are extraordinarily bright at millimeter (mm) wavelengths.

  3. Late-time attractor for the cubic nonlinear wave equation

    SciTech Connect

    Szpak, Nikodem

    2010-08-15

    We apply our recently developed scaling technique for obtaining late-time asymptotics to the cubic nonlinear wave equation and explain the appearance and approach to the two-parameter attractor found recently by Bizon and Zenginoglu.

  4. Late-time Observations of GRB 080319B: Jet Break, Host Galaxy, and Accompanying Supernova

    NASA Astrophysics Data System (ADS)

    Tanvir, N. R.; Rol, E.; Levan, A. J.; Svensson, K.; Fruchter, A. S.; Granot, J.; O'Brien, P. T.; Wiersema, K.; Starling, R. L. C.; Jakobsson, P.; Fynbo, J.; Hjorth, J.; Curran, P. A.; van der Horst, A. J.; Kouveliotou, C.; Racusin, J. L.; Burrows, D. N.; Genet, F.

    2010-12-01

    The Swift-discovered GRB 080319B was by far the most distant source ever observed at naked-eye brightness, reaching a peak apparent magnitude of 5.3 at a redshift of z = 0.937. We present our late-time optical (Hubble Space Telescope, Gemini, and Very Large Telescope) and X-ray (Chandra) observations, which confirm that an achromatic break occurred in the power-law afterglow light curve at ~11 days post-burst. This most likely indicates that the gamma-ray burst (GRB) outflow was collimated, which for a uniform jet would imply a total energy in the jet E jet >~ 1052 erg. Our observations also show a late-time excess of red light, which is well explained if the GRB was accompanied by a supernova (SN), similar to those seen in some other long-duration GRBs. The latest observations are dominated by light from the host and show that the GRB took place in a faint dwarf galaxy (r(AB) ≈ 27.0, rest frame MB ≈ -17.2). This galaxy is small even by the standards of other GRB hosts, which is suggestive of a low-metallicity environment. Intriguingly, the properties of this extreme event—a small host and bright SN—are entirely typical of the very low luminosity bursts such as GRB 980425 and GRB 060218.

  5. LATE-TIME OBSERVATIONS OF GRB 080319B: JET BREAK, HOST GALAXY, AND ACCOMPANYING SUPERNOVA

    SciTech Connect

    Tanvir, N. R.; O'Brien, P. T.; Wiersema, K.; Starling, R. L. C.; Rol, E.; Levan, A. J.; Svensson, K.; Fruchter, A. S.; Granot, J.; Jakobsson, P.; Fynbo, J.; Hjorth, J.; Curran, P. A.; Burrows, D. N.; Genet, F.

    2010-12-10

    The Swift-discovered GRB 080319B was by far the most distant source ever observed at naked-eye brightness, reaching a peak apparent magnitude of 5.3 at a redshift of z = 0.937. We present our late-time optical (Hubble Space Telescope, Gemini, and Very Large Telescope) and X-ray (Chandra) observations, which confirm that an achromatic break occurred in the power-law afterglow light curve at {approx}11 days post-burst. This most likely indicates that the gamma-ray burst (GRB) outflow was collimated, which for a uniform jet would imply a total energy in the jet E{sub jet} {approx}> 10{sup 52} erg. Our observations also show a late-time excess of red light, which is well explained if the GRB was accompanied by a supernova (SN), similar to those seen in some other long-duration GRBs. The latest observations are dominated by light from the host and show that the GRB took place in a faint dwarf galaxy (r(AB) {approx} 27.0, rest frame M{sub B} {approx} -17.2). This galaxy is small even by the standards of other GRB hosts, which is suggestive of a low-metallicity environment. Intriguingly, the properties of this extreme event-a small host and bright SN-are entirely typical of the very low luminosity bursts such as GRB 980425 and GRB 060218.

  6. Bright gamma-ray flares of the quasars 3C 279 and PKS 1222+216 observed at the highest energies with Fermi-LAT and VERITAS

    NASA Astrophysics Data System (ADS)

    Errando, Manel

    2014-08-01

    Flat spectrum radio quasars (FSRQs) are the most powerful sources continuously detected at gamma-ray energies, with luminosities exceeding 1048 erg s-1. The high-energy emission of quasars peaks in the MeV-GeV band, and only a few episodic detections have been reported at very high energies (VHE, E>100 GeV). We will present the first results from an observing campaign on the FSRQ 3C 279 in April 2014 during the brightest gamma-ray outburst ever recorded for this object, with flux exceeding the historic 1991 flare seen by EGRET. Observations include simultaneous coverage with the Fermi-LAT satellite and the VERITAS ground-based array spanning four decades in energy from 100 MeV to 1 TeV with unprecedented sensitivity. We will also report on the detection of persistent VHE emission from the quasar PKS 1222+216 over a week-long period in March 2014. These observations present strong challenges to current models of energy dissipation in relativistic jets. The implications of the absence/presence of VHE emission in connection with flaring activity in the MeV-GeV regime will be discussed, especially concerning the role of ambient photon fields in the radiation mechanisms, and the size and location of the gamma-ray emission region.

  7. Late-Time Spectral Observations of Type IIP Supernovae

    NASA Astrophysics Data System (ADS)

    Silverman, Jeffrey M.; Pickett, Stephanie; Wheeler, J. Craig; Filippenko, Alexei

    2016-01-01

    Type II-Plateau supernovae (SNe IIP) are H-rich explosions that come from red supergiant (RSG) progenitors. Despite the fact that they are the most common subtype of SN, little work has been done on late-time observations of SNe IIP owing to their relative faintness at these epochs. We analyze 91 late-time (older than about 100 days past explosion) optical spectra of 38 SNe IIP, making this the largest sample of SN IIP nebular spectra ever studied. Quantitative criteria from the spectra themselves are employed to determine if an observation is truly nebular, and thus should be included in the study. We measure the fluxes, shapes, and velocities of various emission lines and investigate their temporal evolution. These values are also compared to photometric data in order to search for correlations that may allow us to gain insight into the RSG progenitors of SNe IIP and learn more about the details of the explosion itself.

  8. Late-time acceleration in higher dimensional cosmology

    SciTech Connect

    Pahwa, Isha; Choudhury, Debajyoti; Seshadri, T.R. E-mail: debajyoti.choudhury@gmail.com

    2011-09-01

    We investigate late time acceleration of the universe in higher dimensional cosmology. The content in the universe is assumed to exert pressure which is different in the normal and extra dimensions. Cosmologically viable solutions are found to exist for simple forms of the equation of state. The parameters of the model are fixed by comparing the predictions with supernovae data. While observations stipulate that the matter exerts almost vanishing pressure in the normal dimensions, we assume that, in the extra dimensions, the equation of state is of the form P∝ρ{sup 1−γ}. For appropriate choice of parameters, a late time acceleration in the universe occurs with q{sub 0} and z{sub tr} being approximately -0.46 and 0.76 respectively.

  9. Domain wall formation in late-time phase transitions

    NASA Technical Reports Server (NTRS)

    Kolb, Edward W.; Wang, Yun

    1992-01-01

    We examine domain wall formulation in late time phase transitions. We find that in the invisible axion domain wall phenomenon, thermal effects alone are insufficient to drive different parts of the disconnected vacuum manifold. This suggests that domain walls do not form unless either there is some supplemental (but perhaps not unreasonable) dynamics to localize the scalar field responsible for the phase transition to the low temperature maximum (to an extraordinary precision) before the onset of the phase transition, or there is some non-thermal mechanism to produce large fluctuations in the scalar field. The fact that domain wall production is not a robust prediction of late time transitions may suggest future directions in model building.

  10. Friedman—Robertson—Walker Models with Late-Time Acceleration

    NASA Astrophysics Data System (ADS)

    Abdussattar; Prajapati, S. R.

    2011-02-01

    In order to account for the observed cosmic acceleration, a modification of the ansatz for the variation of density in Friedman—Robertson—Walker (FRW) FRW models given by Islam is proposed. The modified ansatz leads to an equation of state which corresponds to that of a variable Chaplygin gas, which in the course of evolution reduces to that of a modified generalized Chaplygin gas (MGCG) and a Chaplygin gas (CG), exhibiting late-time acceleration.

  11. MAGIC UPPER LIMITS FOR TWO MILAGRO-DETECTED BRIGHT FERMI SOURCES IN THE REGION OF SNR G65.1+0.6

    SciTech Connect

    Aleksic, J.; Blanch, O.; Antonelli, L. A.; Bonnoli, G.; Antoranz, P.; Backes, M.; Barrio, J. A.; Bose, D.; Bastieri, D.; Gonzalez, J. Becerra; Berger, K.; Bednarek, W.; Berdyugin, A.; Bernardini, E.; Biland, A.; Boller, A.; Bock, R. K.; Tridon, D. Borla; Bordas, P.; Bosch-Ramon, V. E-mail: decea@ieec.uab.e

    2010-12-20

    We report on the observation of the region around supernova remnant G65.1+0.6 with the stand-alone MAGIC-I telescope. This region hosts the two bright GeV gamma-ray sources 1FGL J1954.3+2836 and 1FGL J1958.6+2845. They are identified as GeV pulsars and both have a possible counterpart detected at about 35 TeV by the Milagro observatory. MAGIC collected 25.5 hr of good quality data and found no significant emission in the range around 1 TeV. We therefore report differential flux upper limits, assuming the emission to be point-like ({<=}0.{sup 0}1) or within a radius of 0.{sup 0}3. In the point-like scenario, the flux limits around 1 TeV are at the level of 3% and 2% of the Crab Nebula flux for the two sources, respectively. This implies that the Milagro emission is either extended over a much larger area than our point-spread function or it must be peaked at energies beyond 1 TeV, resulting in a photon index harder than 2.2 in the TeV band.

  12. Late-Time UV Spectroscopic Signatures from Circumstellar Interaction in Type IIn Supernovae

    NASA Astrophysics Data System (ADS)

    Fox, Ori

    2013-10-01

    Type IIn supernovae {SNe IIn} are defined by their relatively narrow spectral features associated with a dense circumstellar medium {CSM} formed by the progenitor star. The nature of the progenitors and mass loss remains relatively unknown. Shock interaction with the dense CSM offers an important probe of the CSM characteristics, progenitor mass-loss history, and ultimately the progenitor itself. While most supernovae tend to be faint in the UV at late times {>200 days}, shock interaction and dust formation in the dense CSM often result in significant emission ranging from X-ray to radio for many years post-explosion. Here we propose HST/STIS observations of 4 relatively bright, nearby SNe IIn that reflect the diversity and significance of the subclass. The SNe 2005ip, 2006gy, 20009ip, and 2010jl are some of the most well-studied SNe IIn, and our team has already compiled a comprehensive set of multi-wavelength data that has resulted in numerous publications, but the UV remains largely unexplored. Recent observations indicate these SNe are still detectable. UV observations will {1} constrain the CSM characteristics, including geometry and composition, {2} confirm shock interaction as the heating source for late-time emission from warm dust, and {3} explore the possible presence of a scattered-light echo in SN 2006gy. Coinciding with Cycle 21's UV Initiative, this program offers new insights regarding both the progenitor and explosion characteristics of the SN IIn subclass.

  13. Hot Dust! Late-Time Infrared Emission From Supernovae

    NASA Astrophysics Data System (ADS)

    Fox, Ori; Skrutskie, M. F.; Chevalier, R. A.

    2010-01-01

    Supernovae light curves typically peak and fade in the course of several months. Some supernovae , however, exhibit late-time infrared emission that in some cases can last for several years. These supernovae tend to be of the Type IIn subclass, which is defined by narrow hydrogen and helium emission lines arising from a dense, pre-existing circumstellar medium excited by the supernova radiation. Such a late-time ``IR excess'' with respect to the optical blackbody counterpart typically indicates the presence of warm dust. The origin and heating mechanism of the dust is not, however, always well constrained. In this talk, I will explore several scenarios that explain the observed late-time emission. In particular, I will discuss the case of the Type IIn SN 2005ip, which has displayed an ``IR excess'' for over 3 years. The results allow us to interpret the progenitor system and better understand the late stages of stellar evolution. Much of the data used for this analysis were obtained with TripleSpec, a medium-resolution near-infrared spectrograph located at Apache Point Observatory, NM, and FanCam, a JHK imager located at Fan Mountain Observatory, just outside of Charlottesville, VA. These two instruments were designed, fabricated, built, and commissioned by our instrumentation group at the University of Virginia. I will also spend some time discussing these instruments. I would like to thank the following for financial support of this work throughout my graduate career: NASA GSRP, NSF AAG-0607737, Spitzer PID 50256, Achievement Reward for College Scientists (ARCS), and the Virginia Space Grant Consortium.

  14. The Late-time Afterglow of the Extremely Energetic Short Burst GRB 090510 Revisited

    NASA Technical Reports Server (NTRS)

    Guelbenzu, A. Nicuesa; Klose, S.; Kruehler, T.; Greiner, J.; Rossi, A.; Kann, D. A.; Olivares, F.; Rau, A.; Afonso, P. M. J.; Elliott, J.; Filgas, R.; Yoldas, A. Kuepcue; McBreen, S.; Nardini, M.; Schady, P.; Schmidl, S.; Sudilovsky, V.; Updike, A. C.; Yoldas, A.

    2012-01-01

    Context. The Swift discovery of the short burst GRB 090510 has raised considerable attention mainly because of two reasons: first, it had a bright optical afterglow, and second it is among the most energetic events detected so far within the entire GRB population (long plus short). The afterglow of GRB 090510 was observed with Swift/UVOT and Swift/XRT and evidence of a jet break around 1.5 ks after the burst has been reported in the literature, implying that after this break the optical and X-ray light curve should fade with the same decay slope. Aims. As noted by several authors, the post-break decay slope seen in the UVOT data is much shallower than the steep decay in the X-ray band, pointing to a (theoretically hard to understand) excess of optical flux at late times. We assess here the validity of this peculiar behavior. Methods. We reduced and analyzed new afterglow light-curve data obtained with the multichannel imager GROND. These additional g'r'i'z' data were then combined with the UVOT and XRT data to study the behavior of the afterglow at late times more stringently. Results. Based on the densely sampled data set obtained with GROND, we find that the optical afterglow of GRB 090510 did indeed enter a steep decay phase starting around 22 ks after the burst. During this time the GROND optical light curve is achromatic, and its slope is identical to the slope of the X-ray data. In combination with the UVOT data this implies that a second break must have occurred in the optical light curve around 22 ks post burst, which, however, has no obvious counterpart in the X-ray band, contradicting the interpretation that this could be another jet break. Conclusions. The GROND data provide the missing piece of evidence that the optical afterglow of GRB 090510 did follow a post-jet break evolution at late times. The break seen in the optical light curve around 22 ks in combination with its missing counterpart in the X-ray band could be due to the passage of the

  15. Late-time Constraints on the Fates of Supernova Impostors

    NASA Astrophysics Data System (ADS)

    Adams, Scott

    2016-01-01

    Transients showing circumstellar interactions, low luminosities and low expansion velocities are generally considered to be non-terminal outbursts. Two main classes of such transients are 'supernova impostors', whose progenitors are massive stars (>20 solar masses) and may be extra-galactic analogs of Eta Car's eruptions, and SN 2008S-like transients, which have lower-mass (~10 solar masses), dust-obscured progenitors. We present late-time Hubble and Spitzer Space Telescope observations of the archetypal 'supernova impostor', SN 1997bs, as well as the prototypes of the SN 2008S class of transients, SN 2008S and NGC 300 2008-OT1. All of these objects have faded below their progenitor luminosities in all bands for which comparisons are possible. We show that it is difficult to reconcile the late-time observations with models where surviving stars are obscured by either ejected shells or thick, dusty winds. Although some supernova impostors, such as SN 1954J, are clearly non-fatal, our results suggest that many of these weak stellar transients with circumstellar interactions may actually be low energy supernovae.

  16. Asphericity in supernova explosions from late-time spectroscopy.

    PubMed

    Maeda, Keiichi; Kawabata, Koji; Mazzali, Paolo A; Tanaka, Masaomi; Valenti, Stefano; Nomoto, Ken'ichi; Hattori, Takashi; Deng, Jinsong; Pian, Elena; Taubenberger, Stefan; Iye, Masanori; Matheson, Thomas; Filippenko, Alexei V; Aoki, Kentaro; Kosugi, George; Ohyama, Youichi; Sasaki, Toshiyuki; Takata, Tadafumi

    2008-02-29

    Core-collapse supernovae (CC-SNe) are the explosions that announce the death of massive stars. Some CC-SNe are linked to long-duration gamma-ray bursts (GRBs) and are highly aspherical. One important question is to what extent asphericity is common to all CC-SNe. Here we present late-time spectra for a number of CC-SNe from stripped-envelope stars and use them to explore any asphericity generated in the inner part of the exploding star, near the site of collapse. A range of oxygen emission-line profiles is observed, including a high incidence of double-peaked profiles, a distinct signature of an aspherical explosion. Our results suggest that all CC-SNe from stripped-envelope stars are aspherical explosions and that SNe accompanied by GRBs exhibit the highest degree of asphericity. PMID:18239091

  17. Late-time Spectral Observations of Type IIP Supernovae

    NASA Astrophysics Data System (ADS)

    Silverman, Jeffrey Michael; Pickett, Stephanie; Wheeler, J. Craig; Filippenko, Alex

    2015-08-01

    We analyse late-time (older than about 150 days past explosion) optical spectra of Type II-Plateau (IIP) supernovae (SNe), which are H-rich SNe that come from red supergiant (RSG) progenitors. The dataset includes over 100 spectra of about 50 objects, making this the largest sample of SN IIP nebular spectra ever investigated. Quantitative criteria from within the spectra themselves are employed to determine if an observation is truly nebular, and thus should be included in the study. We present the temporal evolution of the fluxes, shapes, and velocities of various emission lines. These measured values are also compared to photometric data in order to search for correlations that can allow us to gain insight into the diversity of RSG progenitors and learn more about the details of the explosion itself.

  18. Mode coupling mechanism for late-time Kerr tails

    NASA Astrophysics Data System (ADS)

    Burko, Lior M.; Khanna, Gaurav

    2014-03-01

    We consider the decay rate for scalar fields in Kerr spacetime. We consider pure initial multipoles l', and focus attention in the decay rate of the multipole l. We use an iterative method proposed by Gleiser, Price, and Pullin, and identify the mode coupling mechanism that gives rise to a decay rate formula recently proposed by Zenginoğlu, Khanna, and Burko through the iterations in powers of the square of the Kerr black hole's specific angular momentum. We also show that one may identify the dominant channel of mode excitation, and obtain approximate results for the mode of interest by studying the dominant channel. The results of the dominant channel approximation approach the full-mode results at late times, and their difference approaches zero quadratically in inverse time.

  19. Late time cosmic acceleration from natural infrared cutoff

    NASA Astrophysics Data System (ADS)

    Gorji, Mohammad Ali

    2016-09-01

    In this paper, inspired by the ultraviolet deformation of the Friedmann-Lemaître-Robertson-Walker geometry in loop quantum cosmology, we formulate an infrared-modified cosmological model. We obtain the associated deformed Friedmann and Raychaudhuri equations and we show that the late time cosmic acceleration can be addressed by the infrared corrections. As a particular example, we applied the setup to the case of matter dominated universe. This model has the same number of parameters as ΛCDM, but a dynamical dark energy generates in the matter dominated era at the late time. According to our model, as the universe expands, the energy density of the cold dark matter dilutes and when the Hubble parameter approaches to its minimum, the infrared effects dominate such that the effective equation of state parameter smoothly changes from weff = 0 to weff = - 2. Interestingly and nontrivially, the unstable de Sitter phase with weff = - 1 is corresponding to Ωm =Ωd = 0.5 and the universe crosses the phantom divide from the quintessence phase with weff > - 1 and Ωm >Ωd to the phantom phase with weff < - 1 and Ωm <Ωd which shows that the model is observationally viable. The results show that the universe finally ends up in a big rip singularity for a finite time proportional to the inverse of the minimum of the Hubble parameter. Moreover, we consider the dynamical stability of the model and we show that the universe starts from the matter dominated era at the past attractor with weff = 0 and ends up in a future attractor at the big rip with weff = - 2.

  20. LATE-TIME OPTICAL EMISSION FROM CORE-COLLAPSE SUPERNOVAE

    SciTech Connect

    Milisavljevic, Dan; Fesen, Robert A.; Chevalier, Roger A.; Kirshner, Robert P.; Challis, Peter; Turatto, Massimo

    2012-05-20

    Ground-based optical spectra and Hubble Space Telescope images of 10 core-collapse supernovae (CCSNe) obtained several years to decades after outburst are analyzed with the aim of understanding the general properties of their late-time emissions. New observations of SN 1957D, 1970G, 1980K, and 1993J are included as part of the study. Blueshifted line emissions in oxygen and/or hydrogen with conspicuous line substructure are a common and long-lasting phenomenon in the late-time spectra. Followed through multiple epochs, changes in the relative strengths and velocity widths of the emission lines are consistent with expectations for emissions produced by interaction between SN ejecta and the progenitor star's circumstellar material. The most distinct trend is an increase in the strength of [O III]/([O I]+[O II]) with age, and a decline in H{alpha}/([O I]+[O II]) which is broadly consistent with the view that the reverse shock has passed through the H envelope of the ejecta in many of these objects. We also present a spatially integrated spectrum of the young Galactic supernova remnant Cassiopeia A (Cas A). Similarities observed between the emission line profiles of the Almost-Equal-To 330 yr old Cas A remnant and decades old CCSNe suggest that observed emission line asymmetry in evolved CCSN spectra may be associated with dust in the ejecta, and that minor peak substructure typically interpreted as 'clumps' or 'blobs' of ejecta may instead be linked with large-scale rings of SN debris.

  1. Mode coupling mechanism for late-time Kerr tails

    NASA Astrophysics Data System (ADS)

    Burko, Lior M.; Khanna, Gaurav

    2014-02-01

    We consider the decay rate for scalar fields in Kerr spacetime. We consider pure initial (azimuthal) multipoles ℓ' with respect to the class that includes Boyer-Lindquist coordinates, and focus attention on the decay rate of the multipole ℓ. We use an iterative method proposed by Gleiser, Price, and Pullin, and identify the mode-coupling mechanism through the iterations in powers of the square of the Kerr black hole's specific angular momentum that gives rise to a decay rate formula recently proposed by Zenginoğlu, Khanna, and Burko. Modes ℓ may be excited through different channels, each leading to its own decay rate. The asymptotic decay rate of the mode ℓ is the slowest of the decay rate of the various channels. In some cases, more than one channel leads to the same decay rate, and then the amplitude of the mode is the sum of the amplitudes of the partial fields generated by the individual channels. We also show that one may identify the asymptotically dominant channel of mode excitations and obtain approximate results for the mode of interest by studying the dominant channel. The results of the dominant channel approximation approach the full-mode results at late times, and their difference approaches zero quadratically in inverse time.

  2. Swift and Fermi Observations of X-Ray Flares: The Case of Late Internal Shock

    NASA Technical Reports Server (NTRS)

    Troja, E.; Piro, L.; Vasileiou, V.; Omodei, N.; Burgess, J. M.; Cutini, S.; Connaughton, V.; McEnery, J. E.

    2015-01-01

    Simultaneous Swift and Fermi observations of gamma-ray bursts (GRBs) offer a unique broadband view of their afterglow emission, spanning more than 10 decades in energy. We present the sample of X-ray flares observed by both Swift and Fermi during the first three years of Fermi operations. While bright in the X-ray band, X-ray flares are often undetected at lower (optical), and higher (MeV to GeV) energies. We show that this disfavors synchrotron self-Compton processes as the origin of the observed X-ray emission. We compare the broadband properties of X-ray flares with the standard late internal shock model, and find that in this scenario, X-ray flares can be produced by a late-time relativistic (gamma greater than 50) outflow at radii R approximately 10(exp 13) - 10(exp 14) cm. This conclusion holds only if the variability timescale is significantly shorter than the observed flare duration, and implies that X-ray flares can directly probe the activity of the GRB central engine.

  3. Remembering Fermi

    SciTech Connect

    Cronin, James

    2005-03-30

    A combination of the discovery of nuclear fission and the circumstances of the 2nd World War brought Enrico Fermi to Chicago, where he led the team that produced the first controlled, self-sustained nuclear chain reaction. Following the war in 1945 Chancellor Hutchins, William Zachariasen, and Walter Bartky convinced Fermi to accept a professorship at the University of Chicago, where the Institute for Nuclear Studies was established. Fermi served as the leading figure in surely the greatest collection of scientists the world has ever seen. Fermi's tenure at Chicago was cut short by his death in 1954. My talk will concentrate on the years 1945-54. Examples of his research notebooks, his speeches, his teaching, and his correspondence will be discussed.

  4. Late-time Spectral Observations of the Strongly Interacting Type Ia Supernova PTF11kx

    NASA Astrophysics Data System (ADS)

    Silverman, Jeffrey M.; Nugent, Peter E.; Gal-Yam, Avishay; Sullivan, Mark; Howell, D. Andrew; Filippenko, Alexei V.; Pan, Yen-Chen; Cenko, S. Bradley; Hook, Isobel M.

    2013-08-01

    PTF11kx was a Type Ia supernova (SN Ia) that showed time-variable absorption features, including saturated Ca II H and K lines that weakened and eventually went into emission. The strength of the emission component of Hα gradually increased, implying that the SN was undergoing significant interaction with its circumstellar medium (CSM). These features, and many others, were blueshifted slightly and showed a P-Cygni profile, likely indicating that the CSM was directly related to, and probably previously ejected by, the progenitor system itself. These and other observations led Dilday et al. to conclude that PTF11kx came from a symbiotic nova progenitor like RS Oph. In this work we extend the spectral coverage of PTF11kx to 124-680 rest-frame days past maximum brightness. The late-time spectra of PTF11kx are dominated by Hα emission (with widths of full width at half-maximum intensity ≈2000 km s-1), strong Ca II emission features (~10,000 km s-1 wide), and a blue "quasi-continuum" due to many overlapping narrow lines of Fe II. Emission from oxygen, He I, and Balmer lines higher than Hα is weak or completely absent at all epochs, leading to large observed Hα/Hβ intensity ratios. The Hα emission appears to increase in strength with time for ~1 yr, but it subsequently decreases significantly along with the Ca II emission. Our latest spectrum also indicates the possibility of newly formed dust in the system as evidenced by a slight decrease in the red wing of Hα. During the same epochs, multiple narrow emission features from the CSM temporally vary in strength. The weakening of the Hα and Ca II emission at late times is possible evidence that the SN ejecta have overtaken the majority of the CSM and agrees with models of other strongly interacting SNe Ia. The varying narrow emission features, on the other hand, may indicate that the CSM is clumpy or consists of multiple thin shells.

  5. Late-time spectroscopy of SN 2002hh: a continued visible light echo with no shock interaction yet

    NASA Astrophysics Data System (ADS)

    Andrews, J. E.; Smith, Nathan; Mauerhan, Jon C.

    2015-08-01

    Supernova (SN) 2002hh was unusual among core-collapse SNe because it was highly reddened, and displayed a bright infrared (IR) excess due to radiatively heated dust in its circumstellar medium (CSM). Estimates for the mass of dust responsible for the IR echo suggested the presence of a massive shell within 0.26 pc of the star. For a velocity of 5000-10 000 km s-1, this material should be hit by the SN blast wave at late times, starting at roughly 12 years post-explosion. We have obtained deep late-time spectra with the Multiple Mirror Telescope (MMT) Blue Channel spectrograph to search for any spectral signatures of ongoing shock interaction. Interaction with a strength comparable to SN 1987A's collision with the equatorial ring would be detected in our data. However, in the spectra reported here, we do not detect clear signs of strong CSM interaction, contrary to expectations based on the reported radii of the dust shell. We do, however, detect emission associated with the old SN, and we find that the broad lines in the spectrum indicate a continuation of an ongoing reflected light echo, which appears similar to the spectrum at peak luminosity for this Type II-P event.

  6. The late time structure of high density contrast, single mode Richtmyer-Meshkov flow

    NASA Astrophysics Data System (ADS)

    Williams, R. J. R.

    2016-07-01

    We study the late time flow structure of Richtmyer-Meshkov instability. Recent numerical work [F. J. Cherne et al. "On shock driven jetting of liquid from non-sinusoidal surfaces into a vacuum," J. Appl. Phys. 118, 185901 (2015)] has suggested a self-similar collapse of the development of this instability at late times, independent of the initial surface profile. Using the form of collapse suggested, we derive an analytic expression for the mass-velocity relation in the spikes, and a global theory for the late time flow structure. We compare these results with fluid dynamical simulation.

  7. Fermi questions

    NASA Astrophysics Data System (ADS)

    Bouffard, Karen

    1999-05-01

    This column contains problems and solutions for the general category of questions known as "Fermi" questions. Forcing the students to use their ability to estimate, giving answers in terms of order-of-magnitude, is not only a challenge for a competition, but a teaching strategy to use in the classroom to develop self-confidence and the ability to analyze answers as to whether or not they make sense, as opposed to relying on the "precision" of a calculator value.

  8. A late-time flattening of light curves in gamma-ray burst afterglows

    SciTech Connect

    Sironi, Lorenzo; Giannios, Dimitrios E-mail: dgiannio@purdue.edu

    2013-12-01

    The afterglow emission from gamma-ray bursts (GRBs) is usually interpreted as synchrotron radiation from relativistic electrons accelerated at the GRB external shock. We investigate the temporal decay of the afterglow emission at late times, when the bulk of the shock-accelerated electrons are non-relativistic (the 'deep Newtonian phase', as denoted by Huang and Cheng). We assume that the electron spectrum in the deep Newtonian phase is a power-law distribution in momentum with slope p, as dictated by the theory of Fermi acceleration in non-relativistic shocks. For a uniform circumburst medium, the deep Newtonian phase begins at t{sub DN}∼3 ϵ{sub e,−1}{sup 5/6}t{sub ST}, where t {sub ST} marks the transition of the blast wave to the non-relativistic, spherically symmetric Sedov-Taylor (ST) solution, and ε {sub e} = 0.1 ε {sub e,–1} quantifies the amount of shock energy transferred to the electrons. For typical parameters, the deep Newtonian stage starts ∼0.5 to several years after the GRB. The radio flux in this phase decays as F {sub ν}∝t {sup –3(p+1)/10}∝t {sup –(0.9÷1.2)}, for a power-law slope 2 < p < 3. This is shallower than the scaling F {sub ν}∝t {sup –3(5p–7)/10}∝t {sup –(0.9÷2.4)} derived by Frail et al., which only applies if the GRB shock is non-relativistic, but the electron distribution still peaks at ultra-relativistic energies (a regime that is relevant for a narrow time interval, and only if t {sub DN} ≳ t {sub ST}, namely, ε {sub e} ≳ 0.03). We discuss how the deep Newtonian phase can be reliably used for GRB calorimetry, and we comment on the good detection prospects of trans-relativistic blast waves at 0.1÷10 GHz with the Karl G. Jansky Very Large Array and LOw-Frequency ARray.

  9. Open EFTs, IR effects & late-time resummations: systematic corrections in stochastic inflation

    NASA Astrophysics Data System (ADS)

    Burgess, C. P.; Holman, R.; Tasinato, G.

    2016-01-01

    Though simple inflationary models describe the CMB well, their corrections are often plagued by infrared effects that obstruct a reliable calculation of late-time behaviour. We adapt to cosmology tools designed to address similar issues in other physical systems with the goal of making reliable late-time inflationary predictions. The main such tool is Open EFTs which reduce in the inflationary case to Stochastic Inflation plus calculable corrections. We apply this to a simple inflationary model that is complicated enough to have dangerous IR behaviour yet simple enough to allow the inference of late-time behaviour. We find corrections to standard Stochastic Inflationary predictions for the noise and drift, and we find these corrections ensure the IR finiteness of both these quantities. The late-time probability distribution, {P}(φ ) , for super-Hubble field fluctuations are obtained as functions of the noise and drift and so these too are IR finite. We compare our results to other methods (such as large- N models) and find they agree when these models are reliable. In all cases we can explore in detail we find IR secular effects describe the slow accumulation of small perturbations to give a big effect: a significant distortion of the late-time probability distribution for the field. But the energy density associated with this is only of order H 4 at late times and so does not generate a dramatic gravitational back-reaction.

  10. Late time tails of the massive vector field in a black hole background

    SciTech Connect

    Konoplya, R. A.; Zhidenko, A.; Molina, C.

    2007-04-15

    We investigate the late-time behavior of the massive vector field in the background of the Schwarzschild and Schwarzschild-de Sitter black holes. For Schwarzschild black hole, at intermediately late times the massive vector field is represented by three functions with different decay law {psi}{sub 0}{approx}t{sup -(l+3/2)}sinmt, {psi}{sub 1}{approx}t{sup -(l+5/2)}sinmt, {psi}{sub 2}{approx}t{sup -(l+1/2)}sinmt, while at asymptotically late times the decay law {psi}{approx}t{sup -5/6}sin(mt) is universal and does not depend on the multipole number l. Together with a previous study of massive scalar and Dirac fields where the same asymptotically late-time decay law was found, it means that the asymptotically late-time decay law {approx}t{sup -5/6}sin(mt) does not depend also on the spin of the field under consideration. For Schwarzschild-de Sitter black holes it is observed in two different regimes in the late-time decay of perturbations: nonoscillatory exponential damping for small values of m and oscillatory quasinormal mode decay for high enough m. Numerical and analytical results are found for these quasinormal frequencies.

  11. Enrico Fermi

    NASA Astrophysics Data System (ADS)

    Yang, Chen Ning

    2013-05-01

    Enrico Fermi was, of all the great physicists of the 20th century, among the most respected and admired. He was respected and admired because of his contributions to both theoretical and experimental physics, because of his leadership in discovering for mankind a powerful new source of energy, and above all, because of his personal character. He was always reliable and trustworthy. He had both of his feet on the ground all the time. He had great strength, but never threw his weight around. He did not play to the gallery. He did not practise one-up-manship. He exemplified, I always believe, the perfect Confucian gentleman...

  12. Rainbow brightness.

    PubMed

    Gedzelman, S D

    1982-08-15

    A theory for the brightness of rainbows is presented. The light reaching the observer consists of a beam of singly scattered sunlight, originating from the directly illuminated portion of a rainswath, which, in turn, has suffered depletion by scattering or absorption in its path through the atmosphere. The model incorporates the relevant features of cloud geometry and solar position in relation to the observer appropriate to rainbows. The model helps explain why the bottom (or near-horizon portion) of the rainbow tends to be both brighter and redder than the top (or horizontal portion furthest above the ground) when the sun is near the horizon. The greater brightness of the bottom of the bow derives principally from the greater length of the directly illuminated part of the rainswath near the horizon, while the increased redness of the bow's bottom is due to the severe depletion of the short-wavelength contribution to the rainbow beam in its passage through the atmosphere. PMID:20396168

  13. Fermi LAT Stacking Analysis of Swift Localized GRBs

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Ajello, M.; Anderson, B.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bhat, P. N.; Bissaldi, E.; Bonino, R.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caragiulo, M.; Caraveo, P. A.; Cecchi, C.; Charles, E.; Chekhtman, A.; Chiang, J.; Chiaro, G.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; D’Ammando, F.; de Angelis, A.; de Palma, F.; Desiante, R.; Di Venere, L.; Drell, P. S.; Favuzzi, C.; Focke, W. B.; Franckowiak, A.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Giglietto, N.; Giordano, F.; Giroletti, M.; Godfrey, G.; Grenier, I. A.; Grove, J. E.; Guiriec, S.; Hewitt, J. W.; Hill, A. B.; Horan, D.; Jóhannesson, G.; Kocevski, D.; Kouveliotou, C.; Kuss, M.; Larsson, S.; Li, J.; Li, L.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Mayer, M.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Murgia, S.; Nemmen, R.; Nuss, E.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orienti, M.; Orlando, E.; Paneque, D.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Porter, T. A.; Racusin, J. L.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Schaal, M.; Schulz, A.; Sgrò, C.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Takahashi, H.; Thayer, J. B.; Tibaldo, L.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Vianello, G.; von Kienlin, A.; Werner, M.; Wood, K. S.

    2016-05-01

    We perform a comprehensive stacking analysis of data collected by the Fermi Large Area Telescope (LAT) of γ-ray bursts (GRBs) localized by the Swift spacecraft, which were not detected by the LAT but which fell within the instrument’s field of view at the time of trigger. We examine a total of 79 GRBs by comparing the observed counts over a range of time intervals to that expected from designated background orbits, as well as by using a joint likelihood technique to model the expected distribution of stacked counts. We find strong evidence for subthreshold emission at MeV to GeV energies using both techniques. This observed excess is detected during intervals that include and exceed the durations typically characterizing the prompt emission observed at keV energies and lasts at least 2700 s after the co-aligned burst trigger. By utilizing a novel cumulative likelihood analysis, we find that although a burst’s prompt γ-ray and afterglow X-ray flux both correlate with the strength of the subthreshold emission, the X-ray afterglow flux measured by Swift’s X-ray Telescope at 11 hr post trigger correlates far more significantly. Overall, the extended nature of the subthreshold emission and its connection to the burst’s afterglow brightness lend further support to the external forward shock origin of the late-time emission detected by the LAT. These results suggest that the extended high-energy emission observed by the LAT may be a relatively common feature but remains undetected in a majority of bursts owing to instrumental threshold effects.

  14. Superluminous Supernovae Powered by Magnetars: Late-time Light Curves and Hard Emission Leakage

    NASA Astrophysics Data System (ADS)

    Wang, S. Q.; Wang, L. J.; Dai, Z. G.; Wu, X. F.

    2015-01-01

    Recently, research performed by two groups has revealed that the magnetar spin-down energy injection model with full energy trapping can explain the early-time light curves of SN 2010gx, SN 2013dg, LSQ12dlf, SSS120810, and CSS121015 but fails to fit the late-time light curves of these superluminous supernovae (SLSNe). These results imply that the original magnetar-powered model is challenged in explaining these SLSNe. Our paper aims to simultaneously explain both the early- and late-time data/upper limits by considering the leakage of hard emissions. We incorporate quantitatively the leakage effect into the original magnetar-powered model and derive a new semianalytical equation. Comparing the light curves reproduced by our revised magnetar-powered model with the observed data and/or upper limits of these five SLSNe, we found that the late-time light curves reproduced by our semianalytical equation are in good agreement with the late-time observed data and/or upper limits of SN 2010gx, CSS121015, SN 2013dg, and LSQ12dlf and the late-time excess of SSS120810, indicating that the magnetar-powered model might be responsible for these SLSNe and that the gamma-ray and X-ray leakages are unavoidable when the hard photons were down-Comptonized to softer photons. To determine the details of the leakage effect and unveil the nature of SLSNe, more high-quality bolometric light curves and spectra of SLSNe are required.

  15. Primordial inhomogeneities in the expanding universe. II - General features of spherical models at late times

    NASA Technical Reports Server (NTRS)

    Olson, D. W.; Silk, J.

    1979-01-01

    This paper studies the density profile that forms around a spherically symmetric bound central core immersed in a homogeneous-background k = 0 or k = -1 Friedmann-Robertson-Walker cosmological model, with zero pressure. Although the density profile in the linearized regime is almost arbitrary, in the nonlinear regime certain universal features of the density profile are obtained that are independent of the details of the initial conditions. The formation of 'halos' ('holes') with densities greater than (less than) the average cosmological density is discussed. It is shown that in most regions 'halos' form, and universal values are obtained for the slope of the ln (density)-ln (radius) profile in those 'halos' at late times, independently of the shape of the initial density profile. Restrictions are derived on where it is possible for 'holes' to exist at late times and on how such 'holes' must have evolved.

  16. On the late-time behavior of tracer test breakthrough curves

    SciTech Connect

    HAGGERTY,ROY; MCKENNA,SEAN A.; MEIGS,LUCY C.

    2000-06-12

    The authors investigated the late-time (asymptotic) behavior of tracer test breakthrough curves (BTCs) with rate-limited mass transfer (e.g., in dual or multi-porosity systems) and found that the late-time concentration, c, is given by the simple expression: c = t{sub ad} (c{sub 0}g {minus} m{sub 0}{partial_derivative}g/{partial_derivative}t), for t >> t{sub ad} and t{sub a} >> t{sub ad} where t{sub ad} is the advection time, c{sub 0} is the initial concentration in the medium, m{sub 0} is the 0th moment of the injection pulse; and t{sub a} is the mean residence time in the immobile domain (i.e., the characteristic mass transfer time). The function g is proportional to the residence time distribution in the immobile domain, the authors tabulate g for many geometries, including several distributed (multirate) models of mass transfer. Using this expression they examine the behavior of late-time concentration for a number of mass transfer models. One key results is that if rate-limited mass transfer causes the BTC to behave as a power-law at late-time (i.e., c {approximately} t{sup {minus}k}), then the underlying density function of rate coefficients must also be a power-law with the form a{sup k{minus}}, as a {r_arrow}0. This is true for both density functions of first-order and diffusion rate coefficients. BTCs with k < 3 persisting to the end of the experiment indicate a mean residence time longer than the experiment and possibly infinite, and also suggest an effective rate coefficient that is either undefined or changes as a function of observation time. They apply their analysis to breakthrough curves from Single-Well Injection-Withdrawal tests at the Waste Isolation Pilot Plant, New Mexico.

  17. Viability of an arctan model of f (R ) gravity for late-time cosmology

    NASA Astrophysics Data System (ADS)

    Dutta, Koushik; Panda, Sukanta; Patel, Avani

    2016-07-01

    f (R ) modification of Einstein's gravity is an interesting possibility to explain the late-time acceleration of the Universe. In this work we explore the cosmological viability of one such f (R ) modification proposed by Kruglov [Phys. Rev. D 89, 064004 (2014)]. We show that the model violates fifth-force constraints. The model is also plagued with the issue of a curvature singularity in a spherically collapsing object, where the effective scalar field reaches the point of diverging scalar curvature.

  18. On the late-time cosmology of a condensed scalar field

    NASA Astrophysics Data System (ADS)

    Ghalee, Amir

    2016-04-01

    We study the late-time cosmology of a scalar field with a kinetic term non-minimally coupled to gravity. It is demonstrated that the scalar field dominate the radiation matter and the cold dark matter (CDM). Moreover, we show that eventually the scalar field will be condensed and results in an accelerated expansion. The metric perturbations around the condensed phase of the scalar field are investigated and it has been shown that the ghost instability and gradient instability do not exist.

  19. Electroosmotic fluid motion and late-time solute transport at non-negligible zeta potentials

    SciTech Connect

    S. K. Griffiths; R. H. Nilson

    1999-12-01

    Analytical and numerical methods are employed to determine the electric potential, fluid velocity and late-time solute distribution for electroosmotic flow in a tube and channel when the zeta potential is not small. The electric potential and fluid velocity are in general obtained by numerical means. In addition, new analytical solutions are presented for the velocity in a tube and channel in the extremes of large and small Debye layer thickness. The electroosmotic fluid velocity is used to analyze late-time transport of a neutral non-reacting solute. Zeroth and first-order solutions describing axial variation of the solute concentration are determined analytically. The resulting expressions contain eigenvalues representing the dispersion and skewness of the axial concentration profiles. These eigenvalues and the functions describing transverse variation of the concentration field are determined numerically using a shooting technique. Results are presented for both tube and channel geometries over a wide range of the normalized Debye layer thickness and zeta potential. Simple analytical approximations to the eigenvalues are also provided for the limiting cases of large and small values of the Debye layer thickness. The methodology developed here for electroosmotic flow is also applied to the Taylor problem of late-time transport and dispersion in pressure-driven flows.

  20. Indications of a late-time interaction in the dark sector.

    PubMed

    Salvatelli, Valentina; Said, Najla; Bruni, Marco; Melchiorri, Alessandro; Wands, David

    2014-10-31

    We show that a general late-time interaction between cold dark matter and vacuum energy is favored by current cosmological data sets. We characterize the strength of the coupling by a dimensionless parameter q(V) that is free to take different values in four redshift bins from the primordial epoch up to today. This interacting scenario is in agreement with measurements of cosmic microwave background temperature anisotropies from the Planck satellite, supernovae Ia from Union 2.1 and redshift space distortions from a number of surveys, as well as with combinations of these different data sets. Our analysis of the 4-bin interaction shows that a nonzero interaction is likely at late times. We then focus on the case q(V)≠0 in a single low-redshift bin, obtaining a nested one parameter extension of the standard ΛCDM model. We study the Bayesian evidence, with respect to ΛCDM, of this late-time interaction model, finding moderate evidence for an interaction starting at z=0.9, dependent upon the prior range chosen for the interaction strength parameter q(V). For this case the null interaction (q(V)=0, i.e., ΛCDM) is excluded at 99% C.L. PMID:25396358

  1. Late-time spectroscopy of envelope-stripped SNe: Figuring the central engine

    NASA Astrophysics Data System (ADS)

    Kawabata, Koji

    2011-01-01

    We propose to perform late-time spectroscopy of envelope-stripped core-collapse supernovae (SNe), i.e., Type Ib/c/IIb SNe. We aim to examine the explosion physics and its dependence on the progenitor mass. The key information is the asphericity and the chemical composition of the inner atmosphere, which can be explored by late-time observations. The difference in [O I] line profiles indicates that GRB-associated energetic SNe Ic (like SN 1998bw) and non-GRB energetic SNe Ic (2003jd) are intrinsically similar aspherical explosions that are differently viewed (pole-on for 1998bw and nearly edge-on for 2003jd). Our continuing study suggests that the asphericity is rather common characteristic even for normal energy SNe without a GRB. However, it is still unclear how the intermediate types of SNe (SNe Ib/IIb) are produced and how they connected with other types of core-collapse SNe. High-quality late-time spectra of SNe Ib/Ic/IIb are still lacking. We propose to obtain a larger number of nebular spectra of envelope-stripped SNe so that we examine the degree of the asphericity as a function of the progenitor’s mass, explosion energy, amount of synthesized ^56Ni, and the physical properties of the central remnant.

  2. Late-time spectroscopy of envelope-stripped SNe: Figuring the central engine

    NASA Astrophysics Data System (ADS)

    Kawabata, Koji

    2012-01-01

    We propose to perform late-time spectroscopy of envelope-stripped core-collapse supernovae (SNe), i.e., Type Ib/c/IIb SNe. We aim to examine the explosion physics and its dependence on the progenitor mass. The key information is the asphericity and the chemical composition of the inner atmosphere, which can be explored by late-time observations. The difference in [O I] line profiles indicates that GRB-associated energetic SNe Ic (like SN 1998bw) and non-GRB energetic SNe Ic (2003jd) are intrinsically similar aspherical explosions that are differently viewed (pole-on for 1998bw and nearly edge-on for 2003jd). Our continuing study suggests that the asphericity is rather common characteristic even for normal energy SNe without a GRB. However, it is still unclear how the intermediate types of SNe (SNe Ib/IIb) are produced and how they connected with other types of core-collapse SNe. High-quality late-time spectra of SNe Ib/Ic/IIb are still lacking. We propose to obtain a larger number of nebular spectra of envelope-stripped SNe including SNe IIb so that we examine the degree of the asphericity explosion energy, amount of synthesized ^56Ni and the physical properties of the central remnant as a function of the progenitor's mass.

  3. Fermi Pulsar Analysis

    NASA Video Gallery

    This animation illustrates how analysis of Fermi data reveals new pulsars. Fermi's LAT records the precise arrival time and approximate direction of the gamma rays it detects, but to identify a pul...

  4. Clues to the nature of SN 2009ip from photometric and spectroscopic evolution to late times

    SciTech Connect

    Graham, M. L.; Sand, D. J.; Valenti, S.; Howell, D. A.; Parrent, J.; Halford, M.; Zaritsky, D.; Bianco, F.; Rest, A.; Dilday, B.

    2014-06-01

    We present time series photometric and spectroscopic data for the transient SN 2009ip from the start of its outburst in 2012 September until 2013 November. These data were collected primarily with the new robotic capabilities of the Las Cumbres Observatory Global Telescope Network, a specialized facility for time domain astrophysics, and includes supporting high-resolution spectroscopy from the Southern Astrophysical Research Telescope, Kitt Peak National Observatory, and Gemini Observatory. Based on our nightly photometric monitoring, we interpret the strength and timing of fluctuations in the light curve as interactions between fast-moving ejecta and an inhomogeneous circumstellar material (CSM) produced by past eruptions of this massive luminous blue variable (LBV) star. Our time series of spectroscopy in 2012 reveals that, as the continuum and narrow Hα flux from CSM interactions declines, the broad component of Hα persists with supernova (SN)-like velocities that are not typically seen in LBVs or SN impostor events. At late times, we find that SN 2009ip continues to decline slowly, at ≲ 0.01 mag day{sup –1}, with small fluctuations in slope similar to Type IIn supernovae (SNe IIn) or SN impostors but no further LBV-like activity. The late-time spectrum features broad calcium lines similar to both late-time SNe and SN impostors. In general, we find that the photometric and spectroscopic evolution of SN 2009ip is more similar to SNe IIn than either continued eruptions of an LBV star or SN impostors but we cannot rule out a nonterminal explosion. In this context, we discuss the implications for episodic mass loss during the late stages of massive star evolution.

  5. Imprints of explosion conditions on late-time spectra of type Ia supernovae

    NASA Astrophysics Data System (ADS)

    Diamond, Tiara R.

    Type Ia supernovae (SNe Ia) play a vital role in the discrimination of different cosmological models. These events have been shown to be standardizable based on properties of their light curves during the early-time photospheric phase. However, the distribution of types of progenitor system, the explosion trigger, and the physics of the explosion are still an active topic of discussion. The details of the progenitors and explosion may provide insight into the variation seen in Type Ia supernova light curves and spectra, and therefore, allow for additional methods of standardization among the group. Late-time near-infrared spectral observations for SNe Ia show numerous strong emission features of forbidden line transitions of cobalt and iron, tracing the central distribution of iron-group burning products. As the spectrum ages, the cobalt features fade as expected from the decay of 56Co to 56Fe. This work will show that the strong and isolated [Fe II] emission line at 1.644 mum provides a unique tool to analyze near-infrared spectra of SNe Ia. Several new methods of analysis will be demonstrated to determine some of the initial conditions of the system. The initial central density, rhoc, and the extent of mixing in the central regions of the explosion have signatures in the line profiles of late-time spectra. An embedded magnetic field, B, of the white dwarf can be determined using the evolution of the lines profiles. Currently magnetic field effects are not included in the hydrodynamics and radiation transport of simulations of SNe Ia. Normalization of spectra to the 1.644 mum line allows separation of features produced by stable versus unstable isotopes of iron group elements. Implications for potential progenitor systems, explosion mechanisms, and the origins and morphology of magnetic fields in SNe Ia, in addition to limitations of the method, are discussed. Observations of the late-time near-infrared emission spectrum at multiple epochs allow for the first ever

  6. Prediction of Late-Time Concentration Tailing Through Characterization of Hydrofacies Distributions

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Benson, D. A.

    2006-12-01

    Anomalous (non-Fickian) diffusion is often manifested in extra mass in the late-time tail of the breakthrough curve (BTC). Current non-local techniques, including the multi-rate mass transfer method (MRMT) and the continuous time random walk (CTRW) method, are a posteriori fitting procedures that assign an appropriate memory function or a transition time distribution function to account for the trapping of solute particles in relatively immobile domains. The MRMT and CTRW are functionally equivalent, but the MRMT method allows a straightforward, a priori construction of the memory function based on readily available information about the statistics of the immobile zone geometry. We explore the quantitative relationship between the memory function and aquitard material heterogeneity using Monte Carlo simulations of the regional-scale alluvial aquifer system at the Lawrence Livermore National Laboratory site. Particle tracking simulations show that the shape of the late-time BTC depends on the thickness and the associated volume fractions of immobile water in "blocks" of fine-grained material. The ensemble solute concentration at later time can be very accurately predicted using a small number of exponential functions with rates dictated by aquitard thicknesses. Specifically, if the volume fraction of immobile layer thicknesses has a power-law probability distribution function (pdf), then a power-law BTC late tail will be guaranteed. When the volume fraction of immobile blocks has an exponential pdf, the late-time BTC will have a transition from power-law to exponential decay. The MRMT solutions are easily generated and accurately predict the later BTC tails. Since the residence time dictated by diffusive motion in the silt and clay layers embedded in typical natural media far exceeds the residence time in a laboratory column, we anticipate that upscaling from lab studies is irrelevant in most cases. The observed relationship between the BTC late tail and the

  7. Late time cosmological phase transitions 1: Particle physics models and cosmic evolution

    NASA Technical Reports Server (NTRS)

    Frieman, Joshua A.; Hill, Christopher T.; Watkins, Richard

    1991-01-01

    We described a natural particle physics basis for late-time phase transitions in the universe. Such a transition can seed the formation of large-scale structure while leaving a minimal imprint upon the microwave background anisotropy. The key ingredient is an ultra-light pseudo-Nambu-Goldstone boson with an astronomically large (O(kpc-Mpc)) Compton wavelength. We analyze the cosmological signatures of and constraints upon a wide class of scenarios which do not involve domain walls. In addition to seeding structure, coherent ultra-light bosons may also provide unclustered dark matter in a spatially flat universe, omega sub phi approx. = 1.

  8. The Fermi-GBM X-ray burst monitor

    NASA Astrophysics Data System (ADS)

    Linares, M.; Fermi GBM X-ray Burst Collaboration

    2010-12-01

    We discuss the first results of the Fermi-GBM all-sky search for X-ray bursts. The very large field of view and X-ray response of the Fermi-GBM make it a unique instrument to study rare, bright and short-lived X-ray bursts. We are performing a systematic search that exploits such capabilities. We present results on long/intermediate type I X-ray bursts, an unusual kind of thermonuclear bursts from accreting neutron stars, and show how Fermi-GBM is giving for the first time robust measurements of their recurrence time.

  9. Investigating SNe Ia progenitor diversity through late-time IR spectroscopy

    NASA Astrophysics Data System (ADS)

    Diamond, Tiara

    2016-01-01

    Late-time spectra of SNe Ia show numerous strong emission features of iron and cobalt throughout the NIR. As the spectrum ages, the cobalt features fade as is expected from the decay of 56Co to 56Fe. The strong 1.64 μm [Fe II] feature is sensitive to the central density of the white dwarf just prior to the thermonuclear runaway of C in the core because of electron capture in the early stages of burning, which increases as a function of density. The line profile is dependent on the extent of mixing during any deflagration burning in addition to asymmetries in the distribution of burning products or an off-center ignition. Normalization of a time-series of spectra to the 1.64 μm line allows separation of features produced by stable versus unstable isotopes of iron group elements. Evolution of the width of this feature probes the strength and morphology of magnetic fields in the expanding ejecta. Results of this technique are shown for SN 2005df, with observations spanning 200-400 days past the explosion. A sample of these late-time spectroscopic observations in the NIR of SNe Ia will provide insight into the natural variety of these objects, improving our understanding of the underlying physical processes and their usability in cosmology.

  10. Late-time cosmological evolution in f (R ) theories with ordinary and collisional matter

    NASA Astrophysics Data System (ADS)

    Oikonomou, V. K.; Karagiannakis, N.

    2015-04-01

    We study the late-time cosmological evolution of f(R) theories of modified gravity, with the matter content of the Universe being that of collisional self-interacting matter. We assume that the Universe is described by a flat Friedmann-Lemaitre-Robertson-Walker metric and that it is matter and dark energy dominated. The results of our numerical analysis for a collisional matter f(R) theory are compared with those resulting from pressureless matter f(R) theory and from the Λ CDM model. As we shall demonstrate, the resulting picture can vary from model to model, indicating that the effect of collisional matter in f(R) theories is strongly model dependent. In all studied cases, the effective equation of state parameter does not cross the phantom divide, both in the collisional matter and pressureless matter f(R) theories. Finally, we thoroughly study the effects of collisional matter on one of the f(R) models that is known to provide a unified description of early time inflation and late-time acceleration. The overall picture of the evolution of the Universe is not drastically affected, apart from the matter era, which is further enhanced with an additional matter energy contribution. However, a fully consistent description of the Universe’s evolution requires the introduction of a dark energy compensate in the total energy density, a concept very well known from the literature.

  11. Examining the Late Time Evolution of the Luminous Type IIn Supernova 2010jl

    NASA Astrophysics Data System (ADS)

    Jencson, Jacob; Prieto, J.; Stanek, K. Z.; Shappee, B.

    2014-01-01

    We present a sequence of 12 optical spectra of Supernova (SN) 2010jl obtained between a few and ~ 900 days following its discovery, as well as an epoch of late-time BVRI photometry. At a distance of ~ 50 Mpc, SN 2010jl is one of the nearest and brightest SNe in recent years, making it an excellent candidate for detailed study. The spectra are dominated by Balmer emission features, particularly Hα, which increase in strength significantly with time, suggesting interaction of the SN ejecta with dense, hydrogen-rich circumstellar material. Helium emission in the spectra show similar evolution. The development of the Ca II IR triplet and Fe II absorption at ~ 144 days indicate that the expanding outer shells of the SN ejecta have become optically thin, allowing us to see deeper into the core. At late times, the spectra begin to show a bluer continuum, but this may be due to contaminating light from the host galaxy. Combining these data with spectroscopic and photometric data already published in the literature, we estimate the optical spectral energy distribution of SN 2010jl as a function of time and construct a bolometric optical light curve. From this light curve we calculate the total energy radiated in optical light by SN 2010jl for approximately the first 800 days to be ~ 3.4×10^50 erg.

  12. Unifying inflation with late-time acceleration by a BIonic system

    NASA Astrophysics Data System (ADS)

    Sepehri, Alireza; Rahaman, Farook; Setare, Mohammad Reza; Pradhan, Anirudh; Capozziello, Salvatore; Sardar, Iftikar Hossain

    2015-07-01

    We propose a cosmological model that unifies inflation, deceleration and acceleration phases of expansion history by a BIonic system. At the beginning, there are k black fundamental strings that transited to the BIon configuration at a given corresponding point. Here, two coupled universes, brane and antibrane, are created interacting each other through a wormhole and inflate. With decreasing temperature, the energy of this wormhole flows into the universe branes and leads to inflation. After a short time, the wormhole evaporates, the inflation ends and a deceleration epoch starts. By approaching the brane and antibrane universes together, a tachyon is born, grows and causes the creation of a new wormhole. At this time, the brane and antibrane universes result connected again and the late-time acceleration era of the universe begins. We compare our model with previous unified phantom models and observational data obtaining some cosmological parameters like temperature in terms of time. We also find that deceleration parameter is negative during inflation and late-time acceleration epochs, while it is positive during the deceleration era. This means that the model is consistent, in principle, with cosmological observations.

  13. The late-time dynamics of the single-mode Rayleigh-Taylor instability

    NASA Astrophysics Data System (ADS)

    Ramaprabhu, P.; Dimonte, Guy; Woodward, P.; Fryer, C.; Rockefeller, G.; Muthuraman, K.; Lin, P.-H.; Jayaraj, J.

    2012-07-01

    We report on numerical simulations of the detailed evolution of the single mode Rayleigh-Taylor [Lord Rayleigh, Scientific Papers II (Cambridge University Press, Cambridge, 1900), p. 200; G. I. Taylor, "The instability of liquid surfaces when accelerated in a direction perpendicular to their plane," Proc. R. Soc. London, Ser. A 201, 192 (1950), 10.1098/rspa.1950.0052; S. Chandrasekhar, Hydrodynamic and Hydromagnetic Stability (Oxford University Press, Oxford, 1961)] instability to late times and high aspect ratios. In contrast to established potential flow models that predict a terminal velocity and a constant Froude number at low Atwood numbers, we observe a complex sequence of events that can be summarized in four stages: I. Exponential growth of imposed perturbations, II. Saturation to terminal velocity, III. Reacceleration to a higher Froude number, and IV. Chaotic mixing. The observed reacceleration away from the Froude number predicted by potential flow theory is attributed to the appearance of secondary Kelvin-Helmholtz structures, and described with a modification to the potential flow model proposed by Betti and Sanz [R. Betti and J. Sanz, "Bubble acceleration in the ablative Rayleigh-Taylor instability," Phys. Rev. Lett. 97, 205002 (2006), 10.1103/PhysRevLett.97.205002]. The secondary KH instability is in turn sensitive to several parameters, and can be suppressed at large Atwood numbers, as well as viscosity (physical or numerical), with the bubble/spike velocity in each case reverting to the potential flow value. Our simulations delineate the change in dynamics of the primary and secondary instabilities due to changes in these flow parameters. When the flow is allowed to evolve to late times, further instability is observed, resulting in chaotic mixing which is quantified here. The increased atomic mixing due to small-scale structures results in a dramatic drop in the late-time Froude number. Spike behavior resembles bubbles at low A, while for large A

  14. Late-time evolution of a self-interacting scalar field in the spacetime of a dilaton black hole

    SciTech Connect

    Moderski, Rafal; Rogatko, Marek

    2001-08-15

    We investigate the late-time tails of self-interacting (massive) scalar fields in the spacetime of a dilaton black hole. Following the no hair theorem we examine the mechanism by which self-interacting scalar hair decays. We reveal that the intermediate asymptotic behavior of the considered field perturbations is dominated by an oscillatory inverse power-law decaying tail. The numerical simulations show that at very late time, massive self-interacting scalar hair decays slower than any power law.

  15. Late-time evolution of charged gravitational collapse and decay of charged scalar hair. II

    NASA Astrophysics Data System (ADS)

    Hod, Shahar; Piran, Tsvi

    1998-07-01

    We study analytically the initial value problem for a charged massless scalar field on Reissner-Nordström space-time. Using the spectral decomposition technique we generalize the results of paper I for arbitrary charges. We show that the charged perturbations decay according to an inverse power-law behavior at future timelike infinity and along future null infinity. Along the future outer horizon we find an oscillatory inverse power-law relaxation of the charged fields. The charged dumping exponents decrease with the charge. The late-time charged tails are determined by multiple scattering of the field, a phenomena not found for neutral fields and in the weak electromagnetic interaction limit.

  16. Novel late time asymptotics: applications to anomalous transport in turbulent flows

    NASA Astrophysics Data System (ADS)

    Prasad Datta, Dhurjati

    2013-10-01

    New nonclassical self-similar intermediate asymptotics considered recently in the context of linear differential equations are shown to have interesting applications in offering a novel explanation of the origin of anomalous transport phenomena in turbulent flows in fluids and plasma devices. The intermediate asymptotics, in the late time or in the inviscid limit, conspire to produce smooth multifractal measures on a turbulent fluid medium leading naturally to generation of stretched Gaussian distributions for passive scalar tracer concentration from the turbulent, integral order, advection-diffusion equation. Such heavy-tailed stretched Gaussian distributions can explain the observed anomalous scaling of the average and mean square displacements of tracer particles in a turbulent medium.

  17. Late-time structure of the Bunch-Davies de Sitter wavefunction

    SciTech Connect

    Anninos, Dionysios; Anous, Tarek; Freedman, Daniel Z.; Konstantinidis, George

    2015-11-30

    We examine the late time behavior of the Bunch-Davies wavefunction for interacting light fields in a de Sitter background. We use perturbative techniques developed in the framework of AdS/CFT, and analytically continue to compute tree and loop level contributions to the Bunch-Davies wavefunction. We consider self-interacting scalars of general mass, but focus especially on the massless and conformally coupled cases. We show that certain contributions grow logarithmically in conformal time both at tree and loop level. We also consider gauge fields and gravitons. The four-dimensional Fefferman-Graham expansion of classical asymptotically de Sitter solutions is used to show that the wavefunction contains no logarithmic growth in the pure graviton sector at tree level. Finally, assuming a holographic relation between the wavefunction and the partition function of a conformal field theory, we interpret the logarithmic growths in the language of conformal field theory.

  18. Late-time particle emission from laser-produced graphite plasma

    SciTech Connect

    Harilal, S. S.; Hassanein, A.; Polek, M.

    2011-09-01

    We report a late-time ''fireworks-like'' particle emission from laser-produced graphite plasma during its evolution. Plasmas were produced using graphite targets excited with 1064 nm Nd: yttrium aluminum garnet (YAG) laser in vacuum. The time evolution of graphite plasma was investigated using fast gated imaging and visible emission spectroscopy. The emission dynamics of plasma is rapidly changing with time and the delayed firework-like emission from the graphite target followed a black-body curve. Our studies indicated that such firework-like emission is strongly depended on target material properties and explained due to material spallation caused by overheating the trapped gases through thermal diffusion along the layer structures of graphite.

  19. Late-time structure of the Bunch-Davies de Sitter wavefunction

    NASA Astrophysics Data System (ADS)

    Anninos, Dionysios; Anous, Tarek; Freedman, Daniel Z.; Konstantinidis, George

    2015-11-01

    We examine the late time behavior of the Bunch-Davies wavefunction for interacting light fields in a de Sitter background. We use perturbative techniques developed in the framework of AdS/CFT, and analytically continue to compute tree and loop level contributions to the Bunch-Davies wavefunction. We consider self-interacting scalars of general mass, but focus especially on the massless and conformally coupled cases. We show that certain contributions grow logarithmically in conformal time both at tree and loop level. We also consider gauge fields and gravitons. The four-dimensional Fefferman-Graham expansion of classical asymptotically de Sitter solutions is used to show that the wavefunction contains no logarithmic growth in the pure graviton sector at tree level. Finally, assuming a holographic relation between the wavefunction and the partition function of a conformal field theory, we interpret the logarithmic growths in the language of conformal field theory.

  20. Extracting the late-time kinetic Sunyaev-Zel'dovich effect

    NASA Astrophysics Data System (ADS)

    Munshi, D.; Iliev, I. T.; Dixon, K. L.; Coles, P.

    2016-08-01

    We propose a novel technique to separate the late-time, post-reionization component of the kinetic Sunyaev-Zeldovich (kSZ) effect from the contribution to it from a (poorly understood and probably patchy) reionization history. The kSZ effect is one of the most promising probe of the missing baryons in the Universe. We study the possibility of reconstructing it in three dimensions (3D), using future spectroscopic surveys such as the Euclid survey. By reconstructing a 3D template from galaxy density and peculiar velocity fields from spectroscopic surveys we cross-correlate the estimator against CMB maps. The resulting cross-correlation can help us to map out the kSZ contribution to CMB in 3D as a function of redshift thereby extending previous results which use tomographic reconstruction. This allows the separation of the late time effect from the contribution owing to reionization. By construction, it avoids contamination from foregrounds, primary CMB, tSZ effect as well as from star forming galaxies. Due to a high number density of galaxies the signal-to-noise (S/N) for such cross-correlational studies are higher, compared to the studies involving CMB power spectrum analysis. Using a spherical Bessel-Fourier (sFB) transform we introduce a pair of 3D power-spectra: {\\cal C}^{allel }_ell (k) and {\\cal C}^{perp }_ell (k) that can be used for this purpose. We find that in a future spectroscopic survey with near all-sky coverage and a survey depth of z ≈ 1, reconstruction of {\\cal C}^{perp }_ell (k) can be achieved in a few radial wave bands k≈ (0.01-0.5 h^{-1}Mpc) with a S/N of upto {\\cal O}(10) for angular harmonics in the range ℓ = (200 - 2000).

  1. LATE-TIME LIGHT CURVES OF TYPE II SUPERNOVAE: PHYSICAL PROPERTIES OF SUPERNOVAE AND THEIR ENVIRONMENT

    SciTech Connect

    Otsuka, Masaaki; Meixner, Margaret; Panagia, Nino; Fabbri, Joanna; Barlow, Michael J.; Wesson, Roger; Clayton, Geoffrey C.; Andrews, Jennifer E.; Gallagher, Joseph S.; Sugerman, Ben E. K.; Ercolano, Barbara; Welch, Douglas E-mail: otsuka@asiaa.sinica.edu.tw

    2012-01-01

    We present BVRIJHK-band photometry of six core-collapse supernovae, SNe 1999bw, 2002hh, 2003gd, 2004et, 2005cs, and 2006bc, measured at late epochs (>2 yr) based on the Hubble Space Telescope (HST), and the Gemini North, and WIYN telescopes. We also show the JHK light curves of supernova impostor SN 2008S up to day 575 because it was serendipitously in our SN 2002hh field of view. Of our 43 HST observations in total, 36 observations are successful in detecting the light from the SNe alone and measuring magnitudes of all the targets. HST observations show a resolved scattered light echo around SN 2003gd at day 1520 and around SN 2002hh at day 1717. Our Gemini and WIYN observations detected SNe 2002hh and 2004et as well. Combining our data with previously published data, we show VRIJHK-band light curves and estimate decline magnitude rates at each band in four different phases. Our prior work on these light curves and other data indicate that dust is forming in our targets from days {approx}300 to 400, supporting SN dust formation theory. In this paper we focus on other physical properties derived from late-time light curves. We estimate {sup 56}Ni masses for our targets (0.5-14 Multiplication-Sign 10{sup -2} M{sub Sun }) from the bolometric light curve of each of days {approx}150-300 using SN 1987A as a standard (7.5 Multiplication-Sign 10{sup -2} M{sub Sun }). The flattening or sometimes increasing fluxes in the late-time light curves of SNe 2002hh, 2003gd, 2004et, and 2006bc indicate the presence of light echoes. We estimate the circumstellar hydrogen density of the material causing the light echo and find that SN 2002hh is surrounded by relatively dense materials (n(H) >400 cm{sup -3}) and SNe 2003gd and 2004et have densities more typical of the interstellar medium ({approx}1 cm{sup -3}). We analyze the sample as a whole in the context of physical properties derived in prior work. The {sup 56}Ni mass appears well correlated with progenitor mass with a slope of 0

  2. Chandra and Swift Observations of Unidentified Fermi-LAT Objects

    NASA Astrophysics Data System (ADS)

    Donato, Davide; Cheung, T.; Gehrels, N.

    2010-03-01

    In the last year we targeted some of the unidentified Fermi-LAT objects (UFOs) at high Galactic latitude with Chandra and Swift in order to determine the basic properties (positions, fluxes, hardness ratios) of all X-ray sources within the Fermi-LAT localization circles. These satellites enable us to detect the X-ray conterparts with a flux limit that is at least an order of magnitude lower than achieved in extant RASS data and to further follow-up at other wavelengths, with the ultimate goal to reveal the nature of these enigmatic gamma-ray sources. Here we present the results obtained with 5 Chandra pointings of high Galactic latitude UFOs in the Fermi-LAT 3-months bright source list. The association of detected X-ray sources within the improved 11-months Fermi-LAT localization circles with available optical and radio observations is discussed.

  3. Imbibition in multiple continuum representations of fractured porous media: Early and late time behaviour

    NASA Astrophysics Data System (ADS)

    March Castaneda Neto, R.; Doster, F.; Geiger, S.

    2015-12-01

    Fractured porous media are notoriously challenging to model but of significant importance for many subsurface applications. In the common modelling approach A fractured geological formation is represented through distinct flow domains, the mobile fractures and the immobile matrix that provides additional storage for the fracture. The rate at which fluids exchange between the domains is represented by a transfer function. For imbibition during two-phase incompressible immiscible flow a simple first-order rate law can be formulated based on the saturation difference between the domains. While this is mathematically convenient it fails to capture the onset of imbibition at early times that is observed in simulations and experiments. Here we present an improved approach that captures the early time behaviour accurately by using semi-analytical self-similarity solutions for capillary driven flow. We also use this concept to predict the transitions from early to late-time-behaviour and construct a new hybrid transfer function. High resolution numerical simulations as well as experimental data are used to validate the results for different wetting and non-wetting phases viscosities and rock types that span a wide range of capillary diffusion coefficient for applications ranging from CO2 storage to oil recovery and beyond.

  4. Limits in late time conversion of cold dark matter into dark radiation

    NASA Astrophysics Data System (ADS)

    Boriero, D.; de Holanda, P. C.; Motta, M.

    2013-06-01

    Structure formation creates high temperature and density regions in the Universe that allow the conversion of matter into more stable states, with a corresponding emission of relativistic matter and radiation. An example of such a mechanism is the supernova event, that releases relativistic neutrinos corresponding to 99% of the binding energy of remnant neutron star. We take this phenomena as a starting point for an assumption that similar processes could occur in the dark sector, where structure formation would generate a late time conversion of cold dark matter into a relativistic form of dark matter. We performed a phenomenological study about the limits of this conversion, where we assumed a transition profile that is a generalized version of the neutrino production in supernovae events. With this assumption, we obtained an interesting modification for the constraint over the cold dark matter density. We show that when comparing with the standard ΛCDM cosmology, there is no preference for conversion, although the best fit is within 1σ from the standard model best fit. The methodology and the results obtained qualify this conversion hypothesis, from the large scale structure point of view, as a viable and interesting model to be tested in the future with small scale data, and mitigate discrepancies between observations at this scale and the pure cold dark matter model.

  5. Late time vortex dynamics for a coherent structure interacting with fine-scale turbulence

    NASA Astrophysics Data System (ADS)

    Stout, Eric; Hussain, Fazle

    2015-11-01

    The vortex dynamics of perturbations to a coherent vortex column with fine-scale turbulence induced axial flow are examined using direct numerical simulation. Turbulence forms into azimuthally oriented filaments, which naturally results in axial flow as the filaments self-advect. Axial flow (W) modifies vorticity generation in two ways: 1) the radial gradient of W causes radial perturbation vorticity to tilt into the axial direction; and 2) axial perturbation vorticity tilts mean azimuthal vorticity (the vortical equivalent of W) into the radial direction. Given the cycle of radial and axial perturbation vorticity generation, with the concomitant generation of azimuthal vorticity by the column's mean strain, this provides a physical explanation for instability due to axial flow (i.e. instability of the Batchelor or q-vortex, where q is the ratio of peak azimuthal to peak axial velocities). Via this interpretation, the role of non-axisymmetric azimuthal modes in q-vortex instability is explained. Vorticity generation due to axial flow is explored using a simplified perturbation consisting of two, antiparallel helical vortex threads encircling a vortex column, which results in late time vorticity generation and energy production.

  6. Late-time behaviour of the tilted Bianchi type VIh models

    NASA Astrophysics Data System (ADS)

    Hervik, S.; van den Hoogen, R. J.; Lim, W. C.; Coley, A. A.

    2007-08-01

    We study tilted perfect fluid cosmological models with a constant equation of state parameter in spatially homogeneous models of Bianchi type VIh using dynamical systems methods and numerical experimentation, with an emphasis on their future asymptotic evolution. We determine all of the equilibrium points of the type VIh state space (which correspond to exact self-similar solutions of the Einstein equations, some of which are new), and their stability is investigated. We find that there are vacuum plane-wave solutions that act as future attractors. In the parameter space, a 'loophole' is shown to exist in which there are no stable equilibrium points. We then show that a Hopf-bifurcation can occur resulting in a stable closed orbit (which we refer to as the Mussel attractor) corresponding to points both inside the loophole and points just outside the loophole; in the former case the closed curves act as late-time attractors while in the latter case these attracting curves will co-exist with attracting equilibrium points. In the special Bianchi type III case, centre manifold theory is required to determine the future attractors. Comprehensive numerical experiments are carried out to complement and confirm the analytical results presented. We note that the Bianchi type VIh case is of particular interest in that it contains many different subcases which exhibit many of the different possible future asymptotic behaviours of Bianchi cosmological models.

  7. Fermi at Six Months

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2009-01-01

    An overview of the Fermi Gamma-ray Space Telescope's first 6 months in operation is provided. The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy rage 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. It contains a Large Area Telescope capable of viewing the entire sky every 3 hours and a Gamma-ray Burst Monitor for viewing the entire unocculted sky. Since its launch on June 11, 2008 Fermi has provided information on pulsars, gamma ray bursts, relativistic jets, the active galactic nucleus, and a globular star cluster. This presentation describes Fermi's development, mission, instruments and recent findings.

  8. Fermi Galactic Center Zoom

    NASA Video Gallery

    This animation zooms into an image of the Milky Way, shown in visible light, and superimposes a gamma-ray map of the galactic center from NASA's Fermi. Raw data transitions to a view with all known...

  9. Fermi, Szilard and Trinity

    ERIC Educational Resources Information Center

    Anderson, Herbert L.

    1974-01-01

    The final installment of the author's recollections of his work with physicists Enrico Fermi, Leo Szilard and others in developing the first controlled nuclear chain reaction and in preparing the test explosion of the first atomic bomb. (GS)

  10. Thermonuclear supernovae: probing magnetic fields by positrons and late-time IR line profiles

    SciTech Connect

    Penney, R.; Hoeflich, P. E-mail: rpenney@g.clemson.edu

    2014-11-01

    We show the importance of γ and positron transport for the formation of late-time spectra in Type Ia supernovae (SNe Ia). The goal is to study the imprint of magnetic fields (B) on late-time IR line profiles, particularly the [Fe II] feature at 1.644 μm, which becomes prominent two to three months after the explosion. As a benchmark, we use the explosion of a Chandrasekhar mass (M {sub Ch}) white dwarf (WD) and, specifically, a delayed detonation model that can reproduce the light curves and spectra for a Branch-normal SN Ia. We assume WDs with initial magnetic surface fields between 1 and 10{sup 9} G. We discuss large-scale dipole and small-scale magnetic fields. We show that positron transport effects must be taken into account for the interpretation of emission features starting at about one to two years after maximum light, depending on the size of B. The [Fe II] line profile and its evolution with time can be understood in terms of the overall energy input by radioactive decay and the transition from a γ-ray to a positron-dominated regime. We find that the [Fe II] line at 1.644 μm can be used to analyze the overall chemical and density structure of the exploding WD up to day 200 without considering B. At later times, positron transport and magnetic field effects become important. After about day 300, the line profile allows one to probe the size of the B-field. The profile becomes sensitive to the morphology of B at about day 500. In the presence of a large-scale dipole field, a broad line is produced in M {sub Ch} mass explosions that may appear flat-topped or rounded depending on the inclination at which the SN is observed. Small or no directional dependence of the spectra is found for small-scale B. We note that narrow-line profiles require central {sup 56}Ni as shown in our previous studies. Persistent broad-line, flat-topped profiles require high-density burning, which is the signature of a WD close to M {sub Ch}. Good time coverage is required to

  11. Thermonuclear Supernovae: Probing Magnetic Fields by Positrons and Late-time IR Line Profiles

    NASA Astrophysics Data System (ADS)

    Penney, R.; Hoeflich, P.

    2014-11-01

    We show the importance of γ and positron transport for the formation of late-time spectra in Type Ia supernovae (SNe Ia). The goal is to study the imprint of magnetic fields (B) on late-time IR line profiles, particularly the [Fe II] feature at 1.644 μm, which becomes prominent two to three months after the explosion. As a benchmark, we use the explosion of a Chandrasekhar mass (M Ch) white dwarf (WD) and, specifically, a delayed detonation model that can reproduce the light curves and spectra for a Branch-normal SN Ia. We assume WDs with initial magnetic surface fields between 1 and 109 G. We discuss large-scale dipole and small-scale magnetic fields. We show that positron transport effects must be taken into account for the interpretation of emission features starting at about one to two years after maximum light, depending on the size of B. The [Fe II] line profile and its evolution with time can be understood in terms of the overall energy input by radioactive decay and the transition from a γ-ray to a positron-dominated regime. We find that the [Fe II] line at 1.644 μm can be used to analyze the overall chemical and density structure of the exploding WD up to day 200 without considering B. At later times, positron transport and magnetic field effects become important. After about day 300, the line profile allows one to probe the size of the B-field. The profile becomes sensitive to the morphology of B at about day 500. In the presence of a large-scale dipole field, a broad line is produced in M Ch mass explosions that may appear flat-topped or rounded depending on the inclination at which the SN is observed. Small or no directional dependence of the spectra is found for small-scale B. We note that narrow-line profiles require central 56Ni as shown in our previous studies. Persistent broad-line, flat-topped profiles require high-density burning, which is the signature of a WD close to M Ch. Good time coverage is required to separate the effects of optical

  12. LATE-TIME RADIO EMISSION FROM X-RAY-SELECTED TIDAL DISRUPTION EVENTS

    SciTech Connect

    Bower, Geoffrey C.; Cenko, S. Bradley; Silverman, Jeffrey M.; Bloom, Joshua S.; Metzger, Brian D.

    2013-02-15

    We present new observations with the Karl G. Jansky Very Large Array of seven X-ray-selected tidal disruption events (TDEs). The radio observations were carried out between 9 and 22 years after the initial X-ray discovery, and thus probe the late-time formation of relativistic jets and jet interactions with the interstellar medium in these systems. We detect a compact radio source in the nucleus of the galaxy IC 3599 and a compact radio source that is a possible counterpart to RX J1420.4+5334. We find no radio counterparts for five other sources with flux density upper limits between 51 and 200 {mu}Jy (3{sigma}). If the detections truly represent late radio emission associated with a TDE, then our results suggest that a fraction, {approx}> 10%, of X-ray-detected TDEs are accompanied by relativistic jets. We explore several models for producing late radio emission, including interaction of the jet with gas in the circumnuclear environment (blast wave model), and emission from the core of the jet itself. Upper limits on the radio flux density from archival observations suggest that the jet formation may have been delayed for years after the TDE, possibly triggered by the accretion rate dropping below a critical threshold of {approx}10{sup -2}-10{sup -3} M-dot {sub Edd}. The non-detections are also consistent with this scenario; deeper radio observations can determine whether relativistic jets are present in these systems. The emission from RX J1420.4+5334 is also consistent with the predictions of the blast wave model; however, the radio emission from IC 3599 is substantially underluminous, and its spectral slope is too flat, relative to the blast wave model expectations. Future radio monitoring of IC 3599 and RX J1420.4+5334 will help to better constrain the nature of the jets in these systems.

  13. Late-time spectra and type Ia supernova models: New clues from the Hubble Space Telescope

    NASA Technical Reports Server (NTRS)

    Ruiz-Lapuente, P.; Kirshner, R. P.; Phillips, M. M.; Challis, P. M.; Schmidt, B. P.; Filippenko, A. V.; Wheeler, J. C.

    1995-01-01

    Calculated late-time spectra of two classical hydrodynamical models for Type Ia supernovae (deflagration model W7 of Nomoto, Thielemann, & Yokoi, and delayed detonation model DD4 of Woosley & Weaver) are compared with observations of SN 1992A and other spectroscopically normal SNe Ia. An important new piece of information is provided by observations done with the Hubble Space Telescope (HST) which cover the ultraviolet range at the nebular phase of a SN Ia: SN 1992A in NGC 1380. For the first time a picture of SN Ia emission from the ultraviolet through the optical is obtained at these phases. Predictions of the classical model (W7 and DD4) are compared with the observed spectrum of SN 1992A and with the optical spectra of SN 1989M in NGC 4579 and SN 1990N in NGC 4639 at similar epochs. The absolute B and V magnitudes of the models are also estimated at these late phases. Taken at face value the nebular spectra of these 'classical' models are more consistent with the long extragalactic distance scale, pointing to distances to NGC 4579 around 21 +/- 3 Mpc and a slightly larger distance, 22 +/- 3 Mpc, to NGC 4639, on the back side of the Virgo Cluster. However, the calculated Fe(+3) luminosity as predicted from the models exceeds the observed limit from the HST data of SN 1992A. Other differences in the ratios of the line intensities between calculated and observed spectra, show some disagreement with the observed spectra at the nebular phases. They may not be the best choice for spectroscopically normal SNe Ia, and their use as an independent calibration of the extragalactic distance scale should be viewed with caution.

  14. Late-time quadratic growth in single-mode Rayleigh-Taylor instability.

    PubMed

    Wei, Tie; Livescu, Daniel

    2012-10-01

    The growth of the two-dimensional single-mode Rayleigh-Taylor instability (RTI) at low Atwood number (A=0.04) is investigated using Direct Numerical Simulations. The main result of the paper is that, at long times and sufficiently high Reynolds numbers, the bubble acceleration becomes stationary, indicating mean quadratic growth. This is contrary to the general belief that single-mode Rayleigh-Taylor instability reaches a constant bubble velocity at long times. At unity Schmidt number, the development of the instability is strongly influenced by the perturbation Reynolds number, defined as Rep≡λsqrt[Agλ/(1+A)]/ν. Thus, the instability undergoes different growth stages at low and high Rep. A new stage, chaotic development, was found at sufficiently high Rep values, after the reacceleration stage. During the chaotic stage, the instability experiences seemingly random acceleration and deceleration phases, as a result of complex vortical motions, with strong dependence on the initial perturbation shape (i.e., wavelength, amplitude, and diffusion thickness). Nevertheless, our results show that the mean acceleration of the bubble front becomes constant at late times, with little influence from the initial shape of the interface. As Rep is lowered to small values, the later instability stages, chaotic development, reacceleration, potential flow growth, and even the exponential growth described by linear stability theory, are subsequently no longer reached. Therefore, the results suggest a minimum Reynolds number and a minimum development time necessary to achieve all stages of single-mode RTI development, requirements which were not satisfied in the previous studies of single-mode RTI. PMID:23214698

  15. Brightness of Moonlight.

    ERIC Educational Resources Information Center

    Garstang, R. H.

    1985-01-01

    Measurement of the brightness of moonlight by comparison with lamp-light from a low wattage light bulb is an elementary project in astronomy which illustrates scientific principles for the freshman level. Two methods used for the comparison (shadow brightness method and grease spot method) are explained, with suggestions and expected answers. (DH)

  16. Late-time Kerr tails: generic and non-generic initial data sets, 'up' modes, and superposition

    NASA Astrophysics Data System (ADS)

    Burko, Lior M.; Khanna, Gaurav

    2011-01-01

    Three interrelated questions concerning Kerr spacetime late-time scalar-field tails are considered numerically, specifically the evolutions of generic and non-generic initial data sets, the excitation of 'up' modes, and the resolution of an apparent paradox related to the superposition principle. We propose to generalize the Barack-Ori formula for the decay rate of any tail multipole given a generic initial data set, to the contribution of any initial multipole mode. Our proposal leads to a much simpler expression for the late-time power-law index. Specifically, we propose that the late-time decay rate of a kinematically allowed Yellm spherical harmonic multipole moment because of an initial Y_{\\ell ^{\\prime } m} multipole is independent of the azimuthal number m and is given by t-n, where n = ell' + ell + 1 for ell < ell' and n = ell' + ell + 3 for ell >= ell'. We also show explicitly that the angular symmetry group of a multipole does not determine its late-time decay rate.

  17. Late-time Near-infrared Observations of SN 2005df

    NASA Astrophysics Data System (ADS)

    Diamond, Tiara R.; Hoeflich, Peter; Gerardy, Christopher L.

    2015-06-01

    We present late-time near-infrared (NIR) spectral evolution, at 200-400 days, for the Type Ia supernova SN 2005df. The spectra show numerous strong emission features of [Co ii], [Co iii], and [Fe ii] throughout the 0.8-1.8 μm region. As the spectrum ages, the cobalt features fade as would be expected from the decay of 56Co to 56Fe. We show that the strong and isolated [Fe ii] emission line at 1.644 μ {m} provides a unique tool to analyze NIR spectra of SNe Ia. Normalization of spectra to this line allows the separation of features produced by stable versus unstable isotopes of iron group elements. We develop a new method of determining the initial central density, {ρ }c, and the magnetic field, B, of the white dwarf (WD) using the width of the 1.644 μ {m} line. The line width (LW) is sensitive because of electron capture in the early stages of burning, which increases as a function of density. The sensitivity of the LW to B increases with time, and the effects of the magnetic field shift toward later times with decreasing {ρ }c. Through comparison with spherical models, the initial central density for SN 2005df is measured as {ρ }c=0.9(+/- 0.2)× {10}9 {g} {{cm}}-3, which corresponds to a WD close to the Chandrasekhar mass, with {M}{WD}=1.31(+/- 0.03) {M}⊙ and systematic error less than 0.04 {M}⊙. This error estimate is based on spherical models. We discuss the potential uncertainties due to multi-dimensional effects, mixing, and rotation. The latter two effects would increase the estimate of the WD mass. Within {M}{Ch} explosions, however, the central density found for SN 2005df is very low for a H-accretor, possibly suggesting a helium star companion or a tidally disrupted WD companion. As an alternative, we suggest mixing of the central region. We find some support for high initial magnetic fields of strength {10}6 {G} for SN 2005df, however, 0 {G} cannot be ruled out because of noise in the spectra combined with low {ρ }c. We discuss our findings in

  18. UNDERSTANDING BLACK HOLE MASS ASSEMBLY VIA ACCRETION AND MERGERS AT LATE TIMES IN COSMOLOGICAL SIMULATIONS

    SciTech Connect

    Kulier, Andrea; Ostriker, Jeremiah P.; Lackner, Claire N.; Cen, Renyue; Natarajan, Priyamvada

    2015-02-01

    %. Quantifying the growth due to mergers at these late times, we calculate the total energy output and strain from gravitational waves emitted by merging SMBHs, and obtain a signal potentially detectable by pulsar timing arrays.

  19. LATE-TIME CIRCUMSTELLAR INTERACTION IN A SPITZER SELECTED SAMPLE OF TYPE IIn SUPERNOVAE

    SciTech Connect

    Fox, Ori D.; Filippenko, Alexei V.; Silverman, Jeffrey M.; Ganeshalingam, Mohan; Cenko, S. Bradley; Clubb, Kelsey I.; Skrutskie, Michael F.

    2013-07-01

    Type IIn supernovae (SNe IIn) are a rare (<10%) subclass of core-collapse SNe that exhibit relatively narrow emission lines from a dense, pre-existing circumstellar medium (CSM). In 2009, a warm Spitzer Space Telescope survey observed 30 SNe IIn discovered in 2003-2008 and detected 10 SNe at distances out to 175 Mpc with unreported late-time infrared emission, in some cases more than 5 yr post-discovery. For this single epoch of data, the warm-dust parameters suggest the presence of a radiative heating source consisting of optical and X-ray emission continuously generated by ongoing CSM interaction. Here we present multi-wavelength follow-up observations of this sample of 10 SNe IIn and the well-studied Type IIn SN 2010jl. A recent epoch of Spitzer observations reveals ongoing mid-infrared emission from nine of the SNe in this sample. We also detect three of the SNe in archival Wide-field Infrared Survey Explorer data, in addition to SNe 1987A, 2004dj, and 2008iy. For at least five of the SNe in the sample, optical and/or X-ray emission confirms the presence of radiative emission from ongoing CSM interaction. The two Spitzer nondetections are consistent with the forward shock overrunning and destroying the dust shell, a result that places upper limits on the dust-shell size. The optical and infrared observations confirm the radiative heating model and constrain a number of model parameters, including progenitor mass-loss characteristics. All of the SNe in this sample experienced an outburst on the order of tens to hundreds of years prior to the SN explosion followed by periods of less intense mass loss. Although all evidence points to massive progenitors, the variation in the data highlights the diversity in SN IIn progenitor evolution. While these observations do not identify a particular progenitor system, they demonstrate that future, coordinated, multi-wavelength campaigns can constrain theoretical mass-loss models.

  20. Bright superior mirages

    NASA Astrophysics Data System (ADS)

    Lehn, Waldemar H.

    2003-01-01

    Superior mirages of unusual brightness are occasionally observed. Two such cases, photographed over the frozen surface of Lake Winnipeg, Canada, are documented. Visually, these mirages appear as featureless bright barriers far out on the lake. They are just images of the lake ice, yet the luminance in one case was 2.5 times (in the other, 1.7 times) the luminance of the ice surface in front of the mirage. The mirage itself can be modeled by means of a conduction inversion, but a proper explanation of the brightness is not yet available.

  1. FermiGrid

    SciTech Connect

    Yocum, D.R.; Berman, E.; Canal, P.; Chadwick, K.; Hesselroth, T.; Garzoglio, G.; Levshina, T.; Sergeev, V.; Sfiligoi, I.; Sharma, N.; Timm, S.; /Fermilab

    2007-05-01

    As one of the founding members of the Open Science Grid Consortium (OSG), Fermilab enables coherent access to its production resources through the Grid infrastructure system called FermiGrid. This system successfully provides for centrally managed grid services, opportunistic resource access, development of OSG Interfaces for Fermilab, and an interface to the Fermilab dCache system. FermiGrid supports virtual organizations (VOs) including high energy physics experiments (USCMS, MINOS, D0, CDF, ILC), astrophysics experiments (SDSS, Auger, DES), biology experiments (GADU, Nanohub) and educational activities.

  2. Star Light, Star Bright.

    ERIC Educational Resources Information Center

    Iadevaia, David G.

    1984-01-01

    Presents a technique for obtaining a rough measure of the brightness among different stars. Materials needed include a standard 35-mm camera, a plastic ruler, and a photo enlarger. Although a telescope can be used, it is not essential. (JN)

  3. More Fermi questions

    NASA Astrophysics Data System (ADS)

    Bouffard, Karen

    1999-09-01

    "Fermi" questions are a popular component of most Physics Olympics meets. Asking students to make a reasonable assumption about a problem and give answers in terms of order of magnitude is not only a great challenge for a competition, but is also a valued teaching strategy in the classroom.

  4. Fermi TGF detection map

    NASA Video Gallery

    Fermi’s Gamma-ray Burst Monitor detected 130 TGFs from August 2008 to the end of 2010. Thanks to instrument tweaks, the team has been able to improve the detection rate to several TGFs per week. ...

  5. Interaction quenches of Fermi gases

    SciTech Connect

    Uhrig, Goetz S.

    2009-12-15

    It is shown that the jump in the momentum distribution of Fermi gases evolves smoothly for small and intermediate times once an interaction between the fermions is suddenly switched on. The jump does not vanish abruptly. The loci in momentum space where the jumps occur are those of the noninteracting Fermi sea. No relaxation of the Fermi surface geometry takes place.

  6. Spitzer Detection of Late-Time (>100 d) Infrared Emission from Warm Dust in 9 Type IIn Supernovae

    NASA Astrophysics Data System (ADS)

    Fox, Ori D.; Chevalier, Roger A.; Skrutskie, Michael F.

    2010-06-01

    Warm Spitzer's Infrared Array Camera (IRAC) observed the locations of 59 Type IIn supernovae with distances <250 Mpc and discovery dates within the past ten years (PID 60122). Nine targets show evidence for late-time mid-infrared emission. The supernovae, coordinates, epochs of observation, and fluxes in IRAC bands 1 & 2 (3.6 & 4.5 microns, respectively) are listed below. The detections suggest the presence of circumstellar dust and we encourage multi-wavelength follow-up observations.

  7. Unifying phantom inflation with late-time acceleration: scalar phantom-non-phantom transition model and generalized holographic dark energy

    NASA Astrophysics Data System (ADS)

    Nojiri, Shin'ichi; Odintsov, Sergei D.

    2006-08-01

    The unifying approach to early-time and late-time universe based on phantom cosmology is proposed. We consider gravity-scalar system which contains usual potential and scalar coupling function in front of kinetic term. As a result, the possibility of phantom-non-phantom transition appears in such a way that universe could have effectively phantom equation of state at early time as well as at late time. In fact, the oscillating universe may have several phantom and non-phantom phases. Role in each of two phase and can be absorbed into the redefinition of the scalar field. Right on the transition point, however, the factor cannot be absorbed into the redefinition and play the role to connect two phases smoothly. Holographic dark energy where infrared cutoff is identified with combination of FRW parameters: Hubble constant, particle and future horizons, cosmological constant and universe life-time (if finite). Depending on the specific choice of the model the number of interesting effects occur: the possibility to solve the coincidence problem, crossing of phantom divide and unification of early-time inflationary and late-time accelerating phantom universe. The bound for holographic entropy which decreases in phantom era is also discussed.

  8. Ultra wide band detection of on body concealed weapons using the out of plane polarized late time response

    NASA Astrophysics Data System (ADS)

    Harmer, Stuart; Andrews, David; Bowring, Nicholas; Rezgui, Nacer; Southgate, Matthew

    2009-09-01

    A method of detecting concealed handguns and knives, both on and off body, has been developed. The method utilizes aspect-independent natural, complex resonances (poles) excited by illuminating the target with frequency swept, ultrawide band microwaves in the range 0.5 - 18 GHz. These natural resonances manifest as a Late Time Response (LTR) that extends significantly (~ 5 ns) beyond the direct reflections from the human body (the Early Time Response) and are of the form of a superposition of exponentially decaying sinusoidal waveforms. Two handguns are examined, both on the human body and in isolation, by the established methodology of applying the Generalised-Pencil-Of-Function to the late time response data of the target. These poles allow the weapon to be effectively classified. Out of plane polarized (cross-polarized) scattered response is used here as this gives improved discrimination between the early and late time responses. Determination of the presence or absence of particular weapons concealed under clothing, on the human body, is demonstrated. A novel bow-tie slot antenna is described which has good pulse and frequency response over the range 0.3-1 GHz and which is suitable for excitation of the fundamental natural resonances.

  9. Bright patches on Ariel

    NASA Technical Reports Server (NTRS)

    1986-01-01

    Distinct bright patches are visible on Ariel, the brightest of Uranus' five largest satellites. Voyager 2 obtained this image Jan. 22, 1986, from a distance of 2.52 million kilometers (1.56 million miles). The clear-filter image, obtained with the narrow-angle camera, shows a resolution of 47 km (29 miles). Ariel is about 1,300 km (800 mi) in diameter. This image shows several distinct bright areas that reflect nearly 45 percent of the incident sunlight; on average, the satellite displays a reflectivity of about 25-30 percent. The bright areas are probably fresh water ice, perhaps excavated by impacts. The south pole of Ariel is slightly off center of the disk in this view. Voyager 2 will obtain its best views of the satellite on Jan. 24, at a closest-approach distance of 127,000 km (79,000 mi). The Voyager project is managed for NASA by the Jet Propulsion Laboratory.

  10. High Brightness Test Stand

    SciTech Connect

    Birx, D.L.; Caporaso, G.J.; Boyd, J.K.; Hawkins, S.A.; Poor, S.E.; Reginato, L.L.; Rogers, D. Jr.; Smith, M.W.

    1985-08-07

    The High Brightness Test Stand is a 2 MeV, less than or equal to 10 kA electron accelerator module. This accelerator module, designed as an upgrade prototype for the Advanced Test Accelerator (ATA), combines solid state nonlinear magnetic drives with state-of-the-art induction linac technology. The facility serves a dual role, as it not only provides a test bed for this new technology, but is used to develop high brightness electron optics. We will both further describe the accelerator, as well as present some of the preliminary electron optics measurements.

  11. THE FIRST FERMI-LAT GAMMA-RAY BURST CATALOG

    SciTech Connect

    Ackermann, M.; Ajello, M.; Asano, K.; Axelsson, M.; Baldini, L.; Ballet, J.; Bastieri, D.; Bechtol, K.; Bloom, E. D.; Bellazzini, R.; Bregeon, J.; Bhat, P. N.; Bissaldi, E.; Bonamente, E.; Bonnell, J.; Brandt, T. J.; Bouvier, A. E-mail: giacomov@slac.stanford.edu; and others

    2013-11-01

    In three years of observations since the beginning of nominal science operations in 2008 August, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope has observed high-energy (∼> 20 MeV) γ-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above ∼20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for the GRB analysis are provided. We summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared with emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.

  12. The First Fermi-LAT Gamma-Ray Burst Catalog

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Ajello, M.; Asano, K.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bhat, P. N.; Bissaldi, E.; Bloom, E. D.; Bonamente, E.; Bonnell, J.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Burgess, J. Michael; Buson, S.; Byrne, D.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cecchi, C.; Charles, E.; Chaves, R. C. G.; Chekhtman, A.; Chiang, J.; Chiaro, G.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Connaughton, V.; Conrad, J.; Cutini, S.; D'Ammando, F.; de Angelis, A.; de Palma, F.; Dermer, C. D.; Desiante, R.; Digel, S. W.; Dingus, B. L.; Di Venere, L.; Drell, P. S.; Drlica-Wagner, A.; Dubois, R.; Favuzzi, C.; Ferrara, E. C.; Fitzpatrick, G.; Foley, S.; Franckowiak, A.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Goldstein, A.; Granot, J.; Grenier, I. A.; Grove, J. E.; Gruber, D.; Guiriec, S.; Hadasch, D.; Hanabata, Y.; Hayashida, M.; Horan, D.; Hou, X.; Hughes, R. E.; Inoue, Y.; Jackson, M. S.; Jogler, T.; Jóhannesson, G.; Johnson, A. S.; Johnson, W. N.; Kamae, T.; Kataoka, J.; Kawano, T.; Kippen, R. M.; Knödlseder, J.; Kocevski, D.; Kouveliotou, C.; Kuss, M.; Lande, J.; Larsson, S.; Latronico, L.; Lee, S.-H.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Massaro, F.; Mayer, M.; Mazziotta, M. N.; McBreen, S.; McEnery, J. E.; McGlynn, S.; Michelson, P. F.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Moretti, E.; Morselli, A.; Murgia, S.; Nemmen, R.; Nuss, E.; Nymark, T.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orienti, M.; Orlando, E.; Paciesas, W. S.; Paneque, D.; Panetta, J. H.; Pelassa, V.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Porter, T. A.; Preece, R.; Racusin, J. L.; Rainò, S.; Rando, R.; Rau, A.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reposeur, T.; Ritz, S.; Romoli, C.; Roth, M.; Ryde, F.; Saz Parkinson, P. M.; Schalk, T. L.; Sgrò, C.; Siskind, E. J.; Sonbas, E.; Spandre, G.; Spinelli, P.; Suson, D. J.; Tajima, H.; Takahashi, H.; Takeuchi, Y.; Tanaka, Y.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tierney, D.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Tronconi, V.; Usher, T. L.; Vandenbroucke, J.; van der Horst, A. J.; Vasileiou, V.; Vianello, G.; Vitale, V.; von Kienlin, A.; Winer, B. L.; Wood, K. S.; Wood, M.; Xiong, S.; Yang, Z.

    2013-11-01

    In three years of observations since the beginning of nominal science operations in 2008 August, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope has observed high-energy (gsim 20 MeV) γ-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above ~20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for the GRB analysis are provided. We summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared with emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.

  13. The First FERMI-LAT Gamma-Ray Burst Catalog

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Asano, K.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bhat, P. N.; Bissaldi, E.; Bloom, E. D.; Bonamente, E.; Bonnell, J.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Burgess, J. Michael; Buson, S.; Byrne, D.; Caliandro, G. A.; Ferrara, E. C.; Gehrels, N.; Guiriec, S.; McEnery, J. E.; Nemmen, R.; Perkins, J. S.; Racusin, J. L.; Thompson, D. J.; Kouveliotou, C.

    2013-01-01

    In three years of observations since the beginning of nominal science operations in 2008 August, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope has observed high-energy great than (20 MeV) gamma-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above approximately 20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for the GRB analysis are provided. We summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared with emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.

  14. Bright Fireball Over Georgia

    NASA Video Gallery

    A camera in Cartersville, Ga., captured this view of a bright fireball over Georgia on the night of Mar. 7, 2012, at approx. 10:19:11 EST. The meteor was first recorded at an altitude of 51.5 miles...

  15. Brightness predictions for comets

    NASA Astrophysics Data System (ADS)

    Green, Daniel W. E.; Marsden, Brian G.; Morris, Charles S.

    2001-02-01

    Daniel W E Green, Brian G Marsden and Charles S Morris write with the aim of illuminating the issue of cometary light curves and brightness predictions, following the publication in this journal last October of the letter by John McFarland (2000).

  16. A Bright Shining Lesson

    ERIC Educational Resources Information Center

    Hurowitz, Amanda

    2010-01-01

    Sometimes students come up with crazy ideas. When this author first started teaching at Thomas Jefferson High School for Science and Technology in Virginia five years ago, she had a sophomore share such an idea with her. He wanted to put solar panels on the school's roof as a way to reduce the school's carbon footprint and set a bright clean…

  17. The Search for Type 1 X-ray Bursts with Fermi/GBM

    NASA Astrophysics Data System (ADS)

    Jenke, Peter; Linares, M.; Connaughton, V.; Camero-Arranz, A.; Finger, M. H.; WIlson-Hodge, C. A.; Van Der Horst, A.; Fermi GBM X-ray Burst Collaboration

    2012-01-01

    We discuss the first results of the Fermi-GBM all-sky search for X-ray bursts. The very large field of view and X-ray response of the Fermi-GBM make it a unique instrument to study rare, bright and short-lived X-ray bursts. We are performing a systematic search that exploits such capabilities. We present results on long/intermediate type I X-ray bursts, an unusual kind of thermonuclear bursts from accreting neutron stars, and show how Fermi-GBM is giving, for the first time, robust measurements of their recurrence time.

  18. Light Echoes and Late-Time Emissions of Type Ia Supernovae

    NASA Astrophysics Data System (ADS)

    Drozdov, Dina

    2016-05-01

    Type Ia supernovae have many applications in astronomy, yet with fundamental properties still not fully understood, new methods for investigating the environment of a supernova need to be developed. A light echo is produced from the scattering of light from a bright source and can be used to analyze the dust in the vicinity of the supernova and learn invaluable information about the source. These techniques can put constraints on explosion and progenitor models. Although light echo detections from Type Ia supernovae are rare, with only seven total extragalactic detections, this could be due to the lack of thorough late-epoch monitoring. Since key information is determined from even a single light echo detection, light echo searches should be undertaken in the future to supplement our understanding of supernovae. As part of our collaborative campaign for studying the emission of supernovae at late epochs, we have added two light echoes to a small sample size of Type Ia supernova light echo detections: SN 2009ig in NGC 1015 and a dual echo from SN 2007af in NGC 5584. Both echoes were observed with the Hubble Space Telescope and allow for the most detailed images of Type Ia supernova light echoes to date. Three filters (F555W, F814W, and F350LP) captured the echoes obtained with the Wide Field Camera 3, and since both host galaxies were imaged as part of the same observing program, these cases will be the best comparable light echo pairs. We also further investigate the light echoes from SN 2006X in NGC 4321 and SN 1998bu in NGC 3368 from Hubble Space Telescope archival images. Analyses performed on the images gives crucial insight into the dusty environment of the host galaxy and the surroundings of the supernova. The outer echo from SN 2007af was created from an interstellar dust sheet located ~800 pc in front of the supernova, while the inner echo could be from interstellar or circumstellar origin. A circumstellar light echo could imply a single degenerate

  19. Bright Streak on Amalthea

    NASA Technical Reports Server (NTRS)

    2000-01-01

    These two images of Jupiter's small, irregularly shaped moon Amalthea, obtained by the camera onboard NASA's Galileo spacecraft in August 1999(left) and November 1999 (right), form a 'stereo pair' that helps scientists determine this moon's shape and the topography of its surface features. Features as small as 3.8 kilometers (2.4 miles) across can be resolved in these images, making them among the highest-resolution images ever taken of Amalthea.

    The large impact crater visible in both images, near the right-hand edge of Amalthea's disk, is about 40 kilometers (about 29 miles) across; two ridges, tall enough to cast shadows, extend from the top of the crater in a V-shape reminiscent of a 'rabbit ears' television antenna. To the left of these ridges, in the top center portion of Amalthea's disk, is a second large impact crater similar in size to the first crater. To the left of this second crater is a linear 'streak' of relatively bright material about 50 kilometers (31 miles) long. In previous spacecraft images of Amalthea taken from other viewing directions, this bright feature was thought to be a small, round, bright 'spot' and was given the name Ida. These new images reveal for the first time that Ida is actually a long, linear 'streak.' This bright streak may represent material ejected during the formation of the adjacent impact crater, or it may just mark the crest of a local ridge. Other patches of relatively bright material can be seen elsewhere on Amalthea's disk, although none of these other bright spots has Ida's linear shape.

    In both images, sunlight is coming from the left and north is approximately up. Note that the north pole of Amalthea is missing in the right-hand image (it was cut off by the edge of the camera frame). The bright streak, Ida, is on the side of the moon that faces permanently away from Jupiter, and the crater near the right-hand edge of the disk is in the center of Amalthea's leading side (the side of the moon that 'leads

  20. Theoretical studies of rotation induced Fermi resonances in HOCl

    SciTech Connect

    Chen, R.; Guo, H.; Skokov, S.; Bowman, J.M.

    1999-10-01

    Theoretical investigations of rotation induced Fermi resonances in HOCl are carried out using several different quantum mechanical methods. Due to shape differences of the eigenfunctions, nearby vibrational levels may be energetically tuned to form Fermi (or anharmonic) resonances by varying rotational quantum numbers. Such rotation induced Fermi resonances have been observed experimentally in HOCl, for example, for bright states (3,2,0) and (4,0,0) by Abel {ital et al.} [J. Chem. Phys. {bold 104}, 3189 (1996) and {ital ibid}. {bold 106}, 3103 (1997)]. Using an {ital ab initio} potential, this work shows that the (3,2,0) state is significantly mixed with the (2,3,3) state near J=28 and K=4, and J=14 and K=3, while the (4,0,0) state forms a Fermi pair with (3,2,1) near J=43 and K=8. The wave functions of the Fermi pairs display significant deformation due to the mixing. Both the rotation induced degeneracy and coupling strength are found to be important. {copyright} {ital 1999 American Institute of Physics.}

  1. Detection of Broad Hα Emission Lines in the Late-time Spectra of a Hydrogen-poor Superluminous Supernova

    NASA Astrophysics Data System (ADS)

    Yan, Lin; Quimby, R.; Ofek, E.; Gal-Yam, A.; Mazzali, P.; Perley, D.; Vreeswijk, P. M.; Leloudas, G.; De Cia, A.; Masci, F.; Cenko, S. B.; Cao, Y.; Kulkarni, S. R.; Nugent, P. E.; Rebbapragada, Umaa D.; Woźniak, P. R.; Yaron, O.

    2015-12-01

    iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z = 0.3434, with a slow-evolving light curve and spectral features similar to SN2007bi. It rises in 83-148 days to reach a peak bolometric luminosity of ˜1.3 × 1044 erg s-1, then decays slowly at 0.015 mag day-1. The measured ejecta velocity is ˜ 13,000 km s-1. The inferred explosion characteristics, such as the ejecta mass (70-220 M⊙), and the total radiative and kinetic energy (Erad ˜ 1051 erg, Ekin ˜ 2 × 1053 erg), are typical of slow-evolving H-poor SLSN events. However, the late-time spectrum taken at +251 days (rest, post-peak) reveals a Balmer Hα emission feature with broad and narrow components, which has never been detected before among other H-poor SLSNe. The broad component has a velocity width of ˜4500 km s-1 and a ˜300 km s-1 blueward shift relative to the narrow component. We interpret this broad Hα emission with a luminosity of ˜2 × 1041 erg s-1 as resulting from the interaction between the supernova ejecta and a discrete H-rich shell, located at a distance of ˜4 × 1016 cm from the explosion site. This interaction causes the rest-frame r-band LC to brighten at late times. The fact that the late-time spectra are not completely absorbed by the shock-ionized H-shell implies that its Thomson scattering optical depth is likely ≤1, thus setting upper limits on the shell mass ≤30 M⊙. Of the existing models, a Pulsational Pair Instability supernova model can naturally explain the observed 30 M⊙ H-shell, ejected from a progenitor star with an initial mass of (95-150) M⊙ about 40 years ago. We estimate that at least ˜15% of all SLSNe-I may have late-time Balmer emission lines.

  2. GRB Studies with Fermi

    NASA Technical Reports Server (NTRS)

    Meegan, Charles A.

    2008-01-01

    This slide presentation reviews the studies of Gamma Ray Bursts (GRB) with the Fermi Gamma Ray Space Telescope. Included are pictures of the observatory, with illustrations of the Large Area Telescope (LAT), and the Gamma-ray Burst Monitor (GBM) including information about both their capabilities. Graphs showing the GBM count rate over time after the GBM trigger for three GRBs, preliminary charts showing the multiple detector light curves the spectroscopy of the main LAT peak and the spectral evolution of GRB 080916C Burst Temporally-extended LAT emission.

  3. Pulsar candidates towards Fermi unassociated sources

    NASA Astrophysics Data System (ADS)

    Frail, D. A.; Mooley, K. P.; Jagannathan, P.; Intema, H. T.

    2016-09-01

    We report on a search for steep spectrum radio sources within the 95 per cent confidence error ellipses of the Fermi unassociated sources from the Large Area Telescope (LAT). Using existing catalogues and the newly released Giant Metrewave Radio Telescope all-sky survey at 150 MHz, we identify compact radio sources that are bright at MHz frequencies but faint or absent at GHz frequencies. Such steep spectrum radio sources are rare and constitute a sample of pulsar candidates, selected independently of period, dispersion measure, interstellar scattering and orbital parameters. We find point-like, steep spectrum candidates towards 11 Fermi sources. Based on the gamma-ray/radio positional coincidence, the rarity of such radio sources, and the properties of the 3FGL sources themselves, we argue that many of these sources could be pulsars. They may have been missed by previous radio periodicity searches due to interstellar propagation effects or because they lie in an unusually tight binary. If this hypothesis is correct, then renewed gamma-ray and radio periodicity searches at the positions of the steep spectrum radio sources may reveal pulsations.

  4. Ther FERMI FEL project at TRIESTE

    SciTech Connect

    Walker, R.P.; Bulfone, D.; Cargnello, F.

    1995-12-31

    The goal of the FERMI project - Free Electron Radiation and Matching Instrumentation - is to construct a new user facility for FEL radiation beams covering a broad spectral range (2-250 {mu}m) to complement the high brightness VUV/Soft-Xray radiation available from the ELETTRA synchrotron radiation facility at Trieste. A unique feature of the project will be the possibility of carrying out {open_quote}pump-probe{close_quote} experiments using synchronized radiation beams from FERMI and ELETTRA on the same sample. The project was launched at a meeting with Italian FEL experts held in Trieste on the 18th November 1994, chaired by C. Rubbia, as a collaboration between Sincrotrone Trieste, ENEA (Frascati), INFN (Frascati) and the University of Naples (Department of Electronic Engineering). The facility will make use of an existing linac, that forms part of the ELETTRA injection system, and a hall into which the beam can be extracted. In addition, for the first phase of the project equipment will be used from the suspended INFN/ENEA {open_quote}SURF{close_quote} FEL experiment, including the undulator, beam transport magnets and optical cavity. In this first International FEL Conference report on the project, we summarize the main features of the project, concentrating in particular on the most recent activities, including: results of measurements of the linac beam in the FEL mode of operation, further studies of the electron beam transport system including possibilities for bunch length manipulations, and further numerical calculations of the FEL performance.

  5. THE FERMI GAMMA-RAY BURST MONITOR

    SciTech Connect

    Meegan, Charles; Lichti, Giselher; Bissaldi, Elisabetta; Diehl, Roland; Greiner, Jochen; Von Kienlin, Andreas; Steinle, Helmut; Bhat, P. N.; Briggs, Michael S.; Connaughton, Valerie; Paciesas, W. S.; Preece, Robert; Wilson, Robert B.; Fishman, Gerald; Kouveliotou, Chryssa; Van der Horst, Alexander J.; McBreen, Sheila

    2009-09-01

    The Gamma-Ray Burst Monitor (GBM) will significantly augment the science return from the Fermi Observatory in the study of gamma-ray bursts (GRBs). The primary objective of GBM is to extend the energy range over which bursts are observed downward from the energy range of the Large Area Telescope (LAT) on Fermi into the hard X-ray range where extensive previous data sets exist. A secondary objective is to compute burst locations onboard to allow re-orienting the spacecraft so that the LAT can observe delayed emission from bright bursts. GBM uses an array of 12 sodium iodide scintillators and two bismuth germanate scintillators to detect gamma rays from {approx}8 keV to {approx}40 MeV over the full unocculted sky. The onboard trigger threshold is {approx}0.7 photons cm{sup -2} s{sup -1} (50-300 keV, 1 s peak). GBM generates onboard triggers for {approx}250 GRBs per year.

  6. Complete cosmic scenario from inflation to late time acceleration: Nonequilibrium thermodynamics in the context of particle creation

    NASA Astrophysics Data System (ADS)

    Chakraborty, Subenoy; Saha, Subhajit

    2014-12-01

    The paper deals with the mechanism of particle creation in the framework of irreversible thermodynamics. The second order nonequilibrium thermodynamical prescription of Israel and Stewart has been presented with particle creation rate, treated as the dissipative effect. In the background of a flat Friedmann-Robertson-Walker (FRW) model, we assume the nonequilibrium thermodynamical process to be isentropic so that the entropy per particle does not change and consequently the dissipative pressure can be expressed linearly in terms of the particle creation rate. Here the dissipative pressure behaves as a dynamical variable having a nonlinear inhomogeneous evolution equation and the entropy flow vector satisfies the second law of thermodynamics. Further, using the Friedmann equations and by proper choice of the particle creation rate as a function of the Hubble parameter, it is possible to show (separately) a transition from the inflationary phase to the radiation era and also from the matter dominated era to late time acceleration. Also, in analogy to analytic continuation, it is possible to show a continuous cosmic evolution from inflation to late time acceleration by adjusting the parameters. It is found that in the de Sitter phase, the comoving entropy increases exponentially with time, keeping entropy per particle unchanged. Subsequently, the above cosmological scenarios have been described from a field theoretic point of view by introducing a scalar field having self-interacting potential. Finally, we make an attempt to show the cosmological phenomenon of particle creation as Hawking radiation, particularly during the inflationary era.

  7. Bright field illumination system

    NASA Technical Reports Server (NTRS)

    Huber, Edward D. (Inventor)

    1998-01-01

    A Bright Field Illumination system for inspecting a range of characteristically different kinds of defects, depressions, and ridges in a selected material surface. The system has an illumination source placed near a first focus of an elliptical reflector. In addition, a camera facing the inspected area is placed near the illumination source and the first focus. The second focus of the elliptical reflector is located at a distance approximately twice the elliptical reflector's distance above the inspected surface. The elliptical reflector directs the light from the source onto the inspected surface. Due to the shape of the elliptical reflector, light that is specularly reflected from the inspected surface is directed into the camera is which located at the position of the reflected second focus of the ellipse. This system creates a brightly lighted background field against which damage sites appear as high contrast dark objects which can be easily detected by a person or an automated inspection system. In addition, the Bright Field Illumination system and method can be used in combination with a vision inspection system providing for multiplexed illumination and data handling of multiple kinds of surface characteristics including abrupt and gradual surface variations and differences between measured characteristics of different kinds and prior instruments.

  8. Singular F(R) cosmology unifying early- and late-time acceleration with matter and radiation domination era

    NASA Astrophysics Data System (ADS)

    Odintsov, S. D.; Oikonomou, V. K.

    2016-06-01

    We present some cosmological models which unify the late- and early-time acceleration eras with the radiation and the matter domination era, and we realize the cosmological models by using the theoretical framework of F(R) gravity. Particularly, the first model unifies the late- and early-time acceleration with the matter domination era, and the second model unifies all the evolution eras of our Universe. The two models are described in the same way at early and late times, and only the intermediate stages of the evolution have some differences. Each cosmological model contains two Type IV singularities which are chosen to occur one at the end of the inflationary era and one at the end of the matter domination era. The cosmological models at early times are approximately identical to the R 2 inflation model, so these describe a slow-roll inflationary era which ends when the slow-roll parameters become of order one. The inflationary era is followed by the radiation era and after that the matter domination era follows, which lasts until the second Type IV singularity, and then the late-time acceleration era follows. The models have two appealing features: firstly they produce a nearly scale invariant power spectrum of primordial curvature perturbations and a scalar-to-tensor ratio which are compatible with the most recent observational data and secondly, it seems that the deceleration–acceleration transition is crucially affected by the presence of the second Type IV singularity which occurs at the end of the matter domination era. As we demonstrate, the Hubble horizon at early times shrinks, as expected for an initially accelerating Universe, then during the matter domination era, it expands and finally after the Type IV singularity, the Hubble horizon starts to shrink again, during the late-time acceleration era. Intriguingly enough, the deceleration–acceleration transition, occurs after the second Type IV singularity. In addition, we investigate which F

  9. Large Bright Ripples

    NASA Technical Reports Server (NTRS)

    2004-01-01

    3 February 2004 Wind is the chief agent of change on Mars today. Wind blows dust and it can move coarser sediment such as sand and silt. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows bright ripples or small dunes on the floors of troughs northeast of Isidis Planitia near 31.1oN, 244.6oW. The picture covers an area 3 km (1.9 mi) wide; sunlight illuminates the scene from the lower left.

  10. Large, Bright Wind Ripples

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-397, 20 June 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows large, relatively bright ripples of windblown sediment in the Sinus Sabaeus region south of Schiaparelli Basin. The surrounding substrate is thickly mantled by very dark material, possibly windblown silt that settled out of the atmosphere. The picture is located near 7.1oS, 343.7oW. Sunlight illuminates the scene from the left.

  11. Signatures of Explosion Asymmetry, Progenitor Density, and Magnetic Fields in Late-Time NIR Spectra of Type Ia SNe

    NASA Astrophysics Data System (ADS)

    Diamond, Tiara; Gerardy, C. L.; Hoeflich, P.

    2014-01-01

    We will present several new model-motivated observational techniques for measuring physical properties in Type Ia SN explosions. Late-time NIR spectra of thermonuclear SNe show numerous strong emission features of [Co II], [Co III] and [Fe II] throughout the 0.8-2.5 micron region. The strong 1.64 micron [Fe II] feature often exhibits a flattened core line profile. Interpreted as an emission hole due to high-density electron capture in the early stages of burning, the width of this feature is sensitive to the central density of the progenitor. The slopes of the red and blue wings of this feature are sensitive to asymmetries in the explosion. Evolution of the width of the line feature probes the strength of magnetic fields in the expanding ejecta. Ratios between different iron lines often show unusual flux ratios not seen in normal nebular spectra and may be indicative of nebular resonances or other non-LTE effects.

  12. Determination of late-time Gamma-Ray (60Co) sensitivity of single diffusion Lot 2N2222A transistors.

    SciTech Connect

    DePriest, Kendall Russell; Kajder, Karen C.; Peters, Curtis D.

    2008-08-01

    Sandia National Laboratories (SNL) has embarked on a program to develop a methodology to use damage relations techniques (alternative experimental facilities, modeling, and simulation) to understand the time-dependent effects in transistors (and integrated circuits) caused by neutron irradiations in the Sandia Pulse Reactor-III (SPR-III) facility. The development of these damage equivalence techniques is necessary since SPR-III was shutdown in late 2006. As part of this effort, the late time {gamma}-ray sensitivity of a single diffusion lot of 2N2222A transistors has been characterized using one of the {sup 60}Co irradiation cells at the SNL Gamma Irradiation Facility (GIF). This report summarizes the results of the experiments performed at the GIF.

  13. Searching for swept-up hydrogen and helium in the late-time spectra of 11 nearby Type Ia supernovae

    NASA Astrophysics Data System (ADS)

    Maguire, K.; Taubenberger, S.; Sullivan, M.; Mazzali, P. A.

    2016-04-01

    The direct detection of a stellar system that explodes as a Type Ia supernova (SN Ia) has not yet been successful. Various indirect methods have been used to investigate SN Ia progenitor systems but none have produced conclusive results. A prediction of single-degenerate models is that H- (or He-) rich material from the envelope of the companion star should be swept up by the SN ejecta in the explosion. Seven SNe Ia have been analysed to date looking for signs of H-rich material in their late-time spectra and none were detected. We present results from new late-time spectra of 11 SNe Ia obtained at the Very Large Telescope using XShooter and FORS2. We present the tentative detection of Hα emission for SN 2013ct, corresponding to ˜0.007 M⊙ of stripped/ablated companion star material (under the assumptions of the spectral modelling). This mass is significantly lower than expected for single-degenerate scenarios, suggesting that >0.1 M⊙ of H-rich is present but not observed. We do not detect Hα emission in the other 10 SNe Ia. This brings the total sample of normal SNe Ia with non-detections (<0.001-0.058 M⊙) of H-rich material to 17 events. The simplest explanation for these non-detections is that these objects did not result from the explosion of a CO white dwarf accreting matter from a H-rich companion star via Roche lobe overflow or symbiotic channels. However, further spectral modelling is needed to confirm this. We also find no evidence of He-emission features, but models with He-rich companion stars are not available to place mass limits.

  14. Lightness, brightness, and anchoring.

    PubMed

    Anderson, Barton L; Whitbread, Michael; de Silva, Chamila

    2014-01-01

    The majority of work in lightness perception has evaluated the perception of lightness using flat, matte, two-dimensional surfaces. In such contexts, the amount of light reaching the eye contains a conflated mixture of the illuminant and surface lightness. A fundamental puzzle of lightness perception is understanding how it is possible to experience achromatic surfaces as specific achromatic shades in the face of this ambiguity. It has been argued that the perception of lightness in such contexts implies that the visual system imposes an "anchoring rule" whereby a specific relative luminance (the highest) serves as a fixed point in the mapping of image luminance onto the lightness scale ("white"). We conducted a series of experiments to explicitly test this assertion in contexts where this mapping seemed most unlikely-namely, low-contrast images viewed in dim illumination. Our results provide evidence that the computational ambiguity in mapping luminance onto lightness is reflected in perceptual experience. The perception of the highest luminance in a two-dimensional Mondrian display varied monotonically with its brightness, ranging from midgray to white. Similar scaling occurred for the lowest luminance and, by implication, all other luminance values. We conclude that the conflation between brightness and lightness in two-dimensional Mondrian displays is reflected in perception and find no support for the claim that any specific relative luminance value acts as a fixed anchor point in this mapping function. PMID:25104828

  15. The synchro-Compton limit of the brightness temperature of nonstationary radio sources

    NASA Astrophysics Data System (ADS)

    Slysh, V. I.

    1992-06-01

    The brightness temperature of synchrotron emission from nonstationary radio sources during the cooling down by the inverse Compton effect is calculated. It is shown that brightness temperatures as high as 5 x 10 exp 15 K at 1 GHz are allowed during the first day after injection of relativistic electrons of sufficiently high energy. This is about four orders of magnitude higher than the canonical synchro-Compton limit introduced by Kellermann and Pauliny-Toth (1969) for stationary radio sources. A stationary situation with the in situ first-order Fermi acceleration will give a brightness temperature of about 10 exp 15 K at 1 GHz due to the compensation of the inverse Compton losses by particle acceleration. The high brightness temperature effect is most pronounced at low frequencies and is proposed as the explanation of the LF variability phenomenon. Strong high-energy emission is predicted during phases of high brightness temperature.

  16. Fermi gamma-ray "bubbles" from stochastic acceleration of electrons.

    PubMed

    Mertsch, Philipp; Sarkar, Subir

    2011-08-26

    Gamma-ray data from Fermi Large Area Telescope reveal a bilobular structure extending up to ∼50° above and below the Galactic Center. It has been argued that the gamma rays arise from hadronic interactions of high-energy cosmic rays which are advected out by a strong wind, or from inverse-Compton scattering of relativistic electrons accelerated at plasma shocks present in the bubbles. We explore the alternative possibility that the relativistic electrons are undergoing stochastic 2nd-order Fermi acceleration by plasma wave turbulence through the entire volume of the bubbles. The observed gamma-ray spectral shape is then explained naturally by the resulting hard electron spectrum modulated by inverse-Compton energy losses. Rather than a constant volume emissivity as in other models, we predict a nearly constant surface brightness, and reproduce the observed sharp edges of the bubbles. PMID:21929220

  17. The Statistical Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Maccone, C.

    In this paper is provided the statistical generalization of the Fermi paradox. The statistics of habitable planets may be based on a set of ten (and possibly more) astrobiological requirements first pointed out by Stephen H. Dole in his book Habitable planets for man (1964). The statistical generalization of the original and by now too simplistic Dole equation is provided by replacing a product of ten positive numbers by the product of ten positive random variables. This is denoted the SEH, an acronym standing for “Statistical Equation for Habitables”. The proof in this paper is based on the Central Limit Theorem (CLT) of Statistics, stating that the sum of any number of independent random variables, each of which may be ARBITRARILY distributed, approaches a Gaussian (i.e. normal) random variable (Lyapunov form of the CLT). It is then shown that: 1. The new random variable NHab, yielding the number of habitables (i.e. habitable planets) in the Galaxy, follows the log- normal distribution. By construction, the mean value of this log-normal distribution is the total number of habitable planets as given by the statistical Dole equation. 2. The ten (or more) astrobiological factors are now positive random variables. The probability distribution of each random variable may be arbitrary. The CLT in the so-called Lyapunov or Lindeberg forms (that both do not assume the factors to be identically distributed) allows for that. In other words, the CLT "translates" into the SEH by allowing an arbitrary probability distribution for each factor. This is both astrobiologically realistic and useful for any further investigations. 3. By applying the SEH it is shown that the (average) distance between any two nearby habitable planets in the Galaxy may be shown to be inversely proportional to the cubic root of NHab. This distance is denoted by new random variable D. The relevant probability density function is derived, which was named the "Maccone distribution" by Paul Davies in

  18. The First Fermi Gamma-ray Burst Monitor (GBM) Terrestrial Gamma-ray Flash (TGF) Catalog

    NASA Astrophysics Data System (ADS)

    Briggs, Michael; Connaughton, Valerie; Stanbro, Matthew; Zhang, Binbin; Bhat, Narayana; Fishman, Gerald; Roberts, Oliver; Fitzpatrick, Gerard; McBreen, Shelia; Grove, Eric; Chekhtman, Alexandre

    2015-04-01

    We present summary results from the first catalog of Terrestrial Gamma-ray Flashes (TGFs) detected with the Gamma-ray Burst Monitor (GBM) on the Fermi Space Telescope. The catalog reports parameters for over 2700 TGFs. Since the launch of Fermi in 2008 the TGF detection sensitivity of GBM has been improved several times, both in the flight software and in ground analysis. Starting in 2010 July individual photons were downloaded for portions of the orbits, enabling an off-line search that found weaker and shorter TGFs. Since 2012 November 26 this telemetry mode has been extended to continuous coverage. The TGF sample is reliable, with cosmic rays rejected using data both from Fermi GBM and from the Large Area Telescope on Fermi. The online catalog include times (UTC and solar), spacecraft geographic positions, durations, count intensities and Bayesian Block durations. The catalog includes separate tables for bright TGFs detected by the flight software and for Terrestrial Electron Beams (TEBs).

  19. High brightness electron accelerator

    DOEpatents

    Sheffield, Richard L.; Carlsten, Bruce E.; Young, Lloyd M.

    1994-01-01

    A compact high brightness linear accelerator is provided for use, e.g., in a free electron laser. The accelerator has a first plurality of acclerating cavities having end walls with four coupling slots for accelerating electrons to high velocities in the absence of quadrupole fields. A second plurality of cavities receives the high velocity electrons for further acceleration, where each of the second cavities has end walls with two coupling slots for acceleration in the absence of dipole fields. The accelerator also includes a first cavity with an extended length to provide for phase matching the electron beam along the accelerating cavities. A solenoid is provided about the photocathode that emits the electons, where the solenoid is configured to provide a substantially uniform magnetic field over the photocathode surface to minimize emittance of the electons as the electrons enter the first cavity.

  20. High brightness electron sources

    SciTech Connect

    Sheffield, R.L.

    1995-07-01

    High energy physics accelerators and free electron lasers put increased demands on the electron beam sources. This paper describes the present research on attaining intense bright electron beams using photoinjectors. Recent results from the experimental programs will be given. The performance advantages and difficulties presently faced by researchers will be discussed, and the following topics will be covered. Progress has been made in photocathode materials, both in lifetime and quantum efficiency. Cesium telluride has demonstrated significantly longer lifetimes than cesium antimonide at 10{sup {minus}8} torr. However, the laser system is more difficult because cesium telluride requires quadrupled YLF instead of the doubled YLF required for cesium antimonide. The difficulty in using photoinjectors is primarily the drive laser, in particular the amplitude stability. Finally, emittance measurements of photoinjector systems can be complicated by the non-thermal nature of the electron beam. An example of the difficulty in measuring beam emittance is given.

  1. Bright Dust Devil Tracks

    NASA Technical Reports Server (NTRS)

    2004-01-01

    9 June 2004 Martian dust devils sometimes disrupt thin coatings of surface dust to create dark streak patterns on the surface. However, not all dust devils make streaks, and not all dust devil streaks are dark. In Syria Planum, the streaks are lighter than the surrounding plains. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows an example from Syria near 8.8oS, 103.6oW. The thin coating of surface dust in this region is darker than the substrate beneath it. This is fairly unusual for Mars, because most dust is bright. This image covers an area about 3 km (1.9 mi) across and is illuminated by sunlight from the left/lower left.

  2. The fermi paradox is neither Fermi's nor a paradox.

    PubMed

    Gray, Robert H

    2015-03-01

    The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth--and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked "Where is everybody?"--apparently suggesting that we do not see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist or suggesting its absence is paradoxical. The claim "they are not here; therefore they do not exist" was first published by Michael Hart, claiming that interstellar travel and colonization of the Galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important, because the Fermi paradox is seen by some as an authoritative objection to searching for evidence of extraterrestrial intelligence--cited in the U.S. Congress as a reason for killing NASA's SETI program on one occasion. But evidence indicates that it misrepresents Fermi's views, misappropriates his authority, deprives the actual authors of credit, and is not a valid paradox. PMID:25719510

  3. Maximizing Brightness in Photoinjectors

    SciTech Connect

    Limborg-Deprey, C.; Tomizawa, H.; /JAERI-RIKEN, Hyogo

    2011-11-30

    If the laser pulse driving photoinjectors could be arbitrarily shaped, the emittance growth induced by space charge effects could be totally compensated for. In particular, for RF guns the photo-electron distribution leaving the cathode should have a 3D-ellipsoidal shape. The emittance at the end of the injector could be as small as the cathode emittance. We explore how the emittance and the brightness can be optimized for photoinjector based on RF gun depending on the peak current requirements. Techniques available to produce those ideal laser pulse shapes are also discussed. If the laser pulse driving photoinjectors could be arbitrarily shaped, the emittance growth induced by space charge effects could be totally compensated for. In particular, for RF guns, the photo-electron distribution leaving the cathode should be close to a uniform distribution contained in a 3D-ellipsoid contour. For photo-cathodes which have very fast emission times, and assuming a perfectly uniform emitting surface, this could be achieved by shaping the laser in a pulse of constant fluence and limited in space by a 3D-ellipsoid contour. Simulations show that in such conditions, with the standard linear emittance compensation, the emittance at the end of the photo-injector beamline approaches the minimum value imposed by the cathode emittance. Brightness, which is expressed as the ratio of peak current over the product of the two transverse emittance, seems to be maximized for small charges. Numerical simulations also show that for very high charge per bunch (10nC), emittances as small as 2 mm-mrad could be reached by using 3D-ellipsoidal laser pulses in an S-Band gun. The production of 3D-ellipsoidal pulses is very challenging, but seems worthwhile the effort. We briefly discuss some of the present ideas and difficulties of achieving such pulses.

  4. Fermi's New Pulsar Detection Technique

    NASA Video Gallery

    To locate a pulsar in Fermi LAT data requires knowledge of the object’s sky position, its pulse period, and how the pulse rate slows over time. Computers check many different combinations of posi...

  5. The Fermi LAT Pulsars

    NASA Astrophysics Data System (ADS)

    Romani, Roger W.

    2011-08-01

    The Large Area Telescope on the Fermi satellite is an impressive pulsar discovery machine, with over 75 pulse detections and counting. The populations of radio-selected, γ-selected and millisecond pulsars are now large enough to display observational patterns in the light curves and luminosities. These patterns are starting to teach us about the physics of the emission zone, which seems dominated by open field lines near the speed of light cylinder. The sample also provides initial inferences about the pulsar population. Apparently a large fraction of neutron stars have a young energetic γ-ray emitting phase, making these objects a good probe of massive star evolution. The long-lived millisecond γ-ray pulsars are even more ubiquitous and may produce a significant fraction of the γ-ray background. In any event, it is clear that the present LAT pulsar sample is dominated by nearby objects, and there is every expectation that the number, and quality, of pulsar detections will increase in years to come.

  6. Intermediate accelerated solutions as generic late-time attractors in a modified Jordan-Brans-Dicke theory

    NASA Astrophysics Data System (ADS)

    Cid, Antonella; Leon, Genly; Leyva, Yoelsy

    2016-02-01

    In this paper we investigate the evolution of a Jordan-Brans-Dicke scalar field, Φ, with a power-law potential in the presence of a second scalar field, phi, with an exponential potential, in both the Jordan and the Einstein frames. We present the relation of our model with the induced gravity model with power-law potential and the integrability of this kind of models is discussed when the quintessence field phi is massless, and has a small velocity. The fact that for some fine-tuned values of the parameters we may get some integrable cosmological models, makes our choice of potentials very interesting. We prove that in Jordan-Brans-Dicke theory, the de Sitter solution is not a natural attractor. Instead, we show that the attractor in the Jordan frame corresponds to an ``intermediate accelerated'' solution of the form a(t) simeq eα1 tp1, as t → ∞ where α1 > 0 and 0 < p1 < 1, for a wide range of parameters. Furthermore, when we work in the Einstein frame we get that the attractor is also an ``intermediate accelerated'' solution of the form fraktur a(fraktur t) simeq eα2 fraktur tp2 as fraktur t → ∞ where α2 > 0 and 0late-time attractor is linked with the exact solution found for the induced gravity model. In this example the ``intermediate accelerated'' solution does not exist, and the attractor solution has an asymptotic de Sitter-like evolution law for the

  7. A high brightness photoinjector

    NASA Astrophysics Data System (ADS)

    Le Sage, Gregory Peter

    Linear colliders, future electron acceleration schemes, and short pulse, ultrawideband millimeter-wave sources require very bright electron beams. Conventional electron injectors including thermionic cathodes and RF bunchers or DC guns have intrinsic limitations which preclude their usage for many of these applications. RF photoinjectors have shown their ability to produce relativistic electron beams with low emittance and energy spread. However, previously developed RF photoinjectors are also subject to significant limitations. These include extreme sensitivity to timing between the RF in the accelerator structure and the drive laser, low efficiency with respect to the number and charge of the electron bunches produced by the injector, and high cost associated with both the RF drive and laser systems. The presently described system has addressed these issues by combining state-of-the-art capabilities in the laser and RF systems, photocathode materials, and new concepts for synchronization. Phase jitter generated by sources including Klystron modulator voltage fluctuation has been measured in detail, and schemes for alleviating this problem have undergone initial proof-of-principle testing. New concepts for the drive laser system have been tested which will lead to further improvements in performance, simplicity, cost-effectiveness, and compactness. The analytical and experimental work associated with the development of a high brightness, high gradient electron accelerator is presented. The presentation emphasizes the systematic progress toward the original design goals of the project, as well as the state-of-the-art innovations characterizing the system. The linear electron accelerator system is based on a 1 1/2 cell side-wall coupled, π-mode standing wave accelerator structure, driven by a 20 MW SLAC Klystron operating at 8.548 GHz, a Ti:Sapphire laser oscillator, and an 8-pass, chirped pulse Ti:Sapphire laser amplifier. Simulations show an rms transverse

  8. How Bright Is the Sun?

    ERIC Educational Resources Information Center

    Berr, Stephen

    1991-01-01

    Presents a sequence of activities designed to allow eighth grade students to deal with one of the fundamental relationships that govern energy distribution. Activities guide students to measure light bulb brightness, discover the inverse square law, compare light bulb light to candle light, and measure sun brightness. (two references) (MCO)

  9. Strongly Interacting Fermi and Bose-Fermi Gases

    NASA Astrophysics Data System (ADS)

    Lee, Ye-Ryoung; Choi, Jae; Christensen, Caleb; Jo, Gyu-Boong; Wang, Tout; Ketterle, Wolfgang; Pritchard, David

    2010-03-01

    We present our recent progress on the study ultracold gases of ^6Li and ^23Na near homonuclear and heteronuclear Feshbach resonances. We discuss new experimental and theoretical developments on itinerant ferromagnetism in a Fermi gas of ultracold atoms [1]. We also report on ultracold gases of ^6Li and ^23Na, including fermionic LiNa molecules. [4pt] [1] G.-B. Jo, Y.-R. Lee, J.-H. Choi, C.A. Christensen, T.H. Kim, J.H. Thywissen, D.E. Pritchard, and W. Ketterle, Observation of itinerant ferromagnetism in a strongly interacting Fermi gas of ultracold atoms, Science 325, 1521 (2009).

  10. Brightness measurements on the Livermore high brightness test stand

    SciTech Connect

    Caporaso, G.J.; Birx, D.L.

    1985-05-09

    Several techniques using small radius collimating pipes with and without axial magnetic fields to measure the brightness of an extracted 1 - 2 kA, 1 - 1.5 MeV electron beam will be described. The output beam of the High Brightness Test Stand as measured by one of these techniques is in excess of 2 x 10/sup 5/ amp/cm/sup 2//steradian. 5 refs., 4 figs.

  11. Strongly Interacting Homogeneous Fermi Gases

    NASA Astrophysics Data System (ADS)

    Mukherjee, Biswaroop; Patel, Parth; Yan, Zhenjie; Struck, Julian; Zwierlein, Martin

    2016-05-01

    We present a homogeneous box potential for strongly interacting Fermi gases. The local density approximation (LDA) allows measurements on traditional inhomogeneous traps to observe a continuous distribution of Fermi gases in a single shot, but also suffer from a broadened response due to line-of-sight averaging over varying densities. We trap ultracold Fermionic (6 Li) in an optical homogeneous potential and characterize its flatness through in-situ tomography. A hybrid approach combining a cylindrical optical potential with a harmonic magnetic trap allows us to exploit the LDA and measure local RF spectra without requiring significant image reconstruction. We extract various quantities from the RF spectra such as the Tan's contact, and discuss further measurements of homogeneous Fermi systems under spin imbalance and finite temperature.

  12. The 2-Year Checkup on 10 SNe IIn Discovered by Spitzer to Exhibit Late-Time (is greater than 100 Day) IR Emission

    NASA Technical Reports Server (NTRS)

    Fox, Ori Dosovitz; Chevalier, R. A.; Skrutskie, A. V.; Filippenko, A. V.; Silverman, J. M.; Ganeshalingam, M.

    2012-01-01

    Two years ago, a warm Spitzer survey of sixty-eight SNe IIn identified between the years 1998-2008 discovered 10 events with unreported late-time infrared (IR) excesses, in some cases more than 5 years post-explosion. These data nearly double the database of existing mid-IR observations of SNe IIn and offer important clues regarding the SN circumstellar.

  13. Fermi Finds Youthful Pulsar Among Ancient Stars

    NASA Video Gallery

    In three years, NASA's Fermi has detected more than 100 gamma-ray pulsars, but something new has appeared. Among a type of pulsar with ages typically numbering a billion years or more, Fermi has fo...

  14. Fermi, Enrico (1901-54)

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    Italian physicist, created the first controlled chain reaction, founded Argonne National Laboratory. His work on the properties of electrons (spin-half particles like electrons are called fermions after him, and the study of their properties is called Fermi-Dirac statistics) enabled the pressure source in white dwarf stars to be identified, and white dwarf star properties to be calculated by CHAN...

  15. Fermi's β-DECAY Theory

    NASA Astrophysics Data System (ADS)

    Yang, Chen Ning

    2013-05-01

    Throughout his lifetime Enrico Fermi (1901-1954) had considered his 1934 β-decay theory as his most important contribution to theoretical physics. E. Segrè (1905-1989) had vividly written about an episode at the inception of that paper:1...

  16. Fermi GBM Early Trigger Characteristics

    SciTech Connect

    Connaughton, Valerie; Briggs, Michael; Paciesas, Bill; Meegan, Charles

    2009-05-25

    Since the launch of the Fermi observatory on June 11 2008, the Gamma-ray Burst Monitor (GBM) has seen approximately 250 triggers of which about 150 were cosmic gamma-ray bursts (GRBs). GBM operates dozens of trigger algorithms covering various energy bands and timescales and is therefore sensitive to a wide variety of phenomena, both astrophysical and not.

  17. Fermi's Large Area Telescope (LAT)

    NASA Video Gallery

    Fermi’s Large Area Telescope (LAT) is the spacecraft’s main scientificinstrument. This animation shows a gamma ray (purple) entering the LAT,where it is converted into an electron (red) and a...

  18. CCC and the Fermi paradox

    NASA Astrophysics Data System (ADS)

    Gurzadyan, V. G.; Penrose, R.

    2016-01-01

    Within the scheme of conformal cyclic cosmology (CCC), information can be transmitted from aeon to aeon. Accordingly, the "Fermi paradox" and the SETI programme --of communication by remote civilizations-- may be examined from a novel perspective: such information could, in principle, be encoded in the cosmic microwave background. The current empirical status of CCC is also discussed.

  19. Lectures of Fermi liquid theory

    SciTech Connect

    Bedell, K.S.

    1993-01-01

    The Fermi liquid theory was first introduced by Landau in 1956 to provide a theoretical basis for the properties of strongly correlated Fermi systems. This theory has proven to be crucial for our understanding of a broad range of materials. These include liquid [sup 3]He, [sup 3]He-[sup 4]He mixtures, simple metals, heavy-fermions, and nuclear matter to name a few. In the high temperature superconductors questions have been raised regarding the applicability of Fermi liquid theory to the normal state behavior of these materials. I will not address this issue in these lectures. My focus will be to summarize the foundations of this theory and to explore the consequences. These lectures are in part a summary of the excellent review article by Baym and Pethick and the books by Pines and Nozieres and Baym and Pethick. They include as well a summary of some articles that I have authored and co-authored. In the main body of the lectures I will not make any additional references to the books or articles. In the absence of reading the original materials, my lectures should provide the essentials of a mini-course in Fermi liquid theory.

  20. Lectures of Fermi liquid theory

    SciTech Connect

    Bedell, K.S.

    1993-07-01

    The Fermi liquid theory was first introduced by Landau in 1956 to provide a theoretical basis for the properties of strongly correlated Fermi systems. This theory has proven to be crucial for our understanding of a broad range of materials. These include liquid {sup 3}He, {sup 3}He-{sup 4}He mixtures, simple metals, heavy-fermions, and nuclear matter to name a few. In the high temperature superconductors questions have been raised regarding the applicability of Fermi liquid theory to the normal state behavior of these materials. I will not address this issue in these lectures. My focus will be to summarize the foundations of this theory and to explore the consequences. These lectures are in part a summary of the excellent review article by Baym and Pethick and the books by Pines and Nozieres and Baym and Pethick. They include as well a summary of some articles that I have authored and co-authored. In the main body of the lectures I will not make any additional references to the books or articles. In the absence of reading the original materials, my lectures should provide the essentials of a mini-course in Fermi liquid theory.

  1. Hunting for treasures among the Fermi unassociated sources: A multiwavelength approach

    SciTech Connect

    Acero, F.; Ojha, R.; Edwards, P. G.; Blanchard, J.; Lovell, J. E. J.; Thompson, D. J.

    2013-12-20

    The Fermi Gamma-Ray Space Telescope has been detecting a wealth of sources where the multiwavelength counterpart is either inconclusive or missing altogether. We present a combination of factors that can be used to identify multiwavelength counterparts to these Fermi unassociated sources. This approach was used to select and investigate seven bright, high-latitude unassociated sources with radio, UV, X-ray, and γ-ray observations. As a result, four of these sources are candidates to be active galactic nuclei, and one to be a pulsar, while two do not fit easily into these known categories of sources. The latter pair of extraordinary sources might reveal a new category subclass or a new type of γ-ray emitter. These results altogether demonstrate the power of a multiwavelength approach to illuminate the nature of unassociated Fermi sources.

  2. Nonanalytic Magnetic Response of Fermi- and non-Fermi Liquids

    NASA Astrophysics Data System (ADS)

    Chubukov, Andrey; Maslov, Dmitrii; Saha, Ronojoy

    2007-03-01

    We revisit the issue of the non-analytic dependence of the static spin susceptibility of a 2D Fermi liquid on temperature and a magnetic field, χs(T, H) = χ0+ A T fχ(μB|H|/T). We show that in a generic Fermi liquid the prefactor A is expressed via complex combinations of the Landau parameters, and does not reduce to the backscattering amplitude, contrary to the case of the specific heat C(T, H). We show that this distinction with the specific heat is mostly relevant near a ferromagnetic QCP -- the non-analytic terms in χs(T,H) are less singular near QCP than those in C(T, H).

  3. Stability of Fermi surfaces and K theory.

    PubMed

    Horava, Petr

    2005-07-01

    Nonrelativistic Fermi liquids in d+1 dimensions exhibit generalized Fermi surfaces: (d-p)-dimensional submanifolds in the (k,omega)-space supporting gapless excitations. We show that the universality classes of stable Fermi surfaces are classified by K theory, with the pattern of stability determined by Bott periodicity. The Atiyah-Bott-Shapiro construction implies that the low-energy modes near a Fermi surface exhibit relativistic invariance in the transverse p+1 dimensions. This suggests an intriguing parallel between nonrelativistic Fermi liquids and D-branes of string theory. PMID:16090638

  4. Using GRB 080723B to cross-calibrate Fermi/GBM and INTEGRAL

    SciTech Connect

    Kienlin, A. von; Briggs, M. S.; Connoughton, V.; Preece, R. D.; McBreen, S.; Sazonov, Sergey; Tsygankov, Sergey; Wilson-Hodge, C. A.

    2009-05-25

    On July 23, 2008 GRB 080723B, a bright GRB lasting about 105 s was detected by the INTEGRAL burst alert system. This burst was also detected by the Fermi Gamma-ray burst monitor. At this time no Fermi/GBM GCN notices were distributed to the public because Fermi was still in commissioning phase. The simultaneous detection of a bright GRB by both satellites gives us the opportunity to cross-calibrate the GBM with the already well-calibrated instruments on-board INTEGRAL, the Spectrometer SPI and the Imager IBIS. Time-resolved spectroscopy of this long and structured GRB is of special importance because Fermi was slewing during the GRB was still ongoing. In this paper we present a first and still preliminary analysis of the GBM spectra and compare them to those obtained by SPI for the same selection of time intervals. A more accurate cross-calibration will be forthcoming when the improved in-flight calibration of GBM is available and the corresponding data and responses can be reprocessed.

  5. An inducible promoter mediates abundant expression from the immediate-early 2 gene region of human cytomegalovirus at late times after infection.

    PubMed Central

    Puchtler, E; Stamminger, T

    1991-01-01

    An abundant late transcript of 1.5 kb originates from the immediate-early 2 (IE-2) gene region of human cytomegalovirus (HCMV) at late times after infection. The transcriptional start of this RNA was precisely mapped, and the putative promoter region was cloned in front of the CAT gene as reporter. This region, which comprises 78 nucleotides of IE-2 sequence upstream of the determined cap site, was strongly activated by viral superinfection at late times in the replicative cycle. As shown by RNase protection analyses, the authentic transcription start is used. No activation of this late promoter was observed after cotransfection with an expression plasmid containing the HCMV IE-1 and -2 gene region. This result suggests that, compared with early and early late promoters of HCMV, different or additional viral functions are required for the activation of true late promoters. Images PMID:1656096

  6. On the Evolution of the Late-time Hubble Space Telescope Imaging of the Outburst of the Recurrent Nova RS Ophiuchi (2006)

    NASA Astrophysics Data System (ADS)

    Ribeiro, V. A. R. M.; Bode, M. F.; Williams, R. E.

    2014-12-01

    We modelled the late-time Hubble Space Telescope imaging of RS Ophiuchi with models from Ribeiro et al. (2009), which at the time due to the unknown availability of simultaneous ground-based spectroscopy left some open questions as to the evolution of the expanding nebular from the early to the late time observations. Initial emission line identifications suggest that no forbidden lines are present in the spectra and that the emission lines arising in the region of the WFPC2 F502N images are due to N II and He I + Fe II. The best model fit to the spectrum is one where the outer faster moving material expands linearly with time while the inner over-density material either suffered some deceleration or did not change in physical size. The origin of this inner over-density requires further exploration.

  7. In Situ Mosaic Brightness Correction

    NASA Technical Reports Server (NTRS)

    Deen, Robert G.; Lorre, Jean J.

    2012-01-01

    In situ missions typically have pointable, mast-mounted cameras, which are capable of taking panoramic mosaics comprised of many individual frames. These frames are mosaicked together. While the mosaic software applies radiometric correction to the images, in many cases brightness/contrast seams still exist between frames. This is largely due to errors in the radiometric correction, and the absence of correction for photometric effects in the mosaic processing chain. The software analyzes the overlaps between adjacent frames in the mosaic and determines correction factors for each image in an attempt to reduce or eliminate these brightness seams.

  8. The EUVE bright source list

    NASA Technical Reports Server (NTRS)

    Stroozas, B.; Mcdonald, K.; Antia, B.; Mcdonald, J.; Wiercigroch, A.

    1993-01-01

    Initial results for bright extreme ultraviolet sources discovered during the EUVE all-sky and deep ecliptic surveys have been published as a Bright Source List (BSL) and released to the astronomical community with a recent NASA research announcement (NRA 93-OSS-02, Appendix F). This paper describes the data processing software, the EUVE survey data set, and the production of the BSL at the Center for EUV Astrophysics. The contents, format, and selection criteria for sources, the data processing strategy, some problems encountered, and a summary of the BSL results are presented.

  9. Fermi resonance in optical microcavities

    NASA Astrophysics Data System (ADS)

    Yi, Chang-Hwan; Yu, Hyeon-Hye; Lee, Ji-Won; Kim, Chil-Min

    2015-04-01

    Fermi resonance is a phenomenon of quantum mechanical superposition, which most often occurs between normal and overtone modes in molecular systems that are nearly coincident in energy. We find that scarred resonances in deformed dielectric microcavities are the very phenomenon of Fermi resonance, that is, a pair of quasinormal modes interact with each other due to coupling and a pair of resonances are generated through an avoided resonance crossing. Then the quantum number difference of a pair of quasinormal modes, which is a consequence of quantum mechanical superposition, equals periodic orbits, whereby the resonances are localized on the periodic orbits. We derive the relation between the quantum number difference and the periodic orbits and confirm it in an elliptic, a rectangular, and a stadium-shaped dielectric microcavity.

  10. Fermi Timing and Synchronization System

    SciTech Connect

    Wilcox, R.; Staples, J.; Doolittle, L.; Byrd, J.; Ratti, A.; Kaertner, F.X.; Kim, J.; Chen, J.; Ilday, F.O.; Ludwig, F.; Winter, A.; Ferianis, M.; Danailov, M.; D'Auria, G.

    2006-07-19

    The Fermi FEL will depend critically on precise timing of its RF, laser and diagnostic subsystems. The timing subsystem to coordinate these functions will need to reliably maintain sub-100fs synchronicity between distant points up to 300m apart in the Fermi facility. The technology to do this is not commercially available, and has not been experimentally demonstrated in a working facility. Therefore, new technology must be developed to meet these needs. Two approaches have been researched by different groups working with the Fermi staff. At MIT, a pulse transmission scheme has been developed for synchronization of RF and laser devices. And at LBL, a CW transmission scheme has been developed for RF and laser synchronization. These respective schemes have advantages and disadvantages that will become better understood in coming years. This document presents the work done by both teams, and suggests a possible system design which integrates them both. The integrated system design provides an example of how choices can be made between the different approaches without significantly changing the basic infrastructure of the system. Overall system issues common to any synchronization scheme are also discussed.

  11. Enrico Fermi and the Dolomites

    NASA Astrophysics Data System (ADS)

    Battimelli, Giovanni; de Angelis, Alessandro

    2014-11-01

    Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scientific discussions held in the region of the Dolomites.

  12. Network based sky Brightness Monitor

    NASA Astrophysics Data System (ADS)

    McKenna, Dan; Pulvermacher, R.; Davis, D. R.

    2009-01-01

    We have developed and are currently testing an autonomous 2 channel photometer designed to measure the night sky brightness in the visual wavelengths over a multi-year campaign. The photometer uses a robust silicon sensor filtered with Hoya CM500 glass. The Sky brightness is measured every minute at two elevation angles typically zenith and 20 degrees to monitor brightness and transparency. The Sky Brightness monitor consists of two units, the remote photometer and a network interface. Currently these devices use 2.4 Ghz transceivers with a free space range of 100 meters. The remote unit is battery powered with day time recharging using a solar panel. Data received by the network interface transmits data via standard POP Email protocol. A second version is under development for radio sensitive areas using an optical fiber for data transmission. We will present the current comparison with the National Park Service sky monitoring camera. We will also discuss the calibration methods used for standardization and temperature compensation. This system is expected to be deployed in the next year and be operated by the International Dark Sky Association SKYMONITOR project.

  13. StarBright Learning Exchange

    ERIC Educational Resources Information Center

    Kalinowski, Michael

    2007-01-01

    This article features StarBright Learning Exchange, a program that provides a cross-cultural exchange between Australian and South African early childhood educators. The program was originated when its president, Carol Allen, and her colleague, Karen Williams, decided that they could no longer sit by and watch the unfolding social catastrophe that…

  14. Bright Transients discovered by PSST

    NASA Astrophysics Data System (ADS)

    Smith, K. W.; Wright, D.; Smartt, S. J.; Young, D. R.; Huber, M.; Chambers, K. C.; Flewelling, H.; Willman, M.; Primak, N.; Schultz, A.; Gibson, B.; Magnier, E.; Waters, C.; Tonry, J.; Wainscoat, R. J.; Foley, R. J.; Jha, S. W.; Rest, A.; Scolnic, D.

    2016-08-01

    Six bright transients have been discovered as part of the Pan-STARRS Survey for Transients (PSST). Information on all objects discovered by the Pan-STARRS Survey for Transients is available at http://star.pst.qub.ac.uk/ps1threepi/ (see Huber et al. ATel #7153).

  15. Bright Transients discovered by PSST

    NASA Astrophysics Data System (ADS)

    Smith, K. W.; Wright, D.; Smartt, S. J.; Huber, M.; Chambers, K. C.; Flewelling, H.; Willman, M.; Primak, N.; Schultz, A.; Gibson, B.; Magnier, E.; Waters, C.; Tonry, J.; Wainscoat, R. J.; Denneau, L.; Stalder, B.; Heinze, A.; Sherstyuk, A.; Foley, R. J.; Jha, S. W.; Rest, A.; Scolnic, D.

    2016-04-01

    Seven bright transients have been discovered as part of the Pan-STARRS Survey for Transients (PSST). Information on all objects discovered by the Pan-STARRS Survey for Transients is available at http://star.pst.qub.ac.uk/ps1threepi/ (see Huber et al. ATel #7153).

  16. Teradiode's high brightness semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Huang, Robin K.; Chann, Bien; Burgess, James; Lochman, Bryan; Zhou, Wang; Cruz, Mike; Cook, Rob; Dugmore, Dan; Shattuck, Jeff; Tayebati, Parviz

    2016-03-01

    TeraDiode is manufacturing multi-kW-class ultra-high brightness fiber-coupled direct diode lasers for industrial applications. A fiber-coupled direct diode laser with a power level of 4,680 W from a 100 μm core diameter, <0.08 numerical aperture (NA) output fiber at a single center wavelength was demonstrated. Our TeraBlade industrial platform achieves world-record brightness levels for direct diode lasers. The fiber-coupled output corresponds to a Beam Parameter Product (BPP) of 3.5 mm-mrad and is the lowest BPP multi-kW-class direct diode laser yet reported. This laser is suitable for industrial materials processing applications, including sheet metal cutting and welding. This 4-kW fiber-coupled direct diode laser has comparable brightness to that of industrial fiber lasers and CO2 lasers, and is over 10x brighter than state-of-the-art direct diode lasers. We have also demonstrated novel high peak power lasers and high brightness Mid-Infrared Lasers.

  17. SLAC All Access: Fermi Gamma-ray Space Telescope

    SciTech Connect

    Romani, Roger

    2013-05-31

    Three hundred and fifty miles overhead, the Fermi Gamma-ray Space Telescope silently glides through space. From this serene vantage point, the satellite's instruments watch the fiercest processes in the universe unfold. Pulsars spin up to 700 times a second, sweeping powerful beams of gamma-ray light through the cosmos. The hyperactive cores of distant galaxies spew bright jets of plasma. Far beyond, something mysterious explodes with unfathomable power, sending energy waves crashing through the universe. Stanford professor and KIPAC member Roger W. Romani talks about this orbiting telescope, the most advanced ever to view the sky in gamma rays, a form of light at the highest end of the energy spectrum that's created in the hottest regions of the universe.

  18. SLAC All Access: Fermi Gamma-ray Space Telescope

    ScienceCinema

    Romani, Roger

    2014-06-24

    Three hundred and fifty miles overhead, the Fermi Gamma-ray Space Telescope silently glides through space. From this serene vantage point, the satellite's instruments watch the fiercest processes in the universe unfold. Pulsars spin up to 700 times a second, sweeping powerful beams of gamma-ray light through the cosmos. The hyperactive cores of distant galaxies spew bright jets of plasma. Far beyond, something mysterious explodes with unfathomable power, sending energy waves crashing through the universe. Stanford professor and KIPAC member Roger W. Romani talks about this orbiting telescope, the most advanced ever to view the sky in gamma rays, a form of light at the highest end of the energy spectrum that's created in the hottest regions of the universe.

  19. Bioterrorism and the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Cooper, Joshua

    2013-04-01

    We proffer a contemporary solution to the so-called Fermi Paradox, which is concerned with conflict between Copernicanism and the apparent paucity of evidence for intelligent alien civilizations. In particular, we argue that every community of organisms that reaches its space-faring age will (1) almost immediately use its rocket-building computers to reverse-engineer its genetic chemistry and (2) self-destruct when some individual uses said technology to design an omnicidal pathogen. We discuss some of the possible approaches to prevention with regard to Homo sapiens' vulnerability to bioterrorism, particularly on a short-term basis.

  20. Generalized second-order Thomas-Fermi method for superfluid Fermi systems

    NASA Astrophysics Data System (ADS)

    Pei, J. C.; Fei, Na; Zhang, Y. N.; Schuck, P.

    2015-12-01

    Using the ℏ expansion of the Green's function of the Hartree-Fock-Bogoliubov equation, we extend the second-order Thomas-Fermi approximation to generalized superfluid Fermi systems by including the density-dependent effective mass and the spin-orbit potential. We first implement and examine the full correction terms over different energy intervals of the quasiparticle spectra in calculations of finite nuclei. Final applications of this generalized Thomas-Fermi method are intended for various inhomogeneous superfluid Fermi systems.

  1. Brightness-equalized quantum dots

    NASA Astrophysics Data System (ADS)

    Lim, Sung Jun; Zahid, Mohammad U.; Le, Phuong; Ma, Liang; Entenberg, David; Harney, Allison S.; Condeelis, John; Smith, Andrew M.

    2015-10-01

    As molecular labels for cells and tissues, fluorescent probes have shaped our understanding of biological structures and processes. However, their capacity for quantitative analysis is limited because photon emission rates from multicolour fluorophores are dissimilar, unstable and often unpredictable, which obscures correlations between measured fluorescence and molecular concentration. Here we introduce a new class of light-emitting quantum dots with tunable and equalized fluorescence brightness across a broad range of colours. The key feature is independent tunability of emission wavelength, extinction coefficient and quantum yield through distinct structural domains in the nanocrystal. Precise tuning eliminates a 100-fold red-to-green brightness mismatch of size-tuned quantum dots at the ensemble and single-particle levels, which substantially improves quantitative imaging accuracy in biological tissue. We anticipate that these materials engineering principles will vastly expand the optical engineering landscape of fluorescent probes, facilitate quantitative multicolour imaging in living tissue and improve colour tuning in light-emitting devices.

  2. Low-brightness quantum radar

    NASA Astrophysics Data System (ADS)

    Lanzagorta, Marco

    2015-05-01

    One of the major scientific thrusts from recent years has been to try to harness quantum phenomena to dramatically increase the performance of a wide variety of classical information processing devices. These advances in quantum information science have had a considerable impact on the development of standoff sensors such as quantum radar. In this paper we analyze the theoretical performance of low-brightness quantum radar that uses entangled photon states. We use the detection error probability as a measure of sensing performance and the interception error probability as a measure of stealthiness. We compare the performance of quantum radar against a coherent light sensor (such as lidar) and classical radar. In particular, we restrict our analysis to the performance of low-brightness standoff sensors operating in a noisy environment. We show that, compared to the two classical standoff sensing devices, quantum radar is stealthier, more resilient to jamming, and more accurate for the detection of low reflectivity targets.

  3. Brightness-equalized quantum dots

    PubMed Central

    Lim, Sung Jun; Zahid, Mohammad U.; Le, Phuong; Ma, Liang; Entenberg, David; Harney, Allison S.; Condeelis, John; Smith, Andrew M.

    2015-01-01

    As molecular labels for cells and tissues, fluorescent probes have shaped our understanding of biological structures and processes. However, their capacity for quantitative analysis is limited because photon emission rates from multicolour fluorophores are dissimilar, unstable and often unpredictable, which obscures correlations between measured fluorescence and molecular concentration. Here we introduce a new class of light-emitting quantum dots with tunable and equalized fluorescence brightness across a broad range of colours. The key feature is independent tunability of emission wavelength, extinction coefficient and quantum yield through distinct structural domains in the nanocrystal. Precise tuning eliminates a 100-fold red-to-green brightness mismatch of size-tuned quantum dots at the ensemble and single-particle levels, which substantially improves quantitative imaging accuracy in biological tissue. We anticipate that these materials engineering principles will vastly expand the optical engineering landscape of fluorescent probes, facilitate quantitative multicolour imaging in living tissue and improve colour tuning in light-emitting devices. PMID:26437175

  4. A New Sky Brightness Monitor

    NASA Astrophysics Data System (ADS)

    Crawford, David L.; McKenna, D.

    2006-12-01

    A good estimate of sky brightness and its variations throughout the night, the months, and even the years is an essential bit of knowledge both for good observing and especially as a tool in efforts to minimize sky brightness through local action. Hence a stable and accurate monitor can be a valuable and necessary tool. We have developed such a monitor, with the financial help of Vatican Observatory and Walker Management. The device is now undergoing its Beta test in preparation for production. It is simple, accurate, well calibrated, and automatic, sending its data directly to IDA over the internet via E-mail . Approximately 50 such monitors will be ready soon for deployment worldwide including most major observatories. Those interested in having one should enquire of IDA about details.

  5. The Blazar's Divide and the Properties of Fermi Blazars

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.

    2010-10-01

    The LAT instrument, onboard the Fermi satellite, in its first three months of operation detected more than 100 blazars at more than the 10σ level. This is already a great improvement with respect to its predecessor, the instrument EGRET onboard the Compton Gamma Ray Observatory. Observationally, the new detections follow and confirm the so-called blazar sequence, relating the bolometric observed non-thermal luminosity to the overall shape of the spectral energy distribution. We have studied the general physical properties of all these bright Fermi blazars, and found that their jets are matter dominated, carrying a large total power that correlates with the luminosity of their accretion disks. We suggest that the division of blazars into the two subclasses of broad line emitting objects (Flat Spectrum Radio Quasars) and line-less BL Lacs is a consequence of a rather drastic change of the accretion mode, becoming radiatively inefficient below a critical value of the accretion rate, corresponding to a disk luminosity of ˜1 per cent of the Eddington one. The reduction of the ionizing photons below this limit implies that the broad line clouds, even if present, cannot produce significant broad lines, and the object becomes a BL Lac.

  6. Iapetus Bright and Dark Terrains

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Saturn's outermost large moon, Iapetus, has a bright, heavily cratered icy terrain and a dark terrain, as shown in this Voyager 2 image taken on August 22, 1981. Amazingly, the dark material covers precisely the side of Iapetus that leads in the direction of orbital motion around Saturn (except for the poles), whereas the bright material occurs on the trailing hemisphere and at the poles. The bright terrain is made of dirty ice, and the dark terrain is surfaced by carbonaceous molecules, according to measurements made with Earth-based telescopes. Iapetus' dark hemisphere has been likened to tar or asphalt and is so dark that no details within this terrain were visible to Voyager 2. The bright icy hemisphere, likened to dirty snow, shows many large impact craters. The closest approach by Voyager 2 to Iapetus was a relatively distant 600,000 miles, so that our best images, such as this, have a resolution of about 12 miles. The dark material is made of organic substances, probably including poisonous cyano compounds such as frozen hydrogen cyanide polymers. Though we know a little about the dark terrain's chemical nature, we do not understand its origin. Two theories have been developed, but neither is fully satisfactory--(1) the dark material may be organic dust knocked off the small neighboring satellite Phoebe and 'painted' onto the leading side of Iapetus as the dust spirals toward Saturn and Iapetus hurtles through the tenuous dust cloud, or (2) the dark material may be made of icy-cold carbonaceous 'cryovolcanic' lavas that were erupted from Iapetus' interior and then blackened by solar radiation, charged particles, and cosmic rays. A determination of the actual cause, as well as discovery of any other geologic features smaller than 12 miles across, awaits the Cassini Saturn orbiter to arrive in 2004.

  7. Holographic thermalization, stability of anti-de sitter space, and the Fermi-Pasta-Ulam paradox.

    PubMed

    Balasubramanian, Venkat; Buchel, Alex; Green, Stephen R; Lehner, Luis; Liebling, Steven L

    2014-08-15

    For a real massless scalar field in general relativity with a negative cosmological constant, we uncover a large class of spherically symmetric initial conditions that are close to anti-de Sitter space (AdS) but whose numerical evolution does not result in black hole formation. According to the AdS/conformal field theory (CFT) dictionary, these bulk solutions are dual to states of a strongly interacting boundary CFT that fail to thermalize at late times. Furthermore, as these states are not stationary, they define dynamical CFT configurations that do not equilibrate. We develop a two-time-scale perturbative formalism that captures both direct and inverse cascades of energy and agrees with our fully nonlinear evolutions in the appropriate regime. We also show that this formalism admits a large class of quasiperiodic solutions. Finally, we demonstrate a striking parallel between the dynamics of AdS and the classic Fermi-Pasta-Ulam-Tsingou problem. PMID:25170699

  8. High-brightness multilaser source

    NASA Astrophysics Data System (ADS)

    Goodman, Douglas S.; Gordon, Wayne L.; Jollay, Richard A.; Roblee, Jeffrey W.; Gavrilovic, Paul; Kuksenkov, Dmitri V.; Goyal, Anish K.; Zu, Qinxin

    1999-04-01

    This paper discusses a high-brightness multi-laser source developed at Polaroid for such applications as coupling light to fibers, pumping fiber lasers, pumping solid state lasers, material processing, and medical procedures. The power and brightness are obtained by imaging the nearfields of up to eight separate multi-mode lasers side by side on a multi-faceted mirror that makes the beams parallel. The lasers are microlensed to equalize the divergences in the two principal meridians. Each laser is aligned in a field- replaceable illuminator module whose output beam, focused at infinity, is bore-sighted in a mechanical cylinder. The illuminators are arranged roughly radially and the nearfields are reimaged on the mirror, which is produced by diamond machining. The array of nearfields is linearly polarized. A customizable afocal relay forms a telecentric image of the juxtaposed nearfields, as required by the application. The lasers can be of differing powers and wavelengths, and they can be independently switched. Light from other sources can be combined. The output can be utilized in free space or it can be coupled into a fiber for transport or a fiber laser for pumping. A linearly polarized free space output can be obtained, which allows two units to be polarization combined to double the power and brightness.

  9. LSST Site: Sky Brightness Data

    NASA Astrophysics Data System (ADS)

    Burke, Jamison; Claver, Charles

    2015-01-01

    The Large Synoptic Survey Telescope (LSST) is an upcoming robotic survey telescope. At the telescope site on Cerro Pachon in Chile there are currently three photodiodes and a Canon camera with a fisheye lens, and both the photodiodes and Canon monitor the night sky continuously. The NIST-calibrated photodiodes directly measure the flux from the sky, and the sky brightness can also be obtained from the Canon images via digital aperture photometry. Organizing and combining the two data sets gives nightly information of the development of sky brightness across a swath of the electromagnetic spectrum, from blue to near infrared light, and this is useful for accurately predicting the performance of the LSST. It also provides data for models of moonlight and twilight sky brightness. Code to accomplish this organization and combination was successfully written in Python, but due to the backlog of data not all of the nights were processed by the end of the summer.Burke was supported by the NOAO/KPNO Research Experiences for Undergraduates (REU) Program which is funded by the National Science Foundation Research Experiences for Undergraduates Program (AST-1262829).

  10. Fermi liquids near Pomeranchuk instabilities

    NASA Astrophysics Data System (ADS)

    Reidy, Kelly Elizabeth

    We explore features of a Fermi liquid near generalized Pomeranchuk instabilities (PIs) starting from both ordered and disordered phases. These PIs can be viewed as quantum critical points in parameter space, and thus provide an alternate viewpoint on quantum criticality. We employ the tractable crossing symmetric equation method, which is a non-perturbative diagrammatic many-particle method used to calculate the Fermi liquid interaction functions and scattering amplitudes. We consider both repulsive and attractive underlying interactions of arbitrary strength. Starting from a ferromagnetically ordered ground state, we find that upon approach to an s-wave instability in one critical channel, the system simultaneously approaches instabilities in non-critical channels. We study origins and implications of this "quantum multicriticality". We also find that a nematic (non-s-wave) instability precedes and is driven by Pomeranchuk instabilities in both the s-wave spin and density channels. Finally, we discuss potential applications of our results to physical systems, such as ferromagnetic superconductors.

  11. Nonanalytic magnetic response of Fermi and non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Maslov, Dmitrii L.; Chubukov, Andrey V.; Saha, Ronojoy

    2006-12-01

    We study the nonanalytic behavior of the static spin susceptibility of two-dimensional fermions as a function of temperature and magnetic field. For a generic Fermi liquid, χs(T,H)=const+c1max{T,μB∣H∣} , where c1 is shown to be expressed via complicated combinations of the Landau parameters, rather than via the backscattering amplitude, contrary to the case of the specific heat. Near a ferromagnetic quantum critical point, the field dependence acquires a universal form χs-1(H)=const-c2∣H∣3/2 , with c2>0 . This behavior implies a first-order transition into a ferromagnetic state. We establish a criterion for such a transition to win over the transition into an incommensurate phase.

  12. Inflation and late-time cosmic acceleration in non-minimal Maxwell-F(R) gravity and the generation of large-scale magnetic fields

    SciTech Connect

    Bamba, Kazuharu; Odintsov, Sergei D E-mail: odintsov@aliga.ieec.uab.es

    2008-04-15

    We study inflation and late-time acceleration in the expansion of the universe in non-minimal electromagnetism, in which the electromagnetic field couples to the scalar curvature function. It is shown that power-law inflation can be realized due to the non-minimal gravitational coupling of the electromagnetic field, and that large-scale magnetic fields can be generated due to the breaking of the conformal invariance of the electromagnetic field through its non-minimal gravitational coupling. Furthermore, it is demonstrated that both inflation and the late-time acceleration of the universe can be realized in a modified Maxwell-F(R) gravity which is consistent with solar-system tests and cosmological bounds and free of instabilities. At small curvature typical for the current universe the standard Maxwell theory is recovered. We also consider the classically equivalent form of non-minimal Maxwell-F(R) gravity, and propose the origin of the non-minimal gravitational coupling function based on renormalization-group considerations.

  13. DISENTANGLING THE ORIGIN AND HEATING MECHANISM OF SUPERNOVA DUST: LATE-TIME SPITZER SPECTROSCOPY OF THE TYPE IIn SN 2005ip

    SciTech Connect

    Fox, Ori D.; Chevalier, Roger A.; Skrutskie, Michael F.; Leisenring, Jarron M.; Dwek, Eli; Sugerman, Ben E. K.

    2010-12-20

    This paper presents late-time near-infrared and Spitzer mid-infrared photometric and spectroscopic observations of warm dust in the Type IIn SN 2005ip in NGC 2906. The spectra show evidence for two dust components with different temperatures. Spanning the peak of the thermal emission, these observations provide strong constraints on the dust mass, temperature, and luminosity, which serve as critical diagnostics for disentangling the origin and heating mechanism of each component. The results suggest that the warmer dust has a mass of {approx}5 x 10{sup -4} M{sub sun}, originates from newly formed dust in the ejecta, or possibly the cool, dense shell, and is continuously heated by the circumstellar interaction. By contrast, the cooler component likely originates from a circumstellar shock echo that forms from the heating of a large, pre-existing dust shell {approx}0.01-0.05 M{sub sun} by the late-time circumstellar interaction. The progenitor wind velocity derived from the blue edge of the He I 1.083 {mu}m P Cygni profile indicates a progenitor eruption likely formed this dust shell {approx}100 years prior to the supernova explosion, which is consistent with a Luminous Blue Variable progenitor star.

  14. Disentangling the Origin and Heating Mechanism of Supernova Dust: Late-Time Spitzer Spectroscopy of the Type IIn SN 2005ip

    NASA Technical Reports Server (NTRS)

    Fox, Ori D.; Chevalier, Roger A.; Dwek, Eli; Skrutskie, Michael F.; Sugerman, Ben E. K.; Leisenring, Jarron M.

    2010-01-01

    This paper presents late-time near-infrared and Spitzer mid-infrared photometric and spectroscopic observations of warm dust in the Type IIn SN 2005ip in NGC 2906. The spectra show evidence for two dust components with different temperatures. Spanning the peak of the thermal emission, these observations provide strong constraints on the dust mass, temperature, and luminosity, which serve as critical diagnostics for disentangling the origin and heating mechanism of each component. The results suggest the warmer dust has a mass of approx. 5 x 10(exp -4) Solar Mass and originates from newly formed dust in the ejecta, continuously heated by the circumstellar interaction. By contrast, the cooler component likely originates from a circumstellar shock echo that forms from the heating of a large, pre-existing dust shell approx. 0.01 - 0.05 Solar Mass by the late-time circumstellar interaction. The progenitor wind velocity derived from the blue edge of the He I 1.083 micro P Cygni profile indicates a progenitor eruption likely formed this dust shell approx.100 years prior to the supernova explosion, which is consistent with a Luminous Blue Variable (LBV) progenitor star. Subject

  15. The Animated Gamma-ray Sky Revealed by the Fermi Gamma-ray Space Telescope

    SciTech Connect

    Isabelle Grenier

    2009-04-01

    The Fermi Gamma-ray Space Telescope has been observing the sky in gamma-rays since August 2008.  In addition to breakthrough capabilities in energy coverage (20 MeV-300 GeV) and angular resolution, the wide field of view of the Large Area Telescope enables observations of 20% of the sky at any instant, and of the whole sky every three hours. It has revealed a very animated sky with bright gamma-ray bursts flashing and vanishing in minutes, powerful active galactic nuclei flaring over hours and days, many pulsars twinkling in the Milky Way, and X-ray binaries shimmering along their orbit. Most of these variable sources had not been seen by the Fermi predecessor, EGRET, and the wealth of new data already brings important clues to the origin of the high-energy emission and particles powered by the compact objects. The telescope also brings crisp images of the bright gamma-ray emission produced by cosmic-ray interactions in the interstellar medium, thus allowing to measure the cosmic nuclei and electron spectra across the Galaxy, to weigh interstellar clouds, in particular in the dark-gas phase. The telescope sensitivity at high energy will soon provide useful constraints on dark-matter annihilations in a variety of environments. I will review the current results and future prospects of the Fermi mission.

  16. The Animated Gamma-ray Sky Revealed by the Fermi Gamma-ray Space Telescope

    SciTech Connect

    Grenier, Isabelle

    2009-04-01

    The Fermi Gamma-ray Space Telescope has been observing the sky in gamma-rays since August 2008. In addition to breakthrough capabilities in energy coverage (20 MeV-300 GeV) and angular resolution, the wide field of view of the Large Area Telescope enables observations of 20% of the sky at any instant, and of the whole sky every three hours. It has revealed a very animated sky with bright gamma-ray bursts flashing and vanishing in minutes, powerful active galactic nuclei flaring over hours and days, many pulsars twinkling in the Milky Way, and X-ray binaries shimmering along their orbit. Most of these variable sources had not been seen by the Fermi predecessor, EGRET, and the wealth of new data already brings important clues to the origin of the high-energy emission and particles powered by the compact objects. The telescope also brings crisp images of the bright gamma-ray emission produced by cosmic-ray interactions in the interstellar medium, thus allowing to measure the cosmic nuclei and electron spectra across the Galaxy, to weigh interstellar clouds, in particular in the dark-gas phase. The telescope sensitivity at high energy will soon provide useful constraints on dark-matter annihilations in a variety of environments. I will review the current results and future prospects of the Fermi mission.

  17. The Animated Gamma-ray Sky Revealed by the Fermi Gamma-ray Space Telescope

    ScienceCinema

    Isabelle Grenier

    2010-01-08

    The Fermi Gamma-ray Space Telescope has been observing the sky in gamma-rays since August 2008.  In addition to breakthrough capabilities in energy coverage (20 MeV-300 GeV) and angular resolution, the wide field of view of the Large Area Telescope enables observations of 20% of the sky at any instant, and of the whole sky every three hours. It has revealed a very animated sky with bright gamma-ray bursts flashing and vanishing in minutes, powerful active galactic nuclei flaring over hours and days, many pulsars twinkling in the Milky Way, and X-ray binaries shimmering along their orbit. Most of these variable sources had not been seen by the Fermi predecessor, EGRET, and the wealth of new data already brings important clues to the origin of the high-energy emission and particles powered by the compact objects. The telescope also brings crisp images of the bright gamma-ray emission produced by cosmic-ray interactions in the interstellar medium, thus allowing to measure the cosmic nuclei and electron spectra across the Galaxy, to weigh interstellar clouds, in particular in the dark-gas phase. The telescope sensitivity at high energy will soon provide useful constraints on dark-matter annihilations in a variety of environments. I will review the current results and future prospects of the Fermi mission.

  18. High brightness beams and applications

    SciTech Connect

    Sheffield, R.L.

    1995-09-01

    This paper describes the present research on attaining intense bright electron beams. Thermionic systems are briefly covered. Recent and past results from the photoinjector programs are given. The performance advantages and difficulties presently faced by researchers using photoinjectors is discussed. The progress that has been made in photocathode materials, both in lifetime and quantum efficiency, is covered. Finally, a discussion of emittance measurements of photoinjector systems and how the measurement is complicated by the non-thermal nature of the electron beam is presented.

  19. Optical klystron SASE at FERMI

    NASA Astrophysics Data System (ADS)

    Penco, G.; Allaria, E. M.; De Ninno, G.; Ferrari, E.; Giannessi, L.

    2015-05-01

    The optical klystron enhancement to a self-amplified spontaneous emission (SASE) free electron laser (FEL) has been deeply studied in theory and in simulations. In this FEL scheme, a relativistic electron beam passes through two undulators, separated by a dispersive section. The latter converts the electron-beam energy modulation produced in the first undulator in density modulation, thus enhancing the free-electron laser gain. We report the first experiment that has been carried out at the FERMI facility in Trieste, of enhancement to a SASE FEL by using the optical klystron scheme. XUV photons have been produced with an intensity several orders of magnitude larger than in pure SASE mode. The impact of the uncorrelated energy spread of the electron beam on the optical klystron SASE performance has been also investigated.

  20. Fermi-LAT Gamma-Ray Detections of Classical Novae V1369 Centauri 2013 and V5668 Sagittarii 2015

    NASA Astrophysics Data System (ADS)

    Cheung, C. C.; Jean, P.; Shore, S. N.; Stawarz, Ł.; Corbet, R. H. D.; Knödlseder, J.; Starrfield, S.; Wood, D. L.; Desiante, R.; Longo, F.; Pivato, G.; Wood, K. S.

    2016-08-01

    We report the Fermi Large Area Telescope (LAT) detections of high-energy (>100 MeV) γ-ray emission from two recent optically bright classical novae, V1369 Centauri 2013 and V5668 Sagittarii 2015. At early times, Fermi target-of-opportunity observations prompted by their optical discoveries provided enhanced LAT exposure that enabled the detections of γ-ray onsets beginning ˜2 days after their first optical peaks. Significant γ-ray emission was found extending to 39–55 days after their initial LAT detections, with systematically fainter and longer-duration emission compared to previous γ-ray-detected classical novae. These novae were distinguished by multiple bright optical peaks that encompassed the time spans of the observed γ-rays. The γ-ray light curves and spectra of the two novae are presented along with representative hadronic and leptonic models, and comparisons with other novae detected by the LAT are discussed.

  1. Fermi-LAT Gamma-Ray Detections of Classical Novae V1369 Centauri 2013 and V5668 Sagittarii 2015

    NASA Astrophysics Data System (ADS)

    Cheung, C. C.; Jean, P.; Shore, S. N.; Stawarz, Ł.; Corbet, R. H. D.; Knödlseder, J.; Starrfield, S.; Wood, D. L.; Desiante, R.; Longo, F.; Pivato, G.; Wood, K. S.

    2016-08-01

    We report the Fermi Large Area Telescope (LAT) detections of high-energy (>100 MeV) γ-ray emission from two recent optically bright classical novae, V1369 Centauri 2013 and V5668 Sagittarii 2015. At early times, Fermi target-of-opportunity observations prompted by their optical discoveries provided enhanced LAT exposure that enabled the detections of γ-ray onsets beginning ∼2 days after their first optical peaks. Significant γ-ray emission was found extending to 39–55 days after their initial LAT detections, with systematically fainter and longer-duration emission compared to previous γ-ray-detected classical novae. These novae were distinguished by multiple bright optical peaks that encompassed the time spans of the observed γ-rays. The γ-ray light curves and spectra of the two novae are presented along with representative hadronic and leptonic models, and comparisons with other novae detected by the LAT are discussed.

  2. Very high brightness diode laser

    NASA Astrophysics Data System (ADS)

    Heinemann, Stefan; Lewis, Ben; Michaelis, Karsten; Schmidt, Torsten

    2012-03-01

    Multiple Single Emitter (MSE) modules allow highest power and highest brightness diode lasers based on standard broad area diodes. 12 single emitters, each rated at 11 W, are stacked in fast axis and with polarization multiplexing 200W are achieved in a fully collimated beam with a beam quality of 7mm*mrad in both axes. Volume Bragg Gratings (VBG) stabilize the wavelength and narrow the linewidth to less than 2nm. Dichroic mirrors are used for dense wavelength multiplexing of 4 channels within 12 nm. 400W are measured from a 0.2 mm fiber, 0.1 NA. Control and drive electronics are integrated into the 200 W platform and represent a basic building block for a variety of applications, such as a flexible turn key system comprising 12 MSE modules. An integrated beam switch directs the light in six 100 μm, or in one 0.2 mm and one 0.1 mm fiber. 800W are measured from the six 0.1 mm fibers and 700W from the 0.2 mm fiber. The technologies can be transferred to other wavelengths to include 793 nm and 1530 nm. Narrow line gratings and optimized spectral combining enable further improvements in spectral brightness and power.

  3. The First Fermi Gamma-ray Burst Monitor (GBM) Terrestrial Gamma-ray Flash (TGF) Catalog

    NASA Astrophysics Data System (ADS)

    Briggs, M. S.; Connaughton, V.; Stanbro, M.; Zhang, B.; Bhat, N.; Fishman, G. J.; Roberts, O.; Fitzpatrick, G.; McBreen, S.; Grove, J. E.; Chekhtman, A.

    2014-12-01

    We present summary results from the first catalog of Terrestrial Gamma-ray Flashes (TGFs) detected with the Gamma-ray Burst Monitor (GBM) on the Fermi Space Telescope. The catalog is expected to contain about 2600 TGFs and will be released both online, to conveniently provide the community with TGF parameters, and as a publication. Since the launch of Fermi in 2008 the TGF detection sensitivity of GBM has been improved several times, both in the flight software and in ground analysis. Starting in 2010 July individual photons were downloaded for portions of the orbits, enabling an off-line search that found weaker and shorter TGFs. Since 2012 November 26 this telemetry mode has been extended to continuous coverage -- in the first year of this data mode 841 TGFs were detected. The TGF sample is reliable, with cosmic rays rejected using data both from Fermi GBM and from the Large Area Telescope on Fermi. The online catalog will include times (UTC and solar), spacecraft geographic positions, durations, count intensities and other parameters (e.g., see the Bayesian Block analysis by O. Roberts). There will be separate tables for bright TGFs detected by the flight software and Terrestrial Electron Beams (TEBs).

  4. Fermi Detection of Delayed GeV Emission from the Short Gamma-Ray Burst 081024B

    NASA Astrophysics Data System (ADS)

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Asano, K.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B. M.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bhat, P. N.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Briggs, M. S.; Brigida, M.; Bruel, P.; Burgess, J. M.; Burnett, T. H.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cecchi, C.; Çelik, Ö.; Chaplin, V.; Charles, E.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Cominsky, L. R.; Connaughton, V.; Conrad, J.; Cutini, S.; Dermer, C. D.; de Angelis, A.; de Palma, F.; Digel, S. W.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Dumora, D.; Farnier, C.; Favuzzi, C.; Fegan, S. J.; Fishman, G.; Focke, W. B.; Fortin, P.; Frailis, M.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giebels, B.; Giglietto, N.; Giommi, P.; Giordano, F.; Glanzman, T.; Godfrey, G.; Granot, J.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Haynes, R. H.; Hays, E.; Horan, D.; Hughes, R. E.; Jackson, M. S.; Jóhannesson, G.; Johnson, A. S.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kawai, N.; Kerr, M.; Kippen, R. M.; Knödlseder, J.; Kocevski, D.; Kocian, M. L.; Komin, N.; Kouveliotou, C.; Kuehn, F.; Kuss, M.; Lande, J.; Latronico, L.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Makeev, A.; Mazziotta, M. N.; McBreen, S.; McEnery, J. E.; McGlynn, S.; Meegan, C.; Mészáros, P.; Meurer, C.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paciesas, W. S.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Piron, F.; Porter, T. A.; Preece, R.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reposeur, T.; Ripken, J.; Ritz, S.; Rochester, L. S.; Rodriguez, A. Y.; Roth, M.; Ryde, F.; Sadrozinski, H. F.-W.; Sanchez, D.; Sander, A.; Saz Parkinson, P. M.; Scargle, J. D.; Schalk, T. L.; Sgrò, C.; Siskind, E. J.; Smith, D. A.; Smith, P. D.; Spandre, G.; Spinelli, P.; Stamatikos, M.; Strickman, M. S.; Suson, D. J.; Tagliaferri, G.; Tajima, H.; Takahashi, H.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Toma, K.; Torres, D. F.; Tosti, G.; Tramacere, A.; Troja, E.; Uchiyama, Y.; Usher, T. L.; van der Horst, A. J.; Vasileiou, V.; Vilchez, N.; Vitale, V.; von Kienlin, A.; Waite, A. P.; Wang, P.; Wilson-Hodge, C.; Winer, B. L.; Wood, K. S.; Wu, X. F.; Yamazaki, R.; Ylinen, T.; Ziegler, M.

    2010-03-01

    We report on the detailed analysis of the high-energy extended emission from the short gamma-ray burst (GRB) 081024B detected by the Fermi Gamma-ray Space Telescope. Historically, this represents the first clear detection of temporal extended emission from a short GRB. The light curve observed by the Fermi Gamma-ray Burst Monitor lasts approximately 0.8 s whereas the emission in the Fermi Large Area Telescope lasts for about 3 s. Evidence of longer lasting high-energy emission associated with long bursts has been already reported by previous experiments. Our observations, together with the earlier reported study of the bright short GRB 090510, indicate similarities in the high-energy emission of short and long GRBs and open the path to new interpretations.

  5. Fermi large area telescope observations of blazar 3C 279 occultations by the sun

    SciTech Connect

    Barbiellini, G.; Bastieri, D.; Buson, S.; Bechtol, K.; Blandford, R. D.; Borgland, A. W.; Buehler, R.; Cameron, R. A.; Chiang, J.; Bellazzini, R.; Bregeon, J.; Bruel, P.; Caraveo, P. A.; Cavazzuti, E.; Ciprini, S.; Cecchi, C.; Chaves, R. C. G.; Cheung, C. C. E-mail: phdmitry@stanford.edu; and others

    2014-04-01

    Observations of occultations of bright γ-ray sources by the Sun may reveal predicted pair halos around blazars and/or new physics, such as, e.g., hypothetical light dark matter particles—axions. We use Fermi Gamma-Ray Space Telescope (Fermi) data to analyze four occultations of blazar 3C 279 by the Sun on October 8 each year from 2008 to 2011. A combined analysis of the observations of these occultations allows a point-like source at the position of 3C 279 to be detected with significance of ≈3σ, but does not reveal any significant excess over the flux expected from the quiescent Sun. The likelihood ratio test rules out complete transparency of the Sun to the blazar γ-ray emission at a 3σ confidence level.

  6. Identifying Unidentified Fermi-LAT Objects (UFOs) at High-Latitude

    NASA Astrophysics Data System (ADS)

    Cheung, Chi Teddy

    2009-09-01

    We propose a Chandra study of 8 high Galactic latitude gamma-ray sources in the Fermi-LAT bright source list. These sources are currently unidentified, i.e., they are not clearly associated with established classes of gamma-ray emitters like blazars and pulsars. The proposed observations will determine the basic properties (fluxes, positions, hardness ratio/spectra) of all X-ray sources down to a 0.3-10 keV flux limit of 1.5e-14 erg/cm2/s within the Fermi-LAT localization circles. This will enable further follow-up at other wavelengths, with the ultimate goal to reveal the nature of these enigmatic gamma-ray sources.

  7. Unidentified Active Galactic Nuclei in the Fermi-2LAC catalogue: identification of candidate sources

    NASA Astrophysics Data System (ADS)

    Klindt, L.; van Soelen, B.; Meintjes, P. J.

    Blazars constitute the most violent astronomical objects with jet emitting radiation at all frequencies. In order to fully understand and model blazars and in particular the accretion-black hole system and superluminal jet structure, multi-wavelength observations are required. In the search for Very High Energy (VHE) sources a target sample of twenty unidentified sources with possible blazar characteristics has been constructed from sources listed in the Fermi-2LAC catalogue. The selected targets are all at high galactic latitude (|b| > 10°) with optical/radio counterparts within the Fermi 95% error circle. The selection criteria, which are based on source properties including radio brightness, photon spectral indices, undetermined redshifts, observability and variability, are presented along with the twenty identified sources.

  8. Fermi-LAT Gamma-ray Bursts and Insight from Swift

    NASA Technical Reports Server (NTRS)

    Racusin, Judith L.

    2011-01-01

    A new revolution in GRB observation and theory has begun over the last 3 years since the launch of the Fermi gamma-ray space telescope. The new window into high energy gamma-rays opened by the Fermi-LAT is providing insight into prompt emission mechanisms and possibly also afterglow physics. The LAT detected GRBs appear to be a new unique subset of extremely energetic and bright bursts. In this talk I will discuss the context and recent discoveries from these LAT GRBs and the large database of broadband observations collected by Swift over the last 7 years and how through comparisons between the Swift, GBM, and LAT GRB samples, we can learn about the unique characteristics and relationships between each population.

  9. Late-time cosmology of a scalar-tensor theory with a universal multiplicative coupling between the scalar field and the matter Lagrangian

    NASA Astrophysics Data System (ADS)

    Minazzoli, Olivier; Hees, Aurélien

    2014-07-01

    We investigate the late-time cosmological behavior of scalar-tensor theories with a universal multiplicative coupling between the scalar field and the matter Lagrangian in the matter era. This class of theory encompasses the case of the massless string dilaton [see Damour and Polyakov, General Relativity and Gravitation 26, 1171 (1994)] as well as a theory with an intrinsic decoupling mechanism in the solar system [see Minazzoli and Hees, Phys. Rev. D 88, 041504 (2013)]. The cosmological evolution is studied in the general relativity limit justified by solar system constraints on the gravitation theory. The behavior of these cosmological evolutions are then compared to two types of observations: the constraints on temporal variations of the constants of nature and the distance-luminosity measurements. In particular, the nonminimal coupling implies that the distance-luminosity relation is modified compared to general relativity. Theories producing a cosmological behavior in agreement with these observations are identified.

  10. Braneworld models with a non-minimally coupled phantom bulk field: a simple way to obtain the -1-crossing at late times

    SciTech Connect

    Setare, M.R.; Saridakis, E.N. E-mail: msaridak@phys.uoa.gr

    2009-03-15

    We investigate general braneworld models, with a non-minimally coupled phantom bulk field and arbitrary brane and bulk matter contents. We show that the effective dark energy of the brane-universe acquires a dynamical nature, as a result of the non-minimal coupling which provides a mechanism for an indirect ''bulk-brane interaction'' through gravity. For late-time cosmological evolution and without resorting to special ansatzes or to specific areas of the parameter space, we show that the -1-crossing of its equation-of-state parameter is general and can be easily achieved. As an example we provide a simple, but sufficiently general, approximate analytical solution, that presents the crossing behavior.

  11. Coalescing binary systems of compact objects to (post) sup 5/2 -Newtonian order: Late-time evolution and gravitational radiation emission

    SciTech Connect

    Lincoln, C.W.

    1990-01-01

    The late-time evolution of binary systems of compact objects (neutron stars or black holes) is studied using the Damour-Derueele (post){sup 5/2}-Newtonian equations of motion with relativistic corrections of all orders up to and including radiation reaction. Using the method of close orbital elements from celestial mechanics, the author evolves the orbits to separations of r {approx} 2 m, where m is the total mass, at which point the (post){sup 5/2}-Newtonian approximation breaks down. With the orbits as input, he calculates the gravitational waveform and luminosity using a post-Newtonian formalism of Wagoner and Will. Results are obtained for systems containing various combinations of compact objects, for various values of the mass ratio m{sub 1}/m{sub 2}, and forg various initial values of the orbital eccentricity.

  12. Crow Instability in Unitary Fermi Gas

    NASA Astrophysics Data System (ADS)

    Gautam, Sandeep

    2013-06-01

    In this paper, we investigate the initiation and subsequent evolution of Crow instability in an inhomogeneous unitary Fermi gas using zero-temperature Galilei-invariant nonlinear Schrödinger equation. Considering a cigar-shaped unitary Fermi gas, we generate the vortex-antivortex pair either by phase-imprinting or by moving a Gaussian obstacle potential. We observe that the Crow instability in a unitary Fermi gas leads to the decay of the vortex-antivortex pair into multiple vortex rings and ultimately into sound waves.

  13. Quantum Mechanical Models Of The Fermi Shuttle

    SciTech Connect

    Sternberg, James

    2011-06-01

    The Fermi shuttle is a mechanism in which high energy electrons are produced in an atomic collision by multiple collisions with a target and a projectile atom. It is normally explained purely classically in terms of the electron's orbits prescribed in the collision. Common calculations to predict the Fermi shuttle use semi-classical methods, but these methods still rely on classical orbits. In reality such collisions belong to the realm of quantum mechanics, however. In this paper we discuss several purely quantum mechanical calculations which can produce the Fermi shuttle. Being quantum mechanical in nature, these calculations produce these features by wave interference, rather than by classical orbits.

  14. Late Time Multi-wavelength Observations of Swift J1644+5734: A Luminous Optical/IR Bump and Quiescent X-Ray Emission

    NASA Astrophysics Data System (ADS)

    Levan, A. J.; Tanvir, N. R.; Brown, G. C.; Metzger, B. D.; Page, K. L.; Cenko, S. B.; O'Brien, P. T.; Lyman, J. D.; Wiersema, K.; Stanway, E. R.; Fruchter, A. S.; Perley, D. A.; Bloom, J. S.

    2016-03-01

    We present late time multi-wavelength observations of Swift J1644+57, suggested to be a relativistic tidal disruption flare (TDF). Our observations extend to >4 years from discovery and show that 1.4 years after outburst the relativistic jet switched off on a timescale less than tens of days, corresponding to a power-law decay faster than t-70. Beyond this point weak X-rays continue to be detected at an approximately constant luminosity of LX ˜ 5 × 1042 erg s-1 and are marginally inconsistent with a continuing decay of t-5/3, similar to that seen prior to the switch-off. Host photometry enables us to infer a black hole mass of MBH = 3 × 106 M⊙, consistent with the late time X-ray luminosity arising from sub-Eddington accretion onto the black hole in the form of either an unusually optically faint active galactic nucleus or a slowly varying phase of the transient. Optical/IR observations show a clear bump in the light curve at timescales of 30-50 days, with a peak magnitude (corrected for host galaxy extinction) of MR ˜ -22 to -23. The luminosity of the bump is significantly higher than seen in other, non-relativistic TDFs and does not match any re-brightening seen at X-ray or radio wavelengths. Its luminosity, light curve shape, and spectrum are broadly similar to those seen in superluminous supervnovae, although subject to large uncertainties in the correction of the significant host extinction. We discuss these observations in the context of both TDF and massive star origins for Swift J1644+5734 and other candidate relativistic tidal flares.

  15. Late-time mid-IR emission from Type Ia and stripped-envelope core-collapse supernovae - possible sign of circumstellar interaction

    NASA Astrophysics Data System (ADS)

    Szalai, Tamas; Vinko, Jozsef; Pooley, David A.; Silverman, Jeffrey Michael; Wheeler, J. Craig

    2016-01-01

    The signs of circumstellar interaction in the late phase (>1 yr) of supernovae (SNe) can be studied in various wavelength regimes from X-ray to radio. These observations offer a chance to reveal information about the type and mass-loss history of the progenitor, the presence of a companion star, and the environment of the SN. While this phenomenon is well-known and well-studied concerning SN IIn, similar processes have not been observed to take place in other types of SNe.We suggest that numeruous objects belong to other types of SNe (SNe Ia, Ib/c or IIb) may also show detectable sign of circumstellar interaction. In these types of SNe, the source of late-time mid-infrared (mid-IR) excess may be some kind of interaction between the SN ejecta and the circumstellar matter (CSM) that originated from the pre-explosion mass-loss of the progenitor and/or its companion star. The observed mid-IR emission from these SNe, especially combined with data from other wavelength regimes, may be a convincing sign of CSM interaction.Here we present some unpublished results based on the archive measurements of the Spitzer Space Telescope. Our study includes the analysis of late-time mid-IR emission from such well-known CSM-interacting SNe like SN Ia-CSM PTF11kx, SN Ibn 2001em, and SN IIb 1993J, as well as from some other interesting Type Ia and stripped-envelope SNe, where CSM interaction may also take place.

  16. How Bright Can Supernovae Get?

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    Supernovae enormous explosions associated with the end of a stars life come in a variety of types with different origins. A new study has examined how the brightest supernovae in the Universe are produced, and what limits might be set on their brightness.Ultra-Luminous ObservationsRecent observations have revealed many ultra-luminous supernovae, which haveenergies that challenge our abilities to explain them usingcurrent supernova models. An especially extreme example is the 2015 discovery of the supernova ASASSN-15lh, which shone with a peak luminosity of ~2*1045 erg/s, nearly a trillion times brighter than the Sun. ASASSN-15lh radiated a whopping ~2*1052 erg in the first four months after its detection.How could a supernova that bright be produced? To explore the answer to that question, Tuguldur Sukhbold and Stan Woosley at University of California, Santa Cruz, have examined the different sources that could produce supernovae and calculated upper limits on the potential luminosities ofeach of these supernova varieties.Explosive ModelsSukhbold and Woosley explore multiple different models for core-collapse supernova explosions, including:Prompt explosionA stars core collapses and immediately explodes.Pair instabilityElectron/positron pair production at a massive stars center leads to core collapse. For high masses, radioactivity can contribute to delayed energy output.Colliding shellsPreviously expelled shells of material around a star collide after the initial explosion, providing additional energy release.MagnetarThe collapsing star forms a magnetar a rapidly rotating neutron star with an incredibly strong magnetic field at its core, which then dumps energy into the supernova ejecta, further brightening the explosion.They then apply these models to different types of stars.Setting the LimitThe authors show that the light curve of ASASSN-15lh (plotted in orange) can be described by a model (black curve) in which a magnetar with an initial spin period of 0.7 ms

  17. [Bright light therapy for elderly].

    PubMed

    Okawa, Masako

    2015-06-01

    Bright light therapy (BLT) holds considerable promise for sleep problems in the elderly. BLT for community-dwelling patients with Alzheimer's disease showed significant improvement in sleep parameters. In the institutional setting, BLT was effective in reducing daytime nap duration. Morning BLT was found to advance the peak circadian rhythm and increase activity level in daytime and melatonin level at night. Light therapy could be used in combination with other nonpharmacological methods such as social activities, outside walking, physical exercises, which showed greater effects than independent BLT on sleep and cognitive function. BLT treatment strategy was proposed in the present paper. We should pay more attentions to BLT in community setting for mental and physical well-being. PMID:26065132

  18. Fermi's Conundrum: Proliferation and Closed Societies

    NASA Astrophysics Data System (ADS)

    Teller, Wendy; Westfall, Catherine

    2007-04-01

    On January 1, 1946 Emily Taft Douglas, a freshman Representative at Large for Illinois, sent a letter to Enrico Fermi. She wanted to know whether, if atomic energy was used for peaceful purposes, it might be possible to clandestinely divert some material for bombs. Douglas first learned about the bomb not quite five months before when Hiroshima was bombed. Even though she was not a scientist she identified a key problem of the nuclear age. Fermi responded with requirements to allow peaceful uses of atomic energy and still outlaw nuclear weapons. First, free interchange of information between people was required, and second, people who reported possible violations had to be protected. Fermi had lived in Mussolini's Italy and worked under the war time secrecy restrictions of the Manhattan Project. He was not optimistic that these conditions could be met. This paper discusses how Douglas came to recognize the proliferation issue and what led Fermi to his solution and his pessimism about its practicality.

  19. Fermi discovers giant bubbles in Milky Way

    NASA Video Gallery

    Using data from NASA's Fermi Gamma-ray Space Telescope, scientists have recently discovered a gigantic, mysterious structure in our galaxy. This feature looks like a pair of bubbles extending above...

  20. Fermi Sees Antimatter-Hurling Thunderstorms

    NASA Video Gallery

    NASA's Fermi Gamma-ray Space Telescope has detected beams of antimatter launched by thunderstorms. Acting like enormous particle accelerators, the storms can emit gamma-ray flashes, called TGFs, an...

  1. RF Spectroscopy on a Homogeneous Fermi Gas

    NASA Astrophysics Data System (ADS)

    Yan, Zhenjie; Mukherjee, Biswaroop; Patel, Parth; Struck, Julian; Zwierlein, Martin

    2016-05-01

    Over the last two decades RF spectroscopy has been established as an indispensable tool to probe a large variety of fundamental properties of strongly interacting Fermi gases. This ranges from measurement of the pairing gap over tan's contact to the quasi-particle weight of Fermi polarons. So far, most RF spectroscopy experiments have been performed in harmonic traps, resulting in an averaged response over different densities. We have realized an optical uniform potential for ultracold Fermi gases of 6 Li atoms, which allows us to avoid the usual problems connected to inhomogeneous systems. Here we present recent results on RF spectroscopy of these homogeneous samples with a high signal to noise ratio. In addition, we report progress on measuring the contact of a unitary Fermi gas across the normal to superfluid transition.

  2. Fermi Proves Supernova Remnants Make Cosmic Rays

    NASA Video Gallery

    The husks of exploded stars produce some of the fastest particles in the cosmos. New findings by NASA's Fermi show that two supernova remnants accelerate protons to near the speed of light. The pro...

  3. Quantum communication with macroscopically bright nonclassical states.

    PubMed

    Usenko, Vladyslav C; Ruppert, Laszlo; Filip, Radim

    2015-11-30

    We analyze homodyne detection of macroscopically bright multimode nonclassical states of light and propose their application in quantum communication. We observe that the homodyne detection is sensitive to a mode-matching of the bright light to the highly intense local oscillator. Unmatched bright modes of light result in additional noise which technically limits detection of Gaussian entanglement at macroscopic level. When the mode-matching is sufficient, we show that multimode quantum key distribution with bright beams is feasible. It finally merges the quantum communication with classical optical technology of visible beams of light. PMID:26698776

  4. Properties of Photospheric Bright Points outside Sunspots

    NASA Astrophysics Data System (ADS)

    Qu, H. X.; Yang, Y. F.; Feng, S.; Wang, F.; Deng, H.; Ji, K. F.

    2015-09-01

    Photospheric bright points are tiny bright features located in intergranular lanes. They are widely believed as the foot points of magnetic flux tubes. In this paper, various properties of bright points outside NOAA 11598 sunspots are analyzed using the TiO-band data detected by the 1-m New Vacuum Solar Telescope of Yunnan Observatories, which is located at the Fuxian Solar Physics Observing Station, Yunnan Province. We divide the periphery of the sunspot into four annular regions based on the dilation technology of image morphology. Then, a Laplacian and morphological dilation algorithm is used to identify bright points, and a three-dimensional segment algorithm is applied to track the evolution of bright points. Finally, we detect the parameters of the bright points in the four annular regions, including the density, intensity, size, shape, and velocity. Statistical results show that the density, size, and velocity of photospheric bright points are obviously affected by the strong magnetic fields of sunspots, and their peak values are in the second region instead of the closest region of the sunspot. The bright points decrease their densities and sizes, but increase their velocities with the distance away from the sunspot center. Additionally, the maximum intensity contrast presents the decreasing trend. However, the bright point shapes are basically invariant, and independent of this distance.

  5. ORIGIN OF THE FERMI BUBBLE

    SciTech Connect

    Cheng, K.-S.; Chernyshov, D. O.; Dogiel, V. A.; Ko, C.-M.; Ip, W.-H.

    2011-04-10

    Fermi has discovered two giant gamma-ray-emitting bubbles that extend nearly 10 kpc in diameter north and south of the Galactic center. The existence of the bubbles was first evidenced in X-rays detected by ROSAT and later WMAP detected an excess of radio signals at the location of the gamma-ray bubbles. We propose that periodic star capture processes by the galactic supermassive black hole, Sgr A*, with a capture rate 3 x 10{sup -5} yr{sup -1} and energy release {approx}3 x 10{sup 52} erg per capture can produce very hot plasma {approx}10 keV with a wind velocity {approx}10{sup 8} cm s{sup -1} injected into the halo and heat up the halo gas to {approx}1 keV, which produces thermal X-rays. The periodic injection of hot plasma can produce shocks in the halo and accelerate electrons to {approx}TeV, which produce radio emission via synchrotron radiation and gamma rays via inverse Compton scattering with the relic and the galactic soft photons.

  6. Observation of Fermi Polarons in a Tunable Fermi Liquid of Ultracold Atoms

    SciTech Connect

    Schirotzek, Andre; Wu, C.-H.; Sommer, Ariel; Zwierlein, Martin W.

    2009-06-12

    We have observed Fermi polarons, dressed spin-down impurities in a spin-up Fermi sea of ultracold atoms. The polaron manifests itself as a narrow peak in the impurities' rf spectrum that emerges from a broad incoherent background. We determine the polaron energy and the quasiparticle residue for various interaction strengths around a Feshbach resonance. At a critical interaction, we observe the transition from polaronic to molecular binding. Here, the imbalanced Fermi liquid undergoes a phase transition into a Bose liquid, coexisting with a Fermi sea.

  7. Fermi-LAT observations of the gamma-ray burst GRB 130427A.

    PubMed

    Ackermann, M; Ajello, M; Asano, K; Atwood, W B; Axelsson, M; Baldini, L; Ballet, J; Barbiellini, G; Baring, M G; Bastieri, D; Bechtol, K; Bellazzini, R; Bissaldi, E; Bonamente, E; Bregeon, J; Brigida, M; Bruel, P; Buehler, R; Burgess, J Michael; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Cecchi, C; Chaplin, V; Charles, E; Chekhtman, A; Cheung, C C; Chiang, J; Chiaro, G; Ciprini, S; Claus, R; Cleveland, W; Cohen-Tanugi, J; Collazzi, A; Cominsky, L R; Connaughton, V; Conrad, J; Cutini, S; D'Ammando, F; de Angelis, A; DeKlotz, M; de Palma, F; Dermer, C D; Desiante, R; Diekmann, A; Di Venere, L; Drell, P S; Drlica-Wagner, A; Favuzzi, C; Fegan, S J; Ferrara, E C; Finke, J; Fitzpatrick, G; Focke, W B; Franckowiak, A; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gehrels, N; Germani, S; Gibby, M; Giglietto, N; Giles, M; Giordano, F; Giroletti, M; Godfrey, G; Granot, J; Grenier, I A; Grove, J E; Gruber, D; Guiriec, S; Hadasch, D; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Horan, D; Hughes, R E; Inoue, Y; Jogler, T; Jóhannesson, G; Johnson, W N; Kawano, T; Knödlseder, J; Kocevski, D; Kuss, M; Lande, J; Larsson, S; Latronico, L; Longo, F; Loparco, F; Lovellette, M N; Lubrano, P; Mayer, M; Mazziotta, M N; McEnery, J E; Michelson, P F; Mizuno, T; Moiseev, A A; Monzani, M E; Moretti, E; Morselli, A; Moskalenko, I V; Murgia, S; Nemmen, R; Nuss, E; Ohno, M; Ohsugi, T; Okumura, A; Omodei, N; Orienti, M; Paneque, D; Pelassa, V; Perkins, J S; Pesce-Rollins, M; Petrosian, V; Piron, F; Pivato, G; Porter, T A; Racusin, J L; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Ritz, S; Roth, M; Ryde, F; Sartori, A; Parkinson, P M Saz; Scargle, J D; Schulz, A; Sgrò, C; Siskind, E J; Sonbas, E; Spandre, G; Spinelli, P; Tajima, H; Takahashi, H; Thayer, J G; Thayer, J B; 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; Winer, B L; Wood, K S; Yamazaki, R; Younes, G; Yu, H-F; Zhu, S J; Bhat, P N; Briggs, M S; Byrne, D; Foley, S; Goldstein, A; Jenke, P; Kippen, R M; Kouveliotou, C; McBreen, S; Meegan, C; Paciesas, W S; Preece, R; Rau, A; Tierney, D; van der Horst, A J; von Kienlin, A; Wilson-Hodge, C; Xiong, S; Cusumano, G; La Parola, V; Cummings, J R

    2014-01-01

    The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest γ-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock. PMID:24263133

  8. Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Ajello, M.; Asano, K.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bissaldi, E.; Bonamente, E.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Burgess, J. Michael; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cecchi, C.; Chaplin, V.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Chiaro, G.; Ciprini, S.; Claus, R.; Cleveland, W.; Cohen-Tanugi, J.; Collazzi, A.; Cominsky, L. R.; Connaughton, V.; Conrad, J.; Cutini, S.; D'Ammando, F.; de Angelis, A.; DeKlotz, M.; de Palma, F.; Dermer, C. D.; Desiante, R.; Diekmann, A.; Di Venere, L.; Drell, P. S.; Drlica-Wagner, A.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Finke, J.; Fitzpatrick, G.; Focke, W. B.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gehrels, N.; Germani, S.; Gibby, M.; Giglietto, N.; Giles, M.; Giordano, F.; Giroletti, M.; Godfrey, G.; Granot, J.; Grenier, I. A.; Grove, J. E.; Gruber, D.; Guiriec, S.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Inoue, Y.; Jogler, T.; Jóhannesson, G.; Johnson, W. N.; Kawano, T.; Knödlseder, J.; Kocevski, D.; Kuss, M.; Lande, J.; Larsson, S.; Latronico, L.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Mayer, M.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mizuno, T.; Moiseev, A. A.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nemmen, R.; Nuss, E.; Ohno, M.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orienti, M.; Paneque, D.; Pelassa, V.; Perkins, J. S.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Pivato, G.; Porter, T. A.; Racusin, J. L.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Ritz, S.; Roth, M.; Ryde, F.; Sartori, A.; Parkinson, P. M. Saz; Scargle, J. D.; Schulz, A.; Sgrò, C.; Siskind, E. J.; Sonbas, E.; Spandre, G.; Spinelli, P.; Tajima, H.; Takahashi, H.; Thayer, J. G.; Thayer, J. B.; 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.; Winer, B. L.; Wood, K. S.; Yamazaki, R.; Younes, G.; Yu, H.-F.; Zhu, S. J.; Bhat, P. N.; Briggs, M. S.; Byrne, D.; Foley, S.; Goldstein, A.; Jenke, P.; Kippen, R. M.; Kouveliotou, C.; McBreen, S.; Meegan, C.; Paciesas, W. S.; Preece, R.; Rau, A.; Tierney, D.; van der Horst, A. J.; von Kienlin, A.; Wilson-Hodge, C.; Xiong, S.; Cusumano, G.; La Parola, V.; Cummings, J. R.

    2014-01-01

    The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest γ-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.

  9. Swift and Fermi Observations of the Early Afterglow of the Short Gamma-Ray Burst 090510

    NASA Astrophysics Data System (ADS)

    De Pasquale, M.; Schady, P.; Kuin, N. P. M.; Page, M. J.; Curran, P. A.; Zane, S.; Oates, S. R.; Holland, S. T.; Breeveld, A. A.; Hoversten, E. A.; Chincarini, G.; Grupe, D.; Abdo, A. A.; Ackermann, M.; Ajello, M.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Briggs, M. S.; Brigida, M.; Bruel, P.; Burnett, T. H.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cecchi, C.; Çelik, Ö.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Connaughton, V.; Conrad, J.; Dermer, C. D.; de Angelis, A.; de Palma, F.; Dingus, B. L.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Dumora, D.; Farnier, C.; Favuzzi, C.; Fegan, S. J.; Fishman, G.; Focke, W. B.; Frailis, M.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giordano, F.; Glanzman, T.; Godfrey, G.; Granot, J.; Greiner, J.; Grenier, I. A.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Harding, A. K.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Jackson, M. S.; Jóhannesson, G.; Johnson, A. S.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kawai, N.; Kerr, M.; Kippen, R. M.; Knödlseder, J.; Kocevski, D.; Kuss, M.; Lande, J.; Latronico, L.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Makeev, A.; Mazziotta, M. N.; McEnery, J. E.; McGlynn, S.; Meegan, C.; Mészáros, P.; Meurer, C.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paciesas, W. S.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Piron, F.; Porter, T. A.; Preece, R.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Reposeur, T.; Ritz, S.; Rochester, L. S.; Rodriguez, A. Y.; Roth, M.; Ryde, F.; Sadrozinski, H. F.-W.; Sander, A.; Saz Parkinson, P. M.; Scargle, J. D.; Schalk, T. L.; Sgrò, C.; Siskind, E. J.; Smith, P. D.; Spandre, G.; Spinelli, P.; Stamatikos, M.; Starck, J.-L.; Stecker, F. W.; Strickman, M. S.; Suson, D. J.; Tajima, H.; Takahashi, H.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Toma, K.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Uehara, T.; Usher, T. L.; van der Horst, A. J.; Vasileiou, V.; Vilchez, N.; Vitale, V.; von Kienlin, A.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Wu, X. F.; Yamazaki, R.; Ylinen, T.; Ziegler, M.

    2010-02-01

    We present the observations of GRB090510 performed by the Fermi Gamma-Ray Space Telescope and the Swift observatory. This is a bright, short burst that shows an extended emission detected in the GeV range. Furthermore, its optical emission initially rises, a feature so far observed only in long bursts, while the X-ray flux shows an initial shallow decrease, followed by a steeper decay. This exceptional behavior enables us to investigate the physical properties of the gamma-ray burst outflow, poorly known in short bursts. We discuss internal and external shock models for the broadband energy emission of this object.

  10. Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Asano, K.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Gehrels, Cornelis

    2013-01-01

    The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest gamma-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.

  11. BKGE: Fermi-LAT Background Estimator

    NASA Astrophysics Data System (ADS)

    Vasileiou, Vlasios

    2014-11-01

    The Fermi-LAT Background Estimator (BKGE) is a publicly available open-source tool that can estimate the expected background of the Fermi-LAT for any observational conguration and duration. It produces results in the form of text files, ROOT files, gtlike source-model files (for LAT maximum likelihood analyses), and PHA I/II FITS files (for RMFit/XSpec spectral fitting analyses). Its core is written in C++ and its user interface in Python.

  12. First Light on GRBs with Fermi

    SciTech Connect

    Dermer, Charles D.

    2010-10-15

    Fermi LAT (Large Area Telescope) and GBM (Gamma ray Burst Monitor) observations of GRBs are briefly reviewed, keeping in mind EGRET expectations. Using {gamma}{gamma} constraints on outflow Lorentz factors, leptonic models are pitted against hadronic models, and found to be energetically favored. Interpretation of the Fermi data on GRBs helps establish whether GRBs accelerate cosmic rays, including those reaching {approx_equal}10{sup 20} eV.

  13. Understanding and Using the Fermi Science Tools

    NASA Astrophysics Data System (ADS)

    Asercion, Joseph; Fermi Science Support Center Team

    2016-01-01

    The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads and a reference manual available on the FSSC website provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide examples of standard analyses, including tips and tricks for improving Fermi science analysis.

  14. FERMI Observations of Gamma -Ray Emission From the Moon

    NASA Technical Reports Server (NTRS)

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Atwoo, W. B.; Baldini, I.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Bouvier, A.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Gehrels, N.; Hays, E.; Thompson, D. J.; McEnery, J. E.; Troja, E.

    2012-01-01

    We report on the detection of high-energy ? -ray emission from the Moon during the first 24 months of observations by the Fermi Large Area Telescope (LAT). This emission comes from particle cascades produced by cosmicray (CR) nuclei and electrons interacting with the lunar surface. The differential spectrum of the Moon is soft and can be described as a log-parabolic function with an effective cutoff at 2-3 GeV, while the average integral flux measured with the LAT from the beginning of observations in 2008 August to the end of 2010 August is F(greater than100 MeV) = (1.04 plus or minus 0.01 [statistical error] plus or minus 0.1 [systematic error]) × 10(sup -6) cm(sup -2) s(sup -1). This flux is about a factor 2-3 higher than that observed between 1991 and 1994 by the EGRET experiment on board the Compton Gamma Ray Observatory, F(greater than100 MeV)˜5×10(sup -7) cm(sup -2) s(sup -1), when solar activity was relatively high. The higher gamma -ray flux measured by Fermi is consistent with the deep solar minimum conditions during the first 24 months of the mission, which reduced effects of heliospheric modulation, and thus increased the heliospheric flux of Galactic CRs. A detailed comparison of the light curve with McMurdo Neutron Monitor rates suggests a correlation of the trends. The Moon and the Sun are so far the only known bright emitters of gamma-rays with fast celestial motion. Their paths across the sky are projected onto the Galactic center and high Galactic latitudes as well as onto other areas crowded with high-energy gamma-ray sources. Analysis of the lunar and solar emission may thus be important for studies of weak and transient sources near the ecliptic.

  15. Spatial Brightness Perception of Trichromatic Stimuli

    SciTech Connect

    Royer, Michael P.; Houser, Kevin W.

    2012-11-16

    An experiment was conducted to examine the effect of tuning optical radiation on brightness perception for younger (18-25 years of age) and older (50 years of age or older) observers. Participants made forced-choice evaluations of the brightness of a full factorial of stimulus pairs selected from two groups of four metameric stimuli. The large-field stimuli were created by systematically varying either the red or the blue primary of an RGB LED mixture. The results indicate that light stimuli of equal illuminance and chromaticity do not appear equally bright to either younger or older subjects. The rank-order of brightness is not predicted by any current model of human vision or theory of brightness perception including Scotopic to Photopic or Cirtopic to Photopic ratio theory, prime color theory, correlated color temperature, V(λ)-based photometry, color quality metrics, linear brightness models, or color appearance models. Age may affect brightness perception when short-wavelength primaries are used, especially those with a peak wavelength shorter than 450 nm. The results suggest further development of metrics to predict brightness perception is warranted, and that including age as a variable in predictive models may be valuable.

  16. Incoherently coupled dark-bright photorefractive solitons

    NASA Astrophysics Data System (ADS)

    Chen, Zhigang; Segev, Mordechai; Coskun, Tamer H.; Christodoulides, Demetrios N.; Kivshar, Yuri S.; Afanasjev, Vsevolod V.

    1996-11-01

    We report the observation of incoherently coupled dark-bright spatial soliton pairs in a biased bulk photorefractive crystal. When such a pair is decoupled, the dark component evolves into a triplet structure, whereas the bright one decays into a self-defocusing beam.

  17. Bright Star Astrometry with URAT

    NASA Astrophysics Data System (ADS)

    Zacharias, N.

    2015-10-01

    The U.S. Naval Observatory Robotic Astrometric Telescope (URAT) is observing the northern sky since April 2012 for an astrometric survey. Multiple overlaps per year are performed in a single bandpass (680-750 nm) using the "redlens" 20 cm aperture astrograph and a mosaic of large CCDs. Besides the regular, deep survey to magnitude 18.5, short exposures with an objective grating are taken to access stars as bright as 3rd magnitude. A brief overview of the program, observing and reductions is given. Positions on the 8 to 20 mas level are obtained of 66,202 Hipparcos stars at current epochs. These are compared to the Hipparcos Catalog to investigate its accuracy. About 20% of the observed Hipparcos stars are found to have inconsistent positions with the Hipparcos Catalog prediction on the 3 sigma level or over (about 75 mas or more discrepant position offsets). Some stars are now seen at an arcsec (or 25 sigma) off their Hipparcos Catalog predicted position.

  18. Brightness alteration with interweaving contours

    PubMed Central

    Roncato, Sergio

    2012-01-01

    Chromatic induction is observed whenever the perceived colour of a target surface shifts towards the hue of a neighbouring surface. Some vivid manifestations may be seen in a white background where thin coloured lines have been drawn (assimilation) or when lines of different colours are collinear (neon effect) or adjacent (watercolour) to each other. This study examines a particular colour induction that manifests in concomitance with an opposite effect of colour saturation (or anti-spread). The two phenomena can be observed when a repetitive pattern is drawn in which outline thin contours intercept wider contours or surfaces, colour spreading appear to fill the surface occupied by surfaces or thick lines whereas the background traversed by thin lines is seen as brighter or filled of a saturated white. These phenomena were first observed by Bozzi (1975) and Kanizsa (1979) in figural conditions that did not allow them to document their conjunction. Here we illustrate various manifestations of this twofold phenomenon and compare its effects with the known effects of brightness and colour induction. Some conjectures on the nature of these effects are discussed. PMID:23483806

  19. Cortical processing of a brightness illusion

    PubMed Central

    Roe, Anna Wang; Lu, Haidong D.; Hung, Chou P.

    2005-01-01

    Several brightness illusions indicate that borders can affect the perception of surfaces dramatically. In the Cornsweet illusion, two equiluminant surfaces appear to be different in brightness because of the contrast border between them. Here, we report the existence of cells in monkey visual cortex that respond to such an “illusory” brightness. We find that luminance responsive cells are located in color-activated regions (cytochrome oxidase blobs and bridges) of primary visual cortex (V1), whereas Cornsweet responsive cells are found preferentially in the color-activated regions (thin stripes) of second visual area (V2). This colocalization of brightness and color processing within V1 and V2 suggests a segregation of contour and surface processing in early visual pathways and a hierarchy of brightness information processing from V1 to V2 in monkeys. PMID:15738406

  20. Upgrading Fermi Without Traveling to Space

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-02-01

    The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has received an upgrade that increased its sensitivity by a whopping 40% and nobody had to travel to space to make it happen! The difference instead stems from remarkable improvement to the software used to analyze Fermi-LATs data, and it has resulted in a new high-energy map of our sky.Animation (click to watch!) comparing the Pass 7 to the Pass 8 Fermi-LAT analysis, in a region in the constellation Carina. Pass 8 provides more accurate directions for incoming gamma rays, so more of them fall closer to their sources, creating taller spikes and a sharper image. [NASA/DOE/Fermi LAT Collaboration]Pass 8Fermi-LAT has been surveying the whole sky since August 2008. It detects gamma-ray photons by converting them into electron-positron pairs and tracking the paths of these charged particles. But differentiating this signal from the charged cosmic rays that also pass through the detector with a flux that can be 10,000 times larger! is a challenging process. Making this distinction and rebuilding the path of the original gamma ray relies on complex analysis software.Pass 8 is a complete reprocessing of all data collected by Fermi-LAT. The software has gone through many revisions before now, but this is the first revision that has taken into account all of the experience that the Fermi team has gained operating the LAT in its orbital environment.The improvements made in Pass 8 include better background rejection of misclassified charged particles, improvements to the point spread function and effective area of the detector, and an extension of the effective energy range from below 100 MeV to beyond a few hundred GeV. The changes made in Pass 8 have increased the sensitivity of Fermi-LAT by an astonishing 40%.Map of the High-Energy SkySky map of the sources in the 2FHL catalog, classified by their most likely association. Click for a better look! [Ackermann et al. 2016]The first result from the

  1. Bright Streaks and Dark Fans

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The south polar region of Mars is covered every year by a layer of carbon dioxide ice. In a region called the 'cryptic terrain,' the ice is translucent and sunlight can penetrate through the ice to warm the surface below.

    The ice layer sublimates (evaporates) from the bottom. The dark fans of dust seen in this image come from the surface below the layer of ice, carried to the top by gas venting from below. The translucent ice is 'visible' by virtue of the effect it has on the tone of the surface below, which would otherwise have the same color and reflectivity as the fans.

    Bright streaks in this image are fresh frost. The CRISM team has identified the composition of these streaks to be carbon dioxide.

    Observation Geometry Image PSP_003113_0940 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 26-Mar-2007. The complete image is centered at -85.8 degrees latitude, 106.0 degrees East longitude. The range to the target site was 244.9 km (153.0 miles). At this distance the image scale is 49.0 cm/pixel (with 2 x 2 binning) so objects 147 cm across are resolved. The image shown here has been map-projected to 50 cm/pixel . The image was taken at a local Mars time of 06:20 PM and the scene is illuminated from the west with a solar incidence angle of 79 degrees, thus the sun was about 11 degrees above the horizon. At a solar longitude of 207.6 degrees, the season on Mars is Northern Autumn.

  2. Bright Sparks of Our Future!

    NASA Astrophysics Data System (ADS)

    Riordan, Naoimh

    2016-04-01

    My name is Naoimh Riordan and I am the Vice Principal of Rockboro Primary School in Cork City, South of Ireland. I am a full time class primary teacher and I teach 4th class, my students are aged between 9-10 years. My passion for education has developed over the years and grown towards STEM (Science, Technology, Engineering and Mathematics) subjects. I believe these subjects are the way forward for our future. My passion and beliefs are driven by the unique after school programme that I have developed. It is titled "Sparks" coming from the term Bright Sparks. "Sparks" is an after school programme with a difference where the STEM subjects are concentrated on through lessons such as Science, Veterinary Science Computer Animation /Coding, Eco engineering, Robotics, Magical Maths, Chess and Creative Writing. All these subjects are taught through activity based learning and are one-hour long each week for a ten-week term. "Sparks" is fully inclusive and non-selective which gives all students of any level of ability an opportunity to engage into these subjects. "Sparks" is open to all primary students in County Cork. The "Sparks" after school programme is taught by tutors from the different Universities and Colleges in Cork City. It works very well because the tutor brings their knowledge, skills and specialised equipment from their respective universities and in turn the tutor gains invaluable teaching practise, can trial a pilot programme in a chosen STEM subject and gain an insight into what works in the physical classroom.

  3. Extending the Fermi - Swift Joint AGN Sample

    NASA Astrophysics Data System (ADS)

    Shrader, Chris R.; Macomb, D. J.

    2014-01-01

    The Swift BAT and the Fermi LAT each provide excellent sky coverage and have led to impressive compilations of extragalactic source catalogs. For the most part they sample separate AGN subpopulations - Swift the lower-luminosity and relatively nearby Seyfert galaxies while the Fermi sample is dominated by blazars and does not include any radio-quiet objects. The overlap between these samples is among the radio-loud subset of the Swift sample as has been discussed elsewhere in the literature. The observable properties at these two bands - flux and spectral indices - are not expected to be well correlated as they sample different portions of the synchrotron self-Compton (SSC) spectral energy distribution. In this contribution we consider an extension of the high-latitude Swift sample by relaxing the significance cut to less than 5 standard deviations and consider the overlap of that subsample with the Fermi AGN catalog. While such a threshold is generally inadvisable as it introduces the strong possibility of spurious detections, the objects of the overlapping sample which are detected at high significance in Fermi can be considered as reasonably high-confidence Swift detections. For example, there are 190 Swift sub-5-sigma Swift sources that have significance >2-sigma with Fermi counterparts, whereas we predict only ~5 due to statistical fluctuation. We also investigate any coincident INTEGRAL/IBIS observations to further bolster or diminish candidate Swift detections. We present our correlation analyses and offer interpretation in the context of the blazar sequence.

  4. FERMI longitudinal diagnostics: results and future challenges

    NASA Astrophysics Data System (ADS)

    Veronese, Marco; Ferrari, E.; Allaria, E.; Cinquegrana, P.; Froelich, L.; Giannessi, L.; Penco, G.; Predonzani, M.; Rossi, F.; Sigalotti, P.; Ferianis, M.

    2015-05-01

    The seeded FEL FERMI has completed the commissioning of both the FEL lines, and it is now providing the user community with a coherent and tunable UV radiation (from 100 nm to 4 nm) in a number of different configurations. These also include original FEL-pump - FEL-probe schemes with twin-seeded FEL pulses. Among the key systems for the operation of FERMI, there is the femtosecond optical timing system and dedicated longitudinal diagnostics, specifically developed for FERMI. In this paper, after a short review of the FERMI optical timing system and of its routinely achieved performances, we focus on the results obtained from the suite of longitudinal diagnostics (Bunch Arrival Monitor, Electro Optical sampling station and RF deflectors) all operating in single shot and with 10s fs resolution which demonstrate the FERMI achieved performances. The longitudinal diagnostics measurements are compared between these device and other device on shot-to-shot basis, looking for correlations between machine parameters. Finally future challenges in terms of improvement of existing diagnostics, planned installations and possible upgrades are discussed.

  5. Understanding and Using the Fermi Science Tools

    NASA Astrophysics Data System (ADS)

    Asercion, Joseph; Fermi Science Support Center

    2015-01-01

    The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. The reference manual gives details of the options available for each tool. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide information on recent updates incorporated in the Science Tools as well as upcoming changes that will be included in the upcoming release of the Science Tools in early 2015.

  6. The influence of depicted illumination on brightness

    PubMed Central

    Williams, S. Mark; McCoy, Allison N.; Purves, Dale

    1998-01-01

    The striking illusions produced by simultaneous brightness contrast generally are attributed to the center-surround receptive field organization of lower order neurons in the primary visual pathway. Here we show that the apparent brightness of test objects can be either increased or decreased in a predictable manner depending on how light and shadow are portrayed in the scene. This evidence suggests that perceptions of brightness are generated empirically by experience with luminance relationships, an idea whose implications we pursue in the accompanying paper. PMID:9789082

  7. Dark lump excitations in superfluid Fermi gases

    NASA Astrophysics Data System (ADS)

    Xu, Yan-Xia; Duan, Wen-Shan

    2012-11-01

    We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases. A Kadomtsev—Petviashvili I (KPI) solitary wave has been realized for superfluid Fermi gases in the limited cases of Bardeen—Cooper—Schrieffer (BCS) regime, Bose—Einstein condensate (BEC) regime, and unitarity regime. One-lump solution as well as one-line soliton solutions for the KPI equation are obtained, and two-line soliton solutions with the same amplitude are also studied in the limited cases. The dependence of the lump propagating velocity and the sound speed of two-dimensional superfluid Fermi gases on the interaction parameter are investigated for the limited cases of BEC and unitarity.

  8. Aspects of non-Fermi-liquid metals

    NASA Astrophysics Data System (ADS)

    Pivovarov, Eugene

    We consider several examples of metallic systems that exhibit non-Fermi-liquid behavior. In these examples the system is not a Fermi liquid due to the presence of a "hidden" order. The primary models are density waves with an odd-frequency-dependent order parameter and density waves with d-wave symmetry. In the first model, the same-time correlation functions vanish and there is a conventional Fermi surface. In the second model, the gap vanishes at the nodes. We derive the phase diagrams and study the thermodynamic and kinetic properties. We also consider the effects of competing orders on the phase diagram when the underlying microscopic interaction has a high symmetry.

  9. The Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    Thompson, Dave; McEnery, Julie

    2011-01-01

    This slide presentation reviews the Gamma Ray Astronomy as enhanced by the Fermi Gamma Ray Space Telescope and Radio Astronomy as a synergistic relationship. Gamma rays often represent a significant part of the energy budget of a source; therefore, gamma-ray studies can be critical to understanding physical processes in such sources. Radio observations offer timing and spatial resolutions vastly superior to anything possible with gamma-ray telescopes; therefore radio is often the key to understanding source structure. Gamma-ray and radio observations can complement each other, making a great team. It reviews the Fermi Guest Investigator (GI) program, and calls for more cooperative work that involves Fermi and the Very Long Baseline Array (VLBA), a system of ten radio telescopes.

  10. Entanglement Entropy and the Fermi Surface

    NASA Astrophysics Data System (ADS)

    Swingle, Brian

    2010-07-01

    Free fermions with a finite Fermi surface are known to exhibit an anomalously large entanglement entropy. The leading contribution to the entanglement entropy of a region of linear size L in d spatial dimensions is S˜Ld-1log⁡L, a result that should be contrasted with the usual boundary law S˜Ld-1. This term depends only on the geometry of the Fermi surface and on the boundary of the region in question. I give an intuitive account of this anomalous scaling based on a low energy description of the Fermi surface as a collection of one-dimensional gapless modes. Using this picture, I predict a violation of the boundary law in a number of other strongly correlated systems.