skip to main content

Title: Time-resolved analysis of Fermi gamma-ray bursts with fast- and slow-cooled synchrotron photon models

Time-resolved spectroscopy is performed on eight bright, long gamma-ray bursts (GRBs) dominated by single emission pulses that were observed with the Fermi Gamma-Ray Space Telescope. Fitting the prompt radiation of GRBs by empirical spectral forms such as the Band function leads to ambiguous conclusions about the physical model for the prompt radiation. Moreover, the Band function is often inadequate to fit the data. The GRB spectrum is therefore modeled with two emission components consisting of optically thin non-thermal synchrotron radiation from relativistic electrons and, when significant, thermal emission from a jet photosphere, which is represented by a blackbody spectrum. To produce an acceptable fit, the addition of a blackbody component is required in five out of the eight cases. We also find that the low-energy spectral index α is consistent with a synchrotron component with α = –0.81 ± 0.1. This value lies between the limiting values of α = –2/3 and α = –3/2 for electrons in the slow- and fast-cooling regimes, respectively, suggesting ongoing acceleration at the emission site. The blackbody component can be more significant when using a physical synchrotron model instead of the Band function, illustrating that the Band function does not serve as a goodmore » proxy for a non-thermal synchrotron emission component. The temperature and characteristic emission-region size of the blackbody component are found to, respectively, decrease and increase as power laws with time during the prompt phase. In addition, we find that the blackbody and non-thermal components have separate temporal behaviors as far as their respective flux and spectral evolutions.« less
Authors:
; ; ; ; ; ; ;  [1] ; ; ; ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10] more »; « less
  1. University of Alabama in Huntsville, 320 Sparkman Drive, Huntsville, AL 35899 (United States)
  2. Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany)
  3. Space Science Office, VP62, NASA/Marshall Space Flight Center, Huntsville, AL 35812 (United States)
  4. Exzellence Cluster "Universe," Technische Universitt Mnchen, Boltzmannstrasse 2, D-85748, Garching (Germany)
  5. Universities Space Research Association, 320 Sparkman Drive, Huntsville, AL 35899 (United States)
  6. Department of Astronomy, Stockholm University, SE-106 91 Stockholm (Sweden)
  7. Rice University, Department of Physics and Astronomy, MS-108, P.O. Box 1892, Houston, TX 77251 (United States)
  8. Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352 (United States)
  9. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm (Sweden)
  10. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics, and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
Publication Date:
OSTI Identifier:
22351520
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 784; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; COOLING; COSMIC GAMMA BURSTS; DATA ANALYSIS; EMISSION; EVOLUTION; GAMMA RADIATION; LIMITING VALUES; PHOTOSPHERE; PULSES; RELATIVISTIC RANGE; SPACE; SPECTRA; SPECTROSCOPY; STARS; SYNCHROTRON RADIATION; TELESCOPES; TIME RESOLUTION