Time resolved analysis of Fermi gamma-ray bursts with fast-and slow-cooled synchrotron photon models
- Univ. of Alabama, Huntsville, AL (United States)
- Max Planck Inst. for Extraterrestrial Physics, Garching (Germany)
- NASA and Marshall Space Flight Center, Huntsville, AL (United States)
- Technical Univ. of Munich, Garching (Germany). Excellence Cluster Universe
- Universities Space Research Association, Huntsville, AL (United States)
- Stockholm Univ. (Sweden). Dept. of Astronomy; The Oskar Klein Centre for Cosmoparticle Physics, Stockholm (Sweden); KTH Royal Inst. of Technology, Stockholm (Sweden). Dept. of Physics
- Rice Univ., Houston, TX (United States). Dept. of Physics and Astronomy
- Naval Research Lab. (NRL), Washington, DC (United States). Space Science Division
- The Oskar Klein Centre for Cosmoparticle Physics, Stockholm (Sweden)
- Stanford Univ. and SLAC National Accelerator Lab., CA (United States). Kavli Inst. for Particle Astrophysics and Cosmology
- The Oskar Klein Centre for Cosmoparticle Physics, Stockholm (Sweden); KTH Royal Inst. of Technology, Stockholm (Sweden). Dept. of Physics
- Stanford Univ. and SLAC National Accelerator Lab., CA (United States). Kavli Inst. for Particle Astrophysics and Cosmology; Interuniversity Consortium for Physical Physics (CIFS), Torino (Italy)
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. Therefore, the GRB spectrum is 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. In order 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 good 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. Additionally, we find that the blackbody and non-thermal components have separate temporal behaviors as far as their respective flux and spectral evolutions.
- Research Organization:
- SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE
- Contributing Organization:
- Fermi LAT Collaboration
- Grant/Contract Number:
- AC02-76SF00515
- OSTI ID:
- 1356534
- Journal Information:
- The Astrophysical Journal, Vol. 784, Issue 1; ISSN 0004-637X
- Publisher:
- Institute of Physics (IOP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Similar Records
Toward a better understanding of the GRB phenomenon: a new model for GRB prompt emission and its effects on the new LiNT$-$Epeak,irest,NT relation
Toward a better understanding of the GRB phenomenon: A new model for GRB PROMPT emission and its effects on the new L{sub i}{sup NT}– E{sub peak,i}{sup rest,NT} relation