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Title: Simulation of Prompt Emission from GRBs with a Photospheric Component and its Detectability by GLAST

Abstract

The prompt emission from gamma-ray bursts (GRBs) still requires a physical explanation. Studies of time-resolved GRB spectra, observed in the keV-MeV range, show that a hybrid model consisting of two components, a photospheric and a non-thermal component, in many cases fits bright, single-pulsed bursts as well as, and in some instances even better than, the Band function. With an energy coverage from 8 keV up to 300 GeV, GLAST will give us an unprecedented opportunity to further investigate the nature of the prompt emission. In particular, it will give us the possibility to determine whether a photospheric component is the determining feature of the spectrum or not. Here we present a short study of the ability of GLAST to detect such a photospheric component in the sub-MeV range for typical bursts, using simulation tools developed within the GLAST science collaboration.

Authors:
 [1];  [2];  [3];  [4]
  1. Stockholm Observatory, AlbaNova University Center, 106 91 Stockholm (Sweden)
  2. Physics Department, Royal Institute of Technology, AlbaNova University Center, SE-106 91 Stockholm (Sweden)
  3. INFN Pisa, Largo B.Pontecorvo 3, 56100 Pisa (Italy)
  4. University and INFN of Trieste, Via Valerio 2, 34100 Trieste (Italy)
Publication Date:
OSTI Identifier:
21057319
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 906; Journal Issue: 1; Conference: Stockholm symposium on GRB's: Gamma-ray bursts prospects for GLAST, Stockholm (Sweden), 1 Sep 2006; Other Information: DOI: 10.1063/1.2737404; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; COMPUTERIZED SIMULATION; COSMIC GAMMA BURSTS; COSMIC GAMMA SOURCES; GAMMA ASTRONOMY; GAMMA DETECTION; GAMMA RADIATION; GEV RANGE; KEV RANGE; MEV RANGE; PHOTON EMISSION; TELESCOPE COUNTERS; TIME RESOLUTION

Citation Formats

Battelino, Milan, Ryde, Felix, Omodei, Nicola, and Longo, Francesco. Simulation of Prompt Emission from GRBs with a Photospheric Component and its Detectability by GLAST. United States: N. p., 2007. Web. doi:10.1063/1.2737404.
Battelino, Milan, Ryde, Felix, Omodei, Nicola, & Longo, Francesco. Simulation of Prompt Emission from GRBs with a Photospheric Component and its Detectability by GLAST. United States. doi:10.1063/1.2737404.
Battelino, Milan, Ryde, Felix, Omodei, Nicola, and Longo, Francesco. Tue . "Simulation of Prompt Emission from GRBs with a Photospheric Component and its Detectability by GLAST". United States. doi:10.1063/1.2737404.
@article{osti_21057319,
title = {Simulation of Prompt Emission from GRBs with a Photospheric Component and its Detectability by GLAST},
author = {Battelino, Milan and Ryde, Felix and Omodei, Nicola and Longo, Francesco},
abstractNote = {The prompt emission from gamma-ray bursts (GRBs) still requires a physical explanation. Studies of time-resolved GRB spectra, observed in the keV-MeV range, show that a hybrid model consisting of two components, a photospheric and a non-thermal component, in many cases fits bright, single-pulsed bursts as well as, and in some instances even better than, the Band function. With an energy coverage from 8 keV up to 300 GeV, GLAST will give us an unprecedented opportunity to further investigate the nature of the prompt emission. In particular, it will give us the possibility to determine whether a photospheric component is the determining feature of the spectrum or not. Here we present a short study of the ability of GLAST to detect such a photospheric component in the sub-MeV range for typical bursts, using simulation tools developed within the GLAST science collaboration.},
doi = {10.1063/1.2737404},
journal = {AIP Conference Proceedings},
number = 1,
volume = 906,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}
  • The prompt emission from gamma-ray bursts (GRBs) still requires a physical explanation. Studies of time-resolved GRB spectra, observed in the keV-MeV range, show that a hybrid model consisting of two components, a photospheric and a non-thermal component, in many cases fits bright, single-pulsed bursts as well as, and in some instances even better than, the Band function. With an energy coverage from 8 keV up to 300 GeV, GLAST will give us an unprecedented opportunity to further investigate the nature of the prompt emission. In particular, it will give us the possibility to determine whether a photospheric component is themore » determining feature of the spectrum or not. Here we present a short study of the ability of GLAST to detect such a photospheric component in the sub-MeV range for typical bursts, using simulation tools developed within the GLAST science collaboration.« less
  • The short GRB 120323A had the highest flux ever detected with the Gamma-Ray Burst Monitor on board the Fermi Gamma-Ray Space Telescope. Here we study its remarkable spectral properties and their evolution using two spectral models: (1) a single emission component scenario, where the spectrum is modeled by the empirical Band function (a broken power law), and (2) a two-component scenario, where thermal (a Planck-like function) emission is observed simultaneously with a non-thermal component (a Band function). We find that the latter model fits the integrated burst spectrum significantly better than the former, and that their respective spectral parameters aremore » dramatically different: when fit with a Band function only, the E{sub peak} of the event is unusually soft for a short gamma-ray burst (GRB; 70 keV compared to an average of 300 keV), while adding a thermal component leads to more typical short GRB values (E{sub peak} {approx} 300 keV). Our time-resolved spectral analysis produces similar results. We argue here that the two-component model is the preferred interpretation for GRB 120323A based on (1) the values and evolution of the Band function parameters of the two component scenario, which are more typical for a short GRB, and (2) the appearance in the data of a significant hardness-intensity correlation, commonly found in GRBs, when we employee two-component model fits; the correlation is non-existent in the Band-only fits. GRB 110721A, a long burst with an intense photospheric emission, exhibits the exact same behavior. We conclude that GRB 120323A has a strong photospheric emission contribution, observed for the first time in a short GRB. Magnetic dissipation models are difficult to reconcile with these results, which instead favor photospheric thermal emission and fast cooling synchrotron radiation from internal shocks. Finally, we derive a possibly universal hardness-luminosity relation in the source frame using a larger set of GRBs (L{sub i}{sup Band} = (1.59 {+-} 0.84) x 10{sup 50} (E{sub peak,i}){sup 1.33{+-}0.07} erg s{sup -1}), which could be used as a possible redshift estimator for cosmology.« less
  • Results of a leptonic jet model for the prompt emission and early afterglows of GRBs are presented. The synchrotron component is modeled with the canonical Band spectrum and the synchrotron self-Compton component is calculated from the implied synchrotron-emitting electron spectrum in a relativistic plasma blob. In the comoving frame the magnetic field is assumed to be tangled and the electron and photon distributions are assumed to be isotropic. The Compton-scattered spectrum is calculated using the full Compton cross-section in the Thomson through Klein-Nishina using the Jones formula. Pair production photoabsorption, both from ambient radiation in the jet and from themore » extragalactic background light (EBL), is taken into account. Results are presented as a function of a small set of parameters: the Doppler factor, the observed variability timescale, the comoving magnetic field, the peak synchrotron flux, and the redshift of the burst. Model predictions will be tested by multiwavelength observations, including the Swift and GLAST satellites, which will provide unprecedented coverage of GRBs.« less
  • It is proposed that the prompt emission observed in bursts that exhibit a thermal component originates from relativistic radiation mediated shocks (RRMS) that form below the photosphere of the gamma-ray burst (GRB) outflow. It is argued that such shocks are expected to form in luminous bursts via collisions of shells that propagate with moderate Lorentz factors {Gamma} {approx}< 500. Faster shells will collide above the photosphere to form collisionless shocks. We demonstrate that in events like GRB 090902B a substantial fraction of the explosion energy is dissipated below the photosphere, in a region of moderate optical depth {tau} {approx}< 300,more » whereas in GRB 080916C the major fraction of the energy dissipates above the photosphere. We show that under conditions anticipated in many GRBs, such RRMS convect enough radiation upstream to render photon production in the shock transition negligible, unlike the case of shock breakout in supernovae. The resulting spectrum, as measured in the shock frame, has a relatively low thermal peak, followed by a broad, nonthermal component extending up to the Klein-Nishina limit.« less
  • Inverse-Compton scattering by cosmic-ray electrons on the CMB and the ISRF produce a major component of the diffuse gamma-ray emission from the Galaxy. The stellar ISRF is not smooth but clumpy due to the large contribution from the most luminous stars. We have shown that the gamma-ray emission from the radiation field of some supergiant stars could be - marginally - detectable by GLAST. We present the basic formalism required and give possible candidate stars to be detected. We also apply the theory to OB associations, showing that inverse-Compton emission produced is not negligible compared to the sensitivity of GLAST.