Simulation of prompt emission from GRBs with a photospheric component and its detectability by GLAST

Abstract

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.

Clustering of gamma-ray burst types in the Fermi GBM catalogue: indications of photosphere and synchrotron emissions during the prompt phase

“…It has therefore been suggested that there is an interplay between different emission mechanisms, either alone or combined with each other (e.g. Mészáros & Rees 2000;Ryde 2005;Battelino et al 2007;Guiriec et al 2011Guiriec et al , 2013. It is then a natural consequence that subgroups of GRBs could exist, that are produced by different emission mechanisms (e.g.…”

Emission from accelerating jets in gamma-ray bursts: radiation-dominated flows with increasing mass outflow rates

“…Finally, we note that the hybrid model has been suggested for bursts in which both a thermal and a non-thermal component have been observed (e.g. Ryde 2005;Battelino et al 2007;Ryde & Pe'er 2009;Guiriec et al 2011;Iyyani et al 2013;Axelsson et al 2012;Burgess et al 2014;Nappo et al 2017). In these cases the magnetic energy is dissipated during the prompt phase, giving rise to emission observed in coincidence with the photospheric emission (e.g.…”

“…This component is often interpreted as synchrotron emission (e.g. Mészáros & Rees 2000;Ryde 2005;Battelino et al 2007). The narrowest possible spectrum in the coasting phase, is from a passively cooled jet without any energy dissipation that can alter the spectrum.…”

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

“…The hybrid model, that may be interpreted as a combination of photospheric and optically-thin synchrotron radiation, fits the spectra of single-pulsed GRBs well [see 13,19]. The problem with the synchrotron "line of death" (α > −2/3) is avoided with this model, since the Rayleigh-Jeans portion of the blackbody component explains the hard spectral slopes seen in many BATSE bursts.…”

“…In our simulations for GLAST we extended the energy range into the GLAST domain, and therefore used an extended time-dependent hybrid model that included a blackbody function that evolves over time and a broken power-law -instead of a single power-law component -with a high-energy cut-off. The blackbody component that evolves over time is described by: We motivated the broken power-law based on the following two facts: a) OTS radiation may according to theory show a break in the energy domain covered by GLAST and b) power-law index values in the BATSE data from the hybrid model fits can be interpreted as being distributed around two values as shown in [19]. These two power law index values may be given a physical interpretation: the higher value (∼ 2.1) stems from a shock-accelerated distribution of electrons and the lower value (∼ 1.5) from the cooling electrons originating from the same distribution.…”