Gamma-ray burst high energy emission from internal shocks

Abstract

Aims. In this paper we study synchrotron and synchrotron self Compton (SSC) emission from internal shocks (IS) during the prompt and X-ray flare phases of gamma-ray bursts (GRBs). The aim is to test the IS model for the flare emission and for whether GRBs can be GeV sources. Methods. We determine the parameters for which the IS model can account for the observed prompt and X-ray flares emission, and study the detectability of the high energy SSC emission by the AGILE and GLAST satellites. Results. We find that the detectability of the SSC emission during the prompt phase of GRBs improves for higher values of the fireball Lorentz factor Γ and of the temporal variability t v . If IS is the mechanism responsible for the flare emission, and the Lorentz factor of the shells producing the flare is Γ ∼ 100, the flare light curves are expected to present some substructures with temporal variability t v = 10−100 ms which are much smaller than the average duration of flares, and similar to those observed during the prompt phase of GRBs. If one assumes lower Lorentz factors, such as Γ ∼ 10 ÷ 25, then a larger temporal variability t v ∼ 40 s can also account for the observed flare properties. However in this case we predict that X-ray flares do not have a counterpart at very high energies (MeV-GeV).Conclusions. An investigation on the substructures of the X-ray flare light curves, and simultaneous X-ray and high energy observations, will allow us to corroborate the hypothesis that late IS are responsible for the X-ray flares.

Prompt high-energy emission from gamma-ray bursts in the internal shock model

“…A high Article published by EDP Sciences energy spectral component is expected within this framework (see e.g. Papathanassiou & Mészáros 1996;Pilla & Loeb 1998;Guetta & Granot 2003;Pe'er & Waxman 2004;Razzaque et al 2004;Asano & Inoue 2007;Gupta & Zhang 2007;Galli & Guetta 2008;Fan & Piran 2008;Ando et al 2008). The typical GRB spectrum in the low gamma-ray range, as observed for instance by BATSE, is a smoothly connected broken power law with a break energy in the range 0.1−1 MeV.…”

“…This has been done either using an approximate analytical or semi-analytical estimate of the spectrum (e.g. Papathanassiou & Mészáros 1996;Guetta & Granot 2003;Gupta & Zhang 2007;Galli & Guetta 2008;Fan & Piran 2008;Ando et al 2008) or a detailed radiative code (Pe'er & Waxman 2004;Asano & Inoue 2007). Such studies allow to discuss different emission mechanisms of high energy photon production during internal shocks and to derive the expected high energy photon spectrum from one single shocked relativistic shell.…”

Gamma-ray burst science in the era of the Cherenkov Telescope Array

“…Investigating the high-energy properties of the X-ray flares in comparison with the prompt emission can reveal their true origin. Fermi detected a few GeV photons during the X-ray flaring activity of GRB 100728A [96], but cannot distinguish whether they originate from internal dissipation processes, long-lasting afterglow emission, or moderately variable EIC emission from external shock electrons [84,97,98,99]. High time resolution studies with the superior photon statistics of CTA will be crucial to determine whether the high-energy photons and the X-ray flares are co-spatial, as well as to constrain the bulk Lorentz factor of the emitting region and their emission mechanism.…”

JITTER SELF-COMPTON PROCESS: GeV EMISSION OF GRB 100728A

“…Therefore, an inverse Compton process or synchrotron self-Compton (SSC) process is proposed naturally to explain the GRB emission above the GeV band (Mészáros et al 1993;Dermer et al 2000;Wang et al 2001;Zhang & Mészáros 2001;Granot & Guetta 2003;Fan et al 2008;Zou et al 2009;Corsi et al 2010). In particular, the possibility was suggested that the photons from X-ray flares can be scattered to the GeV band by those relativistic electrons (Wang et al 2006;Galli & Guetta 2008).…”