Photospheric emission in gamma-ray bursts

Abstract

A major breakthrough in our understanding of gamma-ray bursts (GRB) prompt emission physics occurred in the last few years, with the realization that a thermal component accompanies the over-all non-thermal prompt spectra. This thermal part is important by itself, as it provides direct probe of the physics in the innermost outflow regions. It further has an indirect importance, as a source of seed photons for inverse-Compton scattering, thereby it contributs to the non-thermal part as well. In this short review, we highlight some key recent developments. Observationally, although so far it was clearly identified only in a minority of bursts, there are indirect evidence that thermal component exists in a very large fraction of GRBs, possibly close to 100%. Theoretically, the existence of thermal component have a large number of implications as a probe of underlying GRB physics. Some surprising implications include its use as a probe of the jet dynamics, geometry and magnetization.

Gamma ray burst studies with THESEUS

“…[67]) or modifications of the standard synchrotron scenario (e.g. inverse Compton scattering, peculiar magnetic field configuration in the emission region, [9,84,96]). The lack of our knowledge on the dominant emission processes responsible for shaping the observed prompt emission spectra did not allow us to make a progress in understanding of the physics of GRBs, i.e., where and how the prompt emission is produced in the GRB jets.…”

Erratum: Primordial black hole origin for thermal gamma-ray bursts

“…Only when the PBH is sufficiently close to the CBH horizon (and, consequently, the Hawking temperature undergoes a significant rise) the corresponding flux density will not be overshadowed by the accretion disk emission. Moreover, provided that there exist different GRBs emission mechanisms (such as the non-thermal synchrotron emission [42][43][44][45] or the Comptonized quasi-thermal bursts [46][47][48]) according with different astrophysical scenarios (mainly, gravitational collapse events from massive progenitors or compact merger episodes), it is fundamental to perform an exhaustive spectral analysis of the Hawking flux density (Eq. ( 11)) in order to discern its probable primordial black hole origin.…”

Diffusive photospheres in gamma-ray bursts

“…Most papers dealing with the photospheric emission, e.g. (Mészáros & Rees 2000;Pe'er 2008;Pe'er & Ryde 2011;Beloborodov 2011;Lundman et al 2013;Santana et al 2016;Bhattacharya et al 2018), for a review see Pe'er & Ryde (2017), adopt the hydrodynamic model of a steady and infinite wind. However, finite duration of GRBs implies finite width of the wind.…”

“…Prompt emission spectra are non-thermal, their origin is usually associated with the synchrotron mechanism in relativistic shock waves (Rees & Meszaros 1994). Photospheric models with possible dissipation of kinetic energy of the outflow are attractive alternative to the synchrotron models since observation of thermal radiation allows determination of basic hydrodynamic characteristics of the outflow from which these bursts originate (Vereshchagin 2014;Pe'er & Ryde 2017). The photons in these models are trapped and advected with the outflow until it becomes transparent.…”