Photospheric Emission in Gamma-Ray Bursts

TL;DR

Recent advances reveal that a thermal component in gamma-ray burst prompt emission provides crucial insights into the physics of the innermost regions and influences the non-thermal spectra through seed photons, with widespread observational evidence.

Contribution

This review summarizes key recent developments highlighting the significance of thermal components in GRB prompt emission and their implications for understanding jet physics.

Findings

Thermal component identified in a minority of bursts but likely present in nearly all.

Thermal emission offers direct insights into jet dynamics, geometry, and magnetization.

Evidence suggests thermal components are common in GRBs, impacting models of prompt emission.

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 contributes 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.