GRBs: when do blackbody spectra look like non-thermal ones?

TL;DR

This paper proposes that nonthermal gamma-ray burst spectra can be explained as superpositions of thermal blackbody spectra, formed through time and space integration, allowing for optically thick emission with high baryon load.

Contribution

It introduces a model where GRB spectra appear nonthermal due to superpositions of thermal spectra, expanding understanding of emission conditions.

Findings

Nonthermal spectra can result from superpositions of thermal blackbody spectra.

Time and space integration can produce nonthermal features in GRB spectra.

Model allows high baryon load without low optical depth constraints.

Abstract

We argue that a nonthermally looking spectrum of a gamma-ray burst (GRB) can be formed as a superposition of a set of thermal blackbody spectra. This superposition may be done by time integration which is present even in `time resolved' GRB spectroscopy. A nonthermal spectrum can be obtained also by the space integration which should take place unless all the emission comes from a plane front moving exactly towards the observer. We propose a model of the gamma-ray burst spectrum formation based on this idea. This model allows the GRB radiation to be optically thick and to have higher values of baryon load. Thus the latter is limited by the energy considerations only, and not by the condition of a small optical depth.