GRB 080916C and GRB 090510: the high energy emission and the afterglow

TL;DR

This paper analyzes the physical composition and emission mechanisms of GRBs 080916C and 090510, suggesting magnetic outflows for the former and baryonic for the latter, and discusses the origin of their GeV afterglow emissions.

Contribution

It introduces a method to estimate seed photon numbers for GeV afterglows and finds synchrotron radiation likely explains the GeV emission.

Findings

GRB 080916C likely has a magnetic outflow

GRB 090510 may have a baryonic outflow

Synchrotron radiation can account for the GeV afterglow

Abstract

We constrain the physical composition of the outflows of GRBs 080916C and 090510 with the prompt emission data and find that the former is likely magnetic while the latter may be baryonic. The X-ray and optical afterglow emission of both GRBs can be reasonably fitted using the standard external shock model but the density profiles of the circum-burst medium are different. We also propose a simple method to estimate the number of the seed photons suppose the GeV afterglow photons are due to the inverse Compton radiation of external forward shock electrons. The seed photons needed in the modeling are too many to be realistic for both events. The synchrotron radiation of the forward shock seems able to account for the GeV afterglow data.