Modeling the early multiwavelength emission in GRB130427A

TL;DR

This paper models the multiwavelength emission of the powerful GRB 130427A, explaining its high-energy gamma rays, optical flash, and extended emission through synchrotron and synchrotron self-Compton processes in different shock regions.

Contribution

It provides a comprehensive model linking GeV gamma-ray, X-ray, and optical emissions of GRB 130427A using synchrotron and SSC mechanisms, highlighting the roles of reverse and forward shocks.

Findings

The 95 GeV photon and flux limits are consistent with synchrotron self-Compton emission.

The optical flash is explained by synchrotron emission from the reverse shock.

Extended LAT emission is attributed to synchrotron radiation from the forward shock.

Abstract

One of the most powerful gamma-ray bursts, GRB 130427A was swiftly detected from GeV $\gamma$-rays to optical wavelengths. In the GeV band, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope observed the highest-energy photon ever recorded of 95 GeV, and a bright peak in the early phase followed by emission temporally extended for more than 20 hours. In the optical band, a bright flash with a magnitude of $7.03\pm 0.03$ in the time interval from 9.31 s to 19.31 s after the trigger was reported by RAPTOR in r-band. We study the origin of the GeV $\gamma$-ray emission, using the multiwavelength observation detected in X-ray and optical bands. The origin of the temporally extended LAT, X-ray and optical flux is naturally interpreted as synchrotron radiation and the 95-GeV photon and the integral flux upper limits placed by the HAWC observatory are consistent with synchrotron self-Compton from an adiabatic forward shock propagating into the stellar wind of its progenitor. The extreme LAT peak and the bright optical flash are explained through synchrotron self-Compton and synchrotron emission from the reverse shock, respectively, when the ejecta evolves in thick-shell regime and carries a significant magnetic field.