Magnetic Energy Injection in GRB 080913

TL;DR

This paper models the optical afterglow of the high-redshift GRB 080913, suggesting its late-time emission is powered by magnetic energy injection from a spinning black hole with strong magnetic fields.

Contribution

It provides a detailed numerical fit to the multi-wavelength data of GRB 080913 and constrains its environment and central engine properties.

Findings

Late optical/X-ray plateau explained by Poynting-flux energy injection

Central engine likely a massive spinning black hole with strong magnetic fields

Constraints on circum-burst environment from data fitting

Abstract

GRB 080913, with a spectroscopically determined redshift of z=6.7, was the record holder of the remotest stellar object before the discovery of the recent gamma-ray burst GRB 090423, whose redshift is about 8.2. The gradually accumulated high redshift GRB sample has shed light on the origin and physics of GRBs during the cosmic re-ionization epoch. We here present a detailed numerical fit to the multi-wavelength data of the optical afterglow of GRB 080913 and then constrain its circum-burst environment and the other model parameters. We conclude that the late optical/X-ray plateau at about one day since the burst is due to the Poynting-flux dominated injection from the central engine which is very likely a massive spinning black hole with super strong magnetic fields.