Properties of Gamma-Ray Burst Progenitor Stars

TL;DR

This paper investigates the properties of stars that produce gamma-ray bursts, estimating core and envelope sizes, density profiles, and rotation speeds based on X-ray data, to better understand their progenitors.

Contribution

It provides the first estimates of core and envelope sizes, density profiles, and rotation speeds of GRB progenitor stars using observational data.

Findings

Core radius ~ 1-3 x 10^10 cm

Envelope radius ~ 1-2 x 10^11 cm

Envelope density profile ~ r^-2

Abstract

We determine some basic properties of stars that produce spectacular gamma-ray bursts at the end of their life. We assume that accretion of the outer portion of the stellar core by a central black hole fuels the prompt emission, and that fall-back and accretion of the stellar envelope later produces the plateau in the X-ray light curve seen in some bursts. Using X-ray data for three bursts we estimate the radius of the stellar core to be ~ 1-3 x 10^10 cm, and that of the stellar envelope to be ~ 1-2 x 10^11 cm. The density profile in the envelope is fairly shallow, with \rho ~ r^-2. The rotation speeds of the core and envelope are ~ 0.05 and ~ 0.2 of the local Keplerian speed, respectively.