Spectral components in the bright, long GRB 061007: properties of the photosphere and the nature of the outflow

TL;DR

This study analyzes the spectral components of GRB 061007, revealing a dominant photospheric emission with a stable multicolour blackbody shape and a high-energy power-law, providing insights into the burst's outflow properties.

Contribution

It demonstrates that the prompt emission can be modeled by a photospheric component plus a power law, offering a natural explanation for spectral correlations and estimating outflow parameters.

Findings

Photospheric component dominates the emission

Stable multicolour blackbody shape throughout the burst

High-energy power-law with slope -1.5

Abstract

We present a time-resolved spectral analysis of the bright, long GRB 061007 (z=1.261) using Swift BAT and Suzaku WAM data. We find that the prompt emission of GRB 061007 can be equally well explained by a photospheric component together with a power law as by a Band function, and we explore the implications of the former model. The photospheric component, which we model with a multicolour blackbody, dominates the emission and has a very stable shape throughout the burst. This component provides a natural explanation for the hardness-intensity correlation seen within the burst and also allows us to estimate the bulk Lorentz factor and the radius of the photosphere. The power-law component dominates the fit at high energies and has a nearly constant slope of -1.5. We discuss the possibility that this component is of the same origin as the high-energy power laws recently observed in some Fermi LAT bursts.