GRB 110205A: Anatomy of a long gamma-ray burst

TL;DR

This paper presents a detailed multi-wavelength analysis of GRB 110205A, revealing distinct emission components, correlations, and re-brightening features, advancing understanding of long gamma-ray burst mechanisms and afterglow physics.

Contribution

It provides a comprehensive observational study of GRB 110205A, highlighting the temporal separation of emission components and discussing implications for the fireball model.

Findings

Detection of prompt optical emission correlated with gamma-ray light curve

Absence of correlation between X-ray and optical during prompt phase

Large optical re-brightening indicating reverse shock presence

Abstract

The Swift burst GRB 110205A was a very bright burst visible in the Northern hemisphere. GRB 110205A was intrinsically long and very energetic and it occurred in a low-density interstellar medium environment, leading to delayed afterglow emission and a clear temporal separation of the main emitting components: prompt emission, reverse shock, and forward shock. Our observations show several remarkable features of GRB 110205A : the detection of prompt optical emission strongly correlated with the BAT light curve, with no temporal lag between the two ; the absence of correlation of the X-ray emission compared to the optical and high energy gamma-ray ones during the prompt phase ; and a large optical re-brightening after the end of the prompt phase, that we interpret as a signature of the reverse shock. Beyond the pedagogical value offered by the excellent multi-wavelength coverage of a GRB with temporally separated radiating components, we discuss several questions raised by our observations: the nature of the prompt optical emission and the spectral evolution of the prompt emission at high-energies (from 0.5 keV to 150 keV) ; the origin of an X-ray flare at the beginning of the forward shock; and the modeling of the afterglow, including the reverse shock, in the framework of the classical fireball model.