GRB 230204B: GIT Discovery of a Fast Fading Afterglow Associated with an Energetic GRB from a Massive-Star Progenitor

TL;DR

This study presents a detailed multi-wavelength analysis of the highly energetic GRB 230204B, revealing a rapidly fading afterglow and evidence supporting a massive star progenitor with a wind-shaped environment.

Contribution

It provides the first comprehensive multi-wavelength characterization of GRB 230204B, including prompt and afterglow emissions, and models its jet and environment to infer a massive star origin.

Findings

Bright afterglow with rapid decay ($t^{-1.82}$)

Detection of thermal photospheric emission in prompt phase

Jet energy $\gtrsim 10^{52}$ erg in wind medium

Abstract

We present a comprehensive multi-wavelength study of a bright gamma-ray burst GRB 230204B, analyzing both prompt and afterglow emissions. This GRB is highly energetic, with an isotropic equivalent energy emission $E_{\mathrm{iso}} \sim 2.2 \times 10^{54}\ \mathrm{erg}$, released during the prompt emission. The GROWTH-India Telescope discovered a bright afterglow ($m_r = 15.55$) that faded rapidly ($\propto t^{-1.82}$). The prompt emission shows strong thermal photospheric emission, along with a non-thermal high-energy component. We explore the evolution of these components and find them to be consistent with theoretical expectations. Afterglow modeling reveals an energetic jet $E_{tot} \gtrsim 10^{52}\ \mathrm{erg}$ expanding into a wind-type medium viewed nearly on-axis, suggesting a massive star progenitor with strong winds. We also explore correlations between the prompt emission and afterglow that may help to understand the complete picture of GRB progenitors.