Time Evolution of Optical Darkness in GRB Afterglow: The Case of GRB 240825A

TL;DR

This study analyzes the optical and X-ray spectral evolution of GRB 240825A's afterglow, revealing dust-obscured environment effects and the temporal behavior of optical darkness in the burst.

Contribution

It provides a detailed time-resolved spectral analysis of GRB 240825A's afterglow, highlighting the evolution of optical darkness and dust extinction properties.

Findings

$eta_{OX}$ decreases then increases, with a minimum at ~1000s

GRB occurred in a dust-obscured environment

At 11 hours, $eta_{OX}$ does not classify as optically dark

Abstract

Long-duration gamma-ray bursts (GRBs) are believed to occur in star-forming regions. The multiwavelength follow-up observations of the early afterglow of GRB 240825A provided insights into the evolution of the optical-to-X-ray spectral feature of the afterglow. We comprehensively investigate the evolution of X-ray spectral properties through time-resolved spectral analysis and calculate optical darkness ($\beta_\mathrm{OX}$) to reveal the physical properties of the afterglow. The X-ray-to-optical SEDs of afterglow in different time intervals are fitted to derive the extinction curves. The $\beta_\mathrm{OX}$ exhibits a trend of decreasing and then increasing, reaching its minimum value at $\sim1000\mathrm{\,s}$ post-trigger. However, at 11 hours post-trigger, $\beta_\mathrm{OX}$ does not meet the criteria for an optically dark burst. The extinction curves in different time intervals indicate that GRB 240825A occurred in a dust-obscured environment.