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arXiv · 2512.15162

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

Rui-Zhi Li·Jirong Mao·Yuan-Pei Yang·Bo-Ting Wang·Fei-Fan Song·Yu-Xin Xin·Jin-Ming Bai
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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.

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Rui-Zhi Li, Jirong Mao, Yuan-Pei Yang, Bo-Ting Wang, Fei-Fan Song, Yu-Xin Xin, Jin-Ming Bai. 2025-12-17. Time Evolution of Optical Darkness in GRB Afterglow: The Case of GRB 240825A. https://doi.org/10.3847/1538-4357%2Fae1e7d

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