Photometric and spectroscopic observations of GRB 190106A: emission from reverse and forward shocks with late-time energy injection

Zi-Pei Zhu, Dong Xu*, Johan P. U. Fynbo, Shao-Yu Fu, Jun-Bo Zhang, Xing Liu, Shuai-Qing Jiang, Shuo Xiao, Wei Xie, Yuan-Chuan Zou, He Gao, Dieter Hartmann, Antonio de Ugarte Postigo, David Alexander Kann, Massimo Della Valle, Pall Jakobsson, Tayabba Zafar, Valerio D'Elia, Li-Ping Xin, Jian-Yan WeiXing Gao, Jin Zhong Liu, Tian-Hua Lu, Wei-Hua Lei*

*Corresponding author for this work

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Early optical observations of gamma-ray bursts can significantly contribute to the study of the central engine and physical processes therein. However, of the thousands observed so far, only a few have data at optical wavelengths in the first minutes after the onset of the prompt emission. Here we report on GRB 190106A, whose afterglow was observed in optical bands just 36 s after the Swift/BAT trigger, i.e., during the prompt emission phase. The early optical afterglow exhibits a bimodal structure followed by a normal decay, with a faster decay after ∼T 0 + 1 day. We present optical photometric and spectroscopic observations of GRB 190106A. We derive the redshift via metal absorption lines from Xinglong 2.16 m/BFOSC spectroscopic observations. From the BFOSC spectrum, we measure z = 1.861 ± 0.002. The double-peak optical light curve is a significant feature predicted by the reverse-forward external-shock model. The shallow decay followed by a normal decay in both the X-ray and optical light curves is well explained with the standard forward-shock model with late-time energy injection. Therefore, GRB 190106A offers a case study for GRB emission from both reverse and forward shocks.

Original languageEnglish
Article number30
Pages (from-to)1-14
Number of pages14
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 1 May 2023

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