2023/03/17 by Zhu, Zi-Pei, Lei, Wei-Hua, Malesani, Daniele B. +26 · 1 citation
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2303.09982
High-redshift gamma-ray bursts (GRBs) provide a powerful tool to probe the early universe, but still for relatively few do we have good observations of the afterglow. We here report the optical and near-infrared observations of the afterglow of a relatively high-redshift event, GRB 220101A, triggered on New Year's Day of 2022. With the optical spectra obtained at XL2.16/BFOSC and NOT/ALFOSC, we determine the redshift of the burst at z= 4.615. Based on our optical and near-infrared data, combined with the X-ray data, we perform multiband fit with the python package afterglowpy. A jet-break at ∼ 0.7 day post-burst is found to constrain the opening angle of the jet as ∼ 3.4 degree. We also determine circumburst density of n0 = 0.15 \rm cm-3 as well as kinetic energy E\rm K, iso = 3.52× 1054 erg. The optical afterglow is among the most luminous ever detected. We also find a ``mirror'' feature in the lightcurve during the prompt phase of the burst from 80 s to 120 s. The physical origin of such mirror feature is unclear.