GRB 200612A: An Ultralong Gamma-Ray Burst Powered by Magnetar Spinning Down

• Published in: Research in astronomy and astrophysics 2024-02, Vol.24 (2), p.25017
• Main Authors: Chen, Liang-Jun, Wang, Xiang-Gao, Yang, De-Long, Liang, En-Wei
• Format: Article
• Language: English
• Subjects: (stars:) gamma-ray burst: general; (stars:) gamma-ray burst: individual (GRB 200612A); Afterglows; Black holes; Decay; Gamma ray astronomy; Gamma ray bursts; Gamma rays; Light curve; Magnetars; stars: magnetars; X-rays
• ISSN: 1674-4527; 2397-6209
• DOI: 10.1088/1674-4527/ad1d2a

GRB 200612A could be classified as an ultralong gamma-ray burst due to its prompt emission lasting up to ∼1020 s and the true timescale of the central engine activity t burst ≥ 4 × 10 4 s. The late X-ray light curve with a decay index of α = 7.53 is steeper than the steepest possible decay from an external shock model. We propose that this X-ray afterglow can be driven by dipolar radiation from the magnetar spindown during its early stage, while the magnetar collapsed into the black hole before its spindown, resulting in a very steep decay of the late X-ray light curve. The optical data show that the light curve is still rising after 1.1 ks, suggesting a late onset. We show that GRB 200612A’s optical afterglow light curve is fitted with the forward shock model by Gaussian structured off-axis jet. This is a special case among GRBs, as it may be an ultralong gamma-ray burst powered by a magnetar in an off-axis observation scenario.