On the Ultra-Long Gamma-Ray Transient GRB 250702B/EP250702
Jin-Peng Zhang, Chen-Wei Wang, Zheng-Hang Yu, Shao-Lin Xiong, Shu-Xu Yi, Jia-Cong Liu, Wang-Chen Xue, Wen-Jun Tan, Zi-Rui Zhang, Rahim Moradi, Hao-Xuan Guo, Chao Zheng, Yan-Qiu Zhang, Yue Wang, Sheng-Lun Xie, Peng Zhang, Yang-Zhao Ren, Cheng-Kui Li, Xiao-Bo Li, Ce Cai, Shuo Xiao, Li-Ming Song, Shuang-Nan Zhang
公開日: 2025/9/30
Abstract
GRB 250702B/EP250702a is an interesting long-duration gamma-ray transient whose nature is in debate. To obtain a full picture in gamma-ray band, we implement a comprehensive targeted search of burst emission in a wide window of 30 days jointly with Insight-HXMT, GECAM and Fermi/GBM data within the ETJASMIN framework. In gamma-ray band, we find there is a 50-second precursor about 25 hours before the 4-hour main burst, which generally consists of 4 emission episodes. Remarkably, we find that the soft X-ray emission (after the main burst) decays as a power-law with start time aligning with the last episode of main emission and index of -5/3 perfectly consistent with the canonical prediction of fallback accretion. We conclude that the properties of precursor, main burst and the following soft X-ray emission strongly support the atypical collapsar Ultra-Long Gamma-Ray Burst (ULGRB) scenario rather than the Tidal Disruption Event (TDE), and all these gamma-ray and soft X-ray emission probably originate from relativistic jet whose luminosity is dominated by the fallback accretion rate during the death collapse of a supergiant star.