TITLE: GCN CIRCULAR NUMBER: 41687 SUBJECT: GRB 250902A: GECAM-B detection DATE: 25/09/04 02:48:15 GMT FROM: zhengchao_astro@foxmail.com Chao Zheng, Chen-Wei Wang, Shao-Lin Xiong and Yue Huang (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 250902A at 2025-09-02T01:30:00.550 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #41648) and SVOM/GRM (Wang et al., GCN #41653). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of a multi-pulses with a duration (T90) of 10.5 +1.0/-1.5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb250902A.png GECAM-B localized this burst to the following position (J2000): Ra: 166.6 deg Dec: 20.5 deg Err: 0.7 deg (1-sigma, statistical only) The time-averaged spectrum from T0-2 s to T0+15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.15 +0.14/-0.14 and the cutoff energy, parameterized as Epeak, is 185 +23/-16 keV. The event fluence (10-1000 keV) in this time interval is (2.69 +/-0.19)E-05 erg/cm^2. Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/41687. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...