TITLE: GCN CIRCULAR NUMBER: 41813 SUBJECT: GRB 250911A: GECAM-B detection DATE: 25/09/12 13:00:39 GMT FROM: zhangjinpeng@ihep.ac.cn Jin-Peng Zhang, Yang-Zhao Ren, Chen-Wei Wang, Shao-Lin Xiong and Yue Huang (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 250911A at 2025-09-11T01:29:28.250 UTC (denoted as T0), which was also observed by Swift (Palmer et al., GCN 41781). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of a weak precursor and a bright pulse with multiple spikes, with a duration (T90) of 35.4 +1.1/-1.7 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb250911A.png GECAM-B localized this burst to the following position (J2000): Ra: 262.0 deg Dec: -20.2 deg Err: 4.1 deg (1-sigma, statistical only) This localization is consistent with Swift observation (Palmer et al., GCN 41781; Beardmore et al., GCN 41784). The time-averaged spectrum from T0 - 5 s to T0 + 40 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.52 +0.10/-0.12 and the cutoff energy, parameterized as Epeak, is 330 +180/-80 keV. The event fluence (10-1000 keV) in this time interval is (3.52 +0.25/-0.32)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 250911A is shown at: https://www.bursthub.cn//admin/static/gecambgrb250911A_amati.png 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/41813. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...