TITLE: GCN CIRCULAR NUMBER: 41749 SUBJECT: GRB 250907A: GECAM-B detection DATE: 25/09/08 15:18:41 GMT FROM: Chenwei Wang at IHEP <cwwang@ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a bright long burst GRB 250907A at 2025-09-07T22:00:52.850 UTC (denoted as T0), which is also detected by Konus-Wind. According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 36.5 +0.5/-3.0 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb250907A.png GECAM-B localized this burst to the following position (J2000): Ra: 337.2 deg Dec: -9.0 deg Err: 1.3 deg (1-sigma, statistical only) 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 -1.08 +0.14/-0.12 and the cutoff energy, parameterized as Epeak, is 535 +192/-129 keV. The event fluence (10-1000 keV) in this time interval is (7.57 +0.51/-0.61)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 250907A is shown at: https://www.bursthub.cn//admin/static/gecambgrb250907A_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/41749. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...