TITLE:   GCN CIRCULAR
NUMBER:  42523
SUBJECT: GRB 251028A: GECAM-B detection
DATE:    25/10/30 15:46:39 GMT
FROM:    guohx@ihep.ac.cn

Hao-Xuan Guo, Chen-Wei Wang, Chao Zheng, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:

GECAM-B was triggered in-flight by a long burst, GRB 251028A, at 2025-10-28T03:26:40.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#42497, GCN#42499), MAXI/GSC (MAXI team, GCN#42498), Glowbug (C.C. Cheung et al., GCN#42506) and SVOM/GRM (SVOM/GRM team, SVOM/ECLAIRs team, GCN#42522).

According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 38 +4/-5 s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb251028A.png

The time-averaged spectrum from T0-10 s to T0+45 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.05 +0.11/-0.11 and the cutoff energy, parameterized as Epeak, is 259 +38/-25 keV. The event fluence (10-1000 keV) in this time interval is (3.12 +0.20/-0.17)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 251028A is shown at: 
https://www.bursthub.cn//admin/static/gecambgrb251028A_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).