GCN Circular 41630

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 250830C at 2025-08-30T14:51:55.100 UTC (denoted as T0). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of a precursor followed by multiple pulses main emission with a duration (T90) of 23.6 +12.0/-8.4 s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecamgrb250830C.png

GECAM-B localized this burst to the following position (J2000): 
Ra: 240.1 deg 
Dec: 40.5 deg
Err: 1.1 deg (1-sigma, statistical only)

The time-averaged spectrum from T0-2 s to T0+40 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.06 +0.23/-0.24 and the cutoff energy, parameterized as Epeak, is 255 +121/-46 keV. The event fluence (10-1000 keV) in this time interval is (2.41 +/-0.36)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 250830C is shown at: 
https://www.bursthub.cn//admin/static/grb250830C_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).