GCN Circular 43244

Chen-Wei Wang, Wen-Jun Tan, Xue-Yuan Zao, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:

GECAM-B was triggered in-flight by a long burst GRB 251226A, at 2025-12-26T08:01:02.550 UTC (denoted as T0), which is also detected by SVOM/GRM and HXMT. 

According to the GECAM-B light curve in about 70-6000 keV, this burst mainly consists of a precursor-like pulse followed by a multi-pulses main emission with a duration (T90) of 35.9 +3.4/-6.0 s. We note that the quiescent time between the precursor-like pulse and the main emission is relatively short. 

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb251226A.png

GECAM-B in-flight localization of this burst is (J2000): 
Ra: 260.2 deg 
Dec: 47.0 deg
Err: 9.1 deg (1-sigma, statistical only)

We note that the localization may be improved since this burst is not detected by Fermi/GBM.

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).