GCN Circular 39768

Yue Wang, Shao-Lin Xiong, Chen-Wei Wang report on behalf of the GECAM team:

GECAM-B was triggered both in-flight and on-ground by a long burst, GRB 250317C, at 2025-03-17T17:31:21.700 UTC (T0). 

According to the event-by-event data, the GECAM-B light curve shows a main pulse with a with a T90 of 23.0 +3.0/-4.0 s in the 40-6000 keV band.

The GECAM-B light curve could be found here: 
https://www.bursthub.cn//admin/static/gecamgrb250317C.png

Using the automatic on-ground localization pipeline, GECAM-B localized this burst to the following position (J2000): 
Ra: 320.42 deg 
Dec: -16.07 deg
Err: 8.59 deg (1-sigma, statistical only)

We note that these results are preliminary. Refined analysis will be reported later.

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM) mission originally consists of two microsatellites (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).