GCN Circular 38923

SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)

report on behalf of the SVOM team:

During the commissioning phase, SVOM/GRM was triggered in-flight by a long burst GRB 250113A (SVOM trigger reference: sb25011303) at 2025-01-13T06:24:36.900 UTC (T0).

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 42 +2/-3 s.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250113A.png

The SVOM/GRM on-ground localization of this burst is (J2000):
RA: 321.4 deg
DEC: -21.6 deg
Error: 2.7 deg (1sigma, statistical only)
We caution that the calibration of SVOM/GRM is undergoing and this localization is subject to systematic errors. 

In addition, the position of this burst, as determined by GRM, is located at about 159 degrees from the SVOM optical axis. This burst was detected by the Count-Rate Trigger onboard ECLAIRs, as an increase in counts over background, but it was not localized by the coded-mask imaging process, which confirms that the burst occurred outside the ECLAIRs field of view.

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.

The SVOM/GRM point of contact for this burst is: Chen-Wei Wang (IHEP) (cwwang@ihep.ac.cn)