GRB 251219A

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

SVOM/ECLAIRs team: Sebastien Guillot (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by a short soft GRB 251219A (SVOM trigger reference: sb25121902) at 2025-12-19T02:36:31.600 UTC (T0), which is also detected by GECAM-B (Wang et al., GCN#43158
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 ).

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.16 +0.12/-0.02 s in the 15-5000 keV band. 

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb251219A.png

In addition, the position of this burst, as determined by GECAM-B (RA= 296.5, DEC= -11.9, ERR=5.6), is located at about 126 degrees from the SVOM optical axis, which is 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 point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)

Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:

GECAM-B was triggered in-flight by a short soft burst GRB 251219A, at 2025-12-19T02:36:31.550 UTC (denoted as T0), which is also detected by SVOM/GRM. 

According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 0.22 +0.08/-0.16 s. The signal is mainly detected in energy lower than 200 keV.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb251219A.png

GECAM-B localized this burst to the following position (J2000): 
Ra: 274.4 deg 
Dec: -4.8 deg
Err: 4.3 deg (1-sigma, statistical only)

We note that the localization is consistent with the magnetar SGR 1830-0645. The short duration and soft spectrum also suggest this is a magnetar X-ray burst.

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).