TITLE:   GCN CIRCULAR
NUMBER:  43158
SUBJECT: GRB 251219A: GECAM-B detection of a possible magnetar X-ray burst from SGR 1830-0645
DATE:    25/12/20 17:41:34 GMT
FROM:    Chenwei Wang at 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).