GCN Circular 42932

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

SVOM/ECLAIRs team: Maria Grazia BERNARDINI (INAF-OAB, LUPM)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by GRB 251201A (SVOM trigger reference: sb25120107) at 2025-12-01T04:37:04.500 (T0), which is also detected by MAXI/GSC (MAXI team, GCN #42913
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 ) and GECAM-B. 

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a multi-pulses followed by a possible flare with a total T90 of 39.3 +5.1/-1.8 s in the 15-5000 keV band, the T90 of the main emission is 4.1 +0.4/-0.2 s.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb251201A.png

In addition, the position of this burst, as determined by MAXI/GSC (RA=309.032, DEC=30.413, GCN #42913
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 ), is located at about 59 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. 

With this localization, the time-averaged spectrum from T0-3 to T0+40 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.55 +0.15/-0.11 and the cutoff energy, parameterized as Epeak, is 352 +308/-144 keV. The event fluence (10-1000 keV) in this time interval is (5.32 +0.54/-0.58)E-06 erg/cm^2.  

The 1s peak spectrum, measured from T0-0.3 to T0+0.7 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -0.51 +0.11/-0.12 and the cutoff energy, parameterized as Epeak, is 154 +11/-9 keV. The flux (10-1000 keV) in this time interval is (1.71 +0.08/-0.07)E-06 erg/cm^2/s.

The localization of GRB 251201A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251201A_amati.png
The localization of GRB 251201A in the 'Yonetoku' relation diagram is shown at: 
https://www.bursthub.cn//admin/static/svgrb251201A_yonetoku.png

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: Yue Wang (IHEP) (yuewang@ihep.ac.cn)