GCN Circular 42995
Subject
GRB 251203A: SVOM/GRM observation
Event
Date
2025-12-05T05:45:12Z (2 days ago)
From
renyz16607@163.com
Via
Web form
SVOM/GRM team: Yang-Zhao Ren, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Jean-Luc Atteia (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered on-ground by GRB 251203A at 2025-12-03T08:18:45.150 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42968).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 14.5 +2.5/-1.5 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb251203A.png
In addition, the position of this burst, as determined by Fermi/GBM (RA = 165.5, Dec = -46.9, GCN #42968), is located at about 94 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.
With this localization, the time-averaged spectrum from T0-2 to T0+20 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.40 +0.23/-0.28 and the cutoff energy, parameterized as Epeak, is 185 +83/-42 keV. The event fluence (10-1000 keV) in this time interval is (7.87 +0.94/-0.88)E-06 erg/cm^2.
The 1s peak spectrum, measured from T0+14.85 to T0+15.85 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -1.65 +0.14/-0.17 and the cutoff energy, parameterized as Epeak, is 1040 +1700/-630 keV. The flux (10-1000 keV) in this time interval is (1.41 +0.13/-0.14)E-06 erg/cm^2/s.
The localization of GRB 251203A in the 'Amati' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb251203A_amati.png
The localization of GRB 251203A in the 'Yonetoku' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb251203A_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 point of contact for this burst is: Yang-Zhao Ren (IHEP)(renyz@ihep.ac.cn)