GCN Circular 41882
Subject
GRB 250919A: SVOM/GRM observation of a very bright GRB
Event
Date
2025-09-19T07:33:19Z (6 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by a very bright burst GRB 250919A (SVOM trigger reference: sb25091901) at 2025-09-19T00:29:15.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41874).
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 158.0 +/-6.0 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250919A.png
In addition, the position of this burst, as determined by Fermi/GBM (RA= 303.5, DEC= 49.8, GCN#41874), is located at about 84 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst still clearly detected by ECLAIRs through the shield due to the high brightness.
With this localization, the time-averaged spectrum from T0-25 to T0+270 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.14 +0.03/-0.02 and the cutoff energy, parameterized as Epeak, is 610 +52/-46 keV. The event fluence (10-1000 keV) in this time interval is (3.01 +/-0.05)E-04 erg/cm^2.
The localization of GRB 250919A in the 'Amati' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb250919A_amati.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: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)