GCN Circular 42090

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

SVOM/ECLAIRs team: Frédéric Piron (LUPM), Jean-Luc Atteia (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by a burst GRB 251001C (SVOM trigger reference: sb25100106) at 2025-10-01T15:07:27.000 UTC (T0), which is also detected by Glowbug gamma-ray telescope (C.C. Cheung et al. 2025, GCN#42049
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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 mainly of a single pulse with a T90 of 11.7 +4.5/-4.1 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb251001C.png

In addition, the position of this burst, as determined by Glowbug gamma-ray telescope (RA= 82.7, DEC= 21.9, GCN#42049
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 ), is located at about 59.47 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+15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.24 +0.19/-0.22 and the cutoff energy, parameterized as Epeak, is 301 +314/-97 keV. The event fluence (10-1000 keV) in this time interval is (3.46 +0.53/-0.50)E-06 erg/cm^2. 

The localization of GRB 251001C in the 'Amati' relation diagram is shown at: 
https://www.bursthub.cn//admin/static/svgrb251001C_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: Zheng-Hang Yu(IHEP)(zhyu@ihep.ac.cn)