TITLE:   GCN CIRCULAR
NUMBER:  41164
SUBJECT: GRB 250725A: SVOM/GRM observation
DATE:    25/07/25 14:18:41 GMT
FROM:    Chenwei Wang at IHEP <cwwang@ihep.ac.cn>

SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, 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 GRB 250725A (SVOM trigger reference: sb25072501) at 2025-07-25T01:51:36.300 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41150), Swift/BAT (P. A. Evans et al., GCN#41152) and Fermi/LAT (A. Holzmann Airasca et al., GCN#41161).

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse followed by a narrow spike with a T90 of 9.7 +/-0.3 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250725A.png

In addition, the position of this burst, as determined by Swift/BAT (RA= 35.47808, DEC= -82.79131, GCN#41152), is located at about 78 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+12 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.61 +0.15/-0.16 and the cutoff energy, parameterized as Epeak, is 323 +73/-51 keV. The event fluence (10-1000 keV) in this time interval is (8.11 +0.88/-0.80)E-06 erg/cm^2. 

With the redshift z = 5.26 by VLT/FORS2 (A. L. Thakur et al., GCN#41160), the Eiso (from 1 keV to 10 MeV in rest frame) of this burst is (4.13 +0.58/-0.48)E53 erg. Thus GRB 250725A is more consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:  
https://www.bursthub.cn//admin/static/grb250725A_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)