TITLE:   GCN CIRCULAR
NUMBER:  43960
SUBJECT: GRB 260308A: SVOM/GRM observation of a short GRB
DATE:    26/03/11 14:33:12 GMT
FROM:    Xinghao Luo at IHEP <2952704891@qq.com>

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

SVOM/ECLAIRs team: Olivier GODET (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by GRB 260308A (SVOM trigger reference: sb26030801) at 2026-03-08T20:05:53.100 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43949).

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 1.50 +/-0.4 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260308A.png

In addition, the position of this burst, as determined by Fermi/GBM (RA=250.2 , DEC=-32.6, Fermi GBM team, GCN #43949), is located at about 62 degrees form the SVOM optical axis, which is outside the ECLAIRs field of view.

With this localization, the time-averaged spectrum from T0-0.8 to T0+0.4 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.86 +0.18/-0.16 and the cutoff energy, parameterized as Epeak, is 643 +346/-180 keV.

The localization of GRB 260308A in the 'Amati' relation diagram is shown at: 
https://www.bursthub.cn//admin/static/svgrb260308A_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: Xing-Hao Luo (luoxh@ihep.ac.cn)