TITLE:   GCN CIRCULAR
NUMBER:  45807
SUBJECT: GRB 260930B: SVOM/GRM observation
DATE:    26/10/05 07:04:03 GMT
FROM:    yzh807926@163.com

SVOM/GRM team: Zheng-Hang Yu, Chao Zheng, Yue Wang, Shao-Lin Xiong(IHEP)

SVOM/ECLAIRs team: O. Godet (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered on-ground by GRB 260930B at 2026-09-30T18:56:57.800 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #45791) and GECAM-B (Yu et al., GCN #45802).

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of two main episodes multiple pulses followed by a single pulse with a T90 of 0.78 +0.74/-0.62 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn/gcn/2026/svgrb260930B.png

In addition, the position of this burst, as determined by GECAM-B (RA = 326.3, Dec = 24.1, Error = 8.6 deg, GCN #45802), is located at about 70 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. 

With this localization, the time-averaged spectrum from T0-0.5 to T0+0.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is 1.08 +0.28/-0.41 and the cutoff energy, parameterized as Epeak, is 348 +856/-151 keV. The event fluence (10-1000 keV) in this time interval is (5.46 +1.34/-1.17)E-07 erg/cm^2. 


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/GRM point of contact for this burst is: Zheng-Hang Yu (IHEP) (zhyu@ihep.ac.cn)