GCN Circular 46096
Subject
GRB 261029A: SVOM/GRM observation of a bright burst
Event
Date
2026-10-29T16:20:14Z (3 days ago)
From
yzh807926@163.com
Via
Web form
SVOM/GRM team: Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong(IHEP)
SVOM/ECLAIRs team: Marius Brunet (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 261029A (SVOM trigger reference: sb26102901) at 2026-10-29T01:27:04.500 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #46071), and SVOM/ECLAIRs (Hatsune Goto et al., GCN#46072).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-episodes with a T90 of 43.50 +/-0.60 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn/gcn/2026/10/svgrb261029A.png
In addition, the localization of this burst, as determined by GOTO (RA = 8.817988, Dec = 34.500138, GCN #46073), is located at about 45 degrees from the SVOM optical axis.
With this localization, the time-averaged spectrum from T0-3 to T0+60 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is 0.94 +/-0.02 and the cutoff energy, parameterized as Epeak, is 897 +55/-52 keV. The event fluence (10-1000 keV) in this time interval is (1.15 +/-0.01)E-04 erg/cm^2.
The 1s peak spectrum, measured from T0+38.5 to T0+39.5 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is 0.79 +/-0.03 and the cutoff energy, parameterized as Epeak, is 838 +56/-50 keV. The flux (10-1000 keV) in this time interval is (1.04 +/-0.18)E-05 erg/cm^2/s.
With the measured redshift z=3.275 (L. Cotter et al., GCN 46081), we calculate the isotropic energy Eiso is about 3.84E54 erg. Thus GRB 261029A is well consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:
https://www.bursthub.cn/gcn/2026/10/svgrb261029A_amati.png
The localization of GRB 261029A in the 'Yonetoku' relation diagram is shown at:
https://www.bursthub.cn/gcn/2026/10/svgrb261029A_yonetoku.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/GRM point of contact for this burst is: Zheng-Hang Yu (IHEP) (zhyu@ihep.ac.cn)