TITLE:   GCN CIRCULAR
NUMBER:  44944
SUBJECT: GRB 260610B: SVOM/GRM observation
DATE:    26/06/15 08:36:29 GMT
FROM:    yzh807926@163.com

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

SVOM/ECLAIRs team: Marius Brunet (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered on-ground by a burst GRB 260610B at 2026-06-10T23:46:14.100 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44901).

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a main episode with two peaks a T90 of 65.0 +/-8.0 s in the 15-5000 keV band. 

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260610B.png

In addition, the position of this burst, as determined by Fermi/GBM (RA= 218.66 deg, DEC= 23.94 deg, ERR=2.77 deg, GCN#44901), is located at about 74 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. 

With this localization, the time-averaged spectrum from T0-10 to T0+60 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.59 +0.18/-0.22 and the cutoff energy, parameterized as Epeak, is 34 +6/-8 keV. The event fluence (10-1000 keV) in this time interval is (9.48 +0.50/-0.47)E-06 erg/cm^2.

The 1s peak spectrum, measured from T0+1.9 to T0+2.9 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -1.62 +0.16/-0.32 and the cutoff energy, parameterized as Epeak, is 25 +8/-7 keV. The flux (10-1000 keV) in this time interval is (3.98 +0.41/-0.37)E-07 erg/cm^2/s.

With the measured redshift z=0.473 (D. O'Neill et al., GCN#44914), we calculate the isotropic energy Eiso is about 8.8E51 erg. Thus GRB 260610B is well consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:
https://www.bursthub.cn//admin/static/svgrb260610B_amati.png
The localization of GRB 260421B in the 'Yonetoku' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb260610B_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 point of contact for this burst is: Zheng-Hang Yu(IHEP)(zhyu@ihep.ac.cn)