GCN Circular 44268

Subject
GRB 260411B: SVOM/GRM observation of a long burst
Event
GRB 260411B
Date
2026-04-11T16:24:34Z (3 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Chao Zheng, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)

SVOM/ECLAIRs team: Frédéric Daigne (IAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight GRB 260411B (SVOM trigger reference: sb26041103) at 2026-04-11T08:04:37.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#44262Loading...
 
 ).

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of two emission episodes with a T90 of 16.2 +2.1/-1.4 s in the 15-5000 keV band. 

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260411B.png

In addition, the position of this burst, as determined by GOTO (RA= 85.567893 deg, DEC= 1.984983 deg, GCN#44265Loading...
 
 ), is located at about 81 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. 

With this localization, the time-averaged spectrum from T0-2.5 to T0+16.4 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.81 +0.09/-0.09 and the cutoff energy, parameterized as Epeak, is 385 +44/-37 keV. The event fluence (10-1000 keV) in this time interval is (2.37 +0.09/-0.09)E-05 erg/cm^2. 

The 1s peak spectrum, measured from T0+6.7 to T0+7.7 s, is also best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.41 +0.09/-0.09 and the cutoff energy, parameterized as Epeak, is 331 +20/-17 keV. The flux (10-1000 keV) in this time interval is (6.34 +0.20/-0.20)E-06 erg/cm^2/s.

The localization of GRB 260411B in the 'Amati' relation diagram is shown at: 
https://www.bursthub.cn//admin/static/svgrb260411B_amati.png
And the localization in the 'Yonetoku' relation diagram is shown at: 
https://www.bursthub.cn//admin/static/svgrb260411B_yonetoku.png 

With the brightness of the prompt emission, the predicted soft X-ray afterglow [1] is shown at: 
https://www.bursthub.cn//admin/static/svgrb260411B_xag_pre.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)

[1] Chen-Wei Wang et al. ApJ 997 353 https://doi.org/10.3847/1538-4357/ae2eaeLoading...