GRB 260611B

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

SVOM/ECLAIRs team: Marius Brunet (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM detected GRB 260611B during the routine ground search at 2026-06-11T21:32:37.000 (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44917
Loading...
 
 ) and CALET (Nakahira et al, GCN #44923
Loading...
 
 ).

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst mainly consists of multiple pulses with a T90 of 26 +4/-2 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260611B.png

In addition, the position of this burst, according to Fermi/GBM localization (RA = 13.3, Dec = 22.6, Fermi GBM Team, GCN #44917
Loading...
 
 ), is located at about 121 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.

With this localization, the time-averaged spectrum from T0-6 to T0+26 s is fitted by a power law function. The power law index is -2.14 +0.12/-0.12. The event fluence (10-1000 keV) in this time interval is (1.41 +0.13/-0.13)E-05 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: Jin-Peng Zhang (IHEP) (zhangjinpeng@ihep.ac.cn)

S. Nakahira (JAXA), A. Yoshida, T. Sakamoto, S. Sugita, 
Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), Y. Asaoka (ICRR), S. Torii,
Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
N. Cannady (GSFC), M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

The CALET Gamma-ray Burst Monitor (CGBM) detected GRB 260611B
at 21:32:32.02 UTC on 11 June 2026 (trigger #1465248636;
https://cgbm.calet.jp/cgbm_trigger/flight/1465248636/index.html).
A CGBM Notice was distributed in near real time.

This event was also reported by Fermi GBM (Fermi GBM Team., GCN #44917
Loading...
 
 ).

The burst signal was seen by all CGBM detectors.
The burst light curve shows a multi-peaked structure starting
at T+0.2 s, peaking at T+14.7 s, and ending at T+28.4 s.
The T90 and T50 durations measured with the SGM data are 24.7 +/- 0.9 s
and 13.5 +/- 1.2 s in the 40-1000 keV band, respectively.


The ground-processed light curve is available at:
https://cgbm.calet.jp/cgbm_trigger/ground/1465248636/

The CALET data used in this analysis were provided by
the Waseda CALET Operation Center located at Waseda University.

The Fermi GBM team reports the detection of a likely LONG GRB

At 21:32:33 UT on 11 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260611B (trigger 802906358.618188 / 260611898).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 13.3, Dec = 22.6 (J2000 degrees, equivalent to J2000 00h 53m, 22d 36'), with a statistical uncertainty of 2.2 degrees.

The angle from the Fermi LAT boresight is 88.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260611898/quicklook/glg_skymap_all_bn260611898.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260611898/quicklook/glg_healpix_all_bn260611898.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260611898/quicklook/glg_lc_medres34_bn260611898.gif