GCN Circular 45477

O. Godet (IRAP), C. Guepin (LUPM), S. Guillot (IRAP) report on behalf of the SVOM mission team:

At 2026-08-31T18:36:12 UTC (T0), SVOM/ECLAIRs triggered and located the possible gamma-ray burst GRB 260831B (SVOM burst-id sb26083106).

The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.

The burst was only detected by the Image Trigger (IMT), which produced a sequence of 5 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.11 in the [8-50] keV energy band over a time window of 655.36 seconds starting at 2026-08-31T18:32:07.

The localization of the best alert is R.A., Dec. 52.977, 43.971 degrees:
R.A. (J2000) = 3h31m54.41s
Dec. (J2000) = 43d58m15.22s
 with a 90% confidence level (C.L.) radius of 8.69 arcmin (including systematic error of 2 arcmin added in quadrature).

The SVOM/ECLAIRs light curve is featureless.

SVOM slewed to the burst.

SVOM/MXT began observing the field about 10 minutes after T0. Using onboard processed data, no source was detected during a > 10 min exposure.
The SVOM/MXT team is waiting for the full dataset to detect and localise the possible SVOM/MXT counterpart.

VT began observing the field after the slew. The analysis of the data will be published in a future circular.

We note that the classical nova V* GK Per that triggered ECLAIRs in the past few weeks is within the ECLAIRs error circle. 

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.

The Burst Advocate (BA) on shift for this alert is Claire Guepin: claire.guepin at lupm.in2p3.fr
Please contact the BA by email if you require additional information.