GCN Circular 45499

GRB 260903A: SVOM detection of a soft faint burst 

M. Brunet, O. Godet, H. Yang (IRAP), R.-C. Chen (NJU), T. Xiao (GXU) report on behalf of the SVOM mission team:

At 2026-09-03T12:37:20 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260903A (SVOM burst-id sb26090302).

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

The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 2 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 7.70 in the [5-8] keV energy band over a time window of 20.40 seconds starting at 2026-09-03T12:36:59 UTC.

The localization of the best alert is R.A., Dec. 25.614, 11.389 degrees:
R.A. (J2000) = 1h42m27.28s
Dec. (J2000) = 11d23m21.52s
 with a 90% confidence level (C.L.) radius of 10.20 arcmin (including systematic error of 2 arcmin added in quadrature).

The SVOM/ECLAIRs light curve showed a broad structure with a duration of about 20 s.

Due to the detection significance being below the slew threshold, no immediate slew was performed on this burst.
No X-ray observation could be performed by SVOM/MXT for the time being.
No optical observation could be performed by SVOM/VT for the time being.
A SVOM ToO has been scheduled.

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 R.-C. Chen: chrczxx@smail.nju.edu.cn.
Please contact the BA by email if you require additional information.