GCN Circular 42308

S. Basa, S. Boissier (LAM), O. Godet, S. Guillot (IRAP), D. Turpin (CEA)

At 2025-10-16T14:59:20 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251016A (SVOM burst-id sb25101602).

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 Count-Rate Trigger (CRT), which produced a sequence of 5 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.16 in the [8-120] keV energy band over a time window of 0.60 seconds starting at 2025-10-16T14:59:19.

The localization of the best alert is R.A., Dec. 266.207, -39.577 degrees:
R.A. (J2000) = 17h44m49.58s
Dec. (J2000) = -39d34m35.95s
 with a 90% confidence level (C.L.) radius of 9.64 arcmin (including systematic error of 2 arcmin added in quadrature).

The SVOM/ECLAIRs light curve showed a single and narrow peak.

This burst also triggered SVOM/GRM at 2025-10-16T14:59:19 on a timescale of 0.10 seconds with an SNR of 37.30.

This burst seems to have been detected by Fermi, but with a declination of about 10 degrees offset.

The satellite did not slew due to Sun constraint. 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.

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 Stephane Basa: stephane.basa@lam.fr.
Please contact the BA by email if you require additional information.