GCN Circular 45398

Bertrand Cordier (CEA), Hatsune Goto (RIKEN, CEA) report on behalf of the SVOM mission team:

At 2026-08-18T20:11:12 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260818B (SVOM burst-id sb26081807).

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 2 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 18.60 in the [8-120] keV energy band over a time window of 0.08 seconds starting at 2026-08-18T20:11:12.

The localization of the best alert is R.A., Dec. 44.9407, 7.4547 degrees:
R.A. (J2000) = 2h59m45.76s
Dec. (J2000) = 7d27m16.93s
 with a 90% confidence level (C.L.) radius of 4.60 arcmin (including systematic error of 2 arcmin added in quadrature).

The SVOM/ECLAIRs light curve showed a single peak structure with a duration of about 1 second.

This burst also triggered SVOM/GRM at 2026-08-18T20:11:12 on a timescale of 0.10 seconds with an SNR of 31.10.

Due to a platform constraint, 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.

We will schedule a SVOM ToO observation for this burst.

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 Bertrand Cordier: bcordier@cea.fr.
Please contact the BA by email if you require additional information.