GCN Circular 42471

Y. H.Cheng (YNU), Y. F. Liang (PMO), O. Godet, S. Guillot (IRAP), S. Schanne (CEA), L. Zhang (IHEP)

At 2025-10-27T09:38:17 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251027A (SVOM burst-id sb25102702).

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 1 alert. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.33 in the [5-20] keV energy band over a time window of 20.40 seconds starting at 2025-10-27T09:37:56.

The localization of the best alert is R.A., Dec. 95.1860, 11.6869 degrees:
R.A. (J2000) = 6h20m44.64s
Dec. (J2000) = 11d41m12.73s
 with a 90% confidence level (C.L.) radius of 9.46 arcmin (including systematic error of 2 arcmin added in quadrature).

The GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb251027A.png

Due to the ECLAIRs detection significance being below the slew threshold, no immediate slew was performed on this burst. But follow-up observations with SVOM/MXT and SVOM/VT have been requested.

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 Yehao Cheng: yhcheng@mail.ynu.edu.cn.
Please contact the BA by email if you require additional information.