GCN Circular 37208

SVOM/ECLAIRs commissioning team: Alexis Coleiro (APC), Stéphane Schanne, Frédéric Chateau, Nicolas Dagoneau, Hervé Le Provost (CEA), Olivier Godet, Laurent Bouchet, Sebastien Guillot, Juliette Alaux (IRAP), Frédéric Piron (LUPM), Karine Mercier, Marie-Claire Charmeau, Stefano Crepaldi (CNES)

SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Jean-Luc Atteia (IRAP), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Bing Zhang (UNLV)

report on behalf of the SVOM team:

GRB 240819A : An X-Ray Transient located on-board by SVOM/ECLAIRs.

During the commissioning phase, the SVOM/ECLAIRs telescope triggered and located an X-Ray Transient (sb24081901), hereafter GRB 240819A, at 2024-08-19T02:35:21.2 UT (T0). 

The following trigger information was received on the ground with low-latency by the SVOM VHF Alert Network: The image SNR is 10.3, measured in the [8-50] keV energy band, over a time window of 40.96 seconds, starting at T0.

The transient location is RA, Dec = 310.91, 49.59  (J2000). This is about 9 degrees from the ECLAIRs optical axis, in the totally coded field of view. The statistical uncertainty on this position is 8.0 arcminutes, to which we recommend to add 10 arcminutes of systematic uncertainty. This location was subsequently observed in X-rays by Swift (GCNC 37203) and Einstein Probe (GCNC 37206), and in the optical by the Thai Robotic Telescope network (GCNC 37207).

We are confident of the reality of this transient, however its location 4° above the galactic plane raises some doubts on its nature: an unknown galactic source or a GRB behind the galactic plane.

While the real-time alert was received within 1 minute of the trigger, we have awaited the availability of the full X-band data to send this GCN, in order to confirm the reality of the source with the full reconstructed sky image.

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), French Space Agency (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by APC, CEA, CNES and IRAP.