TITLE:   GCN CIRCULAR
NUMBER:  38557
SUBJECT: EP 241208A : Detection of a long soft transient by SVOM/ECLAIRs
DATE:    24/12/13 14:10:43 GMT
FROM:    SVOM_group <svomgroup@bao.ac.cn>

SVOM/ECLAIRs Commissioning Team: Jean-Luc Atteia, Laurent Bouchet, Marius Brunet,
Sebastien Guillot, Juliette Alaux, Hui Yang (IRAP), Stéphane Schanne, Damien Turpin,
Nicolas Dagoneau, Frédéric Chateau, Hervé Le Provost (CEA), Wenjin Xie, Donghua Zhao
(NAOC), Floriane Cangemi (APC), Tais Maiolino (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), Olivier Godet (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:

During the commissioning phase, the SVOM/ECLAIRs telescope detected and localized the
long soft transient EP241208A, also detected by Einstein Probe ( GCN circular 38477) at 2024-12-08T16:35:50.016 UTC (Tb) through an offline search with the event-by-event data downloaded through the X-band ground station.

The burst was detected by several methods and within several energy ranges and
timescales. The best detection is obtained by the image trigger with a signal-to-noise ratio of
6.1 within 4-8 keV over a time window of 10.24 seconds starting at Tb. The lightcurve shows
a single peak of duration of about 10s. No emission has been detected above 20 keV.

The localization of the best Alert is RA, Dec = 127.785, 48.861 (J2000) which is consistent
with EP one.The statistical uncertainty on this position is 13 arcminutes, to which we
recommend adding 2 arcminutes of systematic uncertainty in quadrature.

Spectral analysis is ongoing and will be published in a future circular.

ECLAIRs did not detect this burst onboard because its significance was below the onboard trigger
Alert threshold.

The Space 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. ECLAIRs was developed jointly by
APC, CEA, CNES, and IRAP.

The SVOM point of contact for this burst is: Marius Brunet (IRAP) marius.brunet@irap.omp.eu