TITLE: GCN CIRCULAR NUMBER: 37325 SUBJECT: GRB 240819A as a likely X-Ray Flash DATE: 24/08/28 19:55:10 GMT FROM: sebastien.guillot@irap.omp.eu
SVOM/ECLAIRs commissioning team: Sebastien Guillot, Olivier Godet, Laurent Bouchet, Juliette Alaux (IRAP), Tais Maiolino (LUPM), Floriane Cangemi (APC), Stéphane Schanne, Frédéric Chateau, Nicolas Dagoneau, Hervé Le Provost (CEA), 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:
Following the trigger of the X-ray transient, named GRB 240819A, by SVOM/ECLAIRs (Coleiro, et al., GCN 37208) at 2024-08-19T02:35:21.2 UT (T0), further analyses of the X-band data from ECLAIRs indicate a rather soft event with most photons below 40 keV (signal-to-noise of ~10 for events between 4 to 40 keV; versus S/N < 4 for events above 40 keV).
In addition, observations by Swift-XRT at T0+0.23 days and T0+0.31 days (D'Avanzo, et al., GCN 37218) and at T0+6.01 days (D’ai, et al. GCN 37311) revealed a fading X-ray source from 11(+3.5, -2.9) x 10^-3 ct/sec to a 3-sigma upper limit of 3.5 x 10^-3 ct/sec. Therefore, the X-ray afterglow of GRB 240819A is likely source 2 (from D’ai, et al. GCN 37311), localized at RA=310.9464 (20:43:47.14) and Dec.=+49.5140 (+49:30:50.3) with a 90% c.l. error circle of 5.8 arcseconds.
The identification of the fading afterglow and the spectral softness of the event described above, are indicative of a likely X-Ray Flash (XRF, i.e., a soft GRB with lower luminosity and located at a closer distance than typical GRBs), rather than a Galactic transient.
We encourage deep optical follow-up observations to attempt the detection of a possible supernova that could be associated with this event. We caution that, due to the low galactic latitude of the transient, a potential supernova will undergo strong visible extinction (Av ~ 5).
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