GCN Circular 37713
Subject
GRB 241001A : ECLAIRs spectral analysis and XRF classification
Date
2024-10-04T16:33:13Z (5 months ago)
From
Jean-Luc Atteia at IRAP <jean-luc.atteia@irap.omp.eu>
Via
Web form
Alexis Coleiro, Floriane Cangemi (APC), Tais Maiolino, F. Piron (LUPM), Jingwei Wang (IAP), Maria-Grazia Bernardini (INAF), Jean-Luc Atteia, Laurent Bouchet, Sebastien Guillot, Juliette Alaux, Hui Yang (IRAP), Nicolas Dagoneau, Stéphane Schanne, Frédéric Chateau, Hervé Le Provost (CEA), Wenjin Xie (NAOC), 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:
Considering the excellent followup for GRB 241001A detected and localized by SVOM/ECLAIRs (GCN 37655), and the redshift measured by the VLT (z = 0.573, GCN 37677), we provide here a spectral analysis showing that this transient qualifies as an X-Ray Flash (XRF).
The following properties have been measured in the 5 - 20 keV energy range (no count is detected beyond 20 keV).
T90 [s] = 11.7 (-4.4 / +2.0)
Fluence [erg cm-2] = 7e-8
Spectral parameters for a broken power law fit (red. chisqr = 0.86):
gamma_1 = -1.7 (-0.6 / +1.3)
E_break [keV] = 9.96 (-2.60 / +2.77)
gamma_2 = -5.4 (-2.2 / +1.9)
With these parameters, the fluence ratio [2-30]/[30-400] keV ≈ 340, well above 1, the empirical limit used to define X-Ray Flashes (Sakamoto et al. 2005).
Moreover:
- A pure PL fit is rejected with high significance (red. chisqr = 2.9), indicating that the spectrum requires a cutoff at a few keV.
- A BB fit is fully acceptable (and preferred over the broken PL, with red. chisqr = 0.56), the best fit temperature is kT=1.8 +/- 0.2 keV
ECLAIRs being in the commissioning phase, the quoted spectral results shall be taken with some caution. In any case, the XRF classification is certain.
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.