TITLE:   GCN CIRCULAR
NUMBER:  42695
SUBJECT: GRB 251013C: joint SVOM/ECLAIRs-GRM refined analysis
DATE:    25/11/15 11:31:15 GMT
FROM:    SVOM_group <svomgroup@bao.ac.cn>

Nicolas Dagoneau (CEA), Chen-Wei Wang (IHEP), Frédéric Piron (LUPM), Jean-Luc Atteia (IRAP) 


Using the event-by-event data downloaded through the X-band ground station, we report the preliminary ECLAIRs-GRM joint analysis of GRB 251013C (SVOM burst-id sb2525101311, GCN 42222) detected at T0 = 2025-10-13T17:39:42, which was also detected Fermi/GBM (GCN 42259). The refined analysis for ECLAIRs only was reported in GCN 42292.

T90s are given in the table below for both ECLAIRs and GRM.

| Instrument      | Energy Range     | T90 (s)         |
|-----------------|------------------|-----------------|
| ECLAIRs         | 4–120 keV        | 19 (-2 / +5) s  |
| GRM             | 50–300 keV       | 13 (-1 / +4) s  |

The ECLAIRs-GRM joint time-averaged spectrum (T0-0.83 s to T0+17.70 s) in the 8-5000 keV energy range is best fitted by a power-law model with a photon index of 1.55 -0.03/+0.02. With this model, the total 10-1000 keV fluence is (4.58 +/- 0.18)e-06 erg/cm^2.

From the likelihood profile of Epeak obtained by iteratively fitting a cutoff power-law model with a frozen Epeak parameter, we derived a 95% confidence level lower limit of approximately 480 keV, which is consistent with the value measured by Fermi (GCN 42259).

With a redshift of z = 0.572 (GCN 42227), the burst isotropic energy Eiso (from 1 keV to 10 MeV in its rest frame) is 5.6e51 erg, which makes this GRB consistent with type I GRBs in the 'Amati' relation diagram (Amati et al. 2002).

All the quoted errors are at the 68% confidence level.

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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC.

The SVOM/ECLAIRs-GRM point of contact for this burst is: Nicolas Dagoneau (nicolas.dagoneau AT cea.fr).