GCN Circular 45612

H. Yang, M. Brunet, O. Godet (IRAP), W. J. Xie (NAOC), Y. F. Liang (PMO), C. Plasse (HKU), H. Goto (RIKEN/CEA) report on behalf of the SVOM/ECLAIRs team:

Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260915A (SVOM burst-id sb26091501 – GCN 45570
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 , trigger time T0 = 2026-09-15T01:12:03 UTC), which was also detected by Fermi/GBM as a sub-threshold (Hamburg, GCN 45574
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 ).

The burst that triggered ECLAIRs onboard shows a broad bump from T0 - 14 s to T0 + 200 s in the 4-120 keV energy band, with a slew performed from T0 + 42 s to T0 + 135 s. The burst duration estimated through the imaging technique is T90 = (167 +10/-6) s in the 4-120 keV energy band. 

The time-averaged spectrum from T0 - 14 s to T0 + 42 s (before the slew) in the 5-120 keV band is best fitted by a power-law model, with alpha= -1.20 +/- 0.05. With this model, the 4-120 keV fluence is (2.6 +/- 0.1)e-6 erg/cm^2 and the 4-120 keV photon flux is (9.9 +/- 0.4)e-1 ph/cm^2/s. 

The time-averaged spectrum from T0 + 135 s to T0 + 200 s (after the slew) in the 5-120 keV band is best fitted by a cutoffpl model, with alpha = -1.4 +0.4/-0.8 and Epeak = 54 +80/-24 keV. With this model, the 4-120 keV fluence is (2.7 +/- 0.6)e-7 erg/cm^2 and the 4-120 keV photon flux is (1.4 +0.3/-0.2)e-1  ph/cm^2/s. 

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 point of contact for this burst is:  Hui Yang (hui.yang at cnrs.fr)