GCN Circular 45405

Subject

GRB 260818B: SVOM/ECLAIRs refined analysis

Event

GRB 260818B

Date

2026-08-19T20:28:53Z (3 days ago)

Edited On

2026-08-20T15:43:01Z (3 days ago)

From

SVOM_group <svomgroup@bao.ac.cn>

Edited By

Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>

Via

Web form

H. Yang, O. Godet, S. Guillot (IRAP),  Bertrand Cordier, S. Schanne (CEA), Hatsune 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 the short burst GRB 260818B (SVOM burst-id sb26081807, GCN 45398Loading...
 
 , trigger time T0 = 2026-08-18T20:11:12.618 UTC). 

The burst that triggered ECLAIRs shows a typical fast-rise, exponential-decay (FRED) light curve in the 4-120 keV band, with T90(4-120 keV) = (0.22 +0.07/-0.02) s. The light curve in the 4-20 keV band shows possible extended emission following the main pulse, with a corresponding T90(4-20 keV) = (0.71 +0.40/-0.39) s. 

The time-averaged spectrum of the main pulse, extracted from T0 to T0 + 0.22 s in the 5-120 keV range, is well fitted by a cutoff power-law model with a photon index of -0.61 +/-0.14, a peak energy of (56 +16/-12) keV, a 4-120 keV photon flux of (32.3 +0.1/-4.8) photons/cm^2/s, and a corresponding 4-120 keV fluence of (2.9 +/-0.2)e-7 erg/cm^2. 

The time-averaged spectrum of the possible extended emission, extracted from T0 + 0.22 s to T0 + 0.71 s in the 5-20 keV, can be well fitted by a blackbody model with a temperature of (1.6 +0.4/-0.3) keV, a 4-120 keV photon flux of (2.1 +0.3/-0.7) photons/cm^2/s, and a corresponding 4-120 keV fluence of (1.1+/-0.3) e-8 erg/cm^2.

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 (IRAP) (hui.yang@cnrs.fr).