GCN Circular 44714

M. Brunet (IRAP), S. Schanne,  N. Dagoneau (CEA), report on behalf of the SVOM/ECLAIRs team

The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 260524A, starting at 2026-05-24T12:01:52 UTC (trigger time T0) through an on-ground search with the event-by-event data downloaded through the X-band ground station.

The burst was detected within several energy ranges and timescales. The best detection is obtained by the Image Trigger with a signal-to-noise ratio of 9.5 within 4-20 keV over a time window of 20.48 seconds starting at T0-20.48s.

The burst shows a single peak lightcurve in the event-by-event data. The burst duration is estimated to be about 36 s in the 4-20 keV energy band through imaging. We note that just before the trigger, the source was masked by the Earth, so that part of the GRB emission may not have been observed by ECLAIRs.

The localization of the source is RA, Dec = 115.192, -55.287 degrees:

RA (J2000) = 07h 40m 46.1s
Dec (J2000) = −55d17m13.2s

with a 90% C.L. radius of 10.1 arcmin (including systematic error of 6 arcmin added in quadrature).

We note that no bright catalogued X-ray sources are found in the error box.

The time-averaged spectrum from T0-32 s to T0+4 s in the energy range 5-50 keV is best fitted by a blackbody model with kT = 2.63 +/-0.27. With this model, the 4-120 keV fluence is (3.3 +0.2/-0.7) e-7 erg/cm² and the 4-120 keV photon flux is 0.63 +0.04/-0.13 ph/cm²/s.

We note that a powerlaw model does not give a good fit. 

Other models such as broken power-law and power-law with an exponential cutoff do not yield constrained parameters.

The spectral parameters indicate that this GRB is very soft and should probably be classified as an X-Ray Flash.

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: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr)