GCN Circular 41593

M.Brunet, O. Godet (IRAP), 

report on behalf of the SVOM team:

The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 250808B, starting at 2025-08-08T08:32:21.85 UTC (T0), through an offline search with the event-by-event data downloaded through the X-band ground station.

The burst was detected within several energy ranges in a 5.12 s timescale. The best detection is obtained by the image trigger with a signal-to-noise ratio of 8.2 within 4-20 keV over a time window of 5.12 seconds starting at T0.

The lightcurve shows a double peak structure lasting around 5 s.

The localization of the source is RA, Dec = 358.829, 15.300 degrees:

RA (J2000) = 23h55m18.96s    
Dec (J2000) = 15d18m00.00s 

with a 90% C.L. radius of 11.2 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 to T0+5s in the energy range 4-20 keV is best fitted by a power law. The powerlaw index is -2.37 -0.57/+0.64. With this model, the total fluence in 4-120 keV is (6.71 +0.68/-3.93)e-8 erg/cm^2.

All quoted errors are at the 68% confidence level.

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.

The SVOM point of contact for this event  is : Marius Brunet : marius.brunet at irap.omp.eu

Please contact him by email if you require additional information regarding the SVOM follow-up of this burst.