TITLE: GCN CIRCULAR NUMBER: 41593 SUBJECT: GRB 250808B: SVOM detection of a burst through offline search DATE: 25/08/29 14:19:30 GMT FROM: SVOM_group svomgroup@bao.ac.cn
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.
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