GCN Circular 43031

M. Brunet, J.-L. Atteia (IRAP), N. Dagoneau (CEA), report on behalf of the SVOM team:

The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 251206A, starting at 2025-12-06T20:48:20.92 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 and timescales. The best detection is obtained by the Image Trigger (IMT) with a signal-to-noise ratio of 8.5 within 4-20 keV over a time window of 20.48 seconds starting at T0-20.48s.

The lightcurve shows an asymmetric double-peaked structure, with a minor peak followed by a major peak, lasting around 20 s.

The localization of the source is RA, Dec = 1.843, -4.404 degrees:

RA (J2000) = 00h07m22.32s    
Dec (J2000) = -04d24m16.85s 

with a 90% C.L. radius of 10.9 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 T0-20.48s to T0 in the energy range 5-120 keV is best fitted by a power law. The powerlaw index is -1.96 -0.15/+0.17. With this model, the total fluence in 4-120 keV is (3.56 +0.28/-0.57)e-7 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.