GCN Circular 39154

A. Saccardi, T. Sadibekova, N. Dagoneau, H. Goto, S. Schanne (CEA), Ch. Van Hove (IJCLab)
report on behalf of the SVOM mission team:

The SVOM/ECLAIRs telescope triggered and located the long duration GRB
250205A (sb25020504) starting at 2025-02-05T21:24:38 UTC (Tb).

The following trigger information was received on the ground with low-latency by the SVOM VHF Alert Network.

The burst was detected by both the on-board Count-Rate Trigger (CRT) and
Image Trigger (IMT) and 8 alerts were received. The best detection is
obtained by IMT with a signal-to-noise ratio of 19.3 in the 8-120 keV energy
band over a time window of 40.96 s starting at Tb.

The localization of the best Alert is RA, Dec = 113.459, 32.365 (J2000).
The uncertainty on this position is 4.5 arcminutes at 90% C.L. which
includes 2 arcminutes of systematic uncertainty in quadrature.

SVOM performed an automatic slew on this burst.

MXT began observing the field at 2025-02-05T21:34:32, 593 seconds after the SVOM trigger.

Using onboard processed data we found an uncatalogued X-ray source located in J2000 at RA, Dec 113.534, 32.370 degrees

RA (J2000) = 7h34m08s
Dec (J2000) = 32d22m14s

with an uncertainty radius at 90% C.L. of 80 arcseconds.
This location is 3.8 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.

VT began observing the field at 2025-02-05T21:41:52, 1033 seconds after the SVOM trigger. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments.

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.

The Burst Advocates (BAs) on shift for this burst are Andrea Saccardi, Tatyana Sadibekova (andrea.saccardi@cea.fr). Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.