TITLE: GCN CIRCULAR NUMBER: 45017 SUBJECT: GRB 260618C: SVOM/ECLAIRs detection of a possible burst through on-ground search DATE: 26/06/22 14:33:28 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> M. Brunet, O. Godet (IRAP), report on behalf of the SVOM/ECLAIRs team: The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 260618C, starting at 2026-06-18T04:02:26.6 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 8.6 within 4-20 keV over a time window of 7 seconds starting at T0-7s. The burst that triggered ECLAIRs onground shows a single peak structure. The burst duration is T90 = 6 +/-1 s in the 4-20 keV energy band. The localization of the source is RA, Dec = 294.933, -65.710 degrees: RA (J2000) = 19h39m43.9s Dec (J2000) = -65d42m36.0s with a 90% C.L. radius of 10.7 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 T0-7 s to T0 in the 5-50 keV energy range is best fitted by a blackbody model with kT = 3.65 +0.47/-0.42 keV.. With this model, the 4-120 keV fluence is (8.3 +0.7/-2.4) e-8 erg/cm^2 and the 4-120 keV photon flux is 0.65 +0.04 /-0.15 ph/cm^2/s. Both broken power-law and power-law with an exponential cutoff models can equally fit the spectrum, however, their parameters can not be constrained due to the faintness of this burst. This event is very soft and if it is a GRB, then it should be probably classified as an X-Ray Flash. All the quoted errors are at the 68% confidence level. A SVOM ToO observation has been requested to follow-up this trigger with both MXT and VT instruments. The results of these observations will be reported later in future circulars. 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) View this GCN Circular online at https://gcn.nasa.gov/circulars/45017. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...