GCN Circular 45534

A. Saccardi, S. Schanne (CEA/Irfu), Y.-H. I. Yin,  C. Plasse (HKU), Y. Huang (APC), B. Cordier, J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM mission team:

At 2026-09-09T11:18:01 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260909A (SVOM burst-id sb26090910).

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

The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 7 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 12.10 in the [8-50] keV energy band over a time window of 20.40 seconds starting at 2026-09-09T11:17:45 (Tb).

The localization of the best alert is R.A., Dec. 13.0009, 24.2188 degrees (J2000) with a 90% confidence level (C.L.) radius of 6.67 arcmin (including systematic error of 2 arcmin added in quadrature).

This burst also triggered SVOM/GRM at 2026-09-09T11:18:01 on a timescale of 1 seconds with an SNR of 7.30.
The SVOM/GRM light curve showed a single peak structure with a duration of about 30 s.

SVOM slewed to the burst.

SVOM/MXT began observing the field at 2026-09-09T11:21:14 UTC, 193 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 13.0346, 24.1956 degrees:
R.A. (J2000) = 0h52m08s
Dec. (J2000) = 24d11m44s
with a 90% C.L. radius of 64 arcseconds.

This location is 2.31 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.

VT began observing the field after the slew. The analysis of the data will be published in a future circular.

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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.

The Burst Advocate (BA) on shift for this alert is Clara Plasse: cplasse@hku.hk
Please contact the BA by email if you require additional information.