GCN Circular 44507

C. Wu, H. L. Li, Y. L. Qiu, L. P. Xin (NAOC), J. T. Palmerio (CEA/Irfu), D. Götz (CEA/Irfu), A. Saccardi (CEA/Irfu), L. Zhang (IHEP), Y. H. Cheng (YNU) on behalf of the SVOM/VT team.

After the trigger by SVOM/ECLAIRs (SVOM burst-id sb26050905) at 2026-05-09T21:51:09 UTC (T0), SVOM/VT began observing the field after the automatic slew on the burst (Götz et al., GCN 44504

) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.

From a preliminary analysis of the 1-bit subimage and source list generated by on-board data processing and downloaded via VHF network, one credible candidate is identified, the details of which are presented below.

VT_ID 722: The position of this candidate is R.A., Dec. 176.8997, 0.2882 degrees, corresponding to:
R.A. (J2000) = 11:47:35.9
Dec. (J2000) = 00:17:17.6
with an uncertainty of 0.50 arcsec.

This candidate was detected in both VT_R and VT_B, and was flagged as an uncatalogued source whose brightness faded during the VT observations. The candidate's magnitudes are:

date-obs (UTC)	mid-time	exposure	VT_B mag(AB)	VT_R mag(AB)
2026-05-09T23:18:31	89.87 min	6x50 sec	20.38 ± 0.03	19.80 ± 0.04
2026-05-09T23:58:59	129.08 min	3x50 sec	20.67 ± 0.05	20.18 ± 0.06

Magnitudes were not corrected for Galactic extinction.

The mean color of VT_B - VT_R = 0.54 is in line with the expectations of an event at redshift z < 4.

The position of this candidate is consisent with the reports (O'Neill et al., GCN 44505

; Saccardi et al., GCN 44506

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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/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.