GCN Circular 44624

Subject

GRB 260515A: SVOM/VT optical candidate from VHF data

Event

GRB 260515A

Date

2026-05-15T20:26:50Z (12 days ago)

From

SVOM_group <svomgroup@bao.ac.cn>

Via

Web form

A. Saccardi, J. T. Palmerio (CEA/Irfu), Y. L. Qiu, C. Wu, L. P. Xin (NAOC) on behalf of the SVOM/VT team.

After the trigger by SVOM/ECLAIRs at 2026-05-15T19:08:19 UTC (T0), SVOM performed an automatic slew on the burst location (Brunet et al., GCN 44622

). SVOM/VT began observing the field at 2026-05-15T19:12:34, 254.71 seconds after T0, 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 downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below.

VT_ID 32: The position of this candidate is R.A., Dec. 227.6852, 24.5562 degrees, corresponding to: R.A. (J2000) = 15h10m44.4s Dec. (J2000) = 24d33m22.4s with an uncertainty of 0.50 arcsec. This location is consistent with the optical afterglow reported by He et al. (GCN 44623

This candidate was detected in both VT_R and VT_Band was flagged as an uncatalogued source. The candidate's magnitudes are:

| date-obs (UTC) | mid-time | exposure | VT_B mag(AB) | VT_R mag(AB) | | -------------------- | ----------- | --------- | ------------- | ------------- | | 2026-05-15T19:12:34 | 5.08 min | 2*50 sec | 16.16 ± 0.01 | 15.78 ± 0.01 |

Magnitudes were not corrected for Galactic reddening.

The mean color of VT_B - VT_R = 0.38 is in line with the expectations of an event at redshift z < 4.

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.

The Burst Advocate (BA) on shift for this alert is Andrea Saccardi: andrea.saccardi@cea.fr. Please contact the BA by email if you require additional information.