GCN Circular 45275

Subject

GRB 260802A: SVOM/VT optical upper limits from VHF data

Event

GRB 260802A

Date

2026-08-02T13:53:21Z (22 days ago)

Edited On

2026-08-03T13:05:57Z (21 days ago)

From

SVOM_group <svomgroup@bao.ac.cn>

Edited By

Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>

Via

Web form

C. Wu, L. P. Xin, Y.L. Qiu (NAOC), J. T. Palmerio (CEA/Irfu), Wenjin Xie (NAOC), Runchao CHEN (NJU) report on behalf of the SVOM/VT team.

After the trigger by SVOM/ECLAIRs at 2026-08-02T09:23:10 UTC (T0), SVOM performed an automatic slew on the burst location (Feng et al., GCN 45270

). SVOM/VT took images of the field 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 the VHF network, no uncatalogued optical source was detected within the MXT localization region (Feng et al., GCN 45270

) in our three sequence images, compared to the Pan-STARRS1 DR1. The suggested position of the magnetar EP J223759.5+531421 (Rea et al. ATel 17870; Coti Zelati et al. ATel 17909) falls within the subimage coverage. No optical counterpart was detected at this position. The 5-sigma upper limits are:

Mid time (min)	Band	Exposure (s)	5-sigma upper limit (mag)
6.43	VT_B	6 * 50	> 21.5
6.43	VT_R	6 * 50	> 21.5
100.32	VT_R	6 * 50	> 21.5

We note that the 1-bit subimage and source list do not fully cover the entire MXT uncertainty region. Radio or infrared follow-up observations are encouraged to further investigate the association with the magnetar candidate EP J223759.5+531421.

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.