GCN Circular 44828

Subject

GRB 260604C: LAST detection of optical counterpart candidate

Event

GRB 260604C

Date

2026-06-04T23:52:38Z (15 hours ago)

Edited On

2026-06-05T14:31:22Z (36 minutes ago)

From

Ruslan Konno at Weizmann Institute of Science <ruslankonno@gmail.com>

Edited By

Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Ruslan Konno at Weizmann Institute of Science <ruslankonno@gmail.com>

Via

Web form

R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) report on behalf of the LAST Collaboration.

We report observations of GRB 260604C, detected by Fermi-GBM (Fermi GBM team, GCN 44822

) and SVOM (Gotz et al, GCN ). Observations were conducted with the Large Array Survey Telescope (LAST; Ofek et al. 2023, PASP 135, 5001; Ben-Ami et al. 2023, PASP 135, 5002).

Observations of GRB 260604C were taken over 4 sequential epochs in clear band (similar to the Gaia Bp band). The first epoch began at 2026-06-04 20:35:04 UTC (T-T0 = 0.275 h). Each epoch consists of 20x20s exposures per telescope.

We detect one credible optical transient within the field reported by SVOM (Gotz et al, GCN 44823

) consistent with the position of (TNS Report No. 307026) reported by MASTER (Lipunov et al, GCN ). The transient is well detected within each epoch and shows a rapid decay, consistent with afterglow emission.

Tmid-T0 (h)	Mag (AB)
0.33	16.42 +/- 0.02
0.45	16.63 +/- 0.02
0.57	16.85 +/- 0.02
0.75	17.12 +/- 0.02

Previous observations of the field yield no detections on the source positions up to 2026-06-01 20:46:47 UTC (T0-T = 3d) with a 5-sigma limiting magnitude of 20.15 (AB).

We encourage further follow-up observations.

LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/).