TITLE: GCN CIRCULAR NUMBER: 44828 SUBJECT: GRB 260604C: LAST detection of optical counterpart candidate DATE: 26/06/04 23:52:38 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno@gmail.com> 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 44823). 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 AT 2026ofi (TNS Report No. 307026) reported by MASTER (Lipunov et al, GCN 44827). The transient is well detected within each epoch and shows a rapid decay, consistent with afterglow emission. | Tmid-T0 (h) | Mag (AB) | | ------------ | ----------- | | 0.33 | 17.12 | | 0.45 | 16.85 | | 0.57 | 16.63 | | 0.75 | 16.42 | 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/). View this GCN Circular online at https://gcn.nasa.gov/circulars/44828. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...