TITLE: GCN CIRCULAR NUMBER: 42226 SUBJECT: GRB 251013C: LAST detection of optical counterpart DATE: 25/10/13 20:58:35 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 251013C, detected by SVOM (Rakotondrainibe et al., GCN 42222) and Fermi (Fermi GBM Team, GCN 42221). 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).
We observed the field of GRB 251013C using four parallel telescopes (each with a 7.4 deg^2 FoV) in clear band (similar to the Gaia Bp band) over several epochs. Each coadd consists of 20x20 s exposures, yielding a limiting magnitude of about 20.5 AB mag.
We clearly detect the optical counterpart reported by Palmerio et al. (GCN 42223) and Perez-Garcia et al. (GCN 42225). The earliest detection (20x20 s coadd) is confirmed at 2025-10-13 18:10:27 UTC (T − T0 = 0.51 h) with AB mag 16.14 +/- 0.02. Preliminary automated photometry shows a rise to 15.20 +/- 0.01 mag at 18:32:15 UTC (T − T0 = 0.87 h), followed by a power-law decay. The source remains detectable.
We encourage continued multi-wavelength follow-up of this bright optical counterpart.
LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/).
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