TITLE: GCN CIRCULAR NUMBER: 39425 SUBJECT: GRB 250221A: Optical counterpart detection by LCO. DATE: 25/02/22 15:06:17 GMT FROM: ankur ghosh at CAPP, University of Johannesburg Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration. We observed the field of the GRB 250221A triggered by Swift (Caputo et al., GCN 39396) in B, r filters of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Cerro Tololo Interamerican Observatory, Chille. The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel). Observations began on February 21, 2025, starting 22.46 hours after the GRB trigger. We clearly detect the optical transient (OT) reported by GCNs ( Francile et al., GCN 39395; Watson et al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo et al., GCN 39412; Muenter et al., GCN 39417; Palmerio et al., GCN 39418; Pankov et al., GCN 39422; Pankov et al., GCN 39424) in our B, r band image. |Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ---------------------------------------------------------------------------------------------------- 2025-02-22 02:02:15.36 22.46 1 x 1200 B B = 21.91 +/- 0.06 2025-02-22 02:10:02.78 22.59 1 x 900 r r = 20.85 +/- 0.06 ---------------------------------------------------------------------------------------------------- The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.