TITLE: GCN CIRCULAR NUMBER: 38779 SUBJECT: GRB 250101A: LCO optical counterpart detection DATE: 25/01/02 16:56:31 GMT FROM: ankur ghosh at CAPP, University of Johannesburg Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration. We observed the field of the GRB 250101A triggered by Swift (Page et. al., GCN 38752) in B, V filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at McDonald Observatory. 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 January 02, 2025, starting from 14.48 hours after the GRB trigger. We clearly detect the optical transient (OT) reported by GCNs (Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755; Budnev et al., GCN 38756; Wu et al., GCN 38758; Moskvitin et al., GCN 38762; Odeh et al., GCN 38763, Hu et al., GCN 38764; D'Avino et al., GCN 38768; Escudero-Coca et al., GCN 38769, Coca et al., Zhang wt al., GCN 38774, Komesh et al., GCN 38777) in our B, V band image. |Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| --------------------------------------------------------------------------------------------------- 2025-01-02 03:51:30.528 14.48 1 x 900 V V = 20.61 +/- 0.04 2025-01-02 06:19:33.312 16.95 2 x 1200 B B = 21.82 +/- 0.03 The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.