TITLE: GCN CIRCULAR NUMBER: 42261 SUBJECT: GRB 251013C: Early and late-time optical counterpart detection by LCO DATE: 25/10/14 15:45:51 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com> 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 251013C triggered by Fermi (Fermi GBM team, GCN circ. 42221), and SVOM (Rakotondrainibe et al., GCN circ. 42222) in V and r filters of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at South African Astronomical Observatory (SAAO). 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 October 13, 2025, starting from 2.88 hours after the GRB trigger. Further observations are still ongoing. We clearly detect the optical transient (OT) reported by GCNs (Konno et al. (GCN circ. 42226), Perez-Garcia et al. (GCN circ. 42225), Martin-Carrillo et al. (GCN circ. 42227), Masi (GCN circ. 42228), Palmerio et al. (GCN circ. 42229), Moskvitin et al. (GCN circ. 42230), Gompertz et al. (GCN circ. 42231), Watson et al. (GCN circ. 42241), López-Cámara et al. (GCN circ. 42242), Zhang et al. (GCN circ. 42248), Brosio et al. (GCN circ. 42251), Quintana-Ansaldo et al. (GCN circ. 42254), and Maksut et al. (GCN circ. 42256)). ------------------------------------------------------------------------------------------------------ |Date| |JDstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ------------------------------------------------------------------------------------------------------ 2025-10-13 2460962.35625 2.88 1 x 300 V V = 16.61 +/- 0.01 2025-10-14 2460963.01397 18.67 1 x 600 V V = 20.73 +/- 0.05 ------------------------------------------------------------------------------------------------------ The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42261. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...