TITLE: GCN CIRCULAR NUMBER: 43262 SUBJECT: GRB 251230A: Early optical counterpart detection by LCO. DATE: 25/12/30 05:52:21 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 251230A triggered by Swift (Lanava et al., GCN 43252) in B, V, and r filter of the 1-m Sinistro telescope and 0.4-m SCICAM QHY600 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) and the 0.4 m SCICAM QHY600 is equipped with 9576 x 6388 pixel CCD (FOV: 1.9 x 1.2 degrees, scale: 0.74 arcsec/pixel). Observations began on October 13, 2025, starting from 0.84 hours after the GRB trigger. Further observations are still ongoing. We clearly detect the optical transient (OT) reported by GCNs (Lanava et al., GCN 43252, Li et al., GCN 43255, Masi et al., GCN 43260). ----------------------------------------------------------------------------------------------------- |Date| |JDstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ----------------------------------------------------------------------------------------------------- 2025-12-30 2461039.59159 0.84 1 x 300 r r = 17.20 +/- 0.01 2025-12-30 2461039.60333 1.12 2 x 300 r r = 17.64 +/- 0.11 ----------------------------------------------------------------------------------------------------- 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/43262. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...