TITLE: GCN CIRCULAR NUMBER: 41913 SUBJECT: GRB 250920C: Optical counterpart detection by LCO DATE: 25/09/20 18:32:10 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 250920C triggered by the Swift (Gupta et al., GCN 41904) in the r, V filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Siding Spring is near Coonabarabran, New South Wales, Australia . 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 September 20, 2025, starting 1.47 hours after the GRB trigger. Further observations are currently ongoing. We clearly detect the optical transient (OT) reported by GCNs (Wortley et al., GCN 41907, Strausbaugh et al., GCN 41911) in our r and V band image. |Date| |JDstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ---------------------------------------------------------------------------------------------------- 2025-09-20 2460939.20389 1.47 1 x 600 r r = 18.47 +/- 0.01 2025-09-20 2460939.22762 2.04 1 x 600 r r = 18.75 +/- 0.01 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/41913. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...