{
  "bibcode": "2025GCN.42261....1G",
  "submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
  "eventId": "GRB 251013C",
  "circularId": 42261,
  "submittedHow": "web",
  "createdOn": 1760456751018,
  "format": "text/plain",
  "subject": "GRB 251013C: Early and late-time optical counterpart detection by LCO",
  "body": "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.\n \nWe 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).\n\nObservations began on October 13, 2025, starting from 2.88 hours after the GRB trigger. Further observations are still ongoing.\n\nWe 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)). \n\n------------------------------------------------------------------------------------------------------\n|Date|\t\t|JDstart|\t|t-T0 (hours)|\t|Exp (sec)|\t|Filter|\t|Magnitude|\n------------------------------------------------------------------------------------------------------       \n2025-10-13\t2460962.35625\t2.88\t\t1 x 300 \tV\t\tV = 16.61 +/- 0.01\n2025-10-14\t2460963.01397\t18.67\t\t1 x 600 \tV\t\tV = 20.73 +/- 0.05\n------------------------------------------------------------------------------------------------------\n\nThe field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.\n"
}