{
  "circularId": 39816,
  "submittedHow": "web",
  "submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
  "format": "text/plain",
  "bibcode": "2025GCN.39816....1G",
  "createdOn": 1742570350504,
  "subject": "EP 250321A: 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 250321A triggered by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 39800) 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).\n\nObservations began on March 21, 2025, starting 5.46 hours after the GRB trigger.\n\nWe clearly detect the optical transient (OT) reported by GCNs (Fu et al. GCN 39804, Perez-Garcia et al al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812, Lee et al., GCN 39815) in our r, V band image. \n\n|Date|\t\t|UTstart|\t|t-T0 (hours)|\t|Exp (sec)|\t|Filter|\t|Magnitude| \n----------------------------------------------------------------------------------------------      \n2025-03-21\t11:38:04.13\t5.468\t\t1 x 900 \tr\t\tr = 21.40 +/- 0.07\n2025-03-21\t11:38:20.54\t5.472\t\t1 x 900 \tV\t\tV = 21.76 +/- 0.09\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",
  "eventId": "EP250321A"
}