{
  "bibcode": "2025GCN.40189....1G",
  "format": "text/plain",
  "circularId": 40189,
  "createdOn": 1745224546172,
  "submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
  "body": "Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration. \n\nWe observed the field of the GRB 250419A triggered by SVOM/ECLAIRs (Wang et al., GCN 40168) in V, r  filters of  the 1-meter Sinistro and B filter of 0.4 m SCICAM QHY600 telescopes at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Siding Spring 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). 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) but we only used the FOV of 30 x 30 arcmin for our observation.\n\nObservations began on , starting from 2025-04-19T10:30:01.728 UT, 8.00 hours after the GRB trigger. Observation for later epochs are still going on.\n\nWe clearly detect the optical transient (OT) reported by GCNs (López et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172; Thakur et al., GCN 40174; Lipunov et al., GCN 40179; Odeh et al., GCN 40180; Perley et al., GCN 40181; Pankov et al., GCN 40182; Pérez-Fournon GCN 40183; Kuin et al., GCN 40185; WU et al., GCN 40186; Xie et al., GCN 40187, Jiang et al., GCN 40188) in our B, V, r band images. \n\n|Date|\t\t|UTstart|\t|t-T0 (hours)|\t|Exp (sec)|\t|Filter|\t|Magnitude| \n-----------------------------------------------------------------------------------------------------      \n2025-04-19\t10:30:01.728\t8.00\t\t1 x 600 \tV\tV = 19.50+/- 0.02\n2025-04-19\t10:41:55.392\t8.21\t\t1 x 600 \tr\tr = 19.35+/- 0.01\n2025-04-19\t14:57:03.744\t12.46\t\t2 x 450\t\tB\tB = 20.51 +/- 0.11\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",
  "eventId": "GRB 250419A",
  "subject": "GRB 250419A: LCO optical observation",
  "submittedHow": "web"
}