{
  "subject": "GRB 250207A: COLIBRÍ/DDRAGO Optical Afterglow Detection",
  "bibcode": "2025GCN.39186....1A",
  "circularId": 39186,
  "createdOn": 1738898408608,
  "submitter": "Camila Angulo Valdez at UNAM <camiangulo@astro.unam.mx>",
  "submittedHow": "web",
  "format": "text/plain",
  "body": "Camila Angulo (UNAM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (Università degli Studi di Roma Tor Vergata), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), and Benjamin Schneider (LAM) report:\n\nWe imaged the field of GRB 250207A detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 39181) and Swift/BAT (Ferro et al., GCN Circ.39182) with the DDRAGO wide-field camera on the COLIBRÍ (SVOM/F-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.\nWe observed from 2025-02-07 02:34 to 02:55 UTC (78 to 99 min after the burst), with a midpoint of 88.5 minutes after the event, and obtained 960 seconds of exposure in the r filter in good weather conditions. The data were reduced and stacked using custom software and then calibrated against the PS1 catalog and analysed using STDPipe (Karpov 2021).\n\nAt the position of the afterglow detected by XRT and UVOT (Ferro et al., GCN Circ. 39182), we detect a source with\n\nr = 18.90 +/- 0.01\n\nand confirm fading relative to the UVOT observation.\n\nOur magnitude is not corrected for Galactic extinction. \n\nFurther observations are planned.\n\nWe warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.\n",
  "eventId": "GRB 250207A"
}