{
  "eventId": "GRB 251111A",
  "subject": "GRB 251111A: SVOM/COLIBRÍ (FM-GFT) optical counterpart detection ",
  "submittedHow": "email",
  "circularId": 42638,
  "bibcode": "2025GCN.42638....1L",
  "createdOn": 1762842232173,
  "body": "Diego López-Cámara (UNAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Yehao Cheng (SWIFAR,YNU), Boting Wang (YNAO):\n\nWe imaged the field of the SVOM GRB 251111A (Cheng et al., GCN Circ. 42637) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-11-11 05:21:36 to 05:37:03 UTC (from 11.4 to 26.8 minutes after the trigger) and obtained 13 minutes of simultaneous exposure in the r and z filters.\n\nThe photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.\n\nWe detect an uncatalogued source revealed by image subtraction using PanSTARRS as template and consistent with the ECLAIRs 7.55 arcmin error circle (Cheng et al., GCN Circ. 42637) at: \n\nRA(J2000) = 02:09:26.82 = 32.361770 degrees\nDec(J2000) = 05:13:40.4 = 5.227888 degrees\n\nwith an uncertainty of 0.5 arcsec.\n\nThe preliminary magnitude derived for that source is:\n\nr = 21.35 +/-  0.05\nz = 20.27 +/-  0.05\n\nThe source fades during our observations, confirming that it is the optical afterglow of the GRB. The red r-z color might indicate a moderately high redshift or extinction due to dust.\n\nFurther observations are ongoing.\n\nWe thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.\n\nCOLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.",
  "submitter": "Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com>"
}