{
  "bibcode": "2026GCN.44037....1F",
  "circularId": 44037,
  "submittedHow": "web",
  "eventId": "EP260316a",
  "format": "text/plain",
  "createdOn": 1773752762686,
  "subject": "EP260316a: COLIBRÍ faint optical counterpart candidate",
  "submitter": "F. Fortin at IRAP <ffortin.sci.edu@gmail.com>",
  "body": "Francis Fortin (IRAP), Fredd Sánchez Álvarez (UNAM), Jean-Luc Atteia (IRAP), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report:\n\nWe imaged the field of the EP260316a (Jiang et al., GCN Circ. 44027, GCN Circ. 44034), also detected by Fermi (Ravasio et al., GCN Circ. 44029)  using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-17 07:56:51 to 10:00:54 UTC (from 19.4 to 21.5 hours after the trigger) and obtained 94 minutes of simultaneous exposure in the r and z filters.\n\nThe data were reduced and coadded with the COLIBRÍ ASU pipeline. The 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 a faint (SNR = 5.7) uncatalogued source located at the edge of the EP/FXT 10 arcsec error circle (Jiang et al., GCN Circ. 44034) at: \n\nRA(J2000) = 15:07:55.62 = 226.98176 degrees\nDec(J2000) = +27:26:53.9 = +27.44830 degrees\n\nwith an uncertainty of 0.5 arcsec.\n\nThe preliminary magnitude derived for that source is:\n\nr = 24.40 +/- 0.19\nz > 23.38 (3-sigma)\n\nWe note that our images are deeper than the PS1 and LS catalogues, hence we cannot fully conclude whether or not this source is a transient. Further observations are planned. Followup of this source with other facilities is also encouraged.\n\nWe thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM.\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.\n"
}