{
  "createdOn": 1775219216945,
  "circularId": 44206,
  "submitter": "antier@ijclab.in2p3.fr",
  "format": "text/plain",
  "eventId": "EP260403a",
  "subject": "EP260403a: COLIBRÍ optical counterpart candidate",
  "submittedHow": "web",
  "body": "Sarah Antier (IJCLAB), Noémie Globus (UNAM), Benjamin Schneider (LAM), Dalya Akl (NYUAD), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), 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), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM) report:\n\nWe imaged the field of the EP260403a (Guo et al., GCN Circ. 44204) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-04 11:06:21 to 11:45:02 (from 37.20 to 76.87 min after the trigger) and obtained 29 min of simultaneous exposure in the r and z filters.\n\nThe data were reduced and coadded with the ASU, COLIBRÍ pipelines and STDWeb/STDPipe (Karpov 2025). 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 an uncatalogued and fading source (revealed by image subtraction using PanSTARRS as template) consistent with the FXT 20 arcsec error circle (Guo et al., GCN Circ. 44204) at: \n\nRA(J2000) = 14:36:37.44 = 219.1560 degrees\nDec(J2000) = -25:30:14.2 = -25.5039 degrees\n\nThe preliminary magnitude derived for that source is:\n\nr = 18.92 +/- 0.02\nz = 18.70 +/- 0.02\n\nFurther observations are ongoing.\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"
}