{
  "body": "Antonio de Ugarte Postigo (LAM), Leonardo García García (UNAM), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (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), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report:\n\nWe imaged the field of EP260321a (Huang et al., GCN Circ. 44068, 44075) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope, following our previous observation (Aguilar-Ruiz et al. GCN Circ. 44076). We observed in two epochs between 2026-03-23 04:40 to 10:04 UTC (between 40.17 and 45.57 hours after the trigger) and obtained  imaging in the g, r, i, z and y bands.\n\nThe data were reduced and coadded with the ASU COLIBRÍ 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\nFrom our first observation, at a mid epoch T+16.33 h after the EP detection, to the second epoch of last night, at a mid epoch of T+43.61 h, the transient reported by Lee et al. (GCN Circ. 44070), has increased in brightness in r-band by 1.3+/-0.1 mag consistently with the reported evolution of the source (Lee et al. GCN Circ. 44070, Aryan et al. GCN Circ. 44081, Tanvir et al. GCN Circ. 44082, Moran et al. GCN Circ. 44083, Ahumada et al. GCN Circ. 44084, Liu et al. GCN Circ. 44087 and Sankar et al. GCN Circ. 44089). Our latest photometric measurement is r = 18.67 +/- 0.02 mag but we caution that the value is likely affected by the contribution of the underlying galaxy.\n\nFurther observations are planned.\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\n",
  "subject": "EP260321a: COLIBRÍ further optical observations and brightening",
  "submitter": "Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com>",
  "circularId": 44091,
  "createdOn": 1774281970120,
  "eventId": "EP260321a",
  "submittedHow": "email",
  "bibcode": "2026GCN.44091....1D"
}