{
  "circularId": 39831,
  "body": "Ramandeep Gill (UNAM), Ny Avo Rakotondrainibe (LAM), Alan M. Watson (UNAM), Rosa L. Becerra (U Roma), Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM) and Antonio de Ugarte Postigo (LAM), and report:\n\nWe continued our observations of the field of EP250321A (Hu et al., GCN Circ. 39800) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.\n\nWe observed from 2025-03-22 03:55 to 05:25 UTC (21.75 to 23.26 hours after the trigger). The data were coadded with the custom software and analysed with STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction.\n\nWe detect the optical counterpart (Fu et al. 2025, GCN Circ. 39804; Perez-Garcia et al. 2025, GCN Circ. 39805; Brivio et al. 2025, GCN Circ. 39807; Zhu et al. 2025, GCN Circ. 39809; Becerra et al. 2025, GCN Circ. 39810; Pérez-Fournon et al. 2025, GCN Circ. 39812; Lee et al. 2025, GCN Circ. 39815; Han et al. 2025, GCN Circ. 39817; Sharma et al. 2025, GCN Circ. 39822) with a magnitude of:\n\ni = 22.5 +/- 0.1\n\nCompared to the latest reported measurement in i (Lee et al, GCN Circ. 39815), this corresponds to a decay with a power-law index of approximately -1.3.\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",
  "createdOn": 1742622658870,
  "bibcode": "2025GCN.39831....1G",
  "eventId": "EP250321A",
  "subject": "EP250321A: COLIBRÍ Continuing Optical Observations",
  "format": "text/plain",
  "submitter": "Alan Watson at UNAM <alan@astro.unam.mx>",
  "submittedHow": "web"
}