TITLE: GCN CIRCULAR NUMBER: 39831 SUBJECT: EP250321A: COLIBRÍ Continuing Optical Observations DATE: 25/03/22 05:50:58 GMT FROM: Alan Watson at UNAM alan@astro.unam.mx
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:
We 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.
We 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.
We 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:
i = 22.5 +/- 0.1
Compared 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.
Further observations are planned.
We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir
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