TITLE: GCN CIRCULAR NUMBER: 40073 SUBJECT: EP250404A: COLIBRÍ/DDRAGO Optical Observations DATE: 25/04/05 08:31:34 GMT FROM: Ny Avo Rakotondrainibe at LAM nyavo.rakotobe@gmail.com
Ny Avo Rakotondrainibe (LAM), Jean-Grégoire Ducoin (CPPM), Rosa L. Becerra (U Roma), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Sarah Antier (OCA/IJCLAB), Stéphane Basa (UAR Pytheas), Diego López-Cámara (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Ramandeep Gill (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Antonio de Ugarte Postigo (LAM) and Benjamin Schneider (LAM) report:
We imaged the field of EP250404A (Hu et al., GCN Circ. 40051) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico on the night of 2025-04-05 UTC.
We observed from 2025-04-05 05:39 to 06:18 UTC (T+15.3 to T+16.0 hours after the trigger) and obtained 1920 seconds of exposure in total in the r filter. Our observations were performed under regular weather conditions. The data were coadded with the COLIBRÍ pipeline and analysed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction.
We detected the optical counterpart (Jiang et al., GCN Circ. 40052, Perez-Garcia et al., GCN Circ. 40053, Du et al., GCN Circ. 40058, Zhu et al., GCN Circ. 40061, Konno et al. GCN Circ. 40063, Odeh et al., GCN Circ. 40064, Lipunov et al., GCN Circ. 40066, He et al., GCN Circ. 40069, Perez-Fournon et al., GCN Circ. 40071, Jelinek et al., GCN Circ. 40072) with an AB magnitude of:
r = 21.99 +/- 0.15.
Compared with the values previously reported, we estimate the fading nature of the OT with a temporal index ~1.4 after T+1.7 hours.
Further observations and analysis are ongoing.
We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40073. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...