TITLE: GCN CIRCULAR NUMBER: 40261 SUBJECT: EP250427A: COLIBRÍ Optical Detection DATE: 25/04/27 10:34:16 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma rosa.becerra@roma2.infn.it
Rosa L. Becerra (U Roma), Benjamin Schneider (LAM), Jean-Luc Atteia (IRAP), Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA/IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM) and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of EP250427A (Wang et al., GCN Circ. 40257) 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 2025-04-27 UTC.
We observed from 2025-04-27 08:54 to 09:27 UTC (T+5.3 to T+5.8 hours after the trigger) and obtained 3-minute exposures in the g, r, and i filters (for each one). 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.
Within the EP/FXT (Wang et al., GCN Circ. 40257) error region, we detect an uncatalogued source at R.A. = 277.2746 deg, DEC = 7.5639 deg (J2000), with an uncertainty of 0.4 arcsec, with magnitudes of:
g= 18.91 +/- 0.04 r= 18.42 +/- 0.04 i= 17.88 +/- 0.04
This source is consistent with the candidate reported by BOOTES-7 (Perez-Garcia et al., GCN Circ. 40259) and TRT (Liu et al., GCN Circ. 40260).
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/40261. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...