TITLE: GCN CIRCULAR NUMBER: 40775 SUBJECT: GRB 250617B: COLIBRÍ optical observations DATE: 25/06/18 10:25:49 GMT FROM: Sarah Antier at OCA sarah.antier@oca.eu
Sarah Antier (OCA/IJCLAB), Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):
We imaged the field of the GRB 250617B (Page et al., GCN 40760; Fermi GBM Team, GCN 40763) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-06-18 08:09:20 to now UTC (started 11.12 hours after the trigger) and obtained a series of 1 min exposure images in the i filter.
The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1/SkyMapper catalog, is in the AB system, and is not corrected for Galactic extinction.
We detected the optical counterpart Page et al., GCN Circ. 40760 (also reported by Moskvitin et al. (GCN 40761), Jelinek et al. (GCN 40762), Grossan et al. (GCN 40771), and Ma et al. (GCN 40772)), at a preliminary magnitude using a 6-min stack image at the beginning of the observations:
i = 21.17 +/- 0.16
Further observations are ongoing.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ 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.
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