TITLE: GCN CIRCULAR NUMBER: 44026 SUBJECT: IceCube-260315A: COLIBRÍ optical observations DATE: 26/03/16 13:05:38 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu@gmail.com> IceCube 260315A: COLIBRÍ optical observations Francis Fortin (IRAP), Leonardo García García (UNAM), Jean-Grégoire Ducoin (CPPM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of IceCube 260315A (The IceCube Collaboration, GCN Circ. 44017) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-16 06:23:48 to 09:13:24 UTC (from 28 to 30.9 hours after the trigger) and obtained 63 minutes of exposure in the g, r filters, and 126 minutes in the z filter. The data were reduced, coadded and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart candidate AT 2026fpm reported by Segura et al., GCN Circ. 44023, at a preliminary magnitude of: g = 19.94 +/- 0.01 r = 19.69 +/- 0.01 z = 19.66 +/- 0.01 The optical counterpart candidate lies on top of a catalogued source in the Legacy Survey with magnitudes of: g = 21.04 r = 20.59 z = 20.48 However, this LS source is flagged as variable. We also note that it is found in PS1 at a much fainter level. This would indicate that AT 2026 fpm is a known variable source. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/44026. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...