TITLE: GCN CIRCULAR NUMBER: 44309 SUBJECT: COLIBRI optical observations of the transient GOTO26djh/AT2026jpw DATE: 26/04/16 06:26:13 GMT FROM: enriquemm@astro.unam.mx GOTO26djh/AT2026jpw: COLIBRÍ optical observations. Enrique Moreno Méndez (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Ramandeep Gill (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), 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 the orphan afterglow candidate GOTO26djh/AT2026jpw reported by O'Neill et al., (GCN Circ. 44301) and also observed by Corcoran et al. (GCN Circ. 44303), Moskvitin et al. (GCN Circ. 44304), Xu et al. (GCN Circ. 44305), and Sosnovskij et al. (GCN Circ. 44306) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-16 03:47:39 to 04:44:41 (from 52.50 to 53.45 hours after the trigger) and obtained 15/15/15/45 minutes of simultaneous exposure in the g/r/i/z filters. The data were reduced and coadded with the 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 reported by D. O'Neill et al., GCN Circ. 44301 at preliminary magnitudes of: g = 22.51 +/- 0.06 r = 22.10 +/- 0.06 i = 21.87 +/- 0.08 z = 21.55 +/- 0.07 Comparing our values with the reported by NOT (Corcoran et al. GCN Circ. 44303), we estimate an optical decay alpha 1.6. Moreover, the detection in the four filters suggests a photo-z < 2.7 using typical IGM absorption. Further observations and analysis are ongoing. 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/44309. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...