GCN 44196: EP260324A / AT 2026hir: COLIBRÍ optical observations

2026-04-03T05:33:45.711Z | rev 0 | event: EP260324a
Noémie Globus (UNAM), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano 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 observed AT2026hir/ZTF26aapviim, the optical counterpart (Anumarlapudi et al., GCN Circ. 44120, Stein et al., GCN Circ. 44194) associated to EP260324a (Wu et al., Atel #17728) with the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-03 03:09:08 to 03:26:20 UTC (from 9.95 to 9.96 days after the discovery time reported in the TNS entry and from 9.84 to 9.85 days after the EP trigger) and obtained 5 minutes of exposure in the g, r, i filters, and 15 minutes of simultaneous exposure in the z filter.

In the stacked image, we detect the optical counterpart. 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.

The preliminary PSF magnitudes revealed after performing image subtraction using PanSTARRS DR1 as template are:

r = 17.73 +/- 0.01,
z = 18.26 +/- 0.02.

Further observations are planned.

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.