TITLE:   GCN CIRCULAR
NUMBER:  45364
SUBJECT: GRB 260808B: SVOM/COLIBRÍ (FM-GFT) confirmation of the optical rebrightening
DATE:    26/08/12 15:30:21 GMT
FROM:    Marion G <marion.guelfand@gmail.com>

Marion Guelfand (CPPM), Fredd Sánchez Álvarez (UNAM), Noémie Globus (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), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP),  Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM),  Alan M. Watson (UNAM) and Michela Maria Dinatolo (U. Milano) report:

We continued imaging the field of the SVOM GRB 260808B (Bouchet et al., GCN 45316) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-08-12 09:54:12 to 10:07:40 UTC (from 91.5 to 91.8 hours after the trigger) and obtained 720 seconds of simultaneous exposure in the r and z filters.

The data were reduced, coadded and analyzed with the ASU COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1r catalog, is in the AB system, and is not corrected for Galactic extinction.

Compared to our previous observation (Basa et al., GCN 45341), where we measured z = 22.21 ± 0.08 at 40.6–42.4 hours after the trigger, we find that the optical counterpart (Turpin et al., GCN 45318; Li et al., GCN 45320; Saccardi et al., GCN 45328; Schneider et al., GCN 45329; Bochenek et al., GCN 45330) has significantly rebrightened, as also reported by Li et al. (GCN 45359). We measure the following preliminary magnitudes:

r = 21.68 ± 0.04,

z = 21.36 ± 0.11.

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.