GCN Circular 42541
Subject
GRB 251026A: SVOM/COLIBRÍ (FM-GFT) confirmation of the optical counterpart
Event
Date
2025-11-03T08:19:16Z (3 days ago)
From
Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com>
Via
email
Antonio de Ugarte Postigo (LAM), Margarita Pereyra (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (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), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Alvarez (UNAM), Benjamin Schneider (LAM), J.X Cao (GXU), X. Tian (GXU):
We reanalysed our earlier observation (de Ugarte Postigo et al., GCN Circ. 42456) of the field of the SVOM GRB 251026A (Cao et al., GCN Circ. 42454) using the DDRAGO wide-field, two-channel imager on the SVOM/COLIBRÍ (FM-GFT) telescope, following the report of the optical counterpart by Li et al. (GCN Circ. 42512). We observed from 2025-10-26 08:49:51 to 11:18:57 UTC (from 22 to 172 minutes after the trigger) and obtained 48 minutes of simultaneous exposure in the r and z filters at three epochs.
The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). 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 Li et al. (GCN Circ. 42512) at preliminary magnitudes of:
r = 22.15 +/- 0.07
z = 20.62 +/- 0.06
We did not previously report this source as it is significantly outside the 90% confidence region for SVOM/MXT (Cao et al., GCN Circ. 42454).
Our light curve is consistent with the report of Li. et al. (GCN Circ. 42512) of an initially fading source followed by a rebrightening at about 3 hours.
Further analysis is 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.