GCN Circular 37900

Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM),
S. Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien
Dornic (CPPM), J.-G. Ducoin (CPPM), Francis Fortin (IRAP), Simona Lombardo
(LAM), Francesco Magnani (CPPM), and Margarita Pereyra (UNAM) report:

We imaged the field of GRB 241026A detected by Fermi/GBM, Swift/BAT, and
Swift/XRT (Fermi GBM Team, GCN Circ. 37894
Not found
 
 
; Melandri et al., GCN Circ.
37896
Not found
 
 
) during the commissioning of the COLIBRÍ (SVOM/F-GFT) telescope at
the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in
Mexico.

We observed with the engineering test camera in a red filter that
approximates SDSS r. We observed from 2024-10-27 01:47 to 02:07 UTC (3.1 to
3.4 hours after the trigger) and obtained 960 seconds of exposure. The data
were reduced using custom software and then analyzed and calibrated against
the PS1 catalog using the STDWeb service (Karpov et al., 2022).

We detect the optical counterpart at RA =293.40029 and Dec = 57.98585
(J2000) with an AB magnitude of:

    r = 19.63 +/- 0.04

This magnitude is similar to that reported by Moskvitin (GCN Circ. 37899
Not found
 
 
)
at about 28 minutes after the trigger.

Further observations are planned.

We warmly thank the COLIBRÍ engineering team and the staff of the
Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.