TITLE:   GCN CIRCULAR
NUMBER:  37889
SUBJECT: GRB 241025A: COLIBRÍ Detection of the Afterglow
DATE:    24/10/26 05:09:44 GMT
FROM:    Alan Watson at UNAM <alan@astro.unam.mx>

Alan M. Watson (UNAM), Margarita Pereyra (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), and Francesco Magnani (CPPM)
report:

We imaged the field of GRB 241025A detected by Swift/BAT, Fermi/GBM, and
SVOM/GRM (GCN Circ. 37859, 37860, 37863) during the commissioning of the
COLIBRÍ (SVOM/F-GFT) telescope at the Observatorio Astronómico Nacional on
the Sierra de San Pedro Mártir in Mexico.

The observations started 39 minutes after the GRB trigger. We observed with
the engineering test camera in a red filter that approximates SDSS r. The
data were reduced using custom software and then analysed and calibrated
against the PS1 catalog using the STDWeb service.

In 1980 seconds of exposure from 2024-10-25 02:15 to 03:00, we detect the
optical counterpart with:

    r = 19.64 +/- 0.04

This magnitude is consistent with other optical observations (GCN Circ.
37862, 37865, 37871, and 37882).

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