GCN Circular 39104

Alan M. Watson (UNAM), Camila Angulo (UNAM), D. Akl (AUS), S. Antier
(OCA), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William
H. Lee (UNAM), Jean-Luc Atteia (IRAP), Rosa Becerra (Università degli
Studi di Roma Tor Vergata), Nathaniel R. Butler (ASU), Damien Dornic
(CPPM), Francis Fortin (IRAP), J.-G. Ducoin (CPPM), Francesco Magnani
(CPPM) and Margarita Pereyra (UNAM) report:

We imaged the field of the Swift GRB 250129A (Beardmore et al., GCN
Circ. 39066
Loading...
 
 ) 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 OGSE engineering test camera in a red filter that
approximates SDSS r from 2025-01-30 07:01 to 12:54 UTC. In the subset
of our data from 2025-01-30 12:01 to 12:54, from 31.27 to 32.15 hours
after the event, with a total exposure of 2220 seconds, we clearly
detect the afterglow with

r = 19.38 +/- 0.04

This magnitude is not corrected for Galactic extinction. The data were
reduced using custom software and then analysed and calibrated against
the PS1 catalog using the STDWeb service.

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.
We warmly thank the GRANDMA IJCLAB team and S. Karpov for the access
of the STDWeb service for STDPipe.