TITLE:   GCN CIRCULAR
NUMBER:  42929
SUBJECT: GRB 251201B: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at Sutherland Observatory
DATE:    25/12/01 22:57:16 GMT
FROM:    Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>

A. Cerón, J. Basurto Merino, P.G. Berdayes, A. Caballero-Almagro,  M. Contreras, 
F. Díaz-Segado, T. Ferrer-Laviña, B. Gandolfi, V. Ghiraldo, J. Hernández Fung, L. Juliá-Maroto, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Schenone-Zanuzzi, A. Selezneva, T. Tundidor Rodríguez, E. Urquijo-Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL).

Following the detection of GRB 251201B by Fermi (Fermi GBM team, GCN Circ. 42923) and Swift (Moss et al., GCN Circ. 42924; Osborne et al., GCN Circ. 42927), we observed the field with one of the three Las Cumbres Observatory (LCO) 1-m telescopes equipped with Sinistro cameras located at the LCO node at Sutherland Observatory, South Africa. The observation, a single exposure of 300 sec in the SDSS r' filter, started on 2025-12-01 at 22:00:22 UT, about 5.73 hours after the Fermi and Swift trigger. The optical counterpart detected by Swift UVOT (Moss et al., GCN Circ. 42924) is clearly detected in our image with a magnitude of r' = 19.78 +/- 0.11 (AB), calibrated against 
the Legacy Imaging Surveys DR10 catalog and not corrected for Galactic extinction. 

This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2025B-010). These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain).

This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5).