TITLE:   GCN CIRCULAR
NUMBER:  38145
SUBJECT: GRB 241108A: Further COLIBRÍ Upper Limits on the Optical Counterpart
DATE:    24/11/09 19:27:40 GMT
FROM:    Alan Watson at UNAM <alan@astro.unam.mx>

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

SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang
(IHEP), Stéphane Basa (LAM), Jean-Luc Atteia (IRAP), Arnaud Claret (CEA),
Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Andrea
Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC),
En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing
Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Bing Zhang (UNLV)

report:

We again imaged the field of GRB 241108A detected by SVOM/ECLAIRs
(Sadibekova et al., GCN Circ. 38132) 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. The data were reduced using custom software and then
analysed and calibrated against the PS1 catalog using the STDWeb service.
Our field is centered on the XRT source detected at 08:14:33.07 -07:05:09.9
J2000 (Burrows et al., GCN Circ. 38139).

In 7080 seconds of exposure from 2024-11-09 09:01 to 12:52 UTC (1.08 to
1.24 days after the trigger), we detect no new sources within the XRT
uncertainty region to a 3-sigma limiting AB magnitude of:

r > 23.6

We do detect a two point source within the uncertainty region and one just
outside it, but these are also present in the earlier PS1 image at a
similar magnitude and therefore are unlikely to be the optical counterpart
of the GRB.

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.