TITLE:   GCN CIRCULAR
NUMBER:  38862
SUBJECT: GRB 250108A: NOT optical upper limit
DATE:    25/01/09 07:58:40 GMT
FROM:    Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>

S. De Wet (DTU Space), D. B. Malesani (DAWN/NBI and Radboud), L. Izzo (INAF/OACn and DARK/NBI), D. Xu (NAOC), S. Grund Sorensen (NOT and Aarhus), N. Pyykkinen (NOT and Turku) report on behalf of a larger collaboration:

We observed the field of the SVOM GRB 250108A (Zheng et al., GRB 38845) using the Nordic Optical Telescope (NOT) equipped with ALFOSC. The observations were carried out in the z band, with a mid time 2025 Jan 9.14 UT (22.72 hr after the GRB), and for a total exposure time of 2000 s.

In the stack of our images, we do not detect any source at either the position of the VT optical afterglow candidate (Qiu et al., GCN 38852), nor within the Swift/XRT localization region of the proposed X-ray counterpart (Ambrosi et al., GCN 38853). The limiting magnitude is approximately z > 22.1 (AB), calibrated against nearby stars from the Pan-STARRS catalog.