TITLE:   GCN CIRCULAR
NUMBER:  39076
SUBJECT: GRB 250128B: OHP/T193 optical upper limit
DATE:    25/01/29 09:08:55 GMT
FROM:    Christophe Adami at LAM <christophe.adami@lam.fr>

C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), A. Saccardi (CEA/Irfu), D. Turpin (CEA/Irfu), F. Schussler (CEA Paris-Saclay), M. Dennefeld (IAP), J. Palmerio (CEA/Irfu) report on behalf of a larger collaboration:

We observed the field of the GRB250128B (Fermi GBM team, GCN 39057; Evans et al., GCN 39058; Izzo et al., GCN 39059; Lipunow et al., GCN 39061; Ulaczyk et al., GCN 39062; Muers et al., GCN 39063; Osborne et al., GCN 39064; Lipunov et al., GCN 39067; Evans et al., GCN 39069) with the T193cm telescope at the Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained a total of 2490sec (1x30s + 1x300s + 3x720s) in the i-band using the red MISTRAL setting from 20250129_043822UT to 20250129_050703UT (mid-time ~12.5h after the trigger).

In the stacked image, we do not detect any new source at the XRT source position (Evans et al., GCN 39069) down to the following 3-sigma limit:

i > 20.6

The photometric calibration was performed using nearby stars from the PanSTARRS catalog.
We acknowledge the excellent support from Observatoire de Haute-Provence, in particular Jean Balcaen, and the Sophie observer Alice Radcliffe