TITLE: GCN CIRCULAR NUMBER: 39080 SUBJECT: GRB 250128B: VLT/FORS2 optical observations DATE: 25/01/29 11:39:39 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma rosa.becerra@roma2.infn.it

Rosa L. Becerra (U Rome), Yu-Han Yang (U Rome), Simone Dichiara (PSU), Eleonora Troja (U Rome) and Roberto Ricci (U Rome) report:

We observed the field of GRB 250128B (Evans et al., GCN 39058, Myers et al., GCN 39063) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations began 0.67 days after the trigger and were carried out in the R filter at an average seeing of 1.1".

We do not detect any new source at the XRT source position (Evans et al., GCN 39069) down to the following 3-sigma limit R>24.8 AB mag calibrated using nearby stars in the PanSTARRS PS1 DR2 catalogue.

In our image we identify a few extended objects close to the XRT localization, however their probability of chance coincidence is Pcc>20 %.

We thank the staff at the VLT, especially Steffen Mieske, for the rapid execution of these observations.

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