TITLE: GCN CIRCULAR NUMBER: 41241 SUBJECT: GRB 250805A: ESO/VLT observations DATE: 25/08/05 18:21:11 GMT FROM: luca.izzo@inaf.it
L. Izzo (INAF/OACn & DARK/NBI), I. F. Giudice (INAF/OACn), N. Tanvir (U. Leicester), A. Levan (Radboud U.), A. Martin-Carrillo (UCD), M. De Pasquale (U. Messina), A. Takur (INAF-IAPS), V. D’Elia (ASI/SSDC) report on behalf of the Stargate collaboration:
We observed the region of the X-ray counterpart (Kennea et al., GCN #42134) of GRB 250805A (Ambrosi et al., GCN #41233) using the ESO/VLT UT3 (Melipal) equipped with the X-Shooter spectrograph.
A 30-second acquisition image in the r-band, initiated on August 05, 2025, at approximately 09:30 UT (3.3 hours post-burst), revealed no optical counterpart within the initial Swift-XRT error region (Kennea et al., GCN #42134). Due to the absence of an optical source within this region, spectroscopic observations were not executed.
However, we have identified the presence of an uncatalogued optical source outside the initial XRT error region, situated approximately 6 arcsec away from the XRT centroid. This source aligns with the enhanced Swift-XRT position reported later by Beardmore et al. (GCN #41238), indicating that it is likely the optical counterpart of GRB 250805A.
We acknowledge the excellent support from the ESO observing staff in Paranal, in particular Robert Klement and Luca Sbordone.
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