TITLE: GCN CIRCULAR NUMBER: 39970 SUBJECT: GRB 250330A: VLT/FORS2 Afterglow Detection DATE: 25/03/31 12:35:19 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), Muskan Yadav (U Rome), Eleonora Troja (U Rome), Lei Hu (CMU) and Roberto Ricci (U Rome) report on behalf of the ERC BHianca team:

We reobserved the field of GRB 250330A (Cenko et al., GCN 39938) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations began at T+19.8 hours after the trigger and were carried out in the R filter at an average seeing of 1.0" and airmass about 2.5.

A comparison to our first epoch (Becerra et al., GCN 39941) reveals a fading source within the XRT enhanced position (Evans et al., GCN 39947), located at RA, Dec (J2000) = 16:51:47.01, -86:52:51.85.

We estimate a preliminary magnitude of R~23.2 AB mag at 1.25 h post-trigger, calibrated using nearby stars from the SkyMapper Southern Survey (SMSS) Fourth Data Release (DR4) catalog (Onken et al., 2024) and not corrected for Galactic extinction.

We thank the staff at the VLT for the rapid execution of these observations.

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