TITLE:   GCN CIRCULAR
NUMBER:  34624
SUBJECT: GRB 230903A: VLT/X-shooter optical observations
DATE:    23/09/05 10:07:06 GMT
FROM:    Emeric Le Floc'h at CEA-Saclay <emeric.lefloch@cea.fr>

D. Pieterse (Radboud University), D. B. Malesani (Radboud and DAWN/NBI), E. Le Floc’h (CEA-Saclay), A. Saccardi (GEPI, Obs. de Paris) and N. R. Tanvir (Univ. of Leicester) report on behalf of the Stargate collaboration :

We observed the field of GRB230903A (Fermi GBM team, GCN 34608 ; D’Ai et al., GCN 34610) using the ESO VLT UT3 (Melipal) equipped with the X-shooter instrument. Three 60s exposures were obtained in the r-band on 2023 September 4.097 UT (T-To ~8.95h). The observations were performed under poor weather conditions, with a seeing of 3.2 arcsec measured in the data. We do not detect any source coinciding with the location of the X-ray afterglow detected by Swift/XRT (D’Ai et al., GCN 34610). We obtain the following upper limit, calibrated using a faint, nearby object from the Legacy Survey (Dey et al. 2019, ApJ, 257, 29).

r > 22.7 mag (AB)

This estimate is not corrected for Galactic extinction and is consistent with the non-detection reported earlier by LCOGT (Strausbaugh et al., GCN 34611).

We acknowledge excellent support from the ESO observing staff in Paranal, in particular Claudia Paladini and Jonathan Smoker.