TITLE: GCN CIRCULAR NUMBER: 33374 SUBJECT: GRB 230217A: VLT/FORS2 optical observations and candidate counterpart DATE: 23/02/24 15:50:32 GMT FROM: Paolo D'Avanzo at INAF-OAB pda.davanzo@gmail.com

P. D'Avanzo, A. Rossi (INAF-OAS), R. Brivio (INAF-OAB), D. B. Malesani (Radboud Univ.and DAWN/NBI), A. Saccardi (GEPI, Observatoire de Paris), S. Campana (INAF-OAB), B. Gompertz (Univ. Birmingham), D. Hartmann (Clemson Univ.), D. A. Kann (Goethe Univ). A. J. Levan (Radboud Univ.), G. Tagliaferri (INAF-OAB), N. R. Tanvir (Univ. Leicester) report on behalf of the Stargate consortium:

We observed the field of the short GRB 230217A (Moss et al. GCN Circ. 33339) with the ESO/VLT equipped with the FORS2 instrument. A series of optical images has been obtained with the I filter on 2023 February 20 (i.e. about 2.5 days after the burst) and on 2023 February 23 (i.e. about 5.5 days after the burst).

Image subtraction carried out between the two epochs shows a residual at the following position: RA (J2000) = 18:43:04.97 Dec (J2000) = -28:50:16.4

+/- 0.3".

This position lies inside the XRT error circle of the X-ray afterglow position (Capalbi et al., GCN Circ. 33365) and is consistent with the position of the radio source reported by Schroeder et al. (GCN Circ. 33358).

From preliminary photometry, we measure for this source a magnitude of I ~ 24.5 (AB) at t-t0 = 2.5 days.

We propose this source as a candidate optical counterpart of GRB 230217A.

Further observations are planned.

We acknowledge excellent support from the ESO observing staff in Paranal, in particular Julia Seidel, Konrad Tristram and Thomas Rivinius.