TITLE: GCN CIRCULAR NUMBER: 41474 SUBJECT: LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits DATE: 25/08/21 19:06:59 GMT FROM: Sylvio Klose at TLS Tautenburg <klose@tls-tautenburg.de> S. Klose, B. Stecklum, A. Nicuesa Guelbenzu, and F. Ludwig (all Tautenburg) report: We observed the optical transient ZTF25abjmnps/AT2025ulz (Stein et al., GCN 41414), possibly associated with the gravitational wave event S250818k (GCN 41437), with the Tautenburg 1.34-m Schmidt telescope using the Sloan filter set. Observations were performed on 20-08-2025 between 20:06 and 20:39 UT as well as between 21:57 and 22:30 UT. They reached a 3-sigma upper limit in r and i of 22.3 and 22.4 mag (AB), respectively. Photometric calibration was performed using Pan-STARRS DR2. At the position of the optical transient (OT) discovered by Stein et al. (GCN 41414; see also Busmann et al., GCN 41421; Hall et al., GCN 41433), no point source superimposed the underlying host galaxy was detected / could be identified. Given the closeness of the OT to the host galaxy's nucleus (Liu et al., GCN 41461) we caution that the photometric limits are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41474. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...