TITLE: GCN CIRCULAR NUMBER: 43193 SUBJECT: IceCube-251218A: No Candidate Transients from the Zwicky Transient Facility DATE: 25/12/22 21:43:04 GMT FROM: Jannis Necker at DESY <jannis.necker@desy.de> Jannis Necker (Leiden University), Akshay Eranhalodi (DESY), Robert Stein (JSI), and Anna Franckowiak (Ruhr University Bochum) report, On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-251218A (Zegarelli et. al, GCN 43151) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the r-band beginning at 2025-12-19 04:45 UTC, approximately 8.4 hours after event time. We covered 100.0% (1.1 sq deg) of the reported localization region. This estimate accounts for chip gaps. The exposure was 300s with a typical depth of 21.0 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019) . No candidate counterparts were detected. This is consistent with previously reported upper limits (Antier et al. 2025, GCN 43153). Observations of this field will continue as part of our standard ToO cadence for high-energy neutrinos (Stein et al. 2023). ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA; WIS, Israel; OKC, Sweden; JSI/UMd, USA; DESY, Germany; TANGO, Taiwan; UW Milwaukee, USA; LANL, USA; TCD, Ireland; IN2P3, France. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019). Alert filtering is performed with the nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf ). View this GCN Circular online at https://gcn.nasa.gov/circulars/43193. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...