TITLE: GCN CIRCULAR NUMBER: 43079 SUBJECT: IceCube-251210A: No Candidate Transients from the Zwicky Transient Facility DATE: 25/12/12 18:25:09 GMT FROM: Jannis Necker at DESY <jannis.necker@desy.de> Robert Stein (JSI), Jannis Necker (Leiden University), Akshay Eranhalodi (DESY) 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-251210A (Zegarelli et. al, GCN 43064) 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 g- and r-band beginning at 2025-12-11 02:31 UTC, approximately 15.4 hours after event time. We covered 97.7% (1.6 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each 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). We are left with the following candidate: +--------------------------------------------------------------------------------+ | ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr | +--------------------------------------------------------------------------------+ | ZTF25acgniiw | ------- | 035.5190217 | +20.3633434 | r | 20.55 | 0.09 | +--------------------------------------------------------------------------------+ ZTF25acgniiw was first detected on 2025-11-24. Its position is coincident with a quasar listed in MILLIQUAS (Flesch et al., 2023). Because there is no sign of contemporaneous flaring activity, ZTF25acgniiw is likely not associated with IceCube-251210A. This is in agreement with previous reports (Becerra et al. 2025, GCN 43071). 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/43079. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...