TITLE: GCN CIRCULAR NUMBER: 29999 SUBJECT: IceCube-210510A: No candidate counterparts from the Zwicky Transient Facility DATE: 21/05/12 14:35:29 GMT FROM: Robert Stein at DESY Robert Stein (DESY), Sven Weimann (Ruhr University Bochum), Jannis Necker (DESY), Simeon Reusch (DESY) and Anna Franckowiak (DESY/Ruhr University Bochum) report, On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: We observed the localization region of the neutrino event IceCube-210510A (Lagunas et. al, GCN 29980) 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 2021-05-10 at 09:56 UT, approximately 5.1 hours after event time. We covered 4.04 sq deg, corresponding to 100% of the reported localization region. This estimate does not account for chip gaps. Both initial exposures were 300s with a typical depth of 21.0 mag. We re-observed the localization area on 2021-05-11 and 2021-05-12 in the g-band with 30s exposure. 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 looked for high-significance transient candidates with our pipeline, lying within the 90.0% localization of the skymap. No compelling candidate counterparts were detected. ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IITB, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. 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 AMPEL Follow-up Pipeline (Stein et al. 2021).