TITLE: GCN CIRCULAR NUMBER: 27721 SUBJECT: IceCube-200512A: No Candidate Counterparts from the Zwicky Transient Facility DATE: 20/05/12 16:47:47 GMT FROM: Simeon Reusch at DESY Simeon Reusch, Robert Stein and Anna Franckowiak (DESY) 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-200512A (Lagunas et. al, GCN 27719) 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-band and r-band beginning at 2020-05-12T09:16:17.700 UTC, approximately 1.7 hours after event time. We covered 9.3 sq deg, corresponding to 99.1% 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) 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 promising source candidates were identified. We note that the reported neutrino localization region lies at low galactic latitude. Given the high galactic extinction, our search was not sensitive to extragalactic objects. Observations of this region will continue as part of routine survey operations. 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).