{
  "bibcode": "2021GCN.30870....1W",
  "body": "Sven Weimann (Ruhr University Bochum), Simeon Reusch, Jannis Necker, Robert Stein (DESY) and Anna Franckowiak (DESY/Ruhr University Bochum),\n\nOn behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations:\n\nWe observed the localization region of the neutrino event IceCube-210922A (Lincetto et. al, GCN 30862) 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 2021-09-23 10:25 UTC, approximately 16.1 hours after event time. We covered 79% (1.2 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.\n\nThe 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).\n\nNo candidate counterparts were detected.\n\nZTF 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.\n\nGROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949.\nAlert distribution service provided by DIRAC@UW (Patterson et al. 2019).\nAlert database searches are done by AMPEL (Nordin et al. 2019).\nAlert filtering is performed with the AMPEL Follow-up Pipeline (Stein et al. 2021).",
  "circularId": 30870,
  "createdOn": 1632411788000,
  "email": "swei@astro.rub.de",
  "subject": "IceCube-210922A: No Candidate Counterparts from the Zwicky Transient Facility",
  "submitter": "Sven Weimann at Ruhr University Bochum  <swei@astro.rub.de>",
  "eventId": "IceCube-210922A"
}