TITLE: GCN CIRCULAR NUMBER: 32480 SUBJECT: IceCube-220822A: One Candidate Counterpart from the Zwicky Transient Facility DATE: 22/08/24 18:20:59 GMT FROM: Jannis Necker at DESY jannis.necker@desy.de

Jannis Necker (DESY), Robert Stein (Caltech), Sven Weimann (Ruhr University Bochum), 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:

As part of the ZTF neutrino follow up program (Stein et al. 2022), we observed the localization region of the neutrino event IceCube-220822A (Lincetto et. al, GCN 32475) 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 2022-08-23 03:53 UTC, approximately 7.4 hours after event time. We covered 84.1% (8.2 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.

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 high-significance transient candidate by our pipeline, lying within the 90.0% localization of the skymap:

+---------------------------------------------------------------------------------+ | ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr | +---------------------------------------------------------------------------------+ | ZTF22aarmiqk | AT2022saw | 272.3184212 | +22.1633981 | r | 21.71 | 0.20 | +---------------------------------------------------------------------------------+

ZTF22aarmiqk/AT2022saw is a possible supernova 50 days post peak. Spectroscopic follow-up is encouraged to determine the type.

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 AMPEL Follow-up Pipeline (Stein et al. 2021).