TITLE: GCN CIRCULAR NUMBER: 32498 SUBJECT: IceCube-220822A: Classification of AT2022saw as a Type Ia supernova DATE: 22/08/28 19:58:48 GMT FROM: Robert Stein at Caltech rdstein@caltech.edu

Robert Stein, Zach Vanderbosch, Ilaria Caiazzo (Caltech), Jannis Necker, Simeon Reusch (DESY), Sven Weimann (Ruhr University Bochum), Mansi Kasliwal, Viraj Karambelkar (Caltech), Anna Franckowiak (DESY/Ruhr University Bochum) and Jesper Sollerman (Stockholm) report:

We observed neutrino IC220822A (Lincetto et. al, GCN 32475) with the Zwicky Transient Facility (Necker et al., GCN 32480) as part of our ZTF neutrino follow-up program (Stein et al. 2022). As part of these observations, we reported the transient ZTF22aarmiqk/AT2022saw as a possible optical counterpart.

We undertook spectroscopic observations of AT2022saw with the Low Resolution Imaging Spectrometer (LRIS, Oke et al. 95) at the Keck I Observatory. Using SNID (Blondin et al. 2007), we classify AT2022saw as a type Ia supernova at redshift z=0.14 (see https://www.wis-tns.org/object/2022saw for the full spectrum), approximately 50 days post peak. Given that type Ia supernovae are not predicted to emit high-energy neutrinos, we therefore exclude AT2022saw as a candidate counterpart to IC220822A.

The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.