TITLE:   GCN CIRCULAR
NUMBER:  33089
SUBJECT: IceCube-221216A: No Candidate Counterparts from the Zwicky Transient Facility
DATE:    22/12/21 16:11:41 GMT
FROM:    Sven Weimann at Ruhr University Bochum  <swei@astro.rub.de>

Sven Weimann (Ruhr University Bochum), Simeon Reusch, Jannis Necker (DESY), Robert Stein (Caltech) 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-221216A (Santander et al., GCN 32037) 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 2022-12-17 04:57 UTC, approximately 23.0 hours after event time. We covered 75.5% (5.4 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 alert database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019).

Two transient detections remained after the automated cuts, but were ruled out as candidate counterparts by visual inspection. We will continue monitoring the localization region with ZTF in the g-band for the next week.

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 nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf).