[vsnet-grb-info 26657] IceCube-201021A: One candidate counterpart from the Zwicky Transient Facility

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28757
SUBJECT: IceCube-201021A: One candidate counterpart from the Zwicky Transient Facility
DATE:    20/10/23 16:28:36 GMT
FROM:    Robert Stein at DESY  <robert.stein at desy.de>

Robert Stein (DESY), Simeon Reusch (DESY), Sven Weimann (Ruhr University Bochum) and Michael Coughlin (University of Minnesota) 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-201021A (Lagunas et. al, GCN 28715) 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 2020-10-23 02:21 UTC, approximately 43.7 hours after event time. We covered 6.3 sq deg at least twice, corresponding to 95.7% 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. 2020) 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 one 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 |
+---------------------------------------------------------------------------------+
| ZTF20acmxnpa |  AT2020ybb | 260.4617133 | +14.7743083 | g      | 20.94 | 0.17   |
+---------------------------------------------------------------------------------+

ZTF20acmxnpa/AT2020ybb was first detected on 2020-10-13 02:37 UTC, and is a candidate supernova around peak. This would be consistent with a CSM-interaction supernova neutrino production model. We encourage spectroscopic follow-up of this object to confirm its nature.

We were unable to retrieve the optical source reported by Im et al. (GCN 28756) with forced photometry of the ZTF science images (at SNR=3). However, our limiting magnitude is comparable to the reported flux level.

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 at 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. 2020).