[vsnet-grb-info 23725] IceCube-190922B: Identification of a Candidate Supernova from the Zwicky Transient Facility

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25824
SUBJECT: IceCube-190922B: Identification of a Candidate Supernova from the Zwicky Transient Facility
DATE:    19/09/23 20:00:06 GMT
FROM:    Robert Stein at DESY  <robert.stein at desy.de>

Robert Stein (DESY), Anna Franckowiak (DESY), Marek Kowalski (DESY), and Mansi Kasliwal (Caltech) 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-190922B (Blaufuss et. al, GCN 25806) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started obtaining target-of-opportunity observations in the g-band and r-band beginning at 2019-09-23
07:03:11.900 UTC, approximately 8.0 hours after event time. Excluding  chip gaps, we covered the entire reported 90.0% probability region. 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) was used to search the alerts database for candidates. We rejected stellar sources (Tachibana and Miller 2018) and moving objects, applied machine learning algorithms (Mahabal et al. 2019) and rejected candidates with a history of variability. We were left with one candidate identified by our pipeline in spatial coincidence with the neutrino localisation. 

+------------------------------------------------------------------------------+
| ZTF Name     | IAU Name  | RA (deg)   | DEC (deg)  | Filter | Mag   | MagErr |
+------------------------------------------------------------------------------+
| ZTF19abxtupj | AT2019pqh | 6.617881   | -1.131493  | r      | 21.07 | 0.15   |
+------------------------------------------------------------------------------+

ZTF19abxtupj, previously reported to the TNS as AT2019pqh, was first detected by ZTF on 2019-09-04. It appears to have peaked on 2019-09-07 and subsequently declined. Given the host spectroscopic redshift of z=0.1334 as reported to the TNS, the absolute magnitude at peak was approximately -18.7 mag in r-band, consistent with expectations for a supernova. The arrival of a neutrino roughly 16 days after peak is also consistent with a supernova CSM-interaction model for neutrino production.

We strongly encourage spectroscopic observations to discern the nature of ZTF19abxtupj/AT2019pqh, and to rule out a classification as a type-Ia supernova.

Additional target-of-opportunity observations of the localisation region of IceCube 190922B will continue, in addition to serendipitous observations as part of the regular survey operations. 

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.