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GCN Circular 27872

IceCube-200530A: Candidate Counterparts from the Zwicky Transient Facility
2020-05-31T14:13:01Z (4 years ago)
Simeon Reusch at DESY <>
Simeon Reusch, Robert Stein, Anna Franckowiak (DESY) and Suvi Gezari (UMD) 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-200530A (Stein et. al, GCN 27865) 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-band and r-band beginning at 2020-05-30T08:04:55.000 UTC, approximately 0.2 hours after event time. We covered 22.0 sq deg, corresponding to 98.9% 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) 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 candidates by our pipeline, all lying within the 90.0% localization of the skymap:

| ZTF Name     | IAU Name   | RA (deg)    | DEC (deg)   | Filter | Mag   | MagErr | Notes |
| ZTF19aatubsj | SN 2019fdr | 257.2785777 | +26.8557286 | r      | 19.43 | 0.11   |  (a)  | 
| ZTF20abbpkpa | AT 2020lam | 254.0980980 | +26.8138379 | r      | 19.00 | 0.08   |  (b)  |
| ZTF20abdnpdo | AT 2020lls | 257.5896488 | +24.4372389 | r      | 19.94 | 0.18   |  (c)  |

(a) ZTF19aatubsj (SN 2019fdr) is a substantial long-duration flare in a Narrow-Line Seyfert 1 galaxy. The flare peaked roughly 300 days ago, but still remains significantly above pre-flare flux.

(b) ZTF20abbpkpa (AT 2020lam) is a probable young supernova. It was first detected 6 days ago, at a magnitude of 19.6, but was not detected 2 days prior to a depth of 20.62. It has a SDSS spectroscopic z = 0.033, suggesting a current abs. magnitude of -16.7.

(c) ZTF20abdnpdo (AT 2020lls) is also consistent with being a young supernova. SDSS photometric z is estimated at 0.052 +/- 0.012, which would result in a current abs. magnitude of -16.9.

Spectroscopic follow-up of ZTF20abbpkpa and ZTF20abdnpdo is recommended.

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@UW (Patterson et al. 2019).
Alert database searches are done by AMPEL (Nordin et al. 2019).
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