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GCN Circular 27068

LIGO/Virgo S200213t: One additional candidate from the Zwicky Transient Facility
2020-02-14T14:00:24Z (4 years ago)
Simeon Reusch at DESY <>

Simeon Reusch (DESY), Robert Stein (DESY), Daniel Perley (LJMU),
Shreya Anand (Caltech)

On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of
Observatories Watching Transients Happen (GROWTH) collaborations:��

We observed the localization region of LIGO/Virgo S200213t 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 2020-02-13T04:34:34.500 UTC, approximately
0.4 hours after event time. We covered 78.5% of the enclosed probability
based on the map in 1999.2 sq deg. This estimate accounts for chip gaps.
Each exposure was 30s with a typical depth of 20.5 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, apply machine learning algorithms
(Mahabal et al. 2019), and remove candidates with history of variability
prior to the merger time. We are left with the following additional
high-significance transient candidate by our pipeline, lying within the
95.0% localization of the skymap.��

| ZTF Name �� �� | IAU Name   | RA (deg)�� �� | DEC (deg)   | Filter | Mag �� | MagErr |
| ZTF20aanakcd | AT 2020cmr | 008.1570525 | +41.3157344 | r�� �� �� | 20.59 | 0.13   |

ZTF20aanakcd (AT 2020cmr) has a host with an estimated photometric
redshift of 0.05 +/- 0.03, derived using ANNz2 (Sadeh et. al., 2015)
based on photometry from the Pan-STARRS survey (Chambers et. al., 2019).
This redshift is compatible with the reported GW distance. We caution
that this value is only a preliminary estimate.

We encourage photometric and spectroscopic follow-up to classify this
additional candidate.

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,

ZTF acknowledges the generous support of the NSF under AST MSIP Grant No

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).


[GCN OPS NOTE(04feb20): Per author's request, in the author list,
Perley's affiliation was corrected from "Caltech" to "LJMU".]
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