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GCN Circular 26416

Subject
LIGO/Virgo S191205ah: Candidates from the Zwicky Transient Facility Public Survey
Date
2019-12-13T20:21:29Z (4 years ago)
From
Igor Andreoni at Caltech <igor.andreoni@gmail.com>
Igor Andreoni (Caltech), Shreya Anand (Caltech), Michael W. Coughlin (Caltech), Kishalay De (Caltech), Mansi M. Kasliwal (Caltech), Dmitry Duev (Caltech), Eric Bellm (UW), Robert Stein (DESY), Simeon Reusch (DESY), Brad Cenko (NASA GSFC), Matthew Graham (Caltech)
on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations

The Zwicky Transient Facility (ZTF; Bellm et al. 2019, Graham et al. 2019) public survey serendipitously imaged part of the skymap of the neutron star-black hole merger candidate S191205ah (LVC, GCN #26350) between 2019-12-06 and 2019-12-13 UT. The first 4 nights after the trigger were heavily affected by bad weather at Palomar Observatory. The integrated localization probability observed at least once during the public survey was about 46%, with median limiting magnitudes r > 19.7 and g > 19.6. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC (Masci et al., 2019).

We queried the ZTF alert stream using the Kowalski infrastructure (Duev et al., 2019). We required at least 2 detections separated by at least 30 minutes to select against moving objects. Furthermore, we cross-matched our candidates with the Minor Planet Center to flag known asteroids. The candidates within the 90% probability contour of S191205ah that passed the automatic selection criteria and human vetting are presented in the table below.

+--------------+-----------+-------------+-------------+--------------+--------+------+----------------+
| Name         | TNS       | RA          | Dec         | JD           | filter | mag  | z      | notes |
+--------------+-----------+-------------+-------------+--------------+--------+------+----------------+
| ZTF19acxpnvd | AT2019wkv | 11:41:26.84 | +08:14:28.3 | 2458829.0670 | r      | 19.4 | 0.0899 | (a)   |
| ZTF19acxoywk | AT2019wix | 09:59:35.08 | +13:54:54.2 | 2458828.0459 | g      | 20.2 | 0.0511 | (b,c) |
| ZTF19acxoyra | AT2019wid | 10:12:22.51 | +08:36:33.6 | 2458828.0459 | g      | 20.2 | 0.0964 | (b)   |
| ZTF19acxowrr | AT2019wib | 10:19:29.15 | +27:53:01.5 | 2458828.0477 | g      | 18.7 | 0.0505 | (b)   |
| ZTF19acxpwlh | AT2019wiy | 10:22:51.11 | +23:36:11.8 | 2458830.9565 | r      | 19.7 | 0.123  | (a,c) |
| ZTF19acyiflj | AT2019wmy | 10:11:35.97 | +23:56:37.8 | 2458830.9330 | r      | 19.9 | -      | (d)   |
| ZTF19acyitga | AT2019wmn | 10:39:11.24 | +05:09:43.0 | 2458830.9587 | r      | 19.3 | 0.0708 | (b,c) |
+--------------+-----------+-------------+-------------+--------------+--------+------+----------------+
(a) SDSS photometric redshift
(b) SDSS spectroscopic redshift
(c) First reported to TNS by ALeRCE
(d) Faint host

Spectroscopic or photometric redshifts from the Sloan Digital Sky Survey (SDSS) are available for most of the probable host galaxies. The redshift of the candidates are compatible with the distance to S191205ah (385 +- 164 Mpc, GCN #26350) within the uncertainties. Where host redshifts are available, the absolute magnitude of the reported transients is significantly brighter than expected for kilonovae at those distances, in particular in comparison with the GW170817 kilonova at similar phases. None of the candidates showed a particularly red color days after the merger, with ZTF19acxoywk/AT2019wix appearing to be the reddest with g-r=0.4 on 2019-12-10.

We detected the transient candidate Gaia19fmm/AT2019wfa (Kostrzewa-Rutkowska et al., GCN #26397) in ZTF data on 2019-12-12 02:08 UT with magnitude g = 18.0. An association between Gaia19fmm/AT2019wfa and S191205ah was ruled out by Hu et al. (GCN #26405) via spectroscopic classification of the transient as a Type Ia supernova.


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 filtering and follow-up coordination is being undertaken by the GROWTH marshal system (Kasliwal et al. 2019). Alert database searches are done with using the Kowalski infrastructure (Duev et al., 2019) and with AMPEL (Nordin et al. 2019).
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