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GCN Circular 26424

Subject
LIGO/Virgo S191213g: Candidates from the Zwicky Transient Facility
Date
2019-12-14T11:22:07Z (4 years ago)
From
Igor Andreoni at Caltech <igor.andreoni@gmail.com>
Igor Andreoni (Caltech), Shreya Anand (Caltech), Eric Bellm (UW), Erik Kool (OKC), Dan Perley (LJMU), Leo Singer (NASA/GSFC), Michael Coughlin (Caltech), Tomas Ahumada (UMD), Harsh Kumar (IIT-B), Mansi M. Kasliwal (Caltech)


We observed the localization region of the gravitational wave trigger S191213g (LVC, GCN #26402) with the Palomar 48-inch telescope equipped with the 47 square degree Zwicky Transient Facility camera (ZTF, Bellm et al. 2019, Graham et al. 2019).

The tiling was optimally determined and triggered using the GROWTH Target of Opportunity marshal (Coughlin et al. 2019a, Kasliwal et al. 2019b). We started obtaining target-of-opportunity observations in the g-band and r-band beginning at 2019-12-14 03:47 UT, covering 29% of the enclosed probability based on the new LALInference skymap (LVC, GCN #26417). Each exposure was 180s with a median depth of 20.3 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). Alert filtering and follow-up coordination was undertaken by the GROWTH Marshal system (Kasliwal et al. 2019). The ZTF alert stream was also queried 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. Candidates that passed our selection are:

+--------------+-----------+-------------+--------------+--------+------+----------+-------+
|     Name     |  IAU Name |      RA     |     Dec      | filter | mag  |   MJD    | Class |
+--------------+-----------+-------------+--------------+--------+------+----------+-------+
| ZTF19acykzsk |    --     | 02:11:37.09 | +34:02:28.85 |   r    | 18.9 | 58831.31 |       | 
| ZTF19acymaru | AT2019wnh | 05:21:50.87 | -19:15:59.04 |   g    | 19.9 | 58831.36 |       |
| ZTF19acykzsp | AT2019wne | 01:53:26.19 | +31:48:03.64 |   g    | 20.2 | 58831.17 |       |
| ZTF19acyfoha | AT2019wkl | 05:40:25.05 | -18:05:51.47 |   r    | 17.5 | 58831.26 | SN Ia |
| ZTF19acymgzk | AT2019vtj | 02:17:03.24 | +45:51:59.87 |   r    | 17.9 | 58831.32 |       |
| ZTF19acymcwv | AT2019wni | 02:24:59.74 | +47:29:52.24 |   r    | 20.1 | 58831.30 |       |
| ZTF19acykwsd | AT2019wnl | 02:12:21.14 | +41:23:19.35 |   g    | 19.4 | 58831.14 |       |
| ZTF19acylvus | AT2019wnk | 05:34:31.47 | -19:25:12.88 |   g    | 19.4 | 58831.35 |       |
| ZTF19acymcna | AT2019wnn | 02:12:49.90 | +40:59:59.01 |   r    | 20.7 | 58831.32 |       |
+--------------+-----------+-------------+--------------+--------+------+----------+-------+

ZTF19acykzsk is interesting because it shows red color (g-r=0.3), it is less than 2 days old and it has an absolute magnitude of -15.5 mag. Upper limits from last night are r>19.85 and g>19.5 on 2019-12-13 05:37 and 2019-12-13 04:26 respectively. We could not report this candidate to TNS as it is less than 5 arcsec from an unrelated transient in 2018 (AT2018fua). The host distance is within 2-sigma of the GW distance estimate. Follow-up of ZTF19acykzsk is encouraged.

ZTF19acymaru/AT2019wnh appears to be located 25.3" from the 2MASX05215209-1915406 galaxy 225 Mpc away (GLADE catalog, Dalya et al., 2016), so within one sigma of the GW distance estimate. 

ZTF19acykzsp/AT2019wne does not show rapid evolution in r band in 1 day and its g-r color is consistent with zero. The photometric redshift from Sloan Digital Sky Survey is z = 0.18 +- 0.02 (Alam et al., 2015). 

ZTF19acyfoha/AT2019wkl was observed with Palomar 60-inch telescope equipped with the SED Machine instrument. The spectrum is consistent with the spectrum of a Type Ia supernova at redshift 0.044. 

ZTF19acymgzk/AT2019vtj appears to have a host with unknown redshift.  The g-r color is consistent with zero and there are no meaningful upper limits prior discovery in ZTF data.

ZTF19acymcwv/AT2019wni appears to be in a galaxy cluster at redshift z=0.113 (NED). Color information is not available for this candidate and non-detections prior to discovery are not constraining. 

ZTF19acykwsd/AT2019wnl appears hostless, has the last non-detection on 2019-12-13 and its g-r color is consistent with zero.

ZTF19acylvus/AT2019wnk has a host galaxy, rose by 0.3 mag in r-band over one night and has a g-r color of 0.1. 

ZTF19acymcna/AT2019wnn is located on top of the nucleus of a galaxy with cataloged redshift of z=0.13775 (GLADE, Dalya et al., 2016).


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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