{
  "bibcode": "2019GCN.25616....1K",
  "body": "Erik Kool (OKC), Robert Stein (DESY), Yashvi Sharma (Caltech), Viraj\nKarambelkar (Caltech), Mansi Kasliwal (Caltech), Daniel Perley (LJMU),\n Valery Brinnel (HU Berlin), Jakob Nordin (HU Berlin), Shreya Anand\n(Caltech), Michael Coughlin (Caltech), Leo P. Singer (NASA GSFC), Igor\nAndreoni (Caltech), Gaurav Waratkar (IITB), Harsh Kumar (IITB), Maitreya\nKhandagale (IITB), Kunal Deshmukh (IITB), Varun Bhalerao (IITB), G. C.\nAnupama (IIA), Dougal Dobie (USyd/CSIRO), Brad Cenko (NASA GSFC), Tomas\nAhmuda (UMD), Eric Bellm (UW), Albert Kong (NTHU), Anna Franckowiak (DESY),\nPradip Gatkine (UMD)\n\nOn behalf of the Zwicky Transient Facility (ZTF) and Global Relay of\nObservatories Watching Transients Happen (GROWTH) collaborations\n\nWe observed the localization region of the gravitational wave trigger\nS190901ap (LVC et al. GCN 25606, GCN 25614) with the Palomar 48-inch\ntelescope equipped with the 47 square degree ZTF camera (Bellm et al. 2019,\nGraham et al. 2019). The tiling was optimally determined and triggered\nusing the GROWTH Target of Opportunity marshal (Coughlin et al. 2019a,\nKasliwal et al. 2019b). We started obtaining target-of-opportunity\nobservations in the g-band and r-band beginning at UT 2019-09-02 03:08 UT.\nWe covered 44% of the enclosed probability based on the new lalinference\nmap (38% of the enclosed probability based on the initial bayestar map) in\n6500 sq deg mapped before we had to close due to clouds. Each exposure was\n30s with a typical depth of 20.7 mag.\n\nThe images were processed in real-time through the ZTF reduction and image\nsubtraction pipelines at IPAC to search for potential counterparts (Masci\net al. 2019). AMPEL (Nordin et al. 2019) was used to search the alerts\ndatabase for candidates. After rejecting stellar sources (Tachibana and\nMiller 2018) and moving objects and applying machine learning algorithms\n(Mahabal et al. 2019), and after removing candidates with history of\nvariability prior to the merger time, the following high-significance\ntransient candidates were identified by our pipeline in the 95%\nlocalization of the new lalinference map (LVC et al. GCN 25614).\n\n------------------------------------------------------------------------\n ZTF Name     | RA (deg)   | DEC (deg)  | Filter | Mag   | Magerr\n------------------------------------------------------------------------\n ZTF19abvizsw | 279.472820 | +61.497984 | r      | 19.45 | 0.11\n ZTF19abvixoy | 279.552972 | +27.420935 | r      | 19.22 | 0.10\n ZTF19abvjnsm | 267.202697 | +44.693203 | r      | 20.23 | 0.20\n ZTF19abvionh | 253.750924 | +14.051330 | g      | 20.73 | 0.31\n------------------------------------------------------------------------\n\nZTF19abvizsw has a red color (g-r ~ 0.5 mag), no underlying host in the\nreference image and is on the outer periphery of the new LVC sky\nlocalization. ZTF has observed this field every night for the past month as\npart of routine survey operations and the first detections of this\ntransient are only after the binary neutron star merger time. ZTF19abvixoy\nhas an upper limit from Aug 30 UT and possibly a faint counterpart in PS1.\nZTF19abvjnsm has an upper limit from Sep 1 UT but its host galaxy has too\nhigh a phot-z estimate from SDSS of 0.51 +/- 0.11. The host galaxy of\nZTF19abvionh has a consistent SDSS phot-z (0.064 +/- 0.016) but the two\ndetections last night are separated by only a short baseline of 7 minutes\n(a moving object in our solar system cannot be ruled out for this\ncandidate). We encourage spectroscopic and photometric follow-up to discern\nthe nature of these transients.\n\nZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC,\nUSA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY,\nGermany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan;\nIIT-B, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA and USyd,\nAustralia. ZTF acknowledges the generous support of the NSF under AST MSIP\nGrant No 1440341. GROWTH acknowledges generous support of the NSF under\nPIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW\n(Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin\net al. 2019). Alert filtering and follow-up co-ordination is being\nundertaken by the GROWTH marshal system (Kasliwal et al. 2019).",
  "circularId": 25616,
  "createdOn": 1567434748000,
  "email": "mansikasliwal@gmail.com",
  "subject": "LIGO/Virgo S190901ap: Candidates from the Zwicky Transient Facility",
  "submitter": "Mansi M. Kasliwal at Caltech/Carnegie  <mansikasliwal@gmail.com>",
  "eventId": "LIGO/Virgo S190901ap"
}