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GCN Circular 25634

Subject
LIGO/Virgo S190901ap: Additional observations from the Zwicky Transient Facility
Date
2019-09-03T19:26:03Z (4 years ago)
From
Robert Stein at DESY <robert.stein@desy.de>
Robert Stein (DESY), Erik Kool (OKC), Viraj Karambelkar (Caltech), Mansi Kasliwal (Caltech), Daniel Perley (LJMU), Shreya Anand (Caltech), Michael Coughlin (Caltech), Yashvi Sharma (Caltech), Leo P. Singer (NASA GSFC), Igor Andreoni (Caltech), Gaurav Waratkar (IITB), Harsh Kumar (IITB), Maitreya Khandagale (IITB), Kunal Deshmukh (IITB), Varun Bhalerao (IITB), G. C. Anupama (IIA), Dougal Dobie (USyd/CSIRO), Brad Cenko (NASA GSFC), Tomas Ahmuda (UMD), Eric Bellm (UW), Albert Kong (NTHU), Anna Franckowiak (DESY), Pradip Gatkine (UMD)

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

We again observed the localization region of the gravitational wave trigger S190901ap (LVC et al. GCN 25606, GCN 25614) with the Palomar 48-inch telescope equipped with the 47 square degree ZTF camera (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 our new target-of-opportunity observations in the g-band and r-band beginning at UT 2019-09-03 03:12 UT. Each exposure was 30s, and due to poor weather images had a typical median depth of 19.5 mag. Moreover, the planned observations were not completed due to dome closure. Between the two nights of observations, we have covered 48% of the enclosed probability based at least once, and 35% of the enclosed probability at least twice. 

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 rejected stellar sources (Tachibana and Miller 2018) and moving objects and applying machine learning algorithms (Mahabal et al. 2019), and removed candidates with history of variability prior to the merger time. One additional object was found by our pipeline, detected twice on our first night of observations (Kool et al. GCN 25616).
 
------------------------------------------------------------------------
ZTF Name     | RA (deg) | DEC (deg)  | Filter | Mag | Magerr
------------------------------------------------------------------------
ZTF19abvitlr | 279.200304 | -11.579390 | r      | 18.89 | 0.08
------------------------------------------------------------------------
 
ZTF19abvitlr is a red transient located in a crowded stellar field at galactic latitude of -2 deg, and was not detected in observations on Aug 30 to a depth of 20.1 mag. It is significantly offset from the nearest PS1 source, and has a steep lightcurve rise. Given these properties it is likely a reddened galactic Cataclysmic Variable. Spectroscopic follow-up would confirm the nature of this transient.
 
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; IIT-B, 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). Alert filtering and follow-up co-ordination is being undertaken by the GROWTH marshal system (Kasliwal et al. 2019).
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