TITLE:   GCN CIRCULAR
NUMBER:  26464
SUBJECT: LIGO/Virgo S191216ap: No Candidates from the Zwicky Transient Facility
DATE:    19/12/17 05:27:12 GMT
FROM:    Shreya Anand at GROWTH Caltech  <sanand@caltech.edu>

Shreya Anand (Caltech), Tomas Ahumada (UMD), Eric Bellm (UW), S. Bradley Cenko (NASA/GSFC), Michael Coughlin (Caltech), Dougal Dobie (USyd/CSIRO), Daniel Goldstein (Caltech), Albert Kong (NTHU), Harsh Kumar (IIT-B) Leo Singer (NASA/GSFC), Igor Andreoni (Caltech), David Kaplan (UWM), and Mansi M. Kasliwal (Caltech) report on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations:

We observed the localization region of the gravitational wave trigger S191216ap (LVC, GCN #26454) 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 2019-12-17 01:47 UT, covering 86% of the integrated probability based on the BAYESTAR skymap (LVC, GCN #26454). Each exposure was 300s, reaching a g-band median depth of 19.8 mag and r-band median depth of 18.5 mag. Due to the severe weather constraints at Palomar we were unable to acquire deeper images.

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 with RB scores greater than 0.15 (Duev et al. 2019) separated by at least 30 minutes to reject artifacts and moving objects. Thus far, no candidate counterparts were identified by our pipeline in the observed area. Further analysis is in progress.


ZTF and GROWTH are worldwide collaborations comprising of 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).