GCN Circular 25343

Leo P. Singer (NASA GSFC), Mansi M. Kasliwal (Caltech), Michael W.
Coughlin (Caltech), Anna Franckowiak (DESY), Robert Stein (DESY), Jannis
Necker (DESY), Jesper Sollerman (OKC), Ariel Goobar (OKC), Shreya Anand
(Caltech), Tomas Ahumada (UMD), Eric Bellm (UW), Igor Andreoni (Caltech),
Dmitry Duev (Caltech), Kishalay De (Caltech), Matt Hankins (Caltech),
Danny Goldstein (Caltech), Samaya Nissanke (UofA), Harsh Kumar (IITB),
Varun Bhalerao (IITB), Joshua S. Bloom (UCB), David Kaplan (UWM), Daniel
A. Perley (LJMU), S. Bradley Cenko (NASA)

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
S190814bv (GCN 25324
Not found
 
 
, GCN 25333
Not found
 
 
) 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 obtaining target-of-opportunity observations in the
g-band, r-band and i-band filters beginning at UT 2019-08-14 10:32 UT. We
covered 86% of the enclosed probability before 12-deg twilight and
analyzed in real-time. Each exposure was 300s with a typical depth of
~20.3 mag due to the high airmass.

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 vet candidates based
on their light curves. After rejecting stellar sources (Tachibana and
Miller 2018) and moving objects and applying machine learning algorithms
(Mahabal et al. 2019), and after removing candidates with history of
variability prior to the merger time, no high-significance transient
candidates were identified by our pipeline in the 90% localization.

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, TTU, 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 co-ordination is being undertaken by the
GROWTH marshal system (Kasliwal et al. 2019).

[GCN OPS NOTE(14aug19): Per author's request, the Subject line containing "S190425z"
was changed to "S190814bv".]