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Abstract

The rise of multi-messenger astronomy has brought with it the need to exploit
all available data streams and learn more about the astrophysical objects that
fall within its breadth. One possible avenue is the search for serendipitous
optical/near-infrared counterparts of gamma-ray bursts (GRBs) and
gravitational-wave (GW) signals, known as kilonovae. With surveys such as the
Zwicky Transient Facility (ZTF), which observes the sky with a cadence of ~
three days, the existing counterpart locations are likely to be observed;
however, due to the significant amount of sky to explore, it is difficult to
search for these fast-evolving candidates. Thus, it is beneficial to optimize
the survey cadence for realtime kilonova identification and enable further
photometric and spectroscopic observations. We explore how the cadence of wide
field-of-view surveys like ZTF can be improved to facilitate such
identifications. We show that with improved observational choices, e.g., the
adoption of three epochs per night on a ~ nightly basis, and the prioritization
of redder photometric bands, detection efficiencies improve by about a factor
of two relative to the nominal cadence. We also provide realistic hypothetical
constraints on the kilonova rate as a form of comparison between strategies,
assuming that no kilonovae are detected throughout the long-term execution of
the respective observing plan. These results demonstrate how an optimal use of
ZTF increases the likelihood of kilonova discovery independent of GWs or GRBs,
thereby allowing for a sensitive search with less interruption of its nominal
cadence through Target of Opportunity programs.