  We present a cadence optimization strategy to unveil a large population of
kilonovae using optical imaging alone. These transients are generated during
binary neutron star and potentially neutron star-black hole mergers and are
electromagnetic counterparts to gravitational-wave signals detectable in nearby
events with Advanced LIGO, Advanced Virgo, and other interferometers that will
come online in the near future. Discovering a large population of kilonovae
will allow us to determine how heavy element production varies with the
intrinsic parameters of the merger and across cosmic time. The rate of binary
neutron star mergers is still uncertain, but only few (less than 15) events
with associated kilonovae may be detectable per year within the horizon of
next-generation ground-based interferometers. The rapid evolution (hours to
days) at optical/infrared wavelengths, relatively low luminosity, and the low
volumetric rate of kilonovae makes their discovery difficult, especially during
blind surveys of the sky. We propose future large surveys to adopt a rolling
cadence in which g-i observations are taken nightly for blocks of 10
consecutive nights. With the current baseline2018a cadence designed for the
Large Synoptic Survey Telescope (LSST), less than 7.5 poorly-sampled kilonovae
are expected to be detected in both the Wide Fast Deep (WFD) and Deep Drilling
Fields (DDF) surveys per year, under optimistic assumptions on their rate,
duration, and luminosity. We estimate the proposed strategy to return up to
about 272 GW170817-like kilonovae throughout the LSST WFD survey, discovered
independently from gravitational-wave triggers.
