LSST Observing Strategy White Paper: LSST Observations of WFIRST Deep
  Fields
  The Wide-Field Infrared Survey Telescope (WFIRST) is expected to launch in
the mid-2020s. With its wide-field near-infrared (NIR) camera, it will survey
the sky to unprecedented detail. As part of normal operations and as the result
of multiple expected dedicated surveys, WFIRST will produce several relatively
wide-field (tens of square degrees) deep (limiting magnitude of 28 or fainter)
fields. In particular, a planned supernova survey is expected to image 3 deep
fields in the LSST footprint roughly every 5 days over 2 years. Stacking all
data, this survey will produce, over all WFIRST supernova fields in the LSST
footprint, ~12-25 deg^2 and ~5-15 deg^2 regions to depths of ~28 mag and ~29
mag, respectively. We suggest LSST undertake mini-surveys that will match the
WFIRST cadence and simultaneously observe the supernova survey fields during
the 2-year WFIRST supernova survey, achieving a stacked depth similar to that
of the WFIRST data. We also suggest additional observations of these same
regions throughout the LSST survey to get deep images earlier, have long-term
monitoring in the fields, and produce deeper images overall. These fields will
provide a legacy for cosmology, extragalactic, and transient/variable science.
