  Fully coherent searches (over realistic ranges of parameter space and
year-long observation times) for unknown sources of continuous gravitational
waves are computationally prohibitive. Less expensive hierarchical searches
divide the data into shorter segments which are analyzed coherently, then
detection statistics from different segments are combined incoherently. The
novel method presented here solves the long-standing problem of how best to do
the incoherent combination. The optimal solution exploits large-scale
parameter-space correlations in the coherent detection statistic. Application
to simulated data shows dramatic sensitivity improvements compared with
previously available (ad hoc) methods, increasing the spatial volume probed by
more than 2 orders of magnitude at lower computational cost.
