A sliding coherence window technique for hierarchical detection of continuous gravitational waves

A novel hierarchical semicoherent technique is presented for all-sky surveys for continuous gravitational-wave sources, such as rapidly spinning non-axisymmetric neutron stars. Analyzing year-long detector data sets over realistic ranges of parameter space using fully-coherent matched-filtering is computationally prohibitive. Thus more efficient, so-called hierarchical techniques are essential. Traditionally, the standard hierarchical approach consists of dividing the data into non-overlapping segments of which each is coherently analyzed and subsequently the matched-filter outputs from all segments are combined incoherently. The present work proposes to break the data into subsegments being shorter than the desired maximum coherence time span (size of the coherence window). Then matched-filter outputs from the different subsegments are efficiently combined by “sliding” the coherence window in time: Subsegments whose time-stamps are closer than coherence window size are combined coherently, otherwise incoherently. Compared to the standard scheme at the same coherence time baseline, data sets longer by about 50%− 100% would have to be analyzed to achieve the same search sensitivity as with the sliding coherence window approach. Numerical simulations attest the analytically estimated improvement.