A semi-coherent search strategy for known continuous wave sources in binary systems

TL;DR

This paper develops a semi-coherent search method for detecting weak continuous signals from sources in binary systems, focusing on constructing an effective parameter space metric for matched-filter searches.

Contribution

It introduces a new metric for binary system signals, simplifies parameter correlations, and proposes two search schemes for improved detection sensitivity.

Findings

The metric can be approximated as diagonal when segment length is much shorter than orbital period.

Parameter distinguishability is independent of total observation span, except for orbital angular frequency.

Semi-coherent and coherent metrics are approximately equal for long segment lengths.

Abstract

We present a method for detection of weak continuous signals from sources in binary systems via the incoherent combination of many "short" coherently-analyzed segments. The main focus of the work is on the construction of a metric on the parameter space for such signals for use in matched-filter based searches. The metric is defined using a maximum likelihood detection statistic applied to a binary orbit phase model including eccentricity. We find that this metric can be accurately approximated by its diagonal form in the regime where the segment length is << the orbital period. Hence correlations between parameters are effectively removed by the combination of many independent observation. We find that the ability to distinguish signal parameters is independent of the total semi-coherent observation span (for the semi-coherent span >> the segment length) for all but the orbital angular frequency. Increased template density for this parameter scales linearly with the observation span. We also present two example search schemes. The first uses a re parameterized phase model upon which we compute the metric on individual short coherently analyzed segments. The second assumes long >> the orbital period segment lengths from which we again compute the coherent metric and find it to be approximately diagonal. In this latter case we also show that the semi-coherent metric is equal to the coherent metric.