Gravitational waves from coalescing binaries and Doppler experiments

TL;DR

This paper discusses how Doppler tracking of interplanetary spacecraft can detect low-frequency gravitational waves from coalescing massive black hole binaries, analyzing sensitivity and optimal data analysis strategies for current and future missions.

Contribution

It explores the Doppler response to in-spiral signals, identifies key parameter regions for data analysis, and assesses the all-sky sensitivity of CASSINI experiments for astrophysical sources.

Findings

Doppler tracking is sensitive to gravitational waves from massive black hole binaries.

Optimal parameter regions for data analysis are identified.

CASSINI's experiments could detect signals from galactic nuclei and galaxy clusters.

Abstract

Doppler tracking of interplanetary spacecraft provides the only method presently available for broad-band searches of low frequency gravitational waves. The instruments have a peak sensitivity around the reciprocal of the round-trip light-time T of the radio link connecting the Earth to the space-probe and therefore are particularly suitable to search for coalescing binaries containing massive black holes in galactic nuclei. A number of Doppler experiments -- the most recent involving the probes ULYSSES, GALILEO and MARS OBSERVER -- have been carried out so far; moreover, in 2002-2004 the CASSINI spacecraft will perform three 40 days data acquisition runs with expected sensitivity about twenty times better than that achieved so far. Central aims of this paper are: (i) to explore, as a function of the relevant instrumental and astrophysical parameters, the Doppler output produced by in-spiral signals -- sinusoids of increasing frequency and amplitude (the so-called chirp); (ii) to identify the most important parameter regions where to concentrate intense and dedicated data analysis; (iii) to analyze the all-sky and all-frequency sensitivity of the CASSINI's experiments, with particular emphasis on possible astrophysical targets, such as our Galactic Centre and the Virgo Cluster.