Gravitational Pulse Astronomy

TL;DR

This paper discusses the detection challenges of gravitational wave signals from white-dwarf binary mergers driven by the Kozai mechanism, emphasizing the need for new search algorithms to identify these sources and their potential as supernova progenitors.

Contribution

It highlights the limitations of existing detection methods for eccentric binary gravitational waves and proposes new algorithms considering 3-body motion and Earth's movement.

Findings

Standard searches cannot detect these signals.

Estimated detection rate of about 200 sources within 1 kpc.

Potential to identify supernova progenitors through combined gravitational and optical observations.

Abstract

Thompson has argued that the Kozai mechanism is primarily responsible for driving white-dwarf binary mergers and so generating type Ia supernovae (SNe). If so, the gravitational wave signal from these systems will be characterized by isolated repeating pulses that are well approximated by parabolic encounters. I show that it is impossible to detect these with searches based on standard assumptions of circular binaries, nor could they be detected by analogs of the repeating-pulse searches that have been carried out at higher frequencies, even if these were modified to barycentric time as a function of putative sky position. Rather, new search algorithms are required that take account of the intrinsic 3-body motion of the source as well as the motion of the Earth. If these eccentric binaries account for even a modest fraction of the observed SN rate, then there should be of order 1 pulse every 20 seconds coming from within 1 kpc, and there should be of order 200 detectable sources in this same volume. I outline methods of identifying these sources both to remove this very pernicious background to other signals, and to find candidate SN Ia progenitors, and I sketch practical methods to find optical counterparts to these sources and so measure their masses and distances.