1201.4613 (Samaya Nissanke et al.)

Gravitational-wave emission from compact Galactic binaries    [PDF]

Samaya Nissanke, Michele Vallisneri, Gijs Nelemans, Thomas A. Prince

Compact Galactic binaries where at least one member is a white dwarf (WD) or neutron star constitute the majority of individually detectable sources for future low-frequency space-based gravitational-wave (GW) observatories; in addition, they form an unresolved continuum, the dominant Galactic foreground at frequencies below a few mHz. A handful of ultra-compact binaries, observed at optical, ultraviolet and X-ray wavelengths, are known verification sources for space-based GW interferometers. Due to the paucity of electromagnetic observations, the majority of studies of Galactic-binary populations so far have been based on population-synthesis simulations. However, recent surveys have reported several new detections of compact binaries including double WDs, providing new constraints for population estimates. In this article, we evaluate the impact of revised local densities of interacting WD binaries on future low-frequency GW observations. Specifically: we consider five scenarios that explain these densities with different assumptions on the formation of interacting systems; we simulate corresponding populations of detached and interacting WD binaries; we estimate the number of individually detectable GW sources and the magnitude of the confusion-noise foreground, in the case of two GW interferometers with armlengths of 1 and 5 Mkm. We confirm earlier estimates of thousands of detached-binary detections, but project only a few ten to a few hundred detections of interacting systems. We also confirm estimates for the confusion-noise foreground (except in one scenario that explains smaller local densities of interacting systems with fewer progenitor detached systems). Last, we provide a general scaling argument that shows that the magnitude of the GW foreground can be derived robustly from the merger rate of Galactic WD binaries, and depends only weakly on the structure of the Galaxy.

View original: http://arxiv.org/abs/1201.4613