Ultracompact binary pulsars as continuous dual-line gravitational wave sources
Chen, Wencong
Binary millisecond pulsars (MSPs) are detached systems consisting of a MSP and a He white dwarf. If the initial orbital periods of binary MSPs are shorter than 0.3 day, they would evolve toward ultracompact binary pulsars due to the rapid orbital shrinkage by the gravitational wave (GW) radiation. During the orbital decay, the MSP with an ellipticity would spin down due to GW radiation and magnetic dipole radiation. Our calculations indicate that the angular momentum loss is dominated by the GW radiation when the ellipticities of the neutron stars (NSs) are in the range of 1-50\times10-7,and the frequencies of high-frequency GW signals from the rotating NSs are 10-100 Hz when the binarypulsars can be visible as low-frequency GW sources. These high-frequency GW signals are possible to be detected by aLIGO and the third-generation GW detectors such as Einstein Telescope, depending on the frequencies and the distances. Therefore, ultracompact binary pulsars have an opportunity to become intriguing dual-line GW sources. By detecting low-frequency GW signals, the NS mass can be accurately derived. A dual-line detection of two band GW signals could provide a constraint on the moment of inertia and the ellipticity of the NS. Thus dual-line GWsources can be potentially applied to constrain the equation of state of NSs.