KiloHertz QPO and Gravitational Wave Emission as the Signature of the Rotation and Precession of a LMXB Neutron Star Near Breakup

Abstract

The basic theory of torque free precession (TFP) of the outer crust of a neutron star (NS) as the signature of the approach to NS breakup is a viable explanation of the uniform properties of kHz Quasi-periodic Oscillations (QPO) observed in X-rays emitted by Low Mass X-ray Binary (LMXB) sources. The theory outlined in this paper relates the intrinsic properties of NS structure to the observed kHz frequencies. The range of kHz frequencies and the observed quality factors (Qs) are also explained by this simple dynamical model. A scenario that begins with the melting of the inner crust of an LMXB NS creates the conditions necessary for the generation of kHz QPO. The theory relates the ratio of the observed kHz frequencies to the ratios of the components of the moments of inertia of the NS, thereby tightly constraining the equation of state (EOS) of NS matter (polytrope index ~1.0). The TFP model is in strong contrast to existing models which primarily relate the kHz QPO phenomenon to the physics of gas dynamics near the inner edge of the accretion disk and the transition flow onto the surface of the NS. We suggest the possibility of the direct detection of very low frequency (~1 kHz) radio waves from magnetic dipole radiation and also predict kHz gravitational wave emission from the LMXB Sco X-1 that may be detectable by LIGO. The high accretion rates consistent with the predicted GW emission indicate the likely conversion of some LMXBs to maximally rotating Kerr black holes (BH) and further suggest that these systems are progenitors of some gamma-ray bursts (GRB).