Mikhail E. Gusakov, Andrey I. Chugunov, Elena M. Kantor
We introduce a new scenario that explains the existence of rapidly rotating warm neutron stars (NSs) observed in low-mass X-ray binaries (LMXBs). The scenario takes into account the interaction between the normal (quadrupole) m=2 r-mode and superfluid inertial modes. This interaction can only occur at some fixed `resonance' stellar temperatures; it leads to formation of the `stability peaks' that stabilize a star in the vicinity of these temperatures. We demonstrate that an NS in LMXB spends a substantial fraction of time on the stability peak, that is in the region of stellar temperatures and spin frequencies, that has been previously thought to be unstable with respect to excitation of r-modes. We also find that the spin frequencies of NSs are limited by the instability of normal (octupole) m=3 r-mode rather than by m=2 r-mode. This result agrees with the predicted value of the cut-off spin frequency ~730 Hz, following from the statistical analysis of the accreting millisecond X-ray pulsars. A comparison of the proposed theory with observations of rotating NSs can impose new important constraints on the properties of superdense matter.
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http://arxiv.org/abs/1305.3825
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