Observational signatures of neutron stars in low-mass X-ray binaries climbing a stability peak

Abstract

In the recent papers by Gusakov, Chugunov, and Kantor (2014) a new scenario describing evolution of rapidly rotating neutron stars in low-mass X-ray binaries was proposed. The scenario accounts for a resonant interaction of normal r modes with superfluid inertial modes at some specific internal stellar temperatures ("resonance temperatures"). This interaction results in an enhanced damping of r mode and appearance of the "stability peaks" in the temperature -- spin frequency plane, which split the r-mode instability window in the vicinity of the resonance temperatures. The scenario suggests that the hot and rapidly rotating NSs spend most of their life climbing up these peaks and, in particular, are observed there at the moment. We analyze in detail possible observational signatures of this suggestion. In particular, we show that these objects may exhibit `anti-glitches' -- sudden frequency jumps on a time scale of hours-months.