Explaining observations of rapidly rotating neutron stars in LMXBs

by Elena Kantor (I.O.F.F.E. Institute, St. Petersburg, Russia)

Thursday 5 Dec 2013, 16:00 → 17:00 Europe/Rome

Aula Conversi (Dip. di Fisica - Edificio G. Marconi)

We consider an instability of rapidly rotating neutron stars in low-mass X-ray binaries (LMXBs) with respect to excitation of r-modes (which are analogous to Earth's Rossby waves controlled by the Coriolis force). We argue that finite temperature effects in the superfluid core of a neutron star lead to a resonance coupling and enhanced damping (and hence stability) of oscillation modes at certain stellar temperatures. We demonstrate that neutron stars with high spin frequency spend a substantial amount of time at these `resonance' temperatures. This finding ! allows us to explain puzzling observations of hot rapidly rotating neutron stars in LMXBs and to impose a new theoretical limit on the neutron star spin frequency, explaining the cut-off spin frequency ~730 Hz, following from the statistical analysis of accreting millisecond X-ray pulsars. Besides explaining the observations, our model provides a new tool to constrain superdense matter properties comparing measured and theoretically predicted resonance temperatures.