Astronomy Colloquium / Spring 2009

March 25

Prof. Rosalba Perna

University of Colorado at Boulder

"Neutron Star Spins: in lonely life and with companions"

How fast do Neutron Stars (NSs) spin at birth? Radio studies have addressed the issue for decades, often yielding wildly different results. Here I will discuss the results of a new method, based on X-ray observations, which suggest that the majority of NSs are born as slow rotators. While isolated NSs can only spin down, accreting X-ray binaries display a wide range of behaviours. Some of them are observed to spin up steadily, others to alternate between spin-up and spin-down states, sometimes superimposed on a longer trend of either spin up or spin down. I will discuss how this rich phenomenology can be interpreted within a new, simple model of the disk-magnetosphere interaction. This model, based on a purely material torque, does not require external perturbations to induce the torque reversals. I will specifically illustrate the model in the cases of the X-ray binaries GX 1+4 and 4U 1626-67.