The ms pulsar - low mass X-ray binary link

Abstract

The recent discovery of a binary millisecond pulsar in the globular cluster M28 that switched between an X-ray pulsar and a radio pulsar state demonstrated the tight link shared by millisecond pulsars and their accreting low-mass X-ray binary progenitors. This pulsar is the prototype of a new class of transitional systems that alternate between accretion and rotation-powered states in response to variations of the rate of mass in-flow, on time scales possibly shorter than a couple of weeks. Observations of this and other similar systems indicate that transitions to the accretion phase not only involve bright X-ray outbursts, but also an X-ray sub-luminous accretion disk state, possibly characterized by centrifugal inhibition of the matter in-flow. The main observed properties of the known transitional ms pulsars, as well as the prospects of finding more sources of this newly established class, are summarized here.