PAPITTO, ALESSANDROALESSANDROPAPITTO2020-05-142020-05-1420160037-8720http://hdl.handle.net/20.500.12386/24829The 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.ELETTRONICOenArticlehttp://sait.oat.ts.astro.it/MSAIt870416/index.html2016MmSAI..87..543PFIS/05 - ASTRONOMIA E ASTROFISICA