Joint Astrophysical Colloquium
Transitional millisecond pulsars
Alessandro Papitto ((INAF - Osservatorio Astronomico di Roma))
Thursday 21/06/2018 @ 11:30, Sala IV piano Battiferro
Millisecond pulsars are the quickest spinning compact objects known and hence the best probes to measure the state of ultradense matter and test the theory of General Relativity. They attain their very fast rotation during a Gyr-long phase of accretion of matter from a low mass companion star, which drives a bright X-ray emission. When the mass transfer stops magnetospheric pulsed emission powered by the star rotation - and observed preferentially in the radio and gamma-ray bands - sets in. This complex evolution has been recently demonstrated by the discovery of transitional millisecond pulsars (Papitto et al. 2013, Nature) that swing between an accretion powered X-ray pulsar regime and a rotationally-powered radio pulsar state on a time scale of a few weeks, or even shorter. These pulsars show an incredibly rich phenomenology that reflects all the possible outcomes of the interaction between the pulsar wind of particles and radiation and matter in an accretion disk. This has been confirmed by the discovery of optical pulsations from a transitional pulsar (Ambrosino, Papitto et al., 2017, Nature Astronomy), the first ever from a millisecond spinning neutron star. The pulsations were observed by using the fast photometer SiFAP at the INAF Galileo Telescope. Optical pulses were detected when the pulsar was surrounded by an accretion disk, but they are most likely originated by a rotation-powered magnetospheric process. The profound implications for our understanding of the pulsar disk/magnetosphere interaction will be discussed.