Millisecond

Abstract: Ordinary radio pulsars1 are neutron stars with magnetic fields of ∼1012 gauss and spin periods in the range 0.1 to 3 seconds. In contrast, millisecond radio pulsars2 have much weaker fields (∼109 gauss) and faster, millisecond spin rates. For both types of pulsar, the energy driving the radio pulsations is thought to be derived from the rotation of the neutron star. The star gradually ‘spins down’ as energy is radiated away. Millisecond radio pulsars are often located in binary systems3. In a widely accepted theoretical model4,5, they started as ordinary pulsars which lost most of their magnetic field and were ‘spun up’ to millisecond periods by the accretion of matter from a companion star in an X-ray binary system. Evidence6,7,8,9,10,11 for this model has gradually mounted, but direct proof—in the form of the predicted coherent millisecond X-ray pulsations in the persistent flux of an X-ray binary has been lacking, despite many searches12,13,14,15. Here we report the discovery16 of such a pulsar, confirming theoretical expectations. The source will probably become a millisecond radio pulsar when the accretion turns off completely.

Abstract: Radio pulsars with millisecond spin periods are thought to have been spun up by the transfer of matter and angular momentum from a low-mass companion star during an x-ray-emitting phase. The spin periods of the neutron stars in several such low-mass x-ray binary (LMXB) systems have been shown to be in the millisecond regime, but no radio pulsations have been detected. Here we report on detection and follow-up observations of a nearby radio millisecond pulsar (MSP) in a circular binary orbit with an optically identified companion star. Optical observations indicate that an accretion disk was present in this system within the past decade. Our optical data show no evidence that one exists today, suggesting that the radio MSP has turned on after a recent LMXB phase.

Abstract: The first millisecond X-ray variability phenomena from accreting compact objects have recently been discovered with the Rossi X-ray Timing Explorer. Three new phenomena are observed from low-mass X-ray binaries containing low-magnetic-field neutron stars: millisecond pulsations, burst oscillations and kiloHertz quasi-periodic oscillations. Models for these new phenomena involve the neutron star spin, and orbital motion closely around the neutron star and rely explicitly on our understanding of strong gravity and dense matter. I review the observations of these new neutron-star phenomena and possibly related ones in black-hole candidates, and describe the attempts to use them to perform measurements of fundamental physical interest in these systems.

Abstract: We investigate the consequences of a continuously injecting central engine on the gamma-ray burst afterglow emission, focusing more specifically on a highly-magnetized millisecond pulsar engine. For initial pulsar parameters within a certain region of the parameter space, the afterglow lightcurves are predicted to show a distinctive achromatic bump feature, the onset and duration of which range from minutes to months, depending on the pulsar and the fireball parameters. The detection of or upper limits on such features would provide constraints on the burst progenitor and on magnetar-like central engine models. An achromatic bump such as that in GRB 000301C afterglow may be caused by a millisecond pulsar with P0=3.4 millisecond and Bp=2.7e14 Gauss.