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We review recent results from the X-ray timing of accreting millisecond pulsars in LMXBs. This is the first time a timing analysis is performed on accreting millisecond pulsars, and for the first time we can obtain information on the behavior of a very fast pulsar subject to accretion torques. We find both spin-up and spin-down behaviors, from which, using available models for the accretion torques, we derive information on the mass accretion rate and magnetic field of the neutron star in these systems. We also find that the phase delays behavior as a function of time in these sources is sometimes quite complex and difficult to interpret, since phase shifts, most probably driven by variations of the X-ray flux, are sometimes present. [ABSTRACT FROM AUTHOR]

We report here on the orbital evolution of the accreting millisecond pulsar SAXJ1808.4–3658. In particular, we find for this source the first estimate of the orbital period derivative in an accreting millisecond pulsar, Porb=(3.40±0.12)×10-12s/s, and a refined estimate of the orbital period, Porb = 7249.156499±(1.2×10-5)s. This derivative is positive and is more than one order of magnitude higher than what is expected from secular evolution driven by angular momentum losses caused by gravitational radiation under the hypothesis of conservative mass transfer. In the hypothesis that the measured derivative of the orbital period reflects the secular evolution of the system, we propose a simple explanation of this puzzling result assuming that during X-ray quiescence the source is ejecting matter (and angular momentum) from the inner Lagrangian point. The proposed orbital evolution of the system suggests a degenerate or fully convective companion star and indicates that this kind of sources are capable to efficiently ablate the companion star, and therefore are black widows visible in X-rays during transient mass accretion episodes. [ABSTRACT FROM AUTHOR]

We review recent results from the X-ray timing of accreting millisecond pulsars in LMXBs. This is the first time a timing analysis is performed on accreting millisecond pulsars, and for the first time we can obtain information on the behavior of a very fast pulsar subject to accretion torques. We find both spin-up and spin-down behaviors, from which, using available models for the accretion torques, we derive information on the mass accretion rate and magnetic field of the neutron star in these systems. We also find that the phase delays behavior as a function of time in these sources is sometimes quite complex and difficult to interpret, since phase shifts, most probably driven by variations of the X-ray flux, are sometimes present. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]