Timing an Accreting Millisecond Pulsar: Measuring the Accretion Torque   in IGR J00291+5934
  We performed a timing analysis of the fastest accreting millisecond pulsar IGR J00291+5934 using RXTE data taken during the outburst of December 2004. We corrected the arrival times of all the events for the orbital (Doppler) effects and performed a timing analysis of the resulting phase delays. In this way we have the possibility to study, for the first time in this class of sources, the spin-up of a millisecond pulsar as a consequence of accretion torques during the X-ray outburst. The accretion torque gives us for the first time an independent estimate of the mass accretion rate onto the neutron star, which can be compared with the observed X-ray luminosity. We also report a revised value of the spin period of the pulsar. 
L. Burderi, T. Di Salvo, G. Lavagetto, M.T. Menna, A. Papitto, A.   Riggio, R. Iaria, F. D'antona, N. R. Robba, L. Stella