Measuring the spin up of the accreting millisecond pulsar XTE J1751–305
ABSTRACT
We perform a timing analysis on RXTE data of the accreting millisecond pulsar XTE J1751−305 observed during the 2002 April outburst. After having corrected for Doppler effects on the pulse phases due to the orbital motion of the source, we performed a timing analysis on the phase delays, which gives, for the first time for this source, an estimate of the average spin frequency derivative 
. We discuss the torque resulting from the spin-up of the neutron star deriving a dynamical estimate of the mass accretion rate and comparing it with the one obtained from X-ray flux. Constraints on the distance to the source are discussed, leading to a lower limit of ∼ 6.7 kpc.
