Measuring the spin up of the Accreting Millisecond Pulsar XTE J1751-305

TL;DR

This paper presents the first measurement of the spin-up rate of the accreting millisecond pulsar XTE J1751-305 during its 2002 outburst, linking observed timing data to accretion physics and source distance constraints.

Contribution

It provides the first estimate of the neutron star's spin frequency derivative and discusses the implications for accretion torque and source distance.

Findings

Measured spin-up rate: (3.7 +/- 1.0)E-13 Hz/s

Estimated lower limit for source distance: ~6.7 kpc

Derived accretion rate consistent with X-ray flux data

Abstract

We perform a timing analysis on RXTE data of the accreting millisecond pulsar XTE J1751-305 observed during the April 2002 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 <nu_dot> = (3.7 +/- 1.0)E-13 Hz/s. 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 \sim 6.7 kpc.