Order in the chaos? The strange case of accreting millisecond pulsars

TL;DR

This paper reviews X-ray timing of accreting millisecond pulsars, revealing complex spin behaviors and providing insights into their accretion processes and magnetic fields, marking a novel analysis in this area.

Contribution

First timing analysis of accreting millisecond pulsars, offering new insights into their spin dynamics and accretion mechanisms.

Findings

Detection of both spin-up and spin-down behaviors

Complex phase delay patterns linked to X-ray flux variations

Estimation of neutron star magnetic fields and accretion rates

Abstract

We review recent results from the X-ray timing of accreting millisecond pulsars in Low Mass X-ray Binaries. 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.