Long-term coherent timing of the accreting millisecond pulsar IGR J17062-6143

TL;DR

This paper presents a four-year coherent timing analysis of the accreting millisecond pulsar IGR J17062-6143, revealing its spin-up, pulse fraction oscillations, and a significant orbital period derivative indicating non-conservative mass transfer.

Contribution

It provides the first phase-coherent timing solution for the pulsar's spin and orbit over multiple years, highlighting unusual orbital evolution.

Findings

Pulsar is spinning up at (3.77±0.09)×10⁻¹⁵ Hz/s.

Pulse fraction varies sinusoidally with a 1210±40 day period.

Orbital period derivative suggests non-conservative mass transfer.

Abstract

We report on a coherent timing analysis of the 163 Hz accreting millisecond X-ray pulsar IGR J17062-6143. Using data collected with the Neutron Star Interior Composition Explorer and XMM-Newton, we investigated the pulsar evolution over a timespan of four years. We obtained a unique phase-coherent timing solution for the stellar spin, finding the source to be spinning up at a rate of $(3.77\pm0.09)\times 10^{-15}$ Hz/s. We further find that the $0.4-6$ keV pulse fraction varies gradually between 0.5% and 2.5% following a sinusoidal oscillation with a $1210\pm40$ day period. Finally, we supplemented this analysis with an archival Rossi X-ray Timing Explorer observation, and obtained a phase coherent model for the binary orbit spanning 12 years, yielding an orbital period derivative measurement of $(8.4\pm2.0) \times 10^{-12}$ s/s. This large orbital period derivative is inconsistent with a binary evolution that is dominated by gravitational wave emission, and is suggestive of highly non-conservative mass transfer in the binary system.