Long-term Coherent Timing of the Accreting Millisecond Pulsar IGR J17062–6143

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 time span 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 ± 0.09) × 10−15 Hz s−1. 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 ± 40 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 yr, yielding an orbital period-derivative measurement of (8.4 ± 2.0) × 10−12 s s−1. This large orbital period derivative is inconsistent with a binary evolution that is dominated by gravitational wave emission and is suggestive of highly nonconservative mass transfer in the binary system.

The stochastic X-ray variability of the accreting millisecond pulsar IGR J17062-6143

“…Note that the data grouping used here is slightly different from the one used in Bult et al (2021a). In particular, where they treat the observations in 2018 November and October separately, these data are grouped together into a single epoch here (epoch 2).…”

“…The time-averaged spectrum of IGR J17062 is welldescribed as an absorbed blackbody and power law, with an additional Gaussian emission line centered at 1 keV (Degenaar et al 2017;van den Eijnden et al 2018;Bult et al 2021a). Adopting the Tübingen-Boulder model for the interstellar absorption (Wilms et al 2000), the analogous spectrum for the complex covariance can be expressed as 2 https://github.com/peterbult/cov-models tbabs × (complex×gauss…”

“…The X-ray transient IGR J17062-6143 (simply IGR J17062 henceforth) is an especially interesting system for testing our understanding of accretion onto a weakly magnetized neutron star. The source was first discovered in Jan/Feb of 2007 (Churazov et al 2007) and has since remained visible at a comparatively low luminosity of L X ≈ 5 × 10 35 erg s −1 (Degenaar et al 2017;van den Eijnden et al 2018;Bult et al 2021a). During this unusually long outburst, IGR J17062 has shown three energetic intermediate duration type I Xray bursts (Degenaar et al 2013;Negoro et al 2015;Nishida et al 2020), but has otherwise remained remarkably stable.…”

“…During this unusually long outburst, IGR J17062 has shown three energetic intermediate duration type I Xray bursts (Degenaar et al 2013;Negoro et al 2015;Nishida et al 2020), but has otherwise remained remarkably stable. Previous studies have investigated its type I X-ray bursts and their interactions with the accretion environment (Degenaar et al 2013;Keek et al 2017;Bult et al 2021b), the X-ray spectroscopy (Degenaar et al 2017;van den Eijnden et al 2018), the optical emission (Hernández Santisteban et al 2019), and the pulsar properties and accretion torques (Strohmayer et al 2018;Bult et al 2021a). One aspect of this source that has so far not yet been covered, is its aperiodic variability.…”

“…Since then, NICER has returned to this target at various times, accumulating a total of 372 ks in unfiltered exposure by 2020 August. These data are available under the NICER program IDs 103410, 260101, 203410, 303410 and 361201, and were presented previously in the pulsar timing study of Bult et al (2021a). Following the data cleaning procedures described by these authors, the data were filtered using nicerdas v7a with standard screening criteria, except for relaxed constraints on the rate of reset triggers (< 400 ct s −1 det −1 ) and on the rate of high energy events (< 1.5 ct s −1 det −1 and < 2.0 × cor sax −0.633 ) 1 .…”