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

TL;DR

This study analyzes the stochastic X-ray variability of the accreting millisecond pulsar IGR J17062-6143, revealing stable noise features, occasional QPOs, and energy-dependent variability linked to a variable Compton-scattering corona and disk reflection.

Contribution

It provides the first detailed spectral and timing analysis of IGR J17062-6143's X-ray variability, highlighting the role of a variable corona and reflection in the observed phenomena.

Findings

Stable broad band-limited noise below 16 Hz

Detection of low-frequency and high-frequency QPOs

Energy-dependent variability linked to corona and disk reflection

Abstract

This work presents an investigation of the stochastic X-ray variability from the 164 Hz accreting millisecond pulsar IGR J17062-6143, based on regular observations collected with the Neutron Star Interior Composition Explorer between 2017 July and 2020 August. Over this period, the power density spectrum showed a stable morphology, with broad $\sim25\%$ rms band-limited noise below 16 Hz. Quasi-periodic oscillations (QPOs) were occasionally observed, with the most notably detections including a low-frequency QPO centered at 2.7 Hz and a sharp QPO centered at 115 Hz that may be a 2:3 resonance with the spin frequency. Further, the energy dependence of the band-limited noise is studied through a spectroscopic analysis of the complex covariance in two frequency intervals. It is found that the power law continuum is the primary driver for the observed variability, although the thermal (blackbody) emission also appears to be intrinsically variable in area ($5\%$ rms) and temperature ($1\%$ rms). Notably, the 1 keV emission feature seen in all X-ray spectra of IGR J17062-6143 varies with the same amplitude as the power law, but systematically lags behind that continuum emission. These results appear consistent with a scenario in which a time variable Compton-scattering corona is the primary source for the observed stochastic variability, with the variability observed in the emission feature and at the lowest photon energies being due to the disk reflection of the power law continuum.