Timing the accretion flow around accreting millisecond pulsars

TL;DR

This paper investigates the timing and variability of accreting millisecond pulsars, revealing new quasi-periodic oscillations, broadband noise characteristics, and spectral states, enhancing understanding of their accretion processes.

Contribution

It presents the first detection of simultaneous kHz QPOs in XTE J1807-294 and characterizes variability in multiple pulsars, including spectral state classification and fluence estimates.

Findings

Detection of simultaneous kHz QPOs in XTE J1807-294

Identification of broadband noise at low frequencies in IGR J00291+5934

Classification of SWIFT J1756.9-2508 as an atoll source

Abstract

At present, ten years after they were first discovered, ten accreting millisecond pulsars are known. I present a study of the aperiodic X-ray variability in three of these systems, which led to the discovery of simultaneous kHz quasi periodic oscillations in XTE J1807-294 and extremely strong broadband noise at unusually low variability frequencies in IGR J00291+5934. Furthermore, we classified SWIFT J1756.9-2508 as an atoll source and measured in its 2007 outburst spectral and variability properties typical of the extreme island state. I also give detailed estimates of the total fluence during the studied outbursts.