Timing Studies on X-Per and Discovery of its Transient QPO Feature

TL;DR

This study analyzes timing data of X Per from 1998 to 2010, revealing accretion mechanisms, a transient QPO feature, and multiple accretion flow components through power spectral analysis.

Contribution

It provides the first detection of a transient QPO at 0.2 Hz and models the source's power spectra with double break models indicating multiple accretion flows.

Findings

Detection of a transient QPO at ~0.2 Hz.

Power spectra fit by double break models.

Frequency derivative power spectrum index of ~-1.

Abstract

We present timing analysis of {\emph{RXTE}}-PCA and {\emph{INTEGRAL}}-ISGRI observations of X Per between 1998 and 2010. All pulse arrival times obtained from the {\emph{RXTE}}-PCA observations are phase connected and a timing solution is obtained using these arrival times. We update the long-term pulse frequency history of the source by measuring its pulse frequencies using {\emph{RXTE}}-PCA and {\emph{INTEGRAL}}-ISGRI data. From the {\emph{RXTE}}-PCA data, the relation between frequency derivative and X-ray flux suggests accretion via the companion's stellar wind. On the other hand, detection of the transient QPO feature peaking at $\sim 0.2$ Hz suggests the existence of an accretion disc. We find that double break models fit the average power spectra well, which suggests that the source has at least two different accretion flow components dominating the overall flow. From the power spectrum of frequency derivatives, we measure a power law index of $\sim -1$ which implies that on short time scales disc accretion dominates over noise, while on time scales longer than the viscous time scales the noise dominates. From pulse profiles, we find a correlation between pulse fraction and count rate of the source.