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

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