Timing studies of X Persei and the discovery of its transient quasi-periodic oscillation feature

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Acuner Z., İNAM S. Ç., Sahiner S., Serim M. M., BAYKAL A., Swank J.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, vol.444, no.1, pp.457-465, 2014 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 444 Issue: 1
  • Publication Date: 2014
  • Doi Number: 10.1093/mnras/stu1351
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.457-465
  • Keywords: accretion, accretion discs, stars: neutron, pulsars: individual: X Persei, X-rays: binaries, PROPORTIONAL COUNTER ARRAY, RED POWER SPECTRA, RAY PULSARS, SAX J2103.5+4545, ACCRETION, RXTE, CALIBRATION, EMISSION, ORBIT, X-1
  • Middle East Technical University Affiliated: Yes


We present a timing analysis of X Persei (X Per) using observations made between 1998 and 2010 with the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) and with the INTEGRAL Soft Gamma-Ray Imager (ISGRI). All pulse arrival times obtained from the 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 RXTE-PCA and ISGRI data. From the RXTE-PCA data, the relation between the frequency derivative and X-ray flux suggests accretion via the companion's stellar wind. However, the detection of a transient quasi-periodic oscillation feature, peaking at similar to 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 similar to-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 the pulse fraction and the count rate of the source.