Studies of quasi-periodic oscillations in the black hole transient XTE J1817–330

We have used archival Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data to investigate the timing and spectral characteristics of the transient XTE J 1817-330. The data pertain to 160 PCA pointed observations made during the outburst period 2006 January 27 to August 2. A detailed analysis of quasi-periodic oscillations (QPOs) in this black hole X-ray binary is carried out. Power density spectra were obtained using the light curves of the source. QPOs have been detected in the 2-8 keV band in 10 of the observations. In eight of these observations, QPOs are present in the 8-14 keV and in five observations in the 15-25 keV band. XTE J1817-330 is the third black hole source from which low-frequency QPOs are clearly detected in hard X-rays. The QPO frequency lies in ≈4-9 Hz and the rms amplitude in the 1.7-13.3 per cent range, the amplitude being higher at higher energies. We have fitted the power density spectra of the observations with Lorentzian and power-law models. Energy spectra are derived for those observations in which the QPOs are detected, in order to investigate any dependence of the QPO characteristic on the spectral parameters. These spectra are well fitted with a two-component model, which includes the disc blackbody component and a power-law component. The QPO characteristics and their variations are discussed and the implications on the origin of QPOs are examined.