Timing and Spectral Analyses of mHz Quasi-periodic Oscillations in 4U 1636-536 Using Hilbert-Huang Transform
Hung-En Hsieh1*, Yi Chou1, Yi-Hao Su1, Fang-Ming Gu1
1Graduate Institute of Astronomy, National Central University, Taoyuan, Taiwan
* Presenter:Hung-En Hsieh
We present the timing properties and the phase-resolved analysis of the spectra, based on Hilbert-Huang Transform (HHT), for millihertz quasi-periodic oscillation (mHz QPOs) in the low-mass X-ray binary 4U 1636-536 detected by a XMM-Newton observation. This ~8 mHz QPO, interpreted as marginally stable nuclear burning on the surface of neutron star, can be clearly seen at the beginning of the observation until the appearance of a type-I X-ray burst. We used the HHT to characterize the timing properties, extract the QPOs instantaneous phases, and construct its phase-resolved spectra. The HHT-based timing properties are consistent with previously reported results but with more details. On the other hand, our phase-resolved spectral analysis is able to give a complete variation of spectral parameters for the whole cycle, which could not be achieved in previous studies. We found that the variation of temperature is uncorrelated with luminosity modulation. More analyses of the XMM-Newton observations for this mHz QPOs in the 4U 1636-536 are still in processing.

Keywords: low-mass X-ray binary, mHz QPOs, Hilbert-Huang Transform