Poster Presentation
On the Evolution and Spectral Variation of QPO in RE J1034+396
RE J1034+396, a narrow-line Seyfert-1 active galactic nucleus (AGN), is the first example of AGN that shows an almost coherent Quasi-Periodic Oscillation (QPO) in X-ray observation. The spectral behaviors and the timing properties of the QPO were further studied since its discovery. We present our analysis of the QPO in RE J1034+396 based on the Hilbert-Huang transform (HHT). Since the HHT is optimize for the non-stationary and non-linear time series, the QPO is suitable for being analyzed by the HHT. We applied the HHT on the data collected by XMM-Newton in 2007. In contrast to other time-frequency analysis methods, the Hilbert spectrum gives us more detailed information in both time and frequency domains. Furthermore, the empirical mode decomposition provides us local band-pass filtered data that can be used in the O−C and correlation analysis. We suggested that the QPO is better to be divided into three epochs according to their different periodicities. Although the QPO cycle lengths vary dramatically even between neighboring cycles, they oscillate around a characteristic period in a specific epoch. From the phase-lag analysis, no significant phase-lags were detected between soft and hard energy bands. Finally, we applied the QPO phase-resolved analysis on the spectral behavior. During one QPO cycle, none of the spectral parameters but the normalizations exhibit significant variation. From the calculated model fluxes, we obtained that the fractional amplitude of the low-temperature Comptonized component is much smaller than that of the hard power law tail but the absolute amplitudes is quite opposite.
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