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M Thunyapong Mahapol - "A Theoretical Fourier-Transformation Model for the Formation of X-ray Time Lags from Black Hole Accretion Disks"
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| Abstract: The complex and rapidly varying X-ray emission from active galactic nuclei (AGNs) may provide insights to the thermal and dynamical structure of the central black hole accretion disk. To analyze the observed variability, X-ray time lags which are the temporal delays between Fourier transforms of light curves in hard and soft X-ray energy channels can be used. These time lags may be either hard lags or soft lags, depending on whether the variability in the hard energy channel follows that in the soft channel or vice versa. The source for the observed X-ray time lags from AGNs has been a subject of debate. In this study, we investigate the scenario where the X-ray time lags are generated by thermal and bulk Comptonization, as well as spatial reverberation of iron L-line and K-line seed photons, which are produced via fluorescence due to local instability. We model the inner region of the accretion flow as a hot, geometrically thick ADAF disc, with the outer radius equal to the shock formation radius located just outside the centrifugal barrier. Using a Fourier-transformed, vertically-averaged transport equation in cylindrical coordinates, we analyze the time-dependent radiative transfer in the inner ADAF region and simulate the X-ray time lag data. We then compare the simulated time lags to the observed time lags for model fitting. Our new model successfully reproduces the complex X-ray variability data for the Seyfert 1 galaxies 1H 0707-495 and Ark 564. |
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