A New Analytical Fourier-Transformation Model for X-ray Time Lags in AGN




Baughman, David

Journal Title

Journal ISSN

Volume Title



The variability of the X-ray emission from black holes is often characterized in terms of the time lags observed between the soft and hard energy bands in the detector. The time lags are usually computed using the complex cross spectrum, which is based on the Fourier transform of the data in the two energy bands. For over a decade, it has been noted that some active galactic nuclei display soft Fourier X-ray time lags, in addition to the more ubiquitous hard lags. In the case of a soft lag, the X-rays in the low-energy channel are received after the corresponding signal is detected in the hard channel. The physical origin of the soft lags is a topic of ongoing research and discussion. In this dissertation I explore the possibility that the soft X-ray time lags result from the thermal and bulk Comptoniza- tion of photons injected into the relatively hot, quasi-spherical coronal region surrounding the cooler accretion disk near the central black hole. I develop a time-dependent analyt- ical model for this process based on a Fourier-transformed radiation transport equation, and demonstrate that the model successfully reproduces both the hard and soft time lags observed in the narrow-line Seyfert 1 galaxy 1H0707-495, based on a unified physical mech- anism operating in a single region. I then develop the quiescent solution and test whether a coronal photonic source is able to generate components of the observed X-ray spectrum.



Physics, Accretion disks, Black holes, Time lags, X-rays