Ionic absorption and emission features in X-ray spectra of active galactic nuclei

I present a comprehensive study of ionic absorption and emission features observed in high-resolution X-ray spectra of active galactic nuclei (AGN). AGN are galaxies that harbor a central, actively-accreting supermassive black hole. Through accretion, gravitational energy is converted into radiation, spread roughly equally (in logarithmic intervals) over the entire electromagnetic spectrum. A simple model of a cone of material irradiated by a variable, featureless power-law spectrum produced at the nucleus plus an additional constant, hard component due to reflection in distant Compton-thick material is sufficient to fit the X-ray spectra of several different AGN. Depending on the orientation of the cone to the observer, the spectrum appears either as ionic absorption of the power law (for lines of sight directly down the cone to the nucleus) or as reprocessed emission in the irradiated material (for lines of sight transverse to the cone and for which the nucleus is highly obscured by some other medium). The hard reflection component is observed in both orientations. A broad density distribution (over several orders of magnitude) at each position in the ionic absorber is also observed. For observations down the cone to the nucleus, I argue that the observed broad spectral features are more likely artifacts of absorption of the featureless power-law spectrum plus some contribution from the constant reflection component rather than relativistically-broadened emission lines arising from the inner regions of an accretion disk. In our model, all discrete and continuous ionic absorption and emission features are based on atomic data calculated using the Flexible Atomic Code (FAC).