Classifying AGN by X-ray Hardness Variability
  The physics behind the dramatic and unpredictable X-ray variability of Active
Galactic Nuclei (AGN) has eluded astronomers since it was discovered. We
present an analysis of Swift XRT observations of 44 AGN with at least 20 Swift
observations. We define HR-slope as the change of Hardness Ratio (HR) with
luminosity ($L$). This slope is measured for all objects in order to: 1.
Classify different AGN according to their HR-HR-slope relation and 2. compare
HR-$L/L_\mathrm{Edd}$ trends with those observed in X-ray binaries for the 27
AGN with well measured black hole masses. We compare results using a
count-based HR definition and an energy-based HR definition. We observe a clear
dichotomy between Seyferts and radio loud galaxies when considering count-based
HR, which disappears when considering energy based HR. This, along with the
fact no correlation is observed between HR parameters and radio loudness,
implies radio loud and radio quiet AGN should not be discriminated by their HR
behavior. We provide schematic physical models to explain the observed
transition between energy defined HR states. We find Seyferts populate the
high, hard, phase of the HR-$L/L_\mathrm{Edd}$ diagram as well as do three
radio loud objects. Two LINERs populate the low, soft, phase part of this
diagram. Finally, radio loud objects are concentrated around small positive
HR-slopes, while Seyferts track the HR phase diagram which may provide clues to
the geometry of the corona.
