X-ray Spectroscopy and Variability of AGN Detected in the 2 Ms Chandra Deep Field-North Survey

Abstract

We investigate the nature of the faint X-ray source population through X-ray spectroscopy and variability analyses of 136 AGN detected in the 2 Ms Chandra Deep Field-North survey with > 200 background-subtracted 0.5-8.0 keV counts [F(0.5-8.0 keV)=(1.4-200)e-15 erg cm^{-2} s^{-1}]. Our preliminary spectral analyses yield median spectral parameters of Gamma=1.61 and intrinsic N_H=6.2e21 cm^{-2} (z=1 assumed when no redshift available) when the AGN spectra are fitted with a simple absorbed power-law model. However, considerable spectral complexity is apparent (e.g., reflection, partial covering) and must be taken into account to model the data accurately. Moreover, the choice of spectral model (i.e., free vs. fixed photon index) has a pronounced effect on the derived N_H distribution and, to a lesser extent, the X-ray luminosity distribution. Ten of the 136 AGN (~7%) show significant Fe Kalpha emission-line features with equivalent widths in the range 0.1-1.3 keV. Two of these emission-line AGN could potentially be Compton thick (i.e., Gamma < 1.0 and large Fe Kalpha equivalent width). Finally, we find that 81 (~60%) of the 136 AGN show signs of variability, and that this fraction increases significantly (~80-90%) when better photon statistics are available.