A soft X-ray study of Type I AGN observed with Chandra HETGS

Abstract

We present the results of a uniform analysis of the soft X-ray spectra of fifteen type I AGN observed with the high resolution X-ray gratings on board \emph{Chandra}. We found that ten of the fifteen AGN exhibit signatures of an intrinsic ionized absorber. The absorbers are photoionized and outflowing, with velocities in the range $\sim 10^{1}-10^{3}$ km $\rm{s}^{-1}$. The column density of the warm absorbing gas is $\sim 10^{20-23} \rm{cm}^{-2}$. Nine of the ten AGN exhibiting warm absorption are best--fit by multiple ionization components and three of the ten AGN \emph{require} multiple kinematic components. The warm absorbing gas in our AGN sample has a wide range of ionization parameter, spanning roughly four orders of magnitude ($\xi \sim 10^{0-4}$ ergs cm $\rm{s}^{-1}$) in total, and often spanning three orders of magnitude in the same gas. Warm absorber components with ionization parameter $\xi<10$ generate an unresolved transition array due to Fe in seven of the ten AGN exhibiting warm absorption. These low ionization state absorbers may also carry away the largest mass outflows from the AGN. The mass outflow rate depends critically on the volume filling factor of the gas, which cannot yet be directly measured. However, upper limits on the mass outflow ratesfor filling factors of unity can be much greater than the expected accretion rate onto the central supermassive black hole and filling factors as small as 1% can give outflow rates comparable to the accretion rate. There appears to be a gap in the outflow velocities in our sample between $\sim 300-500$ km $\rm{s}^{-1}$, the origin of which is not clear. The outflow components with velocities below this gap tend to be associated with lower column densities than those with velocities above the gap.