A soft X-ray study of type I active galactic nuclei observed with Chandra high-energy transmission grating spectrometer

Abstract

We present the results of a uniform analysis of the soft X-ray spectra of\nfifteen type I AGN observed with the high resolution X-ray gratings on board\n\\emph{Chandra}. We found that ten of the fifteen AGN exhibit signatures of an\nintrinsic ionized absorber. The absorbers are photoionized and outflowing, with\nvelocities in the range $\\sim 10^{1}-10^{3}$ km $\\rm{s}^{-1}$. The column\ndensity of the warm absorbing gas is $\\sim 10^{20-23} \\rm{cm}^{-2}$. Nine of\nthe ten AGN exhibiting warm absorption are best--fit by multiple ionization\ncomponents and three of the ten AGN \\emph{require} multiple kinematic\ncomponents. The warm absorbing gas in our AGN sample has a wide range of\nionization parameter, spanning roughly four orders of magnitude ($\\xi \\sim\n10^{0-4}$ ergs cm $\\rm{s}^{-1}$) in total, and often spanning three orders of\nmagnitude in the same gas. Warm absorber components with ionization parameter\n$\\xi<10$ generate an unresolved transition array due to Fe in seven of the ten\nAGN exhibiting warm absorption. These low ionization state absorbers may also\ncarry away the largest mass outflows from the AGN. The mass outflow rate\ndepends critically on the volume filling factor of the gas, which cannot yet be\ndirectly measured. However, upper limits on the mass outflow ratesfor filling\nfactors of unity can be much greater than the expected accretion rate onto the\ncentral supermassive black hole and filling factors as small as 1% can give\noutflow rates comparable to the accretion rate. There appears to be a gap in\nthe outflow velocities in our sample between $\\sim 300-500$ km $\\rm{s}^{-1}$,\nthe origin of which is not clear. The outflow components with velocities below\nthis gap tend to be associated with lower column densities than those with\nvelocities above the gap.\n