IONIZED ABSORBERS, IONIZED EMITTERS, AND THE X-RAY-SPECTRUM OF ACTIVEGALACTIC NUCLEI

Broad absorption features are common in the X-ray spectrum of low-lumi nosity AGNs. The features have been modeled by leaky neutral absorbers or by highly ionized gas that completely occult the continuum source. Such models are incomplete since they do not take into account all th e physical processes in the gas. In particular, no previous model incl uded the X-ray emission by the ionized absorbing gas and the reflectio n of the continuum source radiation. The present work discusses the em ission, absorption, and reflection properties of photoionized gases wi th emphasis on conditions thought to prevail in AGNs. It shows that su ch gas is likely to produce intense X-ray line and continuum radiation and to reflect a sizable fraction of the nonstellar continuum at all energies. If such gas is indeed responsible for the observed X-ray abs orption, then absorption edges are much weaker than commonly assumed, and some residual X-ray continuum is likely to be observed even if the line of sight is completely blocked. Moreover, X-ray emission feature s may show up in sources not showing X-ray absorption. This has immens e consequences for medium-resolution X-ray missions, such as BBXRT and Astro-D, and for the planned high-resolution experiments on board XMM and AXAF.