On why the iron K-shell absorption in AGN is not a signature of the local warm/hot intergalactic medium

We present a comparison between the 2001 XMM-Newton and 2005 Suzaku observations of the quasar, PG1211+143, at z = 0.0809. Variability is observed in the 7 keV iron K-shell absorption line (at 7.6 keV in the quasar frame), which is significantly weaker in 2005 than during the 2001 XMM-Newton observation. From a recombination time-scale of <4 yr, this implies an absorber density n > 4 × 10³cm^-3, while the absorber column is 5 × 10²² < N_H < 1 × 10²⁴cm^-2. Thus, the size scale of the absorber is too compact (pc scale) and the surface brightness of the dense gas too high (by 9-10 orders of magnitude) to arise from local hot gas, such as the local bubble, group or warm/hot intergalactic medium (WHIM), as suggested by McKernan, Yaqoob & Reynolds. Instead, the iron K-shell absorption must be associated with an active galactic nucleus (AGN) outflow with mildly relativistic velocities. Finally, we show that the association of the absorption in PG1211+143 with local hot gas is simply a coincidence, and the comparison between the recession and iron K absorber outflow velocities in other AGN does not reveal a one-to-one kinematic correlation.