XMM-Newton Survey of Local O VII Absorption Lines in the Spectra of
  Active Galactic Nuclei
  Highly ionized, z=0 metal absorption lines detected in the X-ray spectra of
background active galactic nuclei (AGNs) provide an effective method to probe
the hot ($T\sim10^6$ K) gas and its metal content in and around the Milky Way.
We present an all-sky survey of the $K_{\alpha}$ transition of the local O VII
absorption lines obtained by Voigt-profile fitting archival XMM-Newton
observations. A total of 43 AGNs were selected, among which 12 are BL Lac-type
AGNs, and the rest are Seyfert 1 galaxies. At above the $3\sigma$ level the
local O VII absorption lines were detected in 21 AGNs, among which 7 were newly
discovered in this work. The sky covering fraction, defined as the ratio
between the number of detections and the sample size, increases from at about
40% for all targets to 100% for the brightest targets, suggesting a uniform
distribution of the O VII absorbers. We correlate the line equivalent width
with the Galactic coordinates and do not find any strong correlations between
these quantities. Some AGNs have warm absorbers that may complicate the
analysis of the local X-ray absorber since the recession velocity can be
compensated by the outflow velocity, especially for the nearby targets. We
discuss the potential impact of the warm absorbers on our analysis. A
comprehensive theoretical modelling of the X-ray absorbers will be presented in
a later paper.
