ChandraandFar Ultraviolet Spectroscopic ExplorerObservations ofz∼ 0 Warm–Hot Gas toward PKS 2155−304

The X-ray bright z=0.116 quasar PKS 2155-304 is frequently observed as aChandra calibration source, with a total of 483 ksec of Low Energy TransmissionGrating (LETG) exposure time accumulated through May 2006. Highly-ionized metalabsorption lines, including numerous lines at z=0 and a putative OVIII K-alphaline at z=0.055, have been reported in past Chandra studies of this source.Using all available Chandra LETG spectra and analysis techniques developed forsuch z=0 X-ray absorption along other sightlines, we revisit these previousdetections. We detect 4 absorption lines at >3\sigma significance (OVIIK-alpha/beta, OVIII K-alpha, and NeIX K-alpha), with OVII K-alpha being a7.3\sigma detection. The 1\sigma ranges of z=0 OVII column density and Dopplerparameter are consistent with those derived for Mrk 421 and within 2\sigma ofthe Mrk 279 absorption. Temperatures and densities inferred from the relativeOVII and other ionic column densities are found to be consistent with eitherthe local warm-hot intergalactic medium or a Galactic corona. Unlike the localX-ray absorbers seen in other sightlines, a link with the low- or high-velocityfar-ultraviolet OVI absorption lines cannot be ruled out. The z=0.055 OVIIIabsorption reported by Fang et al. is seen with 3.5\sigma confidence in theACIS/LETG spectrum, but no other absorption lines are found at the sameredshift.Comment: 11 pages, 9 figures; minor changes, accepted to Ap