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We present new observations on PKS 2155-304 with the Chandra Low EnergyTransmission Grating Spectrometer (LETG), using the Advanced CCD ImagingSpectrometer (ACIS). We confirm the detection of an absorption line plausiblyidentified as OVIII Ly-alpha from the warm-hot intergalactic medium associatedwith a small group of galaxies along the line of sight, as originally reportedby Fang et al. 2002 (here after FANG02). Combining the previous observations inFANG02 and five new, long observations on the same target, we increase thetotal exposure time by a factor of three, and the total counts per resolutionelement by a factor of five. The measured line equivalent width is smaller thanthat observed in FANG02, but still consistent at 90% confidence. We alsoanalyze the XMM-Newton observations on the same target, as well as observationsusing the Chandra LETG and the High Resolution Camera (HRC) combination. Theseobservations have been used to challenge our reported detection. While no lineis seen in either the XMM-Newton and the Chandra LETG+HRC data, we find thatour result is consistent with the upper limits from both data sets. Weattribute the non-detection to (1) higher quality of the Chandra LETG+ACISspectrum, and (2) the rather extended wings of the line spread functions ofboth the XMM RGS and the Chandra LETG+HRC. We discuss the implication of ourobservation on the temperature and density of the absorber. We also confirm thedetection of z ~ 0 OVII absorption and, comparing with previous Chandraanalysis, we obtain much tighter constraints on the line properties.

Confirming the Detection of an Intergalactic X-ray Absorber Toward PKS 2155-304