Abstract
We present XMM-Newton grating spectra of the bright BL Lac object PKS 2155−304 taken in November 2000. Various absorption features are detected in the range 5–38 Å. The results are compared with those recently obtained with Chandra gratings [ApJ 573 (2002) 157; Nature, 421 (2003) 719]. We discuss whether the absorption occurs at the source (in the host galaxy or in a jet), in the Galactic halo, or in the intervening cluster. We are not able to confirm the proposal by [ApJL 572 (2002) L127] that a hot medium is responsible for an absorption feature at an intermediate redshift.
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