X-ray absorption lines in the Seyfert 1 galaxy NGC 5548 discovered with Chandra-LETGS

We present for the first time a high-resolution X-ray spectrum of a Seyfert galaxy. The Chandra-LETGS spectrum of NGC 5548 shows strong, narrow absorption lines from highly ionised species (the H-like and He-like ions of C, N, O, Ne, Na, Mg, Si, as well as Fexiv -F exxi). The lines are blueshifted by a few hundred km/s. The corresponding continuum absorption edges are weak or absent. The absorbing medium can be mod- elled by an outflowing, thin and warm shell in photoionization equilibrium. The absorption lines are similar to lower ioniza- tion absorption lines observed in the UV, although these UV lines originate from a different location or phase of the absorb- ing medium. Redshifted with respect to the absorption lines, emission from the Oviii Ly line as well as the Ovii triplet is visible. The flux of these lines is consistent with emission from the absorbing medium. The Ovii triplet intensity ratios demonstrate that photoionization dominates and yield an upper limit to the electron density of 7 10 16 m 3 .