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Astron. Astrophys. 354, L83-L86 (2000)

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Letter to the Editor

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

J.S. Kaastra 1, R. Mewe 1, D.A. Liedahl 2, S. Komossa 3 and A.C. Brinkman 1

1 SRON Laboratory for Space Research Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Physics Department, Lawrence Livermore National Laboratory, P.O. Box 808, L-11, Livermore, CA 94550, USA
3 Max-Planck-Institut für Extraterrestrische Physik, Postfach 1603, 85740 Garching, Germany

Received 2 February 2000 / Accepted 4 February 2000


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 - FeXXI ). The lines are blueshifted by a few hundred km/s. The corresponding continuum absorption edges are weak or absent. The absorbing medium can be modelled by an outflowing, thin and warm shell in photoionization equilibrium. The absorption lines are similar to lower ionization absorption lines observed in the UV, although these UV lines originate from a different location or phase of the absorbing medium. Redshifted with respect to the absorption lines, emission from the OVIII Ly[FORMULA] 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 [FORMULA] m-3.

Key words: galaxies: individual: NGC 5548 – galaxies: Seyfert – galaxies: quasars: absorption lines – X-rays: galaxies

Send offprint requests to: J.S. Kaastra

Correspondence to: J.Kaastra@sron.nl

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© European Southern Observatory (ESO) 2000

Online publication: February 25, 2000