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Abteilung Astronomie

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Preprint 08b/95

X-ray Spectra of BL Lac Objects from the ROSAT Archive

G. Lamer(1), H. Brunner(1,2), R. Staubert(1)

(1)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2)Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany

Poster presented at the Conference Röntgenstrahlung from the Universe, Würzburg, Germany, September 25-29, 1995
to be published in the Proceedings of this Conference

Abstract. We present ROSAT PSPC spectra of 74 BL Lacertae objects observed in the pointed observation phase. We have investigated the soft X-ray properties and broad band energy distributions and find a strong interdependence of X-ray spectral slope and radio to X-ray energy distribution. Objects with extreme values of alpha_rx have flatter X-ray spectra than objects of intermediate alpha_rx. The properties of the objects can be modelled by a two component multifrequency spectrum with a hard (Compton) component and a steepening soft (synchrotron) component. We show that the differences between X-ray selected BL Lacs (XBLs) and radio selected objects (RBLs) are caused by a broad range of the synchrotron cutoff energies.

Paper (43k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de)
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