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Abteilung Astronomie

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Preprint 01c/96

Absorption features in the hard X-ray spectra of A 0535+26 and Vela X-1

P. Kretschmar(1), H. C. Pan(2,5), E. Kendziorra(1), M. Kunz(1), M. Maisack(1), R. Staubert(1), W. Pietsch(3), J. Trümper(3), V. Efremov(4), and R. Sunyaev(4)

(1)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2)School of Physics and Space Research, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
(3)Max-Planck-Institut für Extraterrestrische Physik, D-85470 Garching, Germany
(4)Space Research Institute, Moscow 117296, Russia
(5)Department of Theoretical Physics, University of Oxford, Oxford OX1 3NP, UK

Contribution to the 3rd COMPTON Gamma Ray Observatory Symposium, München, Germany, June 12-14, 1995
accepted by Astronomy & Astrophysics Suppl.

Abstract. We present the results of broad band (2-200 keV), pulse-phase-resolved spectral analysis of A 0535+26 and Vela X-1 , observed by the instruments HEXE and TTM on Mir-KVANT. Both sources show a double peaked pulse profile at energies > 10 keV with pulses distinctly different in shape. Convincing evidence for cyclotron absorption features has been found for A 0535+26, similar features - though less significant - are also found in the Vela X-1 spectra. For both sources these features are pulse phase dependent and occur especially strong in the pulse getting more prominent with increasing energy.

Key words: pulsars: individual: A 0535+26 - pulsars: individual: Vela X-1 - Stars: magnetic fields - X-rays: stars

Paper (61k gzip'ed Postscript including figures)

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