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Preprint 12f/99


I. Kreykenbohm (1), J. Wilms (1), P. Kretschmar (1;3), R. Staubert (1), R. E. Rothschild (2), W. A. Heindl (2), D. E. Gruber (2)

(1) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2) CASS, University of California, San Diego, La Jolla, CA 92093, U.S.A.
(3) INTEGRAL Science Data Center, ISDC, 1290 Versoix, Switzerland

To appear in: CONFERENCE PROCEEDINGS X-ray Astronomy '99, published in Astrophysical Letters and Communications, 1999,

Abstract. We present light curves and spectra of a ~35 ksec RXTE observation of Vela X-1 and a ~300 ksec observation of Cen X-3.
Both light curves show strong absorption which increases from no absorption at low orbital phases to large values at high orbital phases; in the case of Vela X-1 by a factor of almost 100. Superimposed are absorption dips which can be observed at any orbital phase, though mostly at high orbital phases. We study an unusually strong dip in Vela X-1 during which the flux is reduced by ~90% and almost no pulses are detectable. The increase of NH and the scattered component show the in- and egress of material in the line of sight. A similar behaviour is observed in a pre-eclipse dip in Cen X-3.

Key words: X-rays: stars - stars: individual: Vela X-1 - stars: individual: Cen X-3

Paper (85k gzip'ed Postscript including figures)

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