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Abteilung Astronomie

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Preprint 13a/96

Preliminary Results from Vela X-1 Observations by RXTE

P. Kretschmar(1,4), I. Kreykenbohm(1), J. Wilms(1), R. Staubert(1), M. Maisack(1),, E. Kendziorra(1), W. Heindl(2), R. Rothschild(2), D. Gruber(2), J.E. Grove(3)

(1)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2)Center for Astrophysics and Space Sience, UCSD, La Jolla, CA 92063, USA
(3)E.O. Hulburt Center for Space Research, Naval Research Laboratory, Washington, DC 20375, USA
(4)Integral Science Data Center, CH-1290 Versoix, Switzerland

Contribution to the Conference The Transparent Universe - 2nd Integral Symposium, St. Malo, France, September 16-20, 1996
to be published in the Proceedings of this Conference

Abstract. We present preliminary results from four observations of Vela X-1 by RXTE during one orbit of the pulsar. We find strong spectral absorption features at ~23 keV and ~57 keV confirming earlier reports by Kendziorra et al. (1992), Makishima et al. (1992) and Kretschmar et al. (1996). The interpretation of these features as fundamental and first harmonic cyclotron feature is tempting, but we find several problems in following this approach. We note that the lower energy feature coincides with the spectral cutoff where a slightly imperfect description of the source continuum may lead to incorrect results and that a fit with independent line energies yields E_2 = 2.5 * E_1 which is difficult to explain even allowing for relativistic corrections. At the current state of our analysis a definite statement on the nature of the lower energy feature is not possible.

Key words: pulsars: individual: Vela X-1 - Stars: magnetic fields - X-rays: stars

Paper (94k gzip'ed Postscript including figures)

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