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Abteilung Astronomie

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Preprint 11b/97

Observations of Vela X-1 with RXTE

P. Kretschmar(1), I. Kreykenbohm(1), R. Staubert(1), J. Wilms(1), M. Maisack(1), E. Kendziorra(1), W. Heindl(2), D. Gruber(2), R. Rothschild(2) and 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 Science,UCSD, La Jolla, CA, USA
(3)E.O. Hulburt Center for Space Research, NRL, Washington DC, USA

Contribution to the 4th COMPTON Symposium on Gamma Ray Astronomy and Astrophysics, Williamsburg, Virginia, USA, April 27-30, 1997

Abstract. We present results from observations of Vela X-1 obtained in February 1996 with RXTE. We have fitted phase averaged spectra with several models and compared our results with prior results obtained with HEXE and GINGA. No acceptable fit is possible with the models normally applied to X-ray binaries, instead we found a best fit using a power law with a Fermi-Dirac cutoff modified by one or two cyclotron absorption lines at ~25 keV and ~58 keV. In phase resolved spectral analysis we find that the cyclotron absorption is detectable only in the pulse, and is deeper in the first stronger pulse.

Paper (93k gzip'ed Postscript including figures)

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