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Abteilung Astronomie

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Preprint 11a/00


I. Kreykenbohm (1), P. Kretschmar (1,3), J. Wilms (1), R. Staubert (1), W. A. Heindl (2), W. Coburn (2), and R. E. Rothschild (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, U.S.A.
(3) INTEGRAL Science Data Centre, Versoix, Switzerland

To appear in: ESA-SP

Abstract. We present phase­resolved spectra from a 30 ksec RXTE­observation of Vela X­1. We created 16 phase­bins to study the evolution of the spectral parameters over the pulse. The NPEX (Negative Positive EXponential) model (Mihara, 1995, see Eq. 1) was used to fit the data, other models either did not work or had too many free param­ eters. A cyclotron absorption line at ~50keV is present, especially in the falling flank of the main pulse, but is also clearly detected in the secondary pulse. However, it is barely present between the two pulses.

Key words: X­rays: stars; stars: magnetic fields; stars: pulsars: individual: Vela X­1

Paper (70k gzip'ed Postscript including figures)

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