Institut für Astronomie und Astrophysik

Abteilung Astronomie

Preprint Ke/98

Cyclotron lines in RXTE spectra of Vela X-1

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

(1)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2)Center for Astrophysics and Space Sciences, UCSD, La Jolla, CA, USA
(3)INTEGRAL Science Data Center, 1290 Versoix, Switzerland

1999, Highlights in X-ray Astronomy, ed. B. Aschenbach, MPE Report, in press

Abstract. We present results of pulse phase resolved spectral analysis from four observations of the wind-accreting X-ray pulsar Vela X-1 by RXTE in February 1996.
The most convincing results were obtained by continuum models with a smooth turnover. In contrast, the commonly used power law with exponential cutoff introduced artificial features in the fit residua. Using a power law with the Fermi-Dirac cutoff modified by photoelectric absorption and an iron line, the best fit spectra are still unacceptable. We interpret the large negative residuals around ~25 and ~55 keV as fundamental and first harmonic cyclotron absorption lines. Modeling the spectra with cyclotron lines, it seems that line energies and widths are connected by a factor larger than 2.
The phase resolved spectra show that the cyclotron lines are strongest in the main pulse while they are barely visible outside the pulses.

Key words: -

Paper (87k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de) Last updated 16-Nov-1998