Institut für Astronomie und Astrophysik

Abteilung Astronomie

Preprint 05/98

Analyzing short-term X-ray variability of Cygnus X-1 with Linear State Space Models

Katja Pottschmidt, Michael König, Jörn Wilms and Rüdiger Staubert

Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany

1998, Astronomy & Astrophysics, 334, 201

Abstract. Cyg X-1 exhibits irregular X-ray variability on all measured timescales. The usually applied shot noise models describe the typical short-term behavior of this source by superposition of randomly occuring shots with a distribution of shot durations. We have reanalyzed EXOSAT ME observations of Cyg X-1 using the more general Linear State Space Models (LSSMs). These models, which explicitly take the observation-noise into account, model the intrinsic system variability with an autoregressive (AR) process. Our fits show that an AR process of first order can reproduce the system variability of Cyg X-1. A possible interpretation is again the superposition of individual shots, but with a single relaxation time tau. This parameter was found to be 0.19 s.

Key words: X-rays: stars - binaries: close - Accretion, accretion disks - Stars: Cyg~X-1 - Methods: statistical

Paper (604k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de) Last updated 24-Jul-1998