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Preprint 14a/99


Monitoring the Short-Term Variability of Cyg X-1

Katja Pottschmidt (1), Jörn Wilms (1), Rüdiger Staubert (1), Michael A. Nowak (2), James B. Dove (3;4), William A. Heindl (5), and David M. Smith (6)

(1) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2) JILA, University of Colorado, Boulder, CO 80309-440, USA
(3) CASA, University of Colorado, Boulder, CO 80309-389, USA
(4) Dept. of Physics, Metropolitan State College of Denver, Denver, CO 80217-3362, USA
(5) University of California San Diego, La Jolla, CA 92093, USA
(6) SSL, University of California Berkeley, Berkeley, CA 94720, USA

To appear in: ESO Workshop on Black Holes, eds. L. Kaper et al., Springer

Abstract. We present first results from an RXTE monitoring campaign of the black hole candidate Cygnus X-1 in 1999. The spectral and temporal properties of this hard state black hole show considerable variability, even though the state does not change. We find that a shortening of the time lags is accompanied by a hardening of the X-ray spectrum, as well as by an increase of the characteristic "shot time scale". We briefly discuss possible physical/geometrical reasons for this variability of the hard state properties.

Key words: -

Paper (33k gzip'ed Postscript including figures)


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