Pottschmidt, KatjaWilms, J.Staubert, R.Nowak, M. A.Dove, J. B.Heindl, W. A.Smith, D. M.2023-10-122023-10-122000-04-12K. Pottschmidt, J. Wilms, R. Staubert, M. A. Nowak, J. B. Dove, W. A. Heindl, D. M. Smith; Monitoring the short-term variability of Cyg X-1: Spectra and timing. AIP Conf. Proc. 12 April 2000; 510 (1): 109–113. https://doi.org/10.1063/1.1303184https://doi.org/10.1063/1.1303184http://hdl.handle.net/11603/30136THE FIFTH COMPTON SYMPOSIUM, 15-17 Sep 1999, Portsmouth, New Hampshire (USA)We present first results from the spectral and temporal analysis of an RXTE monitoring campaign of the black hole candidate Cygnus X-1 in 1999. The timing properties of this hard state black hole show considerable variability, even though the state does not change. This has previously been noted for the power spectral density, but is probably even more pronounced for the time lags. From an analysis of four monitoring observations of Cyg X-1, separated by 2 weeks from each other, we find that a shortening of the time lags is associated with a hardening of the X-ray spectrum, as well as with a longer characteristic “shot time scale.” We briefly discuss possible physical/geometrical reasons for this variability of the hard state properties.5 pagesen-USThis article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in K. Pottschmidt, J. Wilms, R. Staubert, M. A. Nowak, J. B. Dove, W. A. Heindl, D. M. Smith; Monitoring the short-term variability of Cyg X-1: Spectra and timing. AIP Conf. Proc. 12 April 2000; 510 (1): 109–113. https://doi.org/10.1063/1.1303184 and may be found at https://pubs.aip.org/aip/acp/article-abstract/510/1/109/559148/Monitoring-the-short-term-variability-of-Cyg-X-1.Text