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M. van der Klis (Astronomical Institute ``Anton Pannekoek", University of Amsterdam)
In a plot of kilohertz QPO frequency vs. X-ray luminosity several parallel tracks are observed both when combining data from several different sources covering two orders of magnitude in luminosity, and when considering data from just one source. This parallel track phenomenon is closely related to other aspects of the correlations between spectral and timing parameters on the one hand and luminosity on the other in accreting neutron stars and black holes. A simple model scenario will be described that may explain the phenomenon. Results will be presented of numerical simulations of this scenario that seem to reproduce the observational results remarkably well.
This work was supported in part by the Netherlands Organization for Scientific Research NWO and the Netherlands Research School for Astronomy NOVA.