EXOSAT Observations of Shortterm Variability in Active Galactic Nuclei

Although X-ray variability in active nuclei (AGN) is well-established on timescales of days or longer, until recently little has been known about short-term variability. Minimum timescales for significant variability are particularly interesting because they can yield information about such quantities as the mass of a central accreting black hole and the efficiency of the X-ray emitting mechanism. The results presented here, for MCG -6-30-15, Mkn 335, NGC 7314, III ZW 2 and Akn 120, show short term variability for a sample of AGN selected to cover a wide luminosity range.