Chaotic Behaviour of X-Ray Lightcurves of AGN / Active Galactic Nuclei

The correlation integral method was used to analyze eight Exosat long X-ray light curves of seven Active Galactic Nuclei (AGN) and to put some constraints on the theoretical model in a model independent way. The character of variability was studied by comparing the shapes of light curve fragments created by d succeeding observational points. The computations proceed for d = 1, 2, 3 ... until the result saturates and the increase of the length of sequences does not include any new information; this means that the system has got no more degrees of freedom. The analysis of NGC 4051 (LE) indicated that deterministic chaos is responsible for variability of this source. It does not necessarily mean that this AGN has a different structure than other studied sources as it is a factor 100 fainter and the sampling frequency in Exosat data may be adequate only for NGC 4051.