%0 Generic
%A Emmanoulopoulos, Dimitrios
%D 2007
%F heidok:7481
%K nichtlinearer Zeitreihenanalysen , Variabilität , Markarian 501 , PKS 2155-304Active Galactic Nuclei , BL Lac object , Markarian 421 , Markarian 501 , nonlinear time series analysis , RXTE , H.E.S.S.
%R 10.11588/heidok.00007481
%T Nonlinear Time Series Analysis of BL Lac Light Curves
%U https://archiv.ub.uni-heidelberg.de/volltextserver/7481/
%X In this work the time properties of the BL Lac objects are elaborated in a detailed manner through linear and nonlinear time series analysis methods. In spite of the large amount of available data in the last 20 years, the variability studies have not provided major progress for understanding the behavior of these objects. Vague time series analysis methods, lacking any mathematical foundation, are usually invoked revealing erroneous time properties in the data sets which then act misleadingly for modeling the dynamics of the system under study. The flaws of some of the current time series analysis methods are reviewed thoroughly throughout this work for specific sources (Mrk 421, Mrk 501) and the need of employing higher order time series analysis methods is demonstrated. An extensive description of the modern nonlinear analysis methods is presented together with examples being implemented in a way to be applicable to astronomical time series. Then, these methods are applied to the X-ray data set of Mrk 421, obtained by RXTE, covering a time period of 9 years, giving some hints to answer the question: Is it possible to explain the variability behavior of these sources based on few physical parameters (deterministic system), or is it the result of numerous components yielding from a stochastic system? Finally the results from the longest multiwavelength campaign, conducted during August--September 2004, for the BL Lac object PKS 2155-304 are presented. The source was observed in the very high energy gamma-rays (>100 GeV) by H.E.S.S., in the X-rays (2-10 keV) by RXTE and in the optical (R-band) by three terrestrial observatories.