Speaker
Description
The proper understanding of blazar and ither AGN flux variability at the various energy bands is one of the most important goals of multifrequency astrophysics. In this frame a peculiar and controversial phenomenology is the periodicity, claimed mostly in radio or optical flux light curves of a restricted group of blazars. Significance estimates are uncertain and the evidence for temporal periodic trends in galaxy-sized systems like blazars is much weaker than it is for X-ray binary star-size systems and microquasars within our Galaxy. Long-term multi-year light curves usually suffer from irregular sampling and large, seasonal, data gaps, affecting the results of time series analysis. A representative case study with multifrequency radio-optical-X-ray data is presented, namely the BL Lac object OJ 287. The ubiquitous role in astrophysical and earth science data of the so called red-noise in time-series data sets is also highlighted.
