Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt........28c&link_type=abstract
Ph.D dissertation, 2004. 251 pages; United States -- Georgia: Georgia State University; 2004. Publication Number: AAT 3170178.
Physics
7
Blazars, Active Galactic Nuclei, Relativistic Jets
Scientific paper
The study of variability in blazars has primarily focused on short-term variations, or microvariability, at all wavelengths. We present results of an intensive investigation of seven X-ray selected blazars from timescales of minutes to decades. These results indicate that the occurrence and amplitude of microvariability is independent of state, a characteristic also found for a radio-selected blazar, BL Lacertae. This result precludes processes that require a discrete amount of energy and implies that the "intensity" of the microvariations scales with the overall intensity of the blazar. However, the amplitude of the observed microvariations for X-ray selected blazars is relatively small compared to the observed micro-variability amplitudes for radio-selected blazars. This remains true after the host galaxy has been deconvolved from the blazar. The amplitude (in magnitudes) of variations, which are believed to be associated with major shocks along a relativistic jet, occuring on intermediate timescales, ~days-week, is also independent of the luminosity state of the blazar. The typical magnitude range for X-ray selected blazars over decades is significantly smaller than that observed for radio- selected blazars (i.e., ~2 magnitudes compared to ~5 magnitudes). Structure function analyses has yielded interesting results. For example, the minimum timescale, which is a measurement of the size of the emission region, has been found to be typically <=20 minutes. The structure function analyses provides evidence that suggests that the size of the emission region may change in a matter of hours. By visual inspection of light curves spanning decades at both optical and X-ray wavelengths, there appears to be several similarities. However, due to the irregular sampling of observations at both the optical and X-ray wavelengths, statistical analyses of these light curves did not yield physically realistic results. There is also evidence that suggests that the occurrence of optical microvariability is related to the strength of the radio jet, in terms of the apparent speed (c) and the rest frame intensity.
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