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Paper: Intraday Variability in BL Lac Objects and Quasars
Volume: 159, BL Lac Phenomenon
Page: 49
Authors: Kraus, A.; Krichbaum, T. P.; Witzel, A.
Abstract: Intraday Variability in the radio regime is a common phenomenon in blazars and is found in about 30% of all objects in this class. While flux density variations of up to 5-10% are typical, peak-to-peak-variations of 25% or more have been seen in selected objects. These rapid variations lead -- for the case of an intrinsic origin -- to brightness temperatures of up to 1018 - 1021 K, violating the inverse Compton limit of 1012K. New observations with the 100m telescope of the MPIfR have revealed variations also in the polarized intensity and polarization angle. While the former ones occur sometimes with higher amplitudes than the total flux density variations (in some cases reaching a factor of two), polarization angle variability can be of the order of a few tens of degrees. Here we present an overview of IDV-observations carried out with the 100m telescope and the VLA both in total flux density and linear polarization. Models to explain IDV and to avoid the violation of the inverse Compton limit will be briefly discussed.
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