N. Marchili, T. P. Krichbaum, X. Liu, H. G. Song, K. É. Gabányi, L. Fuhrmann, A. Witzel, J. A. Zensus
The BLLac object S4 0954+65 is one of the main targets of the Urumqi monitoring program for IntraDay Variable (IDV) sources. Between August 2005 and December 2009, the source was included in 41 observing sessions, carried out at a frequency of 4.8 GHz. The time analysis of the collected light curves, performed through both a structure function analysis and a specifically developed wavelet-based algorithm, disclosed the existence of an annual cycle in the variability timescales, suggesting a fundamental contribution of interstellar scintillation to the IDV pattern of the source. The combined use of the two analysis methods also revealed a dramatic change in the variability characteristics of the source between February and March 2008, at the starting time of a strong outburst phase. The analysis' results suggest that the flaring state of the source coincides with the appearance of multiple timescales in its light curves, indicating that changes in the structure of the relativistically moving emitting region may strongly influence the variability observed on IDV timescales.
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http://arxiv.org/abs/1204.5012
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