2009/12/09 by V. M. Larionov, M. Villata, C. M. Raiteri · 3 citations
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Blazar #Flux (metallurgy) #Gamma ray #Geology #Infrared #Light curve #Physics #Radio Astronomy Observations and Technology #Remote sensing #Solar and Space Plasma Dynamics #Telescope #astro-ph.CO
paper · pdf · doi:10.1051/0004-6361/200913536
6 pages, 8 figures, accepted by A&A
arxiv created 2009/12/09 · openalex publication_date 2010/01/15 · arxiv updated 2015/05/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
<i>Context. <i/>Since 1997, BL Lacertae has undergone a phase of high optical activity, with the occurrence of several prominent outbursts. Starting in 1999, the Whole Earth Blazar Telescope (WEBT) consortium has organised various multifrequency campaigns on this blazar, collecting tens of thousands of data points. One of the main issues in the analysis of this huge dataset has been the study of colour variability.<i>Aims. <i/>The immense amount of optical and near-infrared data collected during the campaigns enables us to perform a thorough analysis of multiband data, with the aim to understand the flux variability mechanisms.<i>Methods. <i/>We use a new approach for the analysis of these data, focusing on the source spectral evolution.<i>Results. <i/>We show that the overall behaviour of the BL Lacertae light and colour curves can be explained in terms of a changing viewing angle of a moving, discrete emitting region, which causes variable Doppler boosting of the corresponding radiation.<i>Conclusions. <i/>A fractal helical structure is suggested to be at the origin of the different time scales of variability.