Dissertation in the field of Space Technology, Venkatessh Ramakrishnan
The title of thesis is Multifrequency connection in blazars: Tool for studying the location and emission mechanisms.
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In the centres of active galaxies lies a supermassive black hole devouring matter in its proximity. In this process, jets of plasma at nearly the speed of light are spewed in opposite directions from the black hole. The emission from these jets makes the galaxy more luminous. Blazars belong to a class of the most luminous galaxies with jets oriented towards the line of sight of the observer. The emission from the jet in blazars is highly variable in the radio through gamma-ray bands. In this work, the variability of blazars is investigated using data from various ground-based and space-borne telescopes. The variability is characterised using time-series analysis, to answer the widely debated question concerning the location of the gamma-ray emission. For the analysis, an unprecedentedly long time-series of data have been used; the radio data spans over twenty years and gamma-ray data over five years. By studying the connection between the variability of the light curves from radio through gamma-rays, the origin of the gamma-ray emission was placed beyond five light-years from the black hole. The findings in this work will thus be valuable for simulations of active galaxies and for understanding their evolution.
Opponent: Professor Stefan Wagner, Landessternwarte Königstuhl, Universität Heidelberg, Germany
Supervisor: Professor Anne Lähteenmäki, Aalto University School of Electrical Engineering, Department of Radio Science and Engineering, Metsähovi Radio Observatory
Contact information:
Venkatessh Ramakrishnan
venkatessh.ramakrishnan@aalto.fi