Publication details

A multi-messenger view on Mrk 501 focusing on its low-state and long-term behavior

Lea Heckmann


Universität Innsbruck

External urlhttps://ulb-dok.uibk.ac.at/ulbtirolhs/content/titleinfo/8281453


The aim of this thesis is to provide a more comprehensive view on the emission of blazars, less biased towards flaring states. Mrk 501 is one of our closest and therefore also brightest blazars which is detectable during all its emission states from radio to Very High Energy (VHE) gamma rays. I make use of the exhaustive MWL monitoring of Mrk 501 taking place since 2008, which allows me to investigate both the low-activity behavior of the blazar in unprecedented detail, as well as explore its long-term behavior. By evaluating the variability and correlation behavior of Mrk 501 using multi-year data sets, I find a strong indication that leptonic scenarios are suited to explain the underlying mechanism for the variable part of the blazar emission, both during quiescent and more active emission states. This claim is supported by various significant correlations found in these data sets, which have been predicted, but not yet observed before. As a remarkable feature, I identify a historically low emission state of Mrk 501 spanning over two years. This stable low-state emission might be a possible baseline emission produced by a standing shock inside the jet, while the more variable part of the emission may be ascribed to additional expanding or traveling shocks somewhere else along the jet. While I focus on describing the evolution towards the low state with one- and two-zone leptonic scenarios, the low state and potential baseline emission can be adequately described by standard one-zone leptonic, hadronic or lepto-hadronic scenarios, which are in agreement with the neutrino flux constraints from IceCube. To further improve our understanding of blazars, I test the capabilities of a new kind of analysis method, using a cluster algorithm to classify emission states of blazars in a less biased way. My first investigations of employing the algorithm on the long-term Mrk 501 data set show promising results. While being able to support many claims made from the more conventional study, the new algorithm provides an unprecedented possibility to group together emission states, which could help to disentangle the underlying mechanisms behind the blazar emission and their different modes. In the future, this method could be extended to enable population and long-term studies on various sources.


Astrophysics / Astro-particle physics / High-energy processes / Multiwavelength / Active galactic nuclei / blazar

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