Public defence in Space Science and Technology, M.Sc. Paola Wara Chamani Velasco
M.Sc. Wara Chamani Velasco will defend the thesis "Measurements of magnetic fields in the jets of active galactic nuclei" on 18 November 2022 at 12 (EET) in Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering, in lecture hall T2, Konemiehentie 2, Espoo.
Opponent: Dr. Andreas Brunthaler, Max-Planck-Institut für Radioastronomie, Germany
Custos: Prof. Anne Lähteenmäki, Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering
Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/
Doctoral theses in the School of Electrical Engineering: https://aaltodoc.aalto.fi/handle/123456789/53
Public defence announcement:
Supermassive black holes are enormous objects weighing millions to billions of solar masses and residing in the centres of most galaxies. The Event Horizon Telescope (EHT) collaboration recently showed Very Long Baseline Interferometry (VLBI) images of the Milky Way and M87 galaxy black holes. When supermassive black holes drag matter from their surroundings, an Active Galactic Nucleus (AGN) is switched on due to the conversion of the gravitational potential energy into disk thermal emission and relativistic plasma jets, which are launched to speeds near the speed of light. The jet acceleration and launching mechanisms are not fully understood. However, jets might be produced by the Blandford and Znajek mechanism. This mechanism uses magnetic fields that extract the black hole's rotational energy for launching powerful relativistic jets. In this scenario, the jet power depends on the black hole spin and the magnetic flux that threads the black hole event horizon. Approximately only 10% of the AGNs in the universe launch powerful jets, and the remaining 90% produce only weak jets or no jets at all. The paramount question is, what controls the jet production efficiency in AGNs? The black hole spin? The magnetic flux or both?
In this thesis, I present magnetic field measurements of two AGN jets obtained by using VLBI observations and applying a so-called “core-shift” analysis technique, which is based on measuring the location at which the jet radio emission becomes visible at different observing frequencies. I studied two independent yet related subjects: the testing of the magnetic flux paradigm and core-shift time variability. In the first study, I measured the black hole spin from XMM-Newton and NuSTAR X-ray satellite observations and magnetic flux from VLBI observations of a low-powered AGN jet (III Zw 2) to test the magnetic flux paradigm. The results suggest that jet power in III Zw 2 is low despite the high black hole spin and its magnetic field is weak compared to sources with powerful jets. The latter indicates that the magnetic field controls the jet production efficiency. In the second study, I studied the time variability of the core-shift effect in the blazar 3C 454.3 to assess the reliability of the AGN jet's magnetic field measurements on parsec scales. The results on 3C454.3 indicate a significant variability of the core-shift measurements, which has important implications for how magnetic field parameters should be estimated in AGN jets.
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