Bayesian modelling of blazars using lepto-hadronic kinetic equations

  • Bruno Jimenez Fernandez

Student thesis: Doctoral ThesisPhD


Blazars are a type of active galactic nucleus characterized by their high luminosity, produced by a variable relativistic jet pointing towards the observer. Due to their connection to galaxy evolution, extra-galactic cosmic rays and neutrinos, they are objects of great importance in high energy astrophysics.
Until now, modelling of blazars involving multiple emission mechanisms and particle species, has been done mostly using simplified leptonic models, with lepto-hadronic models gaining more popularity recently. This has been caused by the increase in available computing power and because of the connection between blazars and neutrinos, which require hadrons in order to be produced at the energies they have been detected.
The increase in high-quality data from satellites such as Swift and Fermi and on ground observatories such as Ice Cube, MAGIC and the future CTA will pave the ground towards obtaining better and more detailed models for the emission of blazars. In particular, this data will help in giving answers to some of the main open questions in blazar physics: What is the geometry and the location of the emission zones? What are the processes that energize the particles to the energies required for emitting TeV photons? Which particles are involved in the emission? Which processes are responsible for the emission of blazars? Are there any degeneracies in the parameters that drive the emission?
In this thesis, we address some of these questions by modelling the emission of blazars using a lepto-hadronic model and Bayesian analysis. First, we simulate the emission from TXS 0506+056, a blazar that has been tentatively connected with a neutrino detection during a flare, with two geometries: sphere and disk, and different injection and steady state models. Second, we analyse the emission from Mrk 421 with leptonic and lepto-hadronic models using Bayesian analysis.
We find that, in order to reproduce the neutrino flux that triggered the investigation of TXS 0506+056, a high ratio of protons to electrons is necessary. For the case of Mrk 421, we find substantial evidence (Bayes factor ∼ 7) in favour of lepto-hadronic models.
Date of Award18 Jul 2022
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorHendrik Van Eerten (Supervisor) & Steven Davies (Supervisor)

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