Accretion discs, jets, and black hole spins: a study of blazars

Abstract

Blazars are among the most powerful astrophysical objects in the universe. Their multiwavelength emission displays traces of non-thermal radiation whose origin is not yet fully understood, and it is dominated by the presence of a relativistic jet. Blazar emission is characterized by high-variability across different wavelenghts, which is associated with a spinning black hole and relativistic effects in the jet. Using blazars as a laboratory, in this thesis we set out to answer a few fundamental questions, such as where and how does the non-thermal emission in blazars originate?, how robust are theoretical models in explaining the efficiency of jet formation?, and can these models accurately predict the spins of the black holes associated with these jets? To answer these questions, we employ two different methods: γ-ray observations and general relativistic magnetohydrodynamic (GRMHD) simulations. In the first study, we used the luminosities of a class of blazars to calculate the jet efficiency, and we estimated the black holes spins. We found a mean spin of a * 0.84 +0.11 −0.25 , with a lower limit estimated at a lower * 0.59. These results show compatibility with cosmological merger-driven evolution of SMBHs which support rapidly rotating black holes. Moreover, we found a correlation between the black hole mass and the γ-ray luminosity L γ . In the second study, we used GRMHD simulations and applied an algorithm to identify the regions in which non-thermal emission must occur. We ran simulations with different initial conditions, varying the magnetic field topology and black hole spin, and we found these regions in all simulations. In particular, we found that this also occurs in the jet for some simulations, thus suggesting i I'm not sure if having taken an Introduction to Astronomy course during my first year as an undergrad counts as having some experience in Astronomy, but this is all Astronomy I had when I decided to switch after a Masters in Theoretical Physics. As it turns out, I ended up doing Theoretical Astrophysics, and the whole transition was smoother than I had anticipated.I thank my advisor Rodrigo Nemmen, for trusting me, for his patience, help, guidance, and for all advice given on the many aspects of doing research, and academia in general. I also thank Prof. Alexander Tchekhovskoy for hosting me during my visit to Northwestern University, and for sharing his vast knowledge on black holes, accretion, jets and especially simulations.