No abstract

Particle acceleration induced by fast magnetic reconnection may help to solve current puzzles related to the interpretation of the very high energy (VHE) and neutrino emissions from AGNs and compact sources in general. Our general relativistic-MHD simulations of accretion disk-corona systems reveal the growth of turbulence driven by MHD instabilities that lead to the development of fast magnetic reconnection in the corona. In addition, our simulations of relativistic MHD jets reveal the formation of several sites of fast reconnection induced by current-driven kink turbulence. The injection of thousands of test particles in these regions cause acceleration up to energies of several PeVs, thus demonstrating the ability of this process to accelerate particles and produce VHE and neutrino emission, specially in blazars. Finally, we discuss how reconnection can also explain the observed VHE luminosity-black hole mass correlation, involving hundreds of non-blazar sources like Perseus A, and black hole binaries.

The ubiquitous relativistic jet phenomena associated with black holes play a major role in high and very-high-energy (VHE) astrophysics. In particular, observations indicate that blazars (active galactic nuclei with highly beamed relativistic jets pointing to the line of sight) show highly variable VHE emission, implying extremely compact emission regions. The real mechanism able to explain the particle acceleration process responsible for this emission is still debated, but magnetic reconnection has been lately discussed as a strong potential candidate. In this thesis, by means of three-dimensional special relativistic magnetohydrodinamical (3D-SRMHD) numerical simulations, we investigate the acceleration of test particles injected in a magnetized relativistic jet subject to currentdriven kink instability (CDKI), which drives turbulence and fast magnetic reconnection. We find that once the turbulence is fully developed in the jet, achieving a nearly stationary state, the amplitude of the excited wiggles along the jet spine also attains a maximum growth, causing the disruption of the magnetic field lines and the formation of several sites of fast reconnection. This occurs after the CDKI achieves a plateau in its nonlinear growth. We performed a systematic search of magnetic reconnection sites in the evolved jet and obtained average magnetic reconnection rates of ∼ 0.05 (in units of the Alfvén speed) which are comparable to the predictions of the theory of turbulence-induced fast reconnection. Hundreds to thousands of protons injected in the nearly stationary snapshots of the jet, experience an exponential acceleration up to maximum energy. For a background magnetic field of B ∼ 0.1 G, this saturation energy is ∼ 10 16 eV, while for B ∼ 10 G it is ∼ 10 18 eV. The Larmor radius of the particles attaining the saturation energy corresponds to the size of the acceleration region, being of the order of the diameter of the perturbed jet. During this exponential acceleration, the velocity component of the particles that is predominantly accelerated is the parallel one to the local magnetic field. This regime of particle acceleration is very similar in all these evolved snapshots and lasts for several hundred hours until the saturation energy. The simulations reveal a clear association of the accelerated particles with the regions of fast reconnection, indicating its dominant role in the acceleration process. Beyond those saturation values, the particles suffer further acceleration to energies up to 100 times larger, but at a slower rate due to drift in the varying magnetic field. In the early stages of the development of the noniii linear growth of CDKI in the jet, when there are still no sites of fast reconnection, injected particles are also efficiently accelerated, but by magnetic curvature drift in the wiggling jet spine. However, in order to particles to be accelerated by this process, they have to be injected with an initial energy much larger than that required for particles to accelerate in reconnection sites. Fi...