Investigating the Emission Mechanism of Blazars S5 0716+714 and Mrk 421 with MAGIC and LST1 in a Multi-wavelength Context

This work of thesis is devoted to the study of very high-energy (VHE) gamma-ray emission from variable blazars. Blazars are objects which emit energy across the entire electromagnetic spectrum, and they are a subclass of Active Galactic Nuclei (AGNs). One of the blazars characteristics is variability, which scales from long to short periods of time. To understand the real nature of blazars, we need multi-wavelength (MWL) simultaneous data, and we need to be able to analyze these data and to do numerical predictions to discriminate between theoretical models. Blazars come in two flavors: Flat Spectrum Radio Quasars (FSRQs) and BL Lacertae objects (BL Lacs). The main difference is in their optical spectra, with the former displaying broad emission lines and the latter being instead characterized by either a featureless continuum, or by a spectrum that displays only absorption features (usually from the host galaxy) or weak narrow emission lines. The radio-to-gamma-ray Spectral Energy Distribution (SED) of blazars typically displays two broad humps where the first hump is associated with synchrotron emission, while the second hump can be described with and inverse Compton emission. The focus of this thesis is on long-term VHE monitoring of the blazar S5 0716+714, a Bl Lac object, over a period of six years between 2015 and 2021. Together with VHE gamma- ray data taken by Major Atmospheric Cherenkov Telescopes (MAGIC), an extensive MWL dataset has been obtained in order to study the broad-band behavior of the source. During the VHE monitoring period, strong flaring activity coming from the source was detected in December 2017 where the flux reached the historical maximum in VHE. During the flaring state, intranight variability in the VHE band was discovered. In order to describe this state of activity, a one-zone leptonic model was used which showed the best agreement with data. In this case for modeling of the data, the open source framework JetSet was used. The given model gives good agreement with the values in the literature which confirms the nature of the blazar S5 0716+714 as intermediate Bl Lac object. Mrk421 is another very well-known blazar. We studied the VHE gamma-ray spectra and light curves using the new generation of ground-based Cherenkov telescope, the Large-Sized Telescope (LST). The data set used in the analysis consists of the data between 2022 and 2024.