Non-Thermal Features in TeV-Blazars and the Galactic Center Region with MAGIC and Prospects for CTA

Our Universe is known to be the venue where extreme, powerful and violent phenomena occur in the most compact objects, interstellar and intergalactic space. Its non-thermal behaviour can be seen with the gamma eyes of space-based and ground-based telescopes, and the observations performed with these innovative instruments represent the novel research field of the Gamma-ray Astronomy. On the balance between the life-and-death in stars lies the presence of extremely energetic particles, the cosmic rays CRs, which are accelerated in compact and massive astrophysical sources, and are responsible for the prominent part of the gamma-ray emission detected at the Earth position. Several theories have been outlined for explaining how CRs are accelerated, and what are the mechanisms accountable for their diffusion and interaction with the interstellar environment of Our and external galaxies. Many questions are still open regarding the location at which the acceleration occurs, and the flavour's origin of the emission. In the gamma-ray astronomy the sources under investigation are both galactic and extra-galactic, and the physical processes governing the observed emission are essentially the same, but what changes is the playground in which they work. Indeed, the channels that are responsible for energy losses in CR propagation (dissipation mechanisms), are invoked for describing the production of high energy photons ( seeding mechanisms). With the current gamma-ray telescopes many exciting studies on the non-thermal nature of the Universe can be done, including also exotic physics. Many new knowledges on the highest energetic face of the Universe have been achieved and many mysteries have been unveiled in the last two decades, when the gamma-ray astronomy has become increasingly important. Accompanied to new discoveries there are always new mysteries and questions to answer. With the present date gamma-ray telescopes many physical informations can be earned, and in the next generation instruments rely the expectation of finding the solutions to the nowadays unresolvable puzzles and questions, exposed by current operating telescopes. In this context this project wants to contribute, by analyzing observational data and interpreting the measurements, in simulating synthetic data with the expectation of attaining explanations on the long-standing discussions and debates. The physical processes and mechanisms responsible for the very high energy (VHE; E>100 GeV) gamma-ray emission from active galactic nuclei (AGNs) are still unclear and poor known. The characterization of the non-thermal features in these sources is a vibrant research field, in which study the variability aspects in blazars, the cosmological origin of the Universe, the strength of the intergalactic magnetic field (IGMF) and its constraint, and the nature of the extragalactic background light (EBL). The extreme side of the Cosmos can further be used to test theories in fundamental physics and unveil new messengers of the novel multi-messenger astronomy. % %The nature of the processes defining the high and very-high energy component of the measured spectra is a vibrant research field, in which the study of the variability aspects in astrophysical sources, and the cosmological origin of Our Universe, constraining the strength of the inter galactic magnetic field, describing the nature of the extra-galactic background light, and finding an application in the novel multi-messenger astronomy and fundamental physics. The origin and transport mechanisms of relativistic CRs and their interplay with the interstellar environment of the Galaxy challenge the efforts of the astroparticle community in providing realistic modelling to describe the evolution of the CRs travel throughout the Milky Way, and the gamma-ray production. Our Own Galaxy is known to be a strong source of gamma-ray diffuse emission associated with the CR propagation within the galaxy. The implementation of increasingly realistic phenomenological models reproducing the gamma-ray emission has a key role in the measurements of the gamma-ray flux from astrophysical objects, since represents the only method providing the background model above which the sources appear. This work has contributed as part of the multi-year observing campaign of the MAGIC experiment on the BL Lac prototype, BL Lacertae. In this context, the data measured by the MAGIC telescopes, and Fermi-LAT satellite have been analyzed and then have been compared with multi-wavelength observations and previous flaring activities in order to define the variability pattern of the source. Moreover, in this project has been investigated the extreme behavior of 1RXS J081201.8 + 023735, an extragalactic source belonging to a peculiar class of blazars, the extreme high frequency peacked BL Lac objects (EBHL). Since the redshift of these objects is low, they represent ideal laboratories where studying the cosmological origin of the Universe, the interplay of gamma rays with the IGMF, and testing emission mechanism models, both leptonic and hadronic in origin. In the key science project of the MAGIC collaboration the hunting and classification of promising candidates to include in the catalog of extreme blazars have a fundamental role. RXJ have been detected for the first time in the VHE regime at 5.21 sigma significance level, its discovery has been presented at the COSPAR 2021 conference, and the source has been included in the TeVcat, the reference catalog of TeV sources, in January 2021. The violent, powerful and extreme behavior is also a facet of Our Galaxy, and in this framework the Galactic Center region is an intriguing playground where the observed gamma-ray emission could arise from several emission channels. Among the suggested scenarios, a definitive explanation seems not to be achievable with currently operating telescopes, and many expectations rely on the next generation imaging Cherenkov telescopes (IACTs), the Cherenkov Telescopes Array (CTA). In this project, the so-called Central Molecular Zone (CMZ) has been considered to test four phenomenological models of the gamma-ray diffuse emission in order to disentangle between the PeVatron and inhomogeneous diffusion scenarios. The need to provide increasingly realistic models of the diffuse gamma-ray emission has a crucial role in the definition of the background model used in the analysis chain of IACT data, and in particular for CTA it is represent a promising opportunity to disentangle among the scenarios. In this project, the unclassified source HESSJ has been considered to test the impact of different background models on the emission that will be measured with CTA. The simulated spectra advise that in the next future a definitive explanation on the Galactic Center intricate panorama could be reached. Moreover, a synthetic population of nowadays unresolved astrophysical particle accelerators residing in the inner parsecs of the Milky Way has been simulated in order to provide a realistic list of sources to include in the second Data gamma rays of CTA.