Very High Energy observations of the blazar 1ES1959+650 with the Large-Sized Telescope (LST-1) in La Palma

Blazars are Active Galactic Nuclei with a jet outflowing from the central black hole pointing towards us. They are known for their broadband non-thermal emission, from radio up to Very High Energy (VHE) gamma-rays. The spectral Energy Distribution of blazars is characterized by two humps: one in low energies and the other between the MeV and GeV (High Energy hump). The Large-Sized Telescope LST1 is a Cherenkov telescope prototype built for the Cherenkov Telescope Array (CTA) observatory in La Palma (Spain). It detects VHE photons from 20 GeV up to tens of TeV. This work aims to be the first analysis performed by a CTA telescope of the blazar 1ES1959+650 (z=0.047). The LST1 observations of the source cover the period from July 2020 to May 2022. Past detections of the blazar revealed extreme behaviour during in periods of strong activity, as occurred in 2002 and 2016. Starting from raw data, LST1 data analysis steps are followed to produce scientific results, in particular Spectral Energy Distributions (SEDs) and Light Curves (LCs). Different approaches to LST1 analysis are discussed. The analysis results of 1ES1959+650 with LST1 are then put in context with detections performed by lower frequencies telescopes in the same period. Gamma-ray emission of the source is characterized by taking into account Fermi-LAT data, so fitting together the two SEDs with a Log Parabola model and examining the evolution of both spectral indexes as function of the fluxes. The former is important to find the High Energy peak in the SED: it is located at around 40 GeV. From the latter, hints of softer-when-brigther trend are found in both. LST1, Fermi-LAT, Swift-XRT (in X-rays) and TELAMON projects (in radio wavelengths) LCs are analysed together. An intra-week flare is claimed in X- and gamma-ray bands during the observations performed in the first week of May 2022. For LST1 the fractional variability amplitude of the flare is around 30%: it reaches its highest flux on the 3rd of May. However, it is more than 7 times smaller than the highest flux achieved during 2016 flare, the most remarkable one in VHE observations of the blazar. The intra-week flare is fitted through an exponential fit for a characterization of the rising/falling timescales. Future further multiwavelength investigations are required to better characterize the source flaring state and the flux-spectral index dependency, as well as LST1 data analysis performance can be improved.