VHE γ-ray observations of Northern sky pulsar wind nebulae with the MAGIC Telescope

The Major Atmospheric Gamma(γ)-ray Imaging Cherenkov (MAGIC) telescope is currently the largest single-dish Imaging Atmospheric Cherenkov Telescope (IACT) in operation. The telescope is located on the Canary Island of La Palma at El Roque de los Muchachos observatory. MAGIC aim is to perform γ-ray astronomy in the energy range from 30 GeV to 30 TeV in the so-called very high energy (VHE) regime. A number of improvements and innovative technologies were required in order to explore the energy range below 300 GeV, which has been inaccessible to previous instruments. This energy range is expected to provide key data to help to understand a wide variety of astrophysical phenomena, like supernova remnant shells, pulsars and their wind nebulae in both isolated and binary systems, active galactic nuclei and γ-ray bursts. Eventually, MAGIC could also be useful to study non-conventional physics like the Lorentz Invariance, or the Dark Matter. This work reports on the development of an analysis method (the Island cleaning) to improve the sensitivity at lower energies, as well as the validation of several analysis methods (selection cuts, flux and spectrum determination) using data from the Crab Nebula, which is the standard candle for TeV instruments located in the Northern hemisphere. In the physics front, a model of the VHE γ-ray emission from pulsar wind nebulae (PWNe) is presented and applied to one particular case: 3C58, known in X-rays and radio wavelengths. Finally, the MAGIC data from 3C58 and from other Northern hemisphere PWN are analyzed. In IACTS the faint Cherenkov light emitted by the ultrarelativistic particles of extended air showers (EAS) is detected by means of a camera containing an array of photomultipliers. In this way, a crude image of the shower is recorded. Traditionally, a two-level cleaning tailcut procedure is applied to remove the signal from the ambient night sky. I developed an alternative algorithm for cleaning the shower images and implemented it in the MAGIC analysis and reconstruction software (MARS): the Island cleaning. This cleaning procedure consists in applying very low cleaning tailcuts. The image is then formed by one or more islands. Each of them is inspected by means of its charge and time information to decide if it was originated in the shower and thus, kept on the image, or if it is likely to be a fluctuation of the noise and thus, rejected for the analysis. Using simulated γ-rays it has been shown that island cleaning allows for a better reconstruction of the events, especially near the current energy threshold of the standard analysis. Between 70 GeV and 100 GeV about 40% more γ-rays are detected. Using Crab Nebula real experimental data, a 20% improvement in the sensitivity at around 100 GeV is observed.