Multi-year campaign of the gamma-ray binary LS I +61º 303 and search for VHE emission from gamma-ray binary candidates with the MAGIC telescopes
School
Universitar Autònoma de Barcelona
Campus UAB, 08193, Bellaterra (Barcelona) Spain
External url: http://www.tdx.cat/handle/10803/283728
Abstract:
This thesis is focused on the study of compact binary systems that emit γ-‐ ray emission, the so-‐called γ-‐ray binaries, with the MAGIC telescopes. The bulk of the non-‐thermal emission of these systems peaks in the γ-‐ray domain. Only five systems are the members of this reduced group. All of them host massive stars and a compact object, remnant of a supernova explosions. Only the compact object of one of these binaries is known, a neutron star. Although none of them display pulsations (associated with neutron stars) or double-‐jet structures (associated with microquasars), most of the theories and observations suggest a neutron star as the compact object. The most accepted scenario to explain the very high energy (VHE) emission of this source class is the pulsar wind scenario. The wind of the massive star and the wind of the neutron star interact, accelerating particles up to relativistic energies with the consequent emission of γ-‐rayphotons. The outline of the thesis is the following: • Chapter 1 is an introduction to VHE γ-‐ ray astronomy. First, a brief history of cosmic rays and their relation with γ rays is introduced. Direct methods for the detection of γ rays in outer space and indirect detection techniques on Earth with ground-‐based observatorios are described. Since this thesis uses data from the MAGIC telescopes, the Imaging Air Cherenkov Technique and its physics principles are introduced. • In Chapter 2, the restrictions of IACTs in terms of the systematic uncertainties due to atmospheric conditions and the need for correcting them is discussed. A LIDAR is introduced as a solution for the next generation of IACTs, the Cherenkov Telescope Array (CTA), to reduce systematic errors and enlarge the duty cycle. The LIDAR which is being developed and characterized at IFAE is described, as well as the performance of this system. • Chapter 3 shows a description of the MAGIC telescopes. The hardware and software components, with a special contribution to the data acquisition system by the author of this thesis, are described. The standard data analysis chain is also collected as well as the special treatment of the data under moderate -‐ strong moonlight conditions. • Chapter 4 is an introduction to compact binary systems. It describes the large variety of these sources in this Universe, finally focussing in X-‐ray binaries and γ-‐ ray binaries. The possible scenarios to account for the γ-‐ ray emission of these sources are also introduced. • Chapter 5 is the complete and detailed description of the γ-‐ray binary LS I +61◦303. The results of a multi-‐year campaign are shown in this Chapter. Studies on the yearly flux variability and the possible existence of a super-‐orbital modulation in the flux are investigated. Furthermore, searches for spectral variability are performed. Finally, a correlation study of the TeV flux with the mass-‐loss rate of the Be star through simultaneous observations with an optical telescope is performed. • In Chapter 6, a search for TeV emission of the γ-‐ray binary candidate MWC 656 is performed. This system is especially interesting for being the first Be star to be proven to host a black hole. • Chapter 7 details the search for VHE γ-‐ray emission of the binary system SS 433, which is a microquasar embedded in a nebula. It is the only super-‐critical accretor in the Galaxy and displays hadronic jets emission. • Finally, concluding remarks from the presented studies and future perspectives are discussed in Chapter 8.
Keywords:
Gamma-ray binaries, binary, LS I +61 303, SS 433, MWC 656