Search for high energy cosmic muon neutrinos from variable gamma-ray sources and time calibration of the optical modules of the ANTARES telescope

Abstract

Since the first evidence of the existence of cosmic rays (c. 1910) and the first hints of a new ghost particle later on named "neutrino"' (c. 1920) has passed a century. During this time, many experiments and theoretical ideas have expanded our knowledge about the most fundamental particle physics and the most extreme astrophysical processes in the Universe. One of these ideas was proposed half a century ago: neutrino telescopes, the feasibility of which has been proven during the last decade. They aim to provide a crucial contribution to the understanding of the physical processes hosted in the many astrophysical objects by the detection of high energy neutrinos. Eventually, they may provide an answer to the origin of the cosmic rays. It has been during the last years that they provided the first evidence of the existence of high energy cosmic neutrinos. This work represents an effort in this direction. In this thesis, multiple analyses have been performed using data of the ANTARES neutrino telescope in order to look for correlations of high energy neutrinos with known gamma-ray astrophysical sources. The ones that have been studied in this work are Active Galactic Nuclei, X-Ray Binaries and the Crab Pulsar Wind Nebula. In addition to the coincidence in space of neutrinos coming from these sources, it has been used the time information expected from their photon emissions at high energies (X-rays and gamma-rays). This reduces substantially the background and therefore the amount of signal required for a discovery in these point source analyses. In parallel, this work also included the improvement of the time calibration procedure for the ANTARES detector. The structure of this manuscript is as follows. First, the physics involved and the justification of the neutrino candidate sources are introduced in chapter 1. Then, the detection principle of neutrino astronomy and the state of the art about neutrino telescopes are presented. In chapter 2, the ANTARES neutrino telescope is described. Performance and simulations are reported in chapter 3. Chapter 4 is devoted to the time calibration of the detector. In particular, the operation of the controlled pulse light devices (optical beacons) and the analysis of their data are described. Its performance along the time has been evaluated and the success of the automation of the processes means a valuable asset for this crucial task in a neutrino telescope, useful for present and future detectors. In chapter 5 the astronomy at X-ray energies and above are described, introducing the telescopes used to obtain the time information of the photon emissions of the candidate sources analysed here. Their characterisation and the definition of the flare periods are also covered. These analyses are based on an extended maximum likelihood ratio technique, which is described in detail in chapter 6 together with the optimisation procedures. Finally, the application of this technique to the analysed sources and the results derived from it are presented in chapter 7, where conclusions and limits on neutrino fluxes are discussed. The analysis of the obtained data have provided strong constrains and also reinforce of IceCube ones regarding possible cosmic neutrino sources. Among the possible analyses that can be performed, the one presented in this work seeks to detect neutrino emission from known promising astrophysical sources improving the analysis performance by the expected time-dependant bond of the signal. This way, the proof of hadronic processes that would link cosmic ray production with them would be find or constrained otherwise.