ACTA UNIVERSITATIS UPSALIENSIS Uppsala Dissertations from the Faculty of Science and Technology 137 Elisabeth Unger The Extremes of Neutrino Astronomy From Fermi Bubbles with IceCube to Ice Studies with ARIANNA Dissertation presented at Uppsala University to be publicly examined in Ångströmlaboratoriet, Å80101, Lägerhyddsvägen 1, Uppsala, Friday, 18 October 2019 at 13:15 for the degree of Doctor of Philosophy. The examination will be conducted in English. Faculty examiner: Professor Antonio Capone (Physics Department, "La Sapienza" in Rome, Italy and Istituto Nazionale Fisica Nucleare, in Rome, Italy). Abstract Unger, E. 2019. The Extremes of Neutrino Astronomy. From Fermi Bubbles with IceCube to Ice Studies with ARIANNA. Uppsala Dissertations from the Faculty of Science and Technology 137. 213 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-513-0682-7. The Fermi bubbles are extended regions of hard gamma-ray emission which were discovered with Fermi-LAT data to exist above and below the Galactic Center. In order to explain the origin of the gamma-rays, different theories are proposed. In particular, within hadronic models, highly-accelerated cosmic rays interact with interstellar matter and create the observed gamma- rays and in addition neutrinos. Data from the neutrino detector IceCube was analyzed using a maximum likelihood method. An upper limit on the possible neutrino flux from the Fermi bubbles at energies between 10 GeV and 200 GeV was determined. While this analysis is performed with the lowest energies IceCube can reach, the ARIANNA (Antarctic Ross Ice-shelf ANtenna Neutrino Array) experiment has the goal to detect the highest energy neutrinos by measuring radio wave radiation produced by their interaction products in the ice. With ARIANNA the propagation of radio waves in the firn (packed snow) of the Ross Ice Shelf was investigated. According to the classical approach the radio waves, produced in the firn, are supposed to bend down because of the changing density, and therefore changing refractive index, an effect which is called “shadowing”. Evidence that the waves can travel horizontally over a long distance will be presented. The horizontally propagating signals between two boreholes and to the ARIANNA stations were analyzed and characterized. Analyses were performed under two hypotheses to determine attenuation lengths for horizontal propagation signals. The results showed attenuation lengths between 310 m ± 83 m and 651 m ± 270 m, depending on the assumed hypothesis and performed analysis. In addition unexpected signals consistent with radio waves propagating along the firn surface, here called pre-pulses, were observed and characterized. Keywords: astroparticle physics, neutrino telescopes, IceCube, Fermi bubbles, ARIANNA, horizontal propagation, surface wave propagation Elisabeth Unger, Department of Physics and Astronomy, High Energy Physics, Box 516, Uppsala University, SE-751 20 Uppsala, Sweden. © Elisabeth Unger 2019 ISSN 1104-2516 ISBN 978-91-513-0682-7 urn:nbn:se:uu:diva-383629 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-383629) To my parents, Larissa and Johann. Моим родителям, Ларисе и Ивану. Contents Acknowledgements ........................................................................................... ix Acronyms ......................................................................................................... xii Preface .............................................................................................................. 15 About this Thesis ....................................................................................... 15 The Author’s Contribution ........................................................................ 16 Units and Conventions .............................................................................. 17 Cover Illustration ....................................................................................... 17 1 Astroparticle Physics ................................................................................. 19 1.1 High Energy Cosmic Rays ............................................................ 19 1.2 Multi-Messenger Astrophysics ..................................................... 24 1.2.1 Relation between CRs, γ-rays, GWs and neutrinos ...... 27 1.3 The Neutrino Flux Spectrum ......................................................... 29 1.4 Atmospheric Background .............................................................. 31 1.5 Neutrino Interaction and Particle Detection ................................. 34 1.6 Energy Losses of Charged Leptons .............................................. 37 1.6.1 Electrons ........................................................................... 37 1.6.2 Muons ............................................................................... 38 1.6.3 Tau Leptons ...................................................................... 38 Part I: Investigation of Neutrinos from the Fermi Bubbles with IceCube ... 39 2 The Fermi Bubbles .................................................................................... 40 2.1 Features in Other Wavelengths ...................................................... 42 2.2 Comparison to Other Galaxies ...................................................... 43 2.3 Origin of the Fermi Bubbles .......................................................... 44 2.3.1 Leptonic Models .............................................................. 44 2.3.2 Hadronic Models ............................................................. 45 2.3.3 Combination of Leptonic and Hadronic Models ........... 45 2.3.4 Chosen Hadronic Model ................................................. 45 3 The IceCube Observatory ......................................................................... 47 3.1 The In-Ice Array ............................................................................. 48 3.1.1 DeepCore ......................................................................... 48 3.2 IceTop ............................................................................................. 49 3.3 Digital Optical Modules ................................................................ 49 3.4 Data Acquisition System ............................................................... 52 3.4.1 Triggering ......................................................................... 52 3.4.2 Processing and Filtering .................................................. 52 3.4.3 Detector Monitoring ........................................................ 53 3.5 The South Pole Ice ......................................................................... 54 3.6 IceCube Monte Carlo Simulation Chain ...................................... 55 3.6.1 Particle Generators .......................................................... 56 3.6.2 Particle Propagator .......................................................... 57 3.6.3 Photon Propagator ........................................................... 57 3.6.4 Detector Response ........................................................... 57 3.7 Event Signatures ............................................................................. 58 3.7.1 Event Signatures at Low Energies .................................. 60 4 Data Processing ......................................................................................... 61 4.1 Data and Simulation Selection ...................................................... 61 4.1.1 Background Simulation ................................................... 62 4.1.2 Signal Simulation ............................................................ 63 4.1.3 Blindness of Real Data .................................................... 63 4.2 Event Selection ............................................................................... 64 4.2.1 Data Reduction ................................................................ 64 4.2.2 Level 2’ ............................................................................ 65 4.2.3 Level 3 .............................................................................. 66 4.2.4 Level 4 .............................................................................. 71 4.2.5 The Final Sample ............................................................. 77 5 Investigating the Fermi Bubbles with Respect to Neutrinos ................... 79 5.1 The Expected Fermi Bubble Neutrino Flux ................................. 79 5.2 Construction of Probability Density Functions ............................ 82 5.2.1 Signal Expectation ........................................................... 83 5.2.2 Background Expectation ................................................. 85 5.2.3 Scrambled Signal ............................................................. 85 5.2.4 Probability Density Function .......................................... 86 5.3 The Analysis Method ..................................................................... 87 5.3.1 Confidence Intervals and Sensitivity .............................. 87 5.3.2 Expected Events .............................................................. 90 5.3.3 The Sensitivity Flux ........................................................ 90 6 Fermi Bubble Analysis Results ................................................................ 92 6.1 Systematics Uncertainties .............................................................. 93 6.1.1 Comparison with ANTARES Upper Limits .................. 97 6.2 Conclusion .....................................................................................