Disputation: The Extremes of Neutrino Astronomy: From Fermi Bubbles with IceCube to Ice Studies with ARIANNA

  • Datum:
  • Plats: Ångströmlaboratoriet, Å80101, Lägerhyddsvägen 1, Uppsala
  • Doktorand: Unger, Elisabeth
  • Om avhandlingen
  • Arrangör: Högenergifysik
  • Kontaktperson: Unger, Elisabeth
  • Disputation

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.

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.