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Nuclear and Particle Physics

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

by Lisa Unger




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 and the result regarding a possible neutrino flux from the Fermi bubbles at energies between 10 GeV and 200 GeV will be shown.

This presentation will concentrate more on the analyses performed with  the ARIANNA (Antarctic Ross Ice-shelf ANtenna Neutrino Array) experiment. While this analysis is performed with the lowest energies IceCube can reach,  ARIANNA 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 demontrated. In addition unexpected signals consistent with radio waves propagating along the firn surface, were observed and possible expiations will be presented.