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Physics & Astronomy Colloquium
October 12, 2016 @ 3:45 pm - 5:00 pmFree
Speaker: Peter L. Biermann
MPI for Radioastronomy, Bonn, Germany
Dept. Physics., Karlsruher Institut für Technologie, Karlsruhe, Germany
Dept. of Phys. & Astron., Univ. of Alabama, Tuscaloosa, AL, USA
Dept. of Phys. & Astron., Univ. of Bonn, Germany
Title: Review of Ultra-High Energy Cosmic Rays (Theory)
The origin of ultra high energy cosmic rays (UHECRs) is still unsettled but with new data becoming available from Kaskade-Grande and LOFAR, in addition to the IceCube, Auger and TA data, a new look is warranted. The data are all consistent with the main nearby sources, one radio galaxy and one starburst galaxy. At the maximum energies the dominant sources may all be radio galaxies, which come in two kinds, i) injection from the local Hydrogen-rich gas, and ii) injection from the normal cosmic rays produced by a starburst. Activity both from the surroundings of a central supermassive black hole and in star formation can both be triggered by a merger of two galaxies, most interesting if also involving the merger of two central super-massive black holes. The latter would also produce an outburst in low frequency gravitational waves, and in the case that the final relativistic jet points at Earth also high energy neutrino emission; this is consistent with the IceCube data. Both types of radio galaxies are exemplified by the radio galaxy Cen A, at about 3 Mpc distance, and the radio galaxy M87, at about 16 Mpc distance. Both were suggested already as cosmic ray sources in 1963 by Ginzburg \& Syrovatskij. This may explain all events above about 50 EeV. However, at slightly lower EeV energies we now detect protons, as expected, that clearly may come from radio galaxies at cosmological distances. A viable alternative to these well established ideas is that many high energy cosmic rays come from gamma ray bursts and relativistic super-novae in the starburst galaxy M82, and the lower EeV energy events may come from the multitude of starburst and normal galaxies. In the case of radio galaxies we have direct data supporting the production of UHECRs in their hot spots, jets and compact sources. The decision between these alternate pictures may come from a) neutrino data, b) TeV gamma ray data, c) future low frequency gravitational wave detections, and d) an understanding of the scattering in arrival directions provided by magnetic fields in our Galaxy. This scattering is almost completely dominated by the magnetic halo wind of our Galaxy. We will go through these arguments, and propose a baseline concept to be tested with future observations.
The colloquia will be preceded by light refreshments in GL227 from 3:30 – 3:45p.m.