| Summary: | In violent astrophysical processes high-energy neutrinos of TeV to PeV energies are expected to be produced along with the highest energy cosmic rays. The acceleration of nuclei to very high energies is assumed to takes place in astrophysical shocks and neutrinos are produced in the interaction of these cosmic rays with ambient baryons or photons. The neutrinos then escape the acceleration region and propagate through space without interaction, while the nuclei are deflected in magnetic fields and no longer carry information about their source position. Unlike gamma-rays, neutrinos are solely produced in hadronic processes and can therefore reveal the sources of charged cosmic rays. The IceCube neutrino detector, which is located at the geographical South Pole, has been build to detect these high-energy astrophysical neutrinos. The deep clear Antarctic ice is instrumented with light sensors on a grid, thus forming a Cherenkov particle detector, which is capable of detecting charged particles induced by neutrinos above 100 GeV. Transient neutrino sources such as Gamma-Ray Bursts (GRBs) and Supernovae (SNe) are hypothesized to emit bursts of high-energy neutrinos on a time-scale of ≤ 100 s. While GRB neutrinos would be produced in the high relativistic jets driven by the central engine, corecollapse SNe might host soft-relativistic jets which become stalled in the outer layers of the progenitor star and lead to an efficient production of high-energy neutrinos. This work aims for an increased sensitivity for these neutrinos and for a possible identification of their sources. Towards this goal, a low-threshold optical follow-up program for neutrino multiplets detected with IceCube has been implemented. If a neutrino multiplet – i.e. two or more neutrinos from the same direction within 100 s – is found by IceCube a trigger is sent to the Robotic Optical Transient Search Experiment (ROTSE). The 4 ROTSE telescopes immediately start an observation program of the corresponding region of the sky in order to detect a ...
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