Optical follow-up program of IceCube multiplets - Testing for soft relativistic jets in Corecollapse Supernovae

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. To increase the sensitivity to detect those neutrinos and identify their sources, an optical follow-up program for neutrinos detected with the IceCube observatory 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 observe the corresponding region in the sky in order to detect an optical counterpart to the neutrino events of IceCube. Data from the first year of operation of the optical follow-up program have been searched for a signal from supernovae. No statistically significant excess in the rate of neutrino multiplets has been observed and further no coincidence with an optical counterpart was found during the first year of data taking. This allows us to restrict current models predicting a high-energy neutrino flux from soft jets in core-collapse SNe. For the first time a stringent limit on the hadronic jet production in core-collapse SNe is derived.