Juan Antonio Aguilar: Interpretation of Current IceCube Results on Galactic and Extragalactic Sources
Neutrinos are not deflected by magnetic fields so they can tell us where they come from. This is important in understanding the origin of cosmic rays. For galactic sources the candidates are SN remnants, for extra-galactic CRs, these may be active galactic sources, gamma ray bursts, and magnetars.
Icecube was already described in a previous talk this morning. The most recent point-source results are obtained by the run of three years. Juan showed a nice plot of point sources in the sky. The two parts of the planisphere is made up of events which are up-going and down-going. There is no evidence of neutrino point sources in the data. To calculate an upper limit on the flux is performed using the Neyman construction. The limit is the best for most of the declination angles.
For Markarian 421, most of the sensitivity is coming from the region between 10 and 100 TeV energies. For southern sources the sensitivity peak moves to higher energies.
The galactic sources rely on the “standard candle”, the crab nebula. This is mainly regarded as a leptonic source, but past gamma-ray flares up to TeV energies challenge the view. IceCube may soon constrain the existing models. Other supernova remnants are far from being constrained by IceCube data, still having limits a factor of four higher than expectations.
There are six TeV associations with supernova remnants based on Milagro. Stacking the signal one may test the model from Halzen et al.
Another galactic source is the mqso. X-Ray binaries, with a haracteristic radio emission believed to come from relativistic jets, that may point to us – when they do we expect neutrino to also be visible. So the flux will show a periodicity. The hottest such source is Cygnus-X3. The collaboration is about to unblind the results of three-year running on this source.
For extra-galactic sources, on GRB the analysis is twofold. There is a model-independent one, “catch-all”, and a model-dependent one. For the latter they were expecting 5.2 events from the model of Guetta et al., but they expect 0, which excludes it. For the model-independent analysis there are two events found, with a more unclear situation.
On active galactic nuclei signals, protons are accelerated together with electrons. They will lose energy in proton-proton and proton-gamma interaction or synchrotron emission. From a paper by Halzen and J.Becker, they assume only pp interactions (arxiv:1302.1015). The resulting neutrino flux can be normalized to the IceCube limits, which can be converted in a limit on the target density.
Another similar approach was doen for pp interactions in Blazars. One may calculate the neutrino flux and normalize it to the Fermi total energy flux. Scanning the parameter space then yields neutrino fluxes, and looking at those parameters that result in fluxes above the limits of IceCube. The resulting limits rest on some assumptions.
In conclusion, there is no evidence of point sources of neutrinos from three years of icecube exposure. Individual SNR are still difficult to detect with IceCube but different analysis techniques such as stacking should allow to bring down the sensitivity to the flux prediction level. The absence of a signal from GRBs challenges the idea of GRBs as the only responsible source of ultra-high-energy cosmic rays.