No abstract

High energy photons from blazars can initiate electromagnetic pair cascades interacting with the extragalactic photon background. The charged component of such cascades is deflected and delayed by extragalactic magnetic fields (EGMF), reducing thereby the observed point-like flux and leading potentially to multi degree images in the GeV energy range. We calculate the fluence of 1ES 0229+200 as seen by Fermi-LAT for different EGMF profiles using a Monte Carlo simulation for the cascade development. The non-observation of 1ES 0229+200 by Fermi-LAT suggests that the EGMF fills at least 60% of space with fields stronger than O(10 −16 − 10 −15 ) G for life times of TeV activity of O(10 2 − 10 4 ) yr. Thus the (non-) observation of GeV extensions around TeV blazars probes the EGMF in voids and puts strong constraints on the origin of EGMFs: Either EGMFs were generated in a space filling manner (e.g. primordially) or EGMFs produced locally (e.g. by galaxies) have to be efficiently transported to fill a significant volume fraction, as e.g. by galactic outflows.

A few seconds after bounce in a core-collapse supernova, the shock wave passes the density region corresponding to resonant neutrino oscillations with the "atmospheric" neutrino mass difference. The transient violation of the adiabaticity condition manifests itself in an observable modulation of the neutrino signal from a future galactic supernova. In addition to the shock wave propagation effects that were previously studied, a reverse shock forms when the supersonically expanding neutrinodriven wind collides with the slower earlier supernova ejecta. This implies that for some period the neutrinos pass two subsequent density discontinuities, giving rise to a "double dip" feature in the average neutrino energy as a function of time. We study this effect both analytically and numerically and find that it allows one to trace the positions of the forward and reverse shocks. We show that the energy dependent neutrino conversion probabilities allow one to detect oscillations even if the energy spectra of different neutrino flavors are the same as long as the fluxes differ. These features are observable in theν e signal for an inverted and in the ν e signal for a normal neutrino mass hierarchy, provided the 13-mixing angle is "large" (sin 2 ϑ 13 ≫ 10 −5 ).

One of the robust features found in simulations of core-collapse supernovae (SNe) is the prompt neutronization burst, i.e. the first ∼ 25 milliseconds after bounce when the SN emits with very high luminosity mainly νe neutrinos. We examine the dependence of this burst on variations in the input of current SN models and find that recent improvements of the electron capture rates as well as uncertainties in the nuclear equation of state or a variation of the progenitor mass have only little effect on the signature of the neutronization peak in a megaton water Cherenkov detector for different neutrino mixing schemes. We show that exploiting the time-structure of the neutronization peak allows one to identify the case of a normal mass hierarchy and large 13-mixing angle ϑ13, where the peak is absent. The robustness of the predicted total event number in the neutronization burst makes a measurement of the distance to the SN feasible with a precision of about 5%, even in the likely case that the SN is optically obscured.

Ultrahigh energy cosmic ray (UHECR) protons interacting with the cosmic microwave background (CMB) produce UHE electrons and gamma-rays that in turn initiate electromagnetic cascades on CMB and infrared photons. As a result, a background of diffuse isotropic gamma radiation is accumulated in the energy range $E\lsim 100$ GeV. The Fermi-LAT collaboration has recently reported a measurement of the extragalactic diffuse background finding it less intense and softer than previously measured by EGRET. We show that this new result constrains UHECR models and the flux of cosmogenic neutrinos. In particular, it excludes models with cosmogenic neutrino fluxes detectable by existing neutrino experiments, while next-generation detectors as e.g. JEM-EUSO can observe neutrinos only for extreme parameters.Comment: 7 pages, 6 eps figures; v2: minor changes, v3: final version, added discussion of EGMF influenc