and 5.1 $\times 10^{-8}$ GeV $\flux4$, depending on the exact location of the source. They excluded a single point source as the origin of 7 neutrinos observed by IceCube in the vicinity of galactic centre. However, an extended source of a few degrees is not excluded.

Since the most likely high-energy neutrino producing mechanisms are the inelastic $p-$nuclei and $p-\gamma$ collisions of protons, where the reaction kinematics result in the energy of the neutrinos to be $\sim 0.05$ that of the protons, the energy of the parent protons should exceed $4 \cdot10^{16}$ eV to explain the IceCube observations. The [$\gamma$-rays]{} produced in these reactions have $\sim 0.1$ of the proton energy [e.g., @halzen13]. Furthermore, the proton accelerators must be very efficient to produce the high-energy neutrino flux of $\nu F_{\nu}\approx 10^{-8}\enfnu$ per flavor in the 0.1-1PeV range detected by IceCube.

Neutrinos from photo-meson $p-\gamma$ interactions in compact particle accelerators, like the cores of active galactic nuclei (AGN) [e.g., @stecker13] and [$\gamma$-ray]{} bursts (GRBs) [e.g., @waxman97; @MW01], along with other models [e.g., @ahlers2013; @Fox13; @Kashiyamaea13; @He2013; @muraseea13; @2014PhRvD..89h3004L; @CRs_mergers_ApJ14; @starburst_neutrinos14; @neutrino_starburst14], have been proposed to explain the origin of these first-ever IceCube neutrinos.

It has been suggested by @neronovea14 that IceCube 