IceCube constraints on the Fermi Bubbles

Abstract

We analyze the IceCube four-year neutrino data in search of a signal from the Fermi bubbles. No signal is found from the bubbles or from their dense shell, even when taking into account the softer background. This imposes a conservative ${\xi }_i<8\%$ upper limit on the cosmic-ray ion (CRI) acceleration efficiency, and an $\eta \equiv {\xi }_e/{\xi }_i\gtrsim 0.006$ lower limit on the electron-to-ion ratio of acceleration efficiencies (at the $2\sigma$ confidence level). For typical ${\xi }_i$, a signal should surface once the number of IceCube neutrinos increases by $\sim$an order of magnitude, unless there is a $<$PeV cutoff on the CRI spectrum.

Revised version to appear in the Astrophysical Journal