# IceCube constraints on the Fermi Bubbles

## TL;DR

This study uses four years of IceCube neutrino data to search for signals from the Fermi bubbles, setting limits on cosmic-ray acceleration efficiency and electron-to-ion ratios, with no detection found.

## Contribution

It provides the first constraints on cosmic-ray acceleration efficiency and electron-to-ion ratios in the Fermi bubbles using neutrino observations.

## Key findings

- No neutrino signal detected from the Fermi bubbles.
- Sets a conservative upper limit of 8% on cosmic-ray ion acceleration efficiency.
- Establishes a lower limit of 0.006 on the electron-to-ion ratio of acceleration efficiencies.

## 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 $\eta\equiv \xi_e/\xi_i \gtrsim0.006$ 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.