Hadronic models of the Fermi bubbles: Future perspectives

TL;DR

This paper reviews hadronic models explaining the Fermi bubbles' gamma-ray emission, discusses recent observational constraints, and explores future prospects for neutrino and gamma-ray detection to distinguish the origin of these emissions.

Contribution

It provides an updated analysis of hadronic models for the Fermi bubbles and discusses how future high-energy observations can test these models.

Findings

Recent HAWC data constrains hadronic model parameters.

Fermi bubbles are unlikely to account for most IceCube neutrinos.

Future gamma-ray and neutrino observations can further test hadronic scenarios.

Abstract

The origin of sub-TeV gamma rays detected by Fermi-LAT from the Fermi bubbles at the Galactic center is still unknown. In a hadronic model, acceleration of protons and/or nuclei and their subsequent interactions with gas in the bubble volume can produce observed gamma rays. Such interactions naturally produce high-energy neutrinos, and detection of those can discriminate between a hadronic and a leptonic origin of gamma rays. Additional constraints on the Fermi bubbles gamma-ray flux in the TeV range from recent HAWC observations restrict hadronic model parameters, which in turn disfavor Fermi bubbles as the origin of a large fraction of neutrino events detected by IceCube along the bubble directions. We revisit our hadronic model and discuss future constraints on parameters from observations in very high-energy gamma rays and neutrinos.