Hard and bright gamma-ray emission at the base of the Fermi bubbles

Understand

The Fermi bubbles (FBs) are large gamma-ray emitting lobes extending up to $55\deg$ in latitude above and below the Galactic center (GC).

• Although the FBs were discovered 8 years ago, their origin and the nature of the gamma-ray emission are still unresolved.
• Understanding the properties of the FBs near the Galactic plane may provide a clue to their origin.
• Previous analyses of the gamma-ray emission at the base of the FBs, what remains after subtraction of Galactic foregrounds, have shown an increased intensity compared to the FBs at high latitudes, a hard power-law spectrum without evidence of a cutoff up to approximately 1 TeV, and a displacement of the emission to negative longitudes relative to the GC.