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The Fermi bubbles were possibly created by large injections of energy intothe Galactic Center (GC), either by an active galactic nucleus (AGN) or bynuclear starburst more than ~10 Myr ago. However, the origin of the diffusegamma-ray emission associated with Loop I, a radio continuum loop spanningacross 100 deg on the sky, is still being debated. The northern-most part ofLoop I, known as the North Polar Spur (NPS), is the brightest arm and is evenclearly visible in the ROSAT X-ray sky map. In this paper, we present acomprehensive review on the X-ray observations of the Fermi bubbles and theirpossible association with the NPS and Loop I structures. Using uniform analysisof archival Suzaku and Swift data, we show that X-ray plasma with kT ~ 0.3 keVand low metal abundance (Z ~ 0.2 Z_solar) is ubiquitous in both the bubbles andLoop I and is naturally interpreted as weakly shock-heated Galactic halo gas.However, the observed asymmetry of the X-ray-emitting gas above and below theGC has still not been resolved; it cannot be fully explained by the inclinationof the axis of the Fermi bubbles to the Galactic disk normal. We argue that theNPS and Loop I may be asymmetric remnants of a large explosion that occurredbefore the event that created the Fermi bubbles, and that the soft gamma-rayemission from Loop I may be due to either pi^0 decay of accelerated protons orelectron bremsstrahlung.

X-ray and Gamma-ray Observations of the Fermi Bubbles and NPS/Loop I Structures