Speaker
Description
The Fermi-LAT discovered giant structures that are barely visible in the EGRET era. The most striking feature is the so-called Fermi bubbles, extending above and below the Galactic center. In addition, Fermi-LAT detected diffuse gamma-ray emissions associated with Loop I. The northern-most part of Loop I is the brightest arm, known as the North Polar Spur (NPS), and is even clearly visible in the ROSAT X-ray sky map. In previous works, we reported on the X-ray observations of the NPS and Galactic halo with the Suzaku and Swift satellites. All the results suggest that the NPS is a giant structure in the Galactic Center (GC) and is heated by the expansion of the Fermi Bubbles with a velocity of Vexp ~ 300 km/s; however, the origin of the X-ray and gamma-ray emissions associated with Loop I is completely unknown. To shed new light on the past activity of the GC, we analyzed all the archival X-ray data pointing toward Loop I with the Suzaku satellite. We argue, for the first time, that the soft gamma-ray spectra of Loop I may be due to π0 decay.
