Origin of the Fermi Bubble

Abstract

Fermi has discovered two giant gamma-ray-emitting bubbles that extend nearly 10kpc in diameter north and south of the galactic center (GC). The existence of the bubbles was first evidenced in X-rays detected by ROSAT and later WMAP detected an excess of radio signals at the location of the gamma-ray bubbles. We propose that periodic star capture processes by the galactic supermassive black hole, Sgr A$^*$, with a capture rate $3\times 10^{-5}$yr$^{-1}$ and energy release $\sim 3\times 10^{52}$erg per capture can produce very hot plasma $\sim 10$keV with a wind velocity $\sim 10^8$cm/s injected into the halo and heat up the halo gas to $\sim 1$keV, which produces thermal X-rays. The periodic injection of hot plasma can produce shocks in the halo and accelerate electrons to $\sim$TeV, which produce radio emission via synchrotron radiation, and gamma-rays via inverse Compton scattering with the relic and the galactic soft photons.