Fermi Bubble

Z.G.,Xiong

Outline

• Observations• Theories• Simulations• Discussion

Observations

• Finkbeiner,2004

• Bland-Hawthorn & Cohen, 2003

• Su et al.,2010

• Characteristics:• size• symmetry• uniform• common origin• morphology• spectrum

Theories

• Bipolar Galactic wind• Echoes of the Last Quasar Outburst• AGN Jet• Cosmic Rays Reservoirs• Star Capture

• Bipolar Galactic wind

• Bland-Hawthorn， 2002• In accord with the stellar record in the Galactic Center, we infer that a

powerful nuclear starburst has taken place within the last several million years

• We infer that the Galactic Center is driving large-scale winds into the halo every 10 − 15 Myr or so.∼

• Echoes of the Last Quasar Outburst• Zubovas,2011• Here we propose an alternative picture where the bubbles are

the remnants of a large–scale wide–angle outflow from the SMBH of our Galaxy.

• the well known star formation event in the inner 0.5pc of the Milky Way 6 Myr ago.

• We estimate that an accreted mass 2 × 10^3M is needed ⊙for the accretion event to power the observed Fermi–LAT lobes.

• This estimate suggests that roughly 50% of the gas was turned into stars, while the rest accreted onto Sgr A∗

• AGN Jet Guo， 2011• we show that the bubbles can be created with a recent AGN

jet activity about 1 - 3 Myr ago, which was active for a duration of 0.1 - 0.5 Myr∼

• Roles of viscosity and cosmic ray diffusion

• Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays

• Crocker,2011• Here we show that the bubbles are naturally explained as due

to a population of relic cosmic ray protons and heavier ions injected by processes associated with extremely long timescale (> 8 Gyr) and high areal density star-formation in the Galactic center.

• Fermi Bubbles as a Result of Star Capture in the Galactic Center

• Dogiel,2011; Cheng,2011; Chernyshov,2011.

• processes of star capture by the central black hole• Dogiel et al. (2009d).

• Star capture by the central black hole• Plasma heating by subrelativistic protons• The hydrodynamic expansion stage• Shock wave acceleration phase and non-

thermal emission

Simulation

• AGN Jet• Equations

• The Galactic Model

• Star Capture• Parameters: the tidal disruption rate; power; …

• Shock stucture:

• Proton spectrum

• Electron spectrum

• Space distribution

• Interactions between shocks:

Discussion

• Young or old?• Leptonic or baryonic?• Common?• Impact• Regulation for CRs

Thank you!