Fermi bubbles: high latitude X-ray supersonic shell

Abstract

The nature of the bipolar, $\gamma$-ray Fermi bubbles (FB) is still unclear, in part because their faint, high-latitude X-ray counterpart has until now eluded a clear detection. We stack ROSAT data at varying distances from the FB edges, thus boosting the signal and identifying an expanding shell behind the southwest, southeast, and northwest edges, albeit not in the dusty northeast sector near Loop I. A Primakoff-like model for the underlying flow is invoked to show that the signals are consistent with halo gas heated by a strong, forward shock to $\sim$keV temperatures. Assuming ion--electron thermal equilibrium then implies a $\sim 10^{56}$ erg event near the Galactic centre $\sim 7$ Myr ago. However, the reported high absorption-line velocities suggest a preferential shock-heating of ions, and thus more energetic ($\sim 10^{57}$ erg), younger ($\lesssim 3$ Myr) FBs.

12 pages, comments welcome; high resolution version at http://physics.bgu.ac.il/~ukeshet/Online.html

References in corpus (9)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• The Spectrum and Morphology of the Fermi Bubbles
• The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays
• Giant Magnetized Outflows from the Centre of the Milky Way
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• Fermi Bubbles Inflated by Winds Launched from the Hot Accretion Flow in Sgr A*
• The Interaction of the Fermi Bubbles with the Milky Way's Hot Gas Halo
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• Fermi bubbles as a source of cosmic rays above 10^{15} eV

Cited by in corpus (9)

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• Analytical and numerical studies of central galactic outflows powered by tidal disruption events -- a model for the Fermi bubbles?
• Fermi bubbles: the collimated outburst needed to explain forward-shock edges
• Radio halos and relics from extended cosmic-ray ion distributions with strong diffusion in galaxy clusters
• Probing the Halo Gas Distribution in the Inner Galaxy with Fermi Bubble Observations
• Evidence for powerful winds and the associated reverse shock as the origin of the Fermi bubbles
• Fermi-bubble bulk and edge analysis reveals dust, cooling breaks, and cosmic-ray diffusion, facilitating a self-consistent model
• Detection of polarized Fermi-bubble synchrotron and dust emission