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Fermi gamma-ray "bubbles" from stochastic acceleration of electrons
Philipp Mertsch1, Subir Sarkar
1Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP, United Kingdom.
Physical Review Letters
|September 21, 2011
Summary
Gamma-ray bubbles near the Galactic Center may be explained by stochastic electron acceleration. This process, driven by plasma waves, naturally produces the observed gamma-ray spectrum and bubble structure.
Area of Science:
- Astrophysics
- High-energy astrophysics
- Cosmic ray physics
Background:
- Fermi Large Area Telescope data reveal bilobular gamma-ray structures extending from the Galactic Center.
- Existing models propose hadronic interactions or inverse-Compton scattering from plasma shocks as the gamma-ray origin.
Purpose of the Study:
- To explore stochastic 2nd-order Fermi acceleration as an alternative mechanism for electron acceleration within the gamma-ray bubbles.
- To explain the observed gamma-ray spectral shape and bubble morphology using this alternative acceleration model.
Main Methods:
- Investigated stochastic 2nd-order Fermi acceleration of relativistic electrons by plasma wave turbulence throughout the bubble volume.
- Modeled the resulting electron spectrum and inverse-Compton energy losses to predict gamma-ray emission.
Main Results:
- The stochastic acceleration model naturally explains the observed gamma-ray spectral shape.
- The model predicts a nearly constant surface brightness, consistent with the sharp edges of the observed bubbles.
- This contrasts with models predicting constant volume emissivity.
Conclusions:
- Stochastic 2nd-order Fermi acceleration provides a compelling alternative explanation for the origin of relativistic electrons in Galactic Center gamma-ray bubbles.
- This mechanism successfully reproduces key observational features, including spectral shape and bubble morphology.
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