Stochastic acceleration in the galactic center hess source

Siming Liu, Fulvio Melia, Vahé Petrosian, Marco Fatuzzo

Research output: Contribution to journalArticle

55 Scopus citations

Abstract

Stochastic acceleration of electrons interacting resonantly with a turbulent magnetic field in a small accretion torus appears to be the likely mechanism responsible for much of Sagittarius A*'s millimeter and shorter wavelength spectrum. The longer wavelength radiation is produced at larger radii by electrons either diffusing from smaller scales or accelerated in situ. An important prediction of this model is the ejection of a significant flux of relativistic protons from a magnetic-field-dominated acceleration site into the wind-shocked medium surrounding the black hole. Recently, several air Cerenkov telescopes, notably HESS, have detected TeV emission from the Galactic center, with characteristics hinting at p-p-induced pion decay process for the γ-ray emission. Given (1) the size of this acceleration region measured in the radio band and (2) the wind-injected ISM mapped with Chandra using the diffuse X-rays, it is feasible to test the idea that protons accelerated within ∼20 Schwarzschild radii of the black hole produce the TeV emission farther out. We show a fraction of TeV protons scattering about once within ∼3 pc of Sagittarius A* and the proton power (∼1037 ergs s -1) produced in concert with the 7 mm radio emission matches the TeV luminosity well. This model explains why the TeV source does not vary on a timescale of a year or less. The particle cascade generated by the p-p scatterings also produces bremsstrahlung, inverse Compton, and synchrotron emission at longer wavelengths from secondary particles. We compare these with current measurements and demonstrate that GLAST will detect this source during its one-year all-sky survey.

Original languageEnglish (US)
Pages (from-to)1099-1105
Number of pages7
JournalAstrophysical Journal
Volume647
Issue number2 I
DOIs
StatePublished - Aug 20 2006

Keywords

  • Acceleration of particles
  • Black hole physics
  • Galaxy: center
  • Gamma rays: theory
  • Plasmas
  • Turbulence

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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