Abstract
Recently, the High Energy Stereoscopic System (HESS) and other air Cerenkov telescopes have detected a source of TeV γ-rays coincident with the Galactic center. It is not yet clear whether the γ-rays are produced via leptonic or hadronic processes, so it is important to consider possible acceleration sites for the charged particles that produce the γ-rays. One exciting possibility for the origin of these particles is the central black hole, Sgr A*, where the turbulent magnetic fields close to the event horizon can accelerate protons to TeV energies. Using a realistic model of the density distribution in a 6 × 6 × 6 pc cube at the Galactic center, we here calculate the trajectories followed by these TeV protons as they gyrate through the turbulent medium surrounding Sgr A*. Diffusing out from the black hole, the protons produce TeV γ-rays via π° decay following a collision with a proton in the surrounding medium. After following over 222,000 such trajectories, we find that the circumnuclear ring around Sgr A* can reproduce the observed 0.1-100 TeV HESS spectrum and flux if the protons are injected into this medium with an effective power-law index ≈0.75, significantly harder than the observed photon index of 2.25. The total energy in the steady state 1-40 TeV proton population surrounding Sgr A* is inferred to be ≈5 × 1045 ergs. Only 31% of the emitted 1-100 TeV protons encounter the circumnuclear torus, leaving a large flux of protons that diffuse outward to contribute to the Galactic ridge emission observed by HESS on scales of ≳1°
| Original language | English (US) |
|---|---|
| Journal | Astrophysical Journal |
| Volume | 657 |
| Issue number | 1 II |
| DOIs | |
| State | Published - Mar 1 2007 |
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Keywords
- Acceleration of particles
- Galaxy: center
- Gamma rays: theory radiation mechanisms: nonthermal
ASJC Scopus subject areas
- Space and Planetary Science
- Astronomy and Astrophysics
Cite this
A possible link between the galactic center hess source and sagittarius a*. / Ballantyne, D. R.; Melia, Fulvio; Liu, Siming; Crocker, Roland M.
In: Astrophysical Journal, Vol. 657, No. 1 II, 01.03.2007.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - A possible link between the galactic center hess source and sagittarius a*
AU - Ballantyne, D. R.
AU - Melia, Fulvio
AU - Liu, Siming
AU - Crocker, Roland M.
PY - 2007/3/1
Y1 - 2007/3/1
N2 - Recently, the High Energy Stereoscopic System (HESS) and other air Cerenkov telescopes have detected a source of TeV γ-rays coincident with the Galactic center. It is not yet clear whether the γ-rays are produced via leptonic or hadronic processes, so it is important to consider possible acceleration sites for the charged particles that produce the γ-rays. One exciting possibility for the origin of these particles is the central black hole, Sgr A*, where the turbulent magnetic fields close to the event horizon can accelerate protons to TeV energies. Using a realistic model of the density distribution in a 6 × 6 × 6 pc cube at the Galactic center, we here calculate the trajectories followed by these TeV protons as they gyrate through the turbulent medium surrounding Sgr A*. Diffusing out from the black hole, the protons produce TeV γ-rays via π° decay following a collision with a proton in the surrounding medium. After following over 222,000 such trajectories, we find that the circumnuclear ring around Sgr A* can reproduce the observed 0.1-100 TeV HESS spectrum and flux if the protons are injected into this medium with an effective power-law index ≈0.75, significantly harder than the observed photon index of 2.25. The total energy in the steady state 1-40 TeV proton population surrounding Sgr A* is inferred to be ≈5 × 1045 ergs. Only 31% of the emitted 1-100 TeV protons encounter the circumnuclear torus, leaving a large flux of protons that diffuse outward to contribute to the Galactic ridge emission observed by HESS on scales of ≳1°
AB - Recently, the High Energy Stereoscopic System (HESS) and other air Cerenkov telescopes have detected a source of TeV γ-rays coincident with the Galactic center. It is not yet clear whether the γ-rays are produced via leptonic or hadronic processes, so it is important to consider possible acceleration sites for the charged particles that produce the γ-rays. One exciting possibility for the origin of these particles is the central black hole, Sgr A*, where the turbulent magnetic fields close to the event horizon can accelerate protons to TeV energies. Using a realistic model of the density distribution in a 6 × 6 × 6 pc cube at the Galactic center, we here calculate the trajectories followed by these TeV protons as they gyrate through the turbulent medium surrounding Sgr A*. Diffusing out from the black hole, the protons produce TeV γ-rays via π° decay following a collision with a proton in the surrounding medium. After following over 222,000 such trajectories, we find that the circumnuclear ring around Sgr A* can reproduce the observed 0.1-100 TeV HESS spectrum and flux if the protons are injected into this medium with an effective power-law index ≈0.75, significantly harder than the observed photon index of 2.25. The total energy in the steady state 1-40 TeV proton population surrounding Sgr A* is inferred to be ≈5 × 1045 ergs. Only 31% of the emitted 1-100 TeV protons encounter the circumnuclear torus, leaving a large flux of protons that diffuse outward to contribute to the Galactic ridge emission observed by HESS on scales of ≳1°
KW - Acceleration of particles
KW - Galaxy: center
KW - Gamma rays: theory radiation mechanisms: nonthermal
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U2 - 10.1086/513103
DO - 10.1086/513103
M3 - Article
AN - SCOPUS:33947536960
VL - 657
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1 II
ER -