Nonthermal emission in the lobes of Fornax A. (arXiv:1902.05797v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Persic_M/0/1/0/all/0/1">Massimo Persic</a> (INAF Trieste, Italy, Physics & Astronomy Dept., Bologna U., Italy), <a href="http://arxiv.org/find/astro-ph/1/au:+Rephaeli_Y/0/1/0/all/0/1">Yoel Rephaeli</a> (School of Physics & Astronomy, Tel Aviv U., Israel, Center for Astrophysics & Space Sciences, UC San Diego, USA)
Current measurements of the spectral energy distribution in radio,
X-and-gamma-ray provide a sufficiently wide basis for determining basic
properties of energetic electrons and protons in the extended lobes of the
radio galaxy Fornax A. Of particular interest is establishing observationally,
for the first time, the level of contribution of energetic protons to the
extended emission observed by the Fermi satellite. Two recent studies concluded
that the observed gamma-ray emission is unlikely to result from Compton
scattering of energetic electrons off the optical radiation field in the lobes,
and therefore that the emission originates from decays of neutral pions
produced in interactions of energetic protons with protons in the lobe plasma,
implying an uncomfortably high proton energy density. However, our exact
calculation of the emission by energetic electrons in the magnetized lobe
plasma leads to the conclusion that all the observed emission can, in fact, be
accounted for by energetic electrons scattering off the ambient optical
radiation field, whose energy density (which, based on recent observations, is
dominated by emission from the central galaxy NGC 1316) we calculate to be
higher than previously estimated.
Current measurements of the spectral energy distribution in radio,
X-and-gamma-ray provide a sufficiently wide basis for determining basic
properties of energetic electrons and protons in the extended lobes of the
radio galaxy Fornax A. Of particular interest is establishing observationally,
for the first time, the level of contribution of energetic protons to the
extended emission observed by the Fermi satellite. Two recent studies concluded
that the observed gamma-ray emission is unlikely to result from Compton
scattering of energetic electrons off the optical radiation field in the lobes,
and therefore that the emission originates from decays of neutral pions
produced in interactions of energetic protons with protons in the lobe plasma,
implying an uncomfortably high proton energy density. However, our exact
calculation of the emission by energetic electrons in the magnetized lobe
plasma leads to the conclusion that all the observed emission can, in fact, be
accounted for by energetic electrons scattering off the ambient optical
radiation field, whose energy density (which, based on recent observations, is
dominated by emission from the central galaxy NGC 1316) we calculate to be
higher than previously estimated.
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