Issue |
A&A
Volume 419, Number 1, May III 2004
|
|
---|---|---|
Page(s) | 89 - 98 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20034231 | |
Published online | 23 April 2004 |
M 87 as a misaligned synchrotron-proton blazar
1
Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- & Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany e-mail: afm@tp4.rub.de
2
Department of Physics and Mathematical Physics, The University of Adelaide, Adelaide SA 5005, Australia e-mail: [rprother; adonea]@physics.adelaide.edu.au
Corresponding author: A. Reimer, afm@tp4.ruhr-uni-bochum.de
Received:
27
August
2003
Accepted:
3
February
2004
The giant radio galaxy M 87 is usually classified as
a Fanaroff-Riley class I source, suggesting that M 87 is a
mis-aligned BL Lac object. Its unresolved nuclear region emits
strong non-thermal emission from radio to X-rays which has
been interpreted as synchrotron radiation.
In an earlier
paper we predicted M 87 as a source of detectable gamma ray
emission in the context of the hadronic Synchrotron-Proton
Blazar (SPB) model.
The subsequent tentative detection of TeV energy photons by the HEGRA-telescope array would, if
confirmed, make it the first radio galaxy to be detected at
TeV-energies. We discuss the emission from the unresolved
nuclear region of M 87 in the context of the SPB model, and
give examples of possible model representations of its
non-simultaneous spectral energy distribution. The low-energy
component can be explained as synchrotron radiation by a
primary relativistic electron population that is injected
together with energetic protons into a highly magnetized
emission region. We find that the γ-ray power output
is dominated either by /
synchrotron or
proton synchrotron radiation depending on whether the primary
electron synchrotron component peaks at low or high energies,
respectively. The predicted γ-ray luminosity peaks at ~100 GeV at a level comparable to that of the low-energy
hump, and this makes M 87 a promising candidate source for the
newly-commissioned high-sensitivity low-threshold Cherenkov
telescopes H.E.S.S., VERITAS, MAGIC and CANGAROO III. Because
of its proximity, the high-energy spectrum of M 87 is
unaffected by absorption in the cosmic infrared (IR)
background radiation field, and could therefore serve as a
template spectrum for the corresponding class of blazar if
corrected for mis-alignment effects. This could significantly
push efforts to constrain the cosmic IR radiation field
through observation of more distant TeV-blazars, and could
have a strong impact on blazar emission models. If M 87 is a
mis-aligned BL-Lac object and produces TeV-photons as recently
detected by the HEGRA-array, in the context of the SPB model
it must also be an efficient proton accelerator.
Key words: galaxies: active / galaxies: individual: M 87 / gamma rays: theory / radiation mechanisms: non-thermal
© ESO, 2004
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