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キーワード:
Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE
要旨:
Galactic cosmic rays are believed to be accelerated at supernova remnant
shocks. Though very popular and robust, this conjecture still needs a
conclusive proof. The strongest support to this idea is probably the fact that
supernova remnants are observed in gamma-rays, which are indeed expected as the
result of the hadronic interactions between the cosmic rays accelerated at the
shock and the ambient gas. However, also leptonic processes can, in most cases,
explain the observed gamma-ray emission. This implies that the detections in
gamma rays do not necessarily mean that supernova remnants accelerate cosmic
ray protons. To overcome this degeneracy, the multi-wavelength emission (from
radio to gamma rays) from individual supernova remnants has been studied and in
a few cases it has been possible to ascribe the gamma-ray emission to one of
the two processes (hadronic or leptonic). Here we adopt a different approach
and, instead of a case-by-case study we aim for a population study and we
compute the number of supernova remnants which are expected to be seen in TeV
gamma rays above a given flux under the assumption that these objects indeed
are the sources of cosmic rays. The predictions found here match well with
current observational results, thus providing a novel consistency check for the
supernova remnant paradigm for the origin of galactic cosmic rays. Moreover,
hints are presented for the fact that particle spectra significantly steeper
than E^-2 are produced at supernova remnants. Finally, we expect that several
of the supernova remnants detected by H.E.S.S. in the survey of the galactic
plane should exhibit a gamma-ray emission dominated by hadronic processes (i.e.
neutral pion decay). The fraction of the detected remnants for which the
leptonic emission dominates over the hadronic one depends on the assumed values
of the physical parameters and can be as high as roughly a half.
