1,341 research outputs found
Theoretical study of ionization profiles of molecular clouds near supernova remnants: Tracing the hadronic origin of GeV gamma radiation
Context: Since a few years, signatures of supernova remnants associated with
molecular clouds have been detected in gamma rays. Whether these gamma rays are
generated by cosmic ray electrons or by cosmic ray protons is usually not
known. The detection of hadronic ionization signatures in spatial coincidence
with gamma ray signatures can help to unambiguously identify supernova remnants
as sources of cosmic ray protons.
Methods: In order to calculate hadronic signatures from cosmic ray-induced
ionization for an examination of the origin of the observed gamma rays, the
transport equation for cosmic ray protons propagating in a molecular cloud,
including the relevant momentum loss processes, is solved analytically and the
proton flux at any position in the cloud is determined.
Results: Since the solution of the transport equation is obtained for
arbitrary source functions, it can be used for a variety of supernova remnants.
The corresponding theoretical ionization rate, as a function of the penetration
depth, is derived and compared to photoinduced ionization profiles in a case
study with four supernova remnants associated with molecular clouds. Three of
the remnants show a clear dominance of the hadronically induced ionization
rate, while for one remnant, X-ray emission seems to dominate by a factor of
10.
Conclusions: This is the first derivation of position-dependent profiles for
cosmic ray-induced ionization with an analytic solution for arbitrary cosmic
ray source spectra. The cosmic ray-induced ionization has to be compared to
X-ray ionization for strong X-ray sources. For sources dominated by cosmic
ray-induced ionization (e.g., W49B), the ionization profiles can be used in the
future to map the spatial structure of hadronic gamma rays and
rotation-vibrational lines induced by cosmic ray protons, helping to identify
sources of hadronic cosmic rays.Comment: published in Astronomy and Astrophysics, 20 pages, 17 figure
Impact of Secondary Acceleration in Gamma-Ray Bursts
We discuss the acceleration of secondary muons, pions, and kaons in gamma-ray
bursts within the internal shock scenario, and their impact on the neutrino
fluxes. We introduce a two-zone model consisting of an acceleration zone (the
shocks) and a radiation zone (the plasma downstream the shocks). The
acceleration in the shocks, which is an unavoidable consequence of the
efficient proton acceleration, requires efficient transport from the radiation
back to the acceleration zone. On the other hand, stochastic acceleration in
the radiation zone can enhance the secondary spectra of muons and kaons
significantly if there is a sufficiently large turbulent region. Overall, it is
plausible that neutrino spectra can be enhanced by up to a factor of two at the
peak by stochastic acceleration, that an additional spectral peaks appears from
shock acceleration of the secondary muons and pions, and that the neutrino
production from kaon decays is enhanced. Depending on the GRB parameters, the
general conclusions concerning the limits to the internal shock scenario
obtained by recent IceCube and ANTARES analyses may be affected by up to a
factor of two by secondary acceleration. Most of the changes occur at energies
above 10^7 GeV, so the effects for next-generation radio-detection experiments
will be more pronounced. In the future, however, if GRBs are detected as
high-energy neutrino sources, the detection of one or several pronounced peaks
around 10^6 GeV or higher energies could help to derive the basic properties of
the magnetic field strength in the GRB.Comment: 10 pages, 5 figures, 1 tabl
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