I. Telezhinsky, V. V. Dwarkadas, M. Pohl
Context. Supernova Remnants (SNRs) are thought to be the main source of
Galactic cosmic rays (CRs) up to the "knee". During the evolution of a SNR, the
bulk of the CRs are confined within the SNR shell. The highest-energy particles
leave the system continuously, while the remaining adiabatically-cooled
particles are released when the SNR has sufficiently expanded and slowed down
so that the magnetic field (MF) at the shock is no longer able to confine them.
Particles escaping from the parent system may end up interacting with nearby
molecular clouds (MCs), producing $\gamma$-rays in the process via pion decay.
The soft gamma-ray spectra observed from a number of SNRs interacting with
molecular clouds (MCs) however challenge current theories of non-linear
particle acceleration that predict harder spectra. Aims. To study how the
spectrum of escaped particles depends on the time-dependent acceleration
history in both type-Ia and core-collapse SNRs, as well as on different
assumptions about the diffusion coefficient in the vicinity of the SNR.
Methods. We solve the CR transport equation in a test-particle approach
combined with numerical simulations of SNR evolution. Results. We extend our
method for calculation of cosmic-ray acceleration in SNRs to trace the escaped
particles in a large volume around SNRs. We calculate the evolution of the
spectra of CRs escaped from a SNR into a molecular cloud or dense shell for two
diffusion models. We find a strong confinement of CRs in a close region around
the SNR, and a strong dilution effect for CRs which were able to propagate out
as far as a few SNR radii.
View original:
http://arxiv.org/abs/1112.3194
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