Time-dependent Diffusive Shock Acceleration in Slow Supernova Remnant Shocks

Abstract

Recent gamma ray observations show that middle aged supernova remnants interacting with molecular clouds can be sources of both GeV and TeV emission. Models involving re-acceleration of pre-existing cosmic rays in the ambient medium and direct interaction between supernova remnant and molecular clouds have been proposed to explain the observed gamma ray emission. For the re-acceleration process, standard DSA theory in the test particle limit produces a steady state particle spectrum that is too flat compared to observations, which suggests that the high energy part of the observed spectrum has not yet reached a steady state. We derive a time dependent DSA solution in the test particle limit for situations involving re-acceleration of pre-existing cosmic rays in the preshock medium. Simple estimates with our time dependent DSA solution plus a molecular cloud interaction model can reproduce the overall shape of the spectra of IC 443 and W44 from GeV to TeV energies through pure ${\pi }^0$-decay emission. We allow for a power law momentum dependence of the diffusion coefficient, finding that a power law index of 0.5 is favored.

26 pages, 5 figures, accepted by ApJ

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Cited by in corpus (11)

• The supernova remnant W44: a case of cosmic-Ray reacceleration
• Cosmic-ray acceleration and escape from post-adiabatic Supernova remnants
• NuSTAR Detection of a Hard X-ray Source in the Supernova Remnant - Molecular Cloud Interaction Site of IC 443
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• SNR G39.2-0.3, an Hadronic Cosmic Rays Accelerator
• Time-dependent shock acceleration of particles. Effect of the time-dependent injection, with application to supernova remnants
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