| 1. |
- Thoudam, Satyendra, et al.
(författare)
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Nearby supernova remnants and the cosmic ray spectral hardening at high energies
- 2012
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 421:2, s. 1209-1214
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Tidskriftsartikel (refereegranskat)abstract
- Recent measurements of cosmic ray spectra of several individual nuclear species by the CREAM, TRACER and ATIC experiments indicate a change in the spectral index of the power laws at TeV energies. Possible explanations among others include non-linear diffusive shock acceleration of cosmic rays, different cosmic ray propagation properties at higher and lower energies in the Galaxy and the presence of nearby sources. In this paper, we show that if supernova remnants are the main sources of cosmic rays in our Galaxy, the effect of the nearby remnants can be responsible for the observed spectral changes. Using a rigidity-dependent escape of cosmic rays from the supernova remnants, we explain the apparent observed property that the hardening of the helium spectrum occurs at relatively lower energies as compared to the protons and also that the spectral hardening does not persist beyond ∼(20–30) TeV energies.
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| 2. |
- Thoudam, Satyendra, et al.
(författare)
-
On the point-source approximation of nearby cosmic ray sources
- 2012
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 419:1, s. 624-637
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we check in detail the validity of the widely adopted point-source approximation for nearby cosmic ray (CR) sources. Under an energy-independent escape model for CRs from the sources, we show that for young nearby sources, the point-source approximation breaks down at lower energies and the CR spectrum depends on the size and the morphology of the source. When applied to the nearby supernova remnants (SNRs), we find that the approximation breaks down for some of the individual remnants like the Vela, but interestingly it still holds good for their combined total spectrum at the Earth. Moreover, we also find that the results obtained under this simple approximation are quite different from those calculated under an energy-dependent escape model which is favoured by diffusive shock acceleration models inside SNRs. Our study suggests that if SNRs are the main sources of CRs in our Galaxy, then the commonly adopted point-source model (with an energy-independent escape scenario) appears flawed for CR studies from the nearby SNRs.
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