Journal Article

On the point-source approximation of nearby cosmic ray sources

Satyendra Thoudam and Jörg R. Hörandel

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 419, issue 1, pages 624-637
Published in print January 2012 | ISSN: 0035-8711
Published online December 2011 | e-ISSN: 1365-2966 | DOI: https://dx.doi.org/10.1111/j.1365-2966.2011.19724.x
On the point-source approximation of nearby cosmic ray sources

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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.

Keywords: cosmic rays; ISM: supernova remnants

Journal Article.  10428 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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