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Title: Realistic modelling of wind and supernovae shocks in star clusters: addressing 22Ne/20Ne and other problems in Galactic cosmic rays
Authors: Gupta, Siddhartha
Nath, Biman B.
Sharma, Prateek
Eichler, D.
Keywords: hydrodynamics – shock waves – methods
numerical – cosmic rays
Issue Date: Apr-2020
Publisher: Oxford University Press on behalf of the Royal Astronomical Society
Citation: Monthly Notices of the Royal Astronomical Society, 2020, Vol.493, p3159–3177
Abstract: Cosmic ray (CR) sources leave signatures in the isotopic abundances of CRs. Current models of Galactic CRs that consider supernovae (SNe) shocks as the main sites of particle acceleration cannot satisfactorily explain the higher 22Ne/20Ne ratio in CRs compared to the interstellar medium. Although stellar winds from massive stars have been invoked, their contribution relative to SNe ejecta has been taken as a free parameter. Here, we present a theoretical calculation of the relative contributions of wind termination shocks (WTSs) and SNe shocks in superbubbles, based on the hydrodynamics of winds in clusters, the standard stellar mass function, and stellar evolution theory. We find that the contribution of WTSs towards the total CR production is at least 25{{ per cent}}, which rises to ≳ 50{{ per cent}} for young (≲10 Myr) clusters, and explains the observed 22Ne/20Ne ratio. We argue that since the progenitors of apparently isolated supernovae remnants (SNRs) are born in massive star clusters, both WTS and SNe shocks can be integrated into a combined scenario of CRs being accelerated in massive clusters. This scenario is consistent with the observed ratio of SNRs to γ-ray bright (Lγ ≳ 1035 erg s-1) star clusters, as predicted by star cluster mass function. Moreover, WTSs can accelerate CRs to PeV energies, and solve other long-standing problems of the standard SN paradigm of CR acceleration.
Description: Open Access
ISSN: 0035-8711
1365-2966 (online)
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Copyright: 2020 The Author(s)
Appears in Collections:Research Papers (A&A)

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