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Title: | Spectrum and ionization rate of low-energy Galactic cosmic rays |
Authors: | Nath, Biman B. Gupta, Nayantara Biermann, P.L. |
Keywords: | ISM cloud cosmic rays molecules |
Issue Date: | Sep-2012 |
Publisher: | Royal Astronomical Society |
Citation: | Monthly Notices of the Royal Astronomical Society, 2012, Vol.425, pL86 |
Abstract: | We consider the rate of ionization of diffuse and molecular clouds in the interstellar medium by Galactic cosmic rays (GCRs) in order to constrain its low-energy spectrum. We extrapolate the GCR spectrum obtained from PAMELA at high energies (≥200 GeV nucleon-1) and a recently derived GCR proton flux at 1-200 GeV from observations of gamma-rays from molecular clouds, and find that the observed average Galactic ionization rate can be reconciled with this GCR spectrum if there is a low-energy cut-off for protons at 10-100 MeV. We also identify the flattening below a few GeV as being due to (a) decrease of the diffusion coefficient and dominance of convective loss at low energy and (b) the expected break in energy spectrum for a constant spectral index in momentum. We show that the inferred CR proton spectrum of ? for Ekin≤ few GeV is consistent with a power-law spectrum in momentum p-2.45± 0.4, which we identify as the spectrum at source. Diffusion loss at higher energies then introduces a steepening by E-α with α˜ 1/3, making it consistent with high-energy measurements. |
Description: | Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations) |
URI: | http://hdl.handle.net/2289/5549 |
ISSN: | 0035-8711 1365-2966(Online) |
Alternative Location: | http://adsabs.harvard.edu/abs/2012MNRAS.425L..86N http://arxiv.org/abs/1204.4239 http://dx.doi.org/10.1111/j.1745-3933.2012.01307.x |
Copyright: | 2012 Royal Astronomical Society |
Appears in Collections: | Research Papers (A&A) |
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2012_MNRAS_Vol.425_pL86.pdf Restricted Access | Restricted Access | 261.19 kB | Adobe PDF | View/Open Request a copy |
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