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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