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p, He, and C to Fe cosmic-ray primary fluxes in diffusion models: Source and transport signatures on fluxes and ratios

Abstract : The propagated fluxes of proton, helium, and heavier primary cosmic-ray species (up to Fe) are a means to indirectly access the source spectrum of cosmic rays. We check the compatibility of the primary fluxes with the transport parameters derived from the B/C analysis, but also if they bring further constraints. Proton data are well described in the simplest model defined by a power-law source spectrum and plain diffusion. They can also be accommodated by models with, e.g., convection and/or reacceleration. There is no need for breaks in the source spectral indices below $\sim 1$ TeV/n. Fits on the primary fluxes alone do not provide physical constraints on the transport parameters. If we let free the source spectrum $dQ/dE = q \beta^{\eta_S} {\cal R}^{-\alpha}$ and fix the diffusion coefficient $K(R)= K_0\beta^{\eta_T} {\cal R}^{\delta}$ such as to reproduce the B/C ratio, the MCMC analysis constrains the source spectral index $\alpha$ to be in the range $2.2-2.5$ for all primary species up to Fe, regardless of the value of the diffusion slope $\delta$. The $\eta_S$ low-energy shape of the source spectrum is degenerate with the low-energy shape $\eta_T$ of the diffusion coefficient: we find $\eta_S-\eta_T\approx 0$ for p and He data, but $\eta_S-\eta_T\approx 1$ for C to Fe primary species. This is consistent with the toy-model calculation in which the shape of the p/He and C/O to Fe/O data is reproduced if $\eta_S-\eta_T\approx 0-1$ (no need for different slopes $\alpha$). When plotted as a function of the kinetic energy per nucleon, the low-energy p/He ratio is shaped mostly by the modulation effect, whereas primary/O ratios are mostly shaped by their destruction rate.
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http://hal.in2p3.fr/in2p3-00532563
Contributor : Emmanuelle Vernay <>
Submitted on : Thursday, November 4, 2010 - 8:57:46 AM
Last modification on : Monday, July 20, 2020 - 9:18:25 AM

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A. Putze, D. Maurin, F. Donato. p, He, and C to Fe cosmic-ray primary fluxes in diffusion models: Source and transport signatures on fluxes and ratios. Astronomy and Astrophysics - A&A, EDP Sciences, 2011, 526, pp.A101. ⟨10.1051/0004-6361/201016064⟩. ⟨in2p3-00532563⟩

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