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- Putze, Antje, et al.
(författare)
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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
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 526, s. A101-
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Tidskriftsartikel (refereegranskat)abstract
- Context. The source spectrum of cosmic rays is not well determined by diffusive shock acceleration models. The propagated fluxes of proton, helium, and heavier primary cosmic-ray species (up to Fe) are a means to indirectly access it. But how robust are the constraints, and how degenerate are the source and transport parameters? Aims. We check the compatibility of the primary fluxes with the transport parameters derived from the B/C analysis, but also ask whether they add further constraints. We study whether the spectral shapes of these fluxes and their ratios are mostly driven by source or propagation effects. We then derive the source parameters (slope, abundance, and low-energy shape). Methods. Simple analytical formulae are used to address the issue of degeneracies between source/transport parameters, and to understand the shape of the p/He and C/O to Fe/O data. The full analysis relies on the USINE propagation package, the MINUIT minimisation routines (chi(2) analysis) and a Markov Chain Monte Carlo (MCMC) technique. Results. 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 similar to 1 TeV/n. Fits to the primary fluxes alone do not provide physical constraints on the transport parameters. If we leave the source spectrum free, parametrised by the form dQ/dE = q beta(eta S)R(-alpha), and fix the diffusion coefficient K(R) = K(0)beta(eta T)R(delta) so as to reproduce the B/C ratio, the MCMC analysis constrains the source spectral index a 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 values of the parameter eta(S) describing the low-energy shape of the source spectrum are degenerate with the parameter eta(T) describing the low-energy shape of the diffusion coefficient: we find eta(S) - eta(T) approximate to 0 for p and He data, but eta(S) - eta(T) approximate to 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) approximate to 0-1 (no need for different slopes a). When plotted as a function of the kinetic energy per nucleon, the low-energy p/He ratio is determined mostly by the modulation effect, whereas primary/O ratios are mostly determined by their destruction rate. Conclusions. Models based on fitting B/C are compatible with primary fluxes. The different spectral indices for the propagated primary fluxes up to a few TeV/n can be naturally ascribed to transport effects only, implying universality of elemental source spectra.
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| 2. |
- Wu, Juan, 1982-, et al.
(författare)
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Constraints on cosmic-ray propagation and acceleration models from recent data
- 2011
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Ingår i: Proceedings of the 32nd International Cosmic Ray Conference, ICRC 2011. - : Institute of High Energy Physics. ; , s. 228-231
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Konferensbidrag (refereegranskat)abstract
- We are studying the constraints obtained on transport and acceleration mechanisms of galactic cosmic rays by using statistical tools in combination with the propagation package GALPROP and recent PAMELA data. Using only PAMELA data allows us to avoid inconsistencies between data sets from different experiments, minimise uncertainties on solar modulation parameters, and have a complementary and precise data set on (anti-)matter as well as primary and secondary nuclei over 3 orders of magnitude in energy. This allows us to simultaneously place strong constraints on cosmic-ray propagation and acceleration models. We describe our methodology and present some preliminary results in this paper.
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