New results on source and diffusion spectral features of Galactic cosmic rays: I $\vec{B/C}$ ratio

Abstract

Abstract. In a previous study , we explored the set of parameters describing diffusive propagation of cosmic rays (galactic convection, reacceleration, halo thickness, spectral index and normalization of the diffusion coefficient), and we identified those giving a good fit to the measured B/C ratio. This study is now extended to take into account a sixth free parameter, namely the spectral index of sources. We use an updated version of our code where the reacceleration term comes from standard minimal reacceleration models. The goal of this paper is to present a general view of the evolution of the goodness of fit to B/C data with the propagation parameters. In particular, we find that, unlike the well accepted picture, and in accordance with our previous study, a Kolmogorov-like power spectrum for diffusion is strongly disfavored. Rather, the χ 2 analysis points towards δ 0.7 along with source spectra index 2.0. Two distinct energy dependences are used for the source spectra: the usual power-law in rigidity and a law modified at low energy, the second choice being only slightly preferred. We also show that the results are not much affected by a different choice for the diffusion scheme. Finally, we compare our findings to recent works, using other propagation models. This study will be further refined in a companion paper, focusing on the fluxes of cosmic ray nuclei.

Systematic uncertainties on the cosmic-ray transport parameters

“…Although such precision is expected given the accuracy of the data, one may wonder whether these results are not dominated by systematic uncertainties from the input ingredients and assumptions made to do the calculation. This is an important issue since in our previous studies, the best-fit slope observed in a diffusion/constantconvection/reacceleration propagation model (Maurin et al 2001(Maurin et al , 2002) -confirmed by our recent MCMC analysis (Paper II) -points to δ ≈ 0.75−0.85. This is at variance with the result of the GALPROP code (Strong & Moskalenko 1998), where the best-fit models correspond to smaller δ ≈ 0.3−0.4 (Lionetto et al 2005) in either a diffusion/linear-convection or a diffusion -reacceleration model.…”

“…In the past years, we have promoted and used a model favouring both convection and reacceleration (e.g., Maurin et al 2001Maurin et al , 2002, and subsequent studies) from statistical criteria. The main and known problem of this model lies in its uncomfortably high value for δ (δ ∼ 0.8).…”

“…Whereas it has a small impact on the diffusion slope δ, the other transport parameters are strongly affected. The change in the parameters can be understood if we look at the grammage of the DM (Maurin et al 2002). In the purely diffusive regime, we have (e.g., Maurin et al 2006)…”

Galactic secondary positron flux at the Earth

“…In Maurin et al (2001Maurin et al ( , 2002, the secondary-to-primary ratio B/C is used to place constraints on the parameter space, and in Donato et al (2002) the information provided by the cosmic ray radioactive species is studied. For the discussion below, it is convenient to isolate three sets of parameters labeled MIN, MED, and MAX, defined in Table 1.…”

Indirect signals from light neutralinos in supersymmetric models without gaugino mass unification

“…[32], to which we refer for details. Here we only recall that the propagation of antiprotons has been considered in a two-zone diffusion model [48,49,50], defined in terms of six free parameters whose role is to take into account the main physical processes which affect the propagation of cosmic rays in the Galaxy: acceleration of primary nuclei, diffusion, convective wind, reacceleration process and interaction with the interstellar medium. These free parameters are constrained by comparing the fluxes of various cosmic ray species calculated in our diffusion model with observations.…”