Systematic uncertainties on the cosmic-ray transport parameters

Maurin, D.; Putze, A.; Derome, L.

doi:10.1051/0004-6361/201014011

Cited by 83 publications

(129 citation statements)

References 22 publications

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“…This scatter in δ was already observed in Jones et al (2001), who also studied different classes of models. The origin of this scatter is consistent with the aforementioned correlations in the parameters (see also Maurin et al 2010).…”

Section: Model Transport Parameterssupporting

confidence: 88%

“…The gain is in the computing time, which is a prerequisite for the use of the MCMC technique, where several tens of thousands of models are calculated. These semi-analytical models reproduce all salient features of full numerical approaches (e.g., Strong & Moskalenko 1998), and they are useful for systematically studying the dependence on key parameters, or some systematics of the parameter determination (Maurin et al 2010).…”

Section: Geometry Of the Galaxy And Simplifying Assumptionsmentioning

confidence: 93%

“…This corresponds to statistical uncertainties only. These uncertainties are of the order of, or smaller than systematics generated from uncertainties in the input ingredients (see details in Maurin et al 2010).…”

Section: Model Transport Parametersmentioning

confidence: 99%

“…The parameter degeneracy is also more easily extracted and understood in this case (Jones et al 2001;Maurin et al 2006). Nevertheless, the results for the 2D geometry are also reported, as it has been used in a series of studies inspecting stable nuclei , β-radioactive nuclei , standard anti-nuclei ) and positrons ).…”

Section: Geometry Of the Galaxy And Simplifying Assumptionsmentioning

confidence: 99%

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A Markov Chain Monte Carlo technique to sample transport and source parameters of Galactic cosmic rays

Putze

Derome

Maurin

2010

A&A

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150

194

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Context. Ongoing measurements of the cosmic radiation (nuclear, electronic, and γ-ray) are providing additional insight into cosmicray physics. A comprehensive picture of these data relies on an accurate determination of the transport and source parameters of propagation models. Aims. A Markov Chain Monte Carlo method is used to obtain these parameters in a diffusion model. By measuring the B/C ratio and radioactive cosmic-ray clocks, we calculate their probability density functions, placing special emphasis on the halo size L of the Galaxy and the local underdense bubble of size r h . We also derive the mean, best-fit model parameters and 68% confidence level for the various parameters, and the envelopes of other quantities. Methods. The analysis relies on the USINE code for propagation and on a Markov Chain Monte Carlo technique previously developed by ourselves for the parameter determination. Results. The B/C analysis leads to a most probable diffusion slope δ = 0.86 +0.04 −0.04 for diffusion, convection, and reacceleration, or δ = 0.234 +0.006 −0.005 for diffusion and reacceleration. As found in previous studies, the B/C best-fit model favours the first configuration, hence pointing to a high value for δ. These results do not depend on L, and we provide simple functions to rescale the value of the transport parameters to any L. A combined fit on B/C and the isotopic ratios ( 10 Be/ 9 Be, 26 Al/ 27 Al, 36 Cl/Cl) leads to L = 8 +8 −7 kpc and r h = 120 +20 −20 pc for the best-fit model. This value for r h is consistent with direct measurements of the local interstallar medium. For the model with diffusion and reacceleration, L = 4 +1 −1 kpc and r h = 3 +70 −3 pc (consistent with zero). We vary δ, because its value is still disputed. For the model with Galactic winds, we find that between δ = 0.2 and 0.9, L varies from O(0) to O(2) if r h is forced to be 0, but it otherwise varies from O(0) to O(1) (with r h ∼ 100 pc for all δ > ∼ 0.3). The results from the elemental ratios Be/B, Al/Mg, and Cl/Ar do not allow independent checks of this picture because these data are not precise enough. Conclusions. We showed the potential and usefulness of the Markov Chain Monte Carlo technique in the analysis of cosmic-ray measurements in diffusion models. The size of the diffusive halo depends crucially on the value of the diffusion slope δ, and also on the presence/absence of the local underdensity damping effect on radioactive nuclei. More precise data from ongoing experiments are expected to clarify this issue.

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Section: Model Transport Parameterssupporting

confidence: 88%

Section: Geometry Of the Galaxy And Simplifying Assumptionsmentioning

confidence: 93%

Section: Model Transport Parametersmentioning

confidence: 99%

Section: Geometry Of the Galaxy And Simplifying Assumptionsmentioning

confidence: 99%

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A Markov Chain Monte Carlo technique to sample transport and source parameters of Galactic cosmic rays

Putze

Derome

Maurin

2010

A&A

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150

194

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“…This CR component is usually interpreted as the result of production by spallation of heavier species during the propagation of primary cosmic rays -whose injected abundance is assumed to closely trace that of the solar system -in the interstellar medium. The ratios of these secondary to primary fluxes have long been recognised as a tool for constraining CR propagation parameters, for some review see for instance Maurin et al (2002) and Strong et al (2007). The boron-to-carbon ratio (B/C), represents the most notable example among them.…”

Section: Introductionmentioning

confidence: 99%

Theoretical uncertainties in extracting cosmic-ray diffusion parameters: the boron-to-carbon ratio

Génolini

Putze

Salati

et al. 2015

A&A

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Context. PAMELA and, more recently, AMS-02, are ushering us into a new era of greatly reduced statistical uncertainties in experimental measurements of cosmic-ray fluxes. In particular, new determinations of traditional diagnostic tools such as the boron-tocarbon ratio (B/C) are expected to significantly reduce errors on cosmic-ray diffusion parameters, with important implications for astroparticle physics, ranging from inferring primary source spectra to indirect dark matter searches. Aims. It is timely to stress, however, that the conclusions obtained crucially depend on the framework in which the data are interpreted as well as on some nuclear input parameters. We aim at assessing the theoretical uncertainties affecting the outcome, with models as simple as possible while still retaining the key dependencies. Methods. We compared different semi-analytical, two-zone model descriptions of cosmic-ray transport in the Galaxy: infinite slab(1D), cylindrical symmetry (2D) with homogeneous sources, cylindrical symmetry (2D) with inhomogeneous source distribution. We tested for the effect of a primary source contamination in the boron flux by parametrically altering its flux. We also tested for nuclear cross-section uncertainties. All hypotheses were compared by χ 2 minimisation techniques to preliminary results from AMS-02. Results. We find that the main theoretical bias on the determination of the diffusion coefficient index δ (up to a factor two) is represented by the assumption that no injection of boron takes place at the source. The next most important uncertainty is represented by cross-section uncertainties, which reach ±20% in δ. As a comparison, nuclear uncertainties are more important than the shift in the best-fit when introducing a convective wind of velocity 30 km s −1 , with respect to a pure diffusive baseline model. Perhaps surprisingly, homogeneous 1D vs. 2D performances are similar in determining diffusion parameters. An inhomogeneous source distribution marginally alters the central value of the diffusion coefficient normalisation (at the 10%, 1σ level). However, the index of the diffusion coefficient δ is basically unaltered, as well as the goodness of fit. Conclusions. Our study suggests that, differently for instance from the leptonic case, realistic modelling of the geometry of the Galaxy and of the source distribution are of minor importance to correctly reproduce B/C data at high energies and thus, to a large extent, for the extraction of diffusion parameters. The ansatz on the lack of primary injection of boron represents the most serious bias and requires multi-messenger studies to be addressed. If this uncertainty could be lifted, nuclear uncertainties would still represent a serious concern; they degrade the systematic error on the inferred parameters to the 20% level, or three times the estimated experimental sensitivity. To reduce this, a new nuclear cross-section measurement campaign might be required.

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Propagation of CR Nuclei: Our Results

Gaggero

2012

Cosmic Ray Diffusion in the Galaxy and Diffuse Gamma Emission

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Systematic uncertainties on the cosmic-ray transport parameters

Cited by 83 publications

References 22 publications

A Markov Chain Monte Carlo technique to sample transport and source parameters of Galactic cosmic rays

A Markov Chain Monte Carlo technique to sample transport and source parameters of Galactic cosmic rays

Theoretical uncertainties in extracting cosmic-ray diffusion parameters: the boron-to-carbon ratio

Propagation of CR Nuclei: Our Results

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