Cosmic ray propagation time scales: lessons from radioactive nuclei and positron data

Abstract

We take a fresh look at high energy radioactive nuclei data reported in the 90's and at the positron data recently reported by PAMELA. Our aim is to study the model independent implications of these data for the propagation time scales of cosmic rays in the Galaxy. Considering radioactive nuclei, using decaying charge to decayed charge ratios -- the only directly relevant data available at relativistic energies -- we show that a rigidity independent residence time is consistent with observations. The data for all nuclei can be described by f_{s,i}=(t_i/100 Myr)^{0.7}, where f_{s,i} is the suppression of the flux due to decay and t_i is the observer frame lifetime for nucleus specie i. Considering positron measurements, we argue that the positron flux is consistent with a secondary origin. Comparing the positron data with radioactive nuclei at the same energy range, we derive an upper bound on the mean electromagnetic energy density traversed by the positrons, \bar U_T<1.25 eV/cm^3 at a rigidity of R=40 GV. Charge ratio measurements within easy reach of the AMS-02 experiment, most notably a determination of the Cl/Ar ratio extending up to R\sim100 GV, will constrain the energy dependence of the positron cooling time. Such constraints can be used to distinguish between different propagation scenarios, as well as to test the secondary origin hypothesis for the positrons in detail.

16 pages, 10 figures

References in corpus (8)

• Observation of an anomalous positron abundance in the cosmic radiation
• PAMELA results on the cosmic-ray antiproton flux from 60 MeV to 180 GeV in kinetic energy
• Parameterization of Gamma, e^+/- and Neutrino Spectra Produced by p-p Interaction in Astronomical Environment
• Fermi LAT observations of cosmic-ray electrons from 7 GeV to 1 TeV
• Measurements of cosmic-ray secondary nuclei at high energies with the first flight of the CREAM balloon-borne experiment
• Galactic secondary positron flux at the Earth
• First Results from the PAMELA Space Mission
• The Cosmic-Ray Positron and Electron Excess: An Experimentalist's Point of View

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• AMS02 results support the secondary origin of cosmic ray positrons
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• Determination of the Cosmic Antideuteron Flux in a Monte Carlo approach
• Super-Knee Cosmic Rays from Galactic Neutron Star Merger Remnants
• $e^{+}$ and $\bar{p}$ production in $pp$ collisions and the cosmic-ray $e^{+}/\bar{p}$ flux ratio
• Extracting the size of the cosmic electron-positron anomaly
• Radio bounds on the mixed dark matter scenarios of primordial black holes and WIMPs
• Cosmic Rays in the Milky Way and Beyond