TeV cosmic-ray proton and helium spectra in the myriad model

Abstract

Context. Recent measurements of cosmic ray proton and helium spectra show a hardening above a few hundred GeV. This excess is hard to understand in the framework of the conventional models of Galactic cosmic ray production and propagation. Aims. We propose here to explain this anomaly by the presence of local sources (myriad model). Methods. Cosmic ray propagation is described as a diffusion process taking place inside a two-zone magnetic halo. We calculate the proton and helium fluxes at the Earth between 50 GeV and 100 TeV. As an improvement over a similar analysis, we consistently derive these fluxes by taking both local and remote sources for which a unique injection rate is assumed into account. Results. We find cosmic ray propagation parameters compatible with B/C measurements for which the proton and helium spectra agree remarkably with the PAMELA and CREAM measurements over four decades in energy.

TeV cosmic-ray proton and helium spectra in the myriad model II

“…For the canonical MED model of CR transport parameters, the average explosion rate ν can be as large as 1.5 per century, or even 1.7 for model D, and becomes close to the fiducial value of 1.9 ± 1.1 found by Diehl et al (2006). This is a significant improvement over the Bernard et al (2013) analysis where ν had to be as small as 0.8 per century, with a reduced chi-square value of 1.3 based on the PAMELA data, to be compared to our best-fit result of 1.47 obtained with the more constraining AMS-02 measurements. We confirm that a higher explosion rate reduces the role of local sources as is clear in Table 1 where The best-fit model D is obtained by setting the explosion rate ν equal to 1.7 per century and by letting the escape index γ vary between 2 and 3.…”

“…In this paper, we fix the propagation parameters to the MED configuration of Donato et al (2004); Bernard et al (2013), where the vertical boundary of halo L has the plausible value of 4 kpc, and also best fits the B/C data (Maurin et al 2001). We perform a scan over supernova explosion rate, which is required to be larger than 0.8 century −1 .…”

“…They can be added to known SNRs as a complementary catalogue. A list of cosmic ray sources derived from the Green catalogue (Green 2009) and ATNF pulsar database (Manchester et al 2005) was presented in Bernard et al (2013), with the millisecond pulsars associated with known SNRs removed to avoid double counting. In this list, the radial distance extends up to 2 kpc from the Sun, and the upper limit on the age is set to 30, 000 years, within which there are 30 sources in total.…”

Proton and Helium Spectra from the CREAM-III Flight

“…The hardening and higher abundances are difficult to explain using general models of cosmic-ray acceleration (Krymskii 1977;Bell 1978;Blandford & Ostriker 1978), and their transport in the Galaxy, which predict single power-law cosmic-ray spectra. Possible explanations for the hardening and higher abundance have been suggested, including but not limited to, effects of the cosmic-ray source spectrum (Biermann et al 2010;Ptuskin et al 2013), effects due to propagation through the Galaxy (Blasi et al 2012;Aloisio & Blasi 2013), or the effect of nearby local sources (Thoudam & Hörandel 2012;Erlykin & Wolfendale 2012;Bernard et al 2013). Other possible causes include cosmic-ray re-acceleration by weak shocks in the Galaxy (Ptuskin et al 2011;Thoudam & Hörandel 2014), injection processes in collisionless shock acceleration (Malkov et al 2012;Ellison et al 1997), and inhomogeneous ambient medium sources, called superbubbles (Drury 2011;Ohira & Ioka 2011;Ohira et al 2016).…”

Precision Measurement of the Proton Flux in Primary Cosmic Rays from Rigidity 1 GV to 1.8 TV with the Alpha Magnetic Spectrometer on the International Space Station

“…In particular, the ATIC-2, CREAM, and PAMELA experiments showed deviations of the proton flux from a single power law. Many models were proposed to account for the hardening of the flux based on different sources, acceleration mechanisms, diffusive propagation effects, and their superposition [7]. In this Letter we report on the precise measurement of the proton flux in primary cosmic rays in the rigidity range from 1 GV to 1.8 TV based on data collected by the Alpha Magnetic Spectrometer (AMS)…”