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

TL;DR

This paper refines the myriad model for cosmic ray spectra by incorporating spiral source distribution and energy-dependent escape times, successfully explaining observed spectral hardening while aligning with other astrophysical constraints.

Contribution

It introduces a more realistic spiral source distribution and energy-dependent escape times into the myriad model, resolving previous tensions and fitting cosmic ray data more accurately.

Findings

Energy-dependent escape times significantly improve model fit.

Spiral source distribution enhances the model's realism.

Model parameters become consistent with other observations.

Abstract

Recent observations show that the cosmic ray nuclei spectra start to harden above 100 GeV, in contradiction with the conventional steady-state cosmic ray model. We had suggested that this anomaly is due to the propagation effect of cosmic rays released from local young cosmic ray sources, the total flux of the cosmic ray should be computed with the myriad model, where contribution from sources in local catalog is added to the background. However, while the hardening could be elegantly explained in this model, the model parameters obtained from the fit skew toward a region with fast diffusion and low supernova rate in the Galaxy, in tension with other observations. In this paper, we further explore this model in order to set up a concordant picture. Two possible improvements related to the cosmic ray sources have been considered. Firstly, instead of the usual axisymmetric disk model, we considered a spiral model of source distribution. Secondly, for the nearby and young sources which are paramount to the hardening, we allow for an energy-dependent escape time. We find that major improvement comes from the energy-dependent escape time of the local sources, and with both modifications, not only the cosmic ray proton and helium anomalies are solved, but also the parameters attain reasonable range values compatible with other analysis.