Breaks in interstellar spectra of positrons and electrons derived from time-dependent AMS data

摘要

Until fairly recently, it was widely accepted that local cosmic-ray spectra were largely featureless power laws, containing limited information about their acceleration and transport. This viewpoint is currently being revised in light of evidence for a variety of spectral breaks in the fluxes of cosmic-ray nuclei. Here, we focus on cosmic-ray electrons and positrons which at the highest energies must be of local origin due to strong radiative losses. We consider a pure diffusion model for their Galactic transport and determine its free parameters by fitting data in a wide energy range: measurements of the interstellar spectrum by Voyager at mega-electron-volt energies, radio synchrotron data (sensitive to giga-electron-volt electrons and positrons), and local observations by AMS up to approximately 1 TeV. For the first time, we also model the time-dependent fluxes of cosmic-ray electrons and positrons at giga-electron-volt energies recently presented by AMS, treating solar modulation in a simple extension of the widely used force-field approximation. We are able to reproduce all the available measurements to date. Our model of the interstellar spectrum of cosmic-ray electrons and positrons requires the presence of a number of spectral breaks, both in the source spectra and the diffusion coefficients. While we remain agnostic as to the origin of these spectral breaks, their presence will inform future models of the microphysics of cosmic-ray acceleration and transport.