The Origin of Galactic Cosmic Rays as Revealed by their Composition

Abstract

Galactic cosmic-rays (GCRs) are thought to be accelerated in strong shocks induced by massive star winds and supernova explosions sweeping across the interstellar medium. But the phase of the interstellar medium from which the CRs are extracted has remained elusive up to now. Here, we study in detail the GCR source composition deduced from recent measurements by the AMS-02, Voyager 1 and SuperTIGER experiments to obtain information on the composition, ionisation state and dust content of the GCR source reservoirs. We show that the volatile elements of the CR material are mainly accelerated from a plasma of temperature > ∼ 2 MK, which is typical of the hot medium found in galactic superbubbles energised by the activity of massive star winds and supernova explosions. Another GCR component, which is responsible for the overabundance of 22 Ne, most likely arises from acceleration of massive star winds in their termination shocks. From the CR-related 𝛾-ray luminosity of the Milky Way, we estimate that the ion acceleration efficiency in both supernova shocks and wind termination shocks is of the order of 10 −5 . The GCR source composition also shows evidence for a preferential acceleration of refractory elements contained in interstellar dust. We suggest that the GCR refractories are also produced in superbubbles, from shock acceleration and subsequent sputtering of dust grains continuously incorporated into the hot plasma through thermal evaporation of embedded molecular clouds. Our model explains well the measured abundances of all primary and mostly primary CRs from H to Zr, including the overabundance of 22 Ne.

Hybrid Origins of the Cosmic-Ray Nucleus Spectral Hardening at a Few Hundred GV

“…An interesting and detailed work on revealing the origin of galactic CRs by their composition has been proposed inTatischeff et al (2021).…”

Hybrid origins of the cosmic-ray nuclei spectral hardening at a few hundred GV

“…8 An interesting and detailed work on revealing the origin of galactic CRs by their composition has been proposed in Ref. [44].…”

Cosmic Ray Source and Solar Energetic Particles

“…Natural elitist energization of charged particles in the cosmos requires, as the artificial one at the LHC, RHIC and other accelerators several phases: ionization, injection and acceleration to high energy via strong energy (electrical) sources. Supernova remnants and stellar winds from Wolf-Rayet stars [24], through their shock waves, and the diffuse acceleration they produce [25], appear to be excellent accelerators or reaccelerators through the shock waves they induce in the surrounding medium. All the mystery condenses in the injection mechanism, through first ionization potential [26] or grain sputtering [27].…”