Galactic Cosmic Ray Origins and OB Associations: Evidence from SuperTIGER Observations of Elements $_{26}$Fe through $_{40}$Zr

TL;DR

This study measures elemental abundances of cosmic rays from iron to zirconium using SuperTIGER, supporting a mixed origin model involving massive star material and interstellar medium, with evidence of preferential acceleration based on element properties.

Contribution

First direct measurements of elements $_{26}$Fe to $_{40}$Zr in cosmic rays, revealing details about their origin and acceleration mechanisms.

Findings

Cosmic-ray source material is a mixture of ~19% massive star material and ~81% interstellar medium.

Refractory elements are accelerated about 4 times more than volatile elements.

Both refractory and volatile elements show a mass-dependent enhancement with similar slopes.

Abstract

We report abundances of elements from $_{26}$Fe to $_{40}$Zr in the cosmic radiation measured by the SuperTIGER (Trans-Iron Galactic Element Recorder) instrument during 55 days of exposure on a long-duration balloon flight over Antarctica. These observations resolve elemental abundances in this charge range with single-element resolution and good statistics. These results support a model of cosmic-ray origin in which the source material consists of a mixture of 19$^{+11}_{-6}$\% material from massive stars and $\sim$81\% normal interstellar medium (ISM) material with solar system abundances. The results also show a preferential acceleration of refractory elements (found in interstellar dust grains) by a factor of $\sim$4 over volatile elements (found in interstellar gas) ordered by atomic mass (A). Both the refractory and volatile elements show a mass-dependent enhancement with similar slopes.