Abundances of 59Co and 59Ni in the cosmic ray flux

TL;DR

This paper investigates the isotopic abundances of 59Co and 59Ni in cosmic rays to evaluate the supernova and superbubble hypotheses for their origin, showing recent stellar models align with observed low 59Ni levels without requiring long delay times.

Contribution

It demonstrates that updated stellar evolution models predict low 59Ni abundance, aligning with cosmic ray measurements and supporting the supernova origin hypothesis without long delay assumptions.

Findings

Recent models predict low 59Ni abundance consistent with observations.

Non-detection of 59Ni does not require long delay times.

Supports supernova hypothesis for cosmic ray origin.

Abstract

Two main hypotheses for the origin of Galactic cosmic rays are the "supernova" and "superbubble" origin hypotheses. We analyse the evidence for the superbubble hypothesis provided by the measurements of the relativive abundances of isotopes of cobalt and nickel in the cosmic ray flux. We compare the measured upper limit on the abundance of 59Ni in the cosmic ray flux with the 59Ni abundance predictions of the up-to-date stellar evolution models. Non-detection of 59Ni in the cosmic ray flux has previously been attributed to a large time delay of the order of 1e5 yr between the moment of supernova explosion and the onset of particle acceleration process. This large time delay was considered as an argument in favour of the "superbubble" scenario. We show that the recent calculation of the 59Ni yield of massive stars, which takes into account the initial mass range up to 120 solar masses and includes stellar rotation, results in prediction of low 59Ni abundance relative to its decay product 59Co. The predicted abundance is consistent with the upper bound on 59Ni abundance in the cosmic ray flux for the supernova parameters assumed. This result removes the necessity of decay of 59Ni in the time interval between the supernova explosion and the onset of acceleration process and restores the consistency of measurements of 59Ni / 59Co abundances with the "supernova" hypothesis of the CR origin.