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

Astronomy DepartmentUniversity of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland
e-mail: andrii.neronov@unige.ch

Received: 16 November 2015
Accepted: 11 February 2016

Abstract

Context. Two main hypotheses for the origin of Galactic cosmic rays are the supernova and superbubble origin hypotheses.

Aims. 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.

Methods. We compare the measured upper limit on the abundance of ⁵⁹Ni in the cosmic ray flux with the ⁵⁹Ni abundance predictions of the most recent stellar evolution models. Non-detection of ⁵⁹Ni in the cosmic ray flux has previously been attributed to a long time delay of the order of 10⁵ yr between the moment of supernova explosion and the onset of particle acceleration process. This long time delay was considered as an argument in favour of the superbubble scenario.

Results. We show that the recent calculation of the ⁵⁹Ni yield of massive stars, which takes the initial mass range up to 120 solar masses into account 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.