Volume 588, April 2016
|Number of page(s)||5|
|Published online||22 March 2016|
Abundances of 59Co and 59Ni in the cosmic ray flux
Astronomy DepartmentUniversity of Geneva,
Ch. d’Ecogia 16,
Received: 16 November 2015
Accepted: 11 February 2016
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.
Key words: nuclear reactions, nucleosynthesis, abundances / stars: massive / supernovae: general / acceleration of particles / cosmic rays
© ESO, 2016
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