Speaker
Adrian Hanusch
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4012.pdf
Mass to Charge Dependence of Particle Injection into DSA
A. Hanusch1 , T. Liseykina1 , M. Malkov2
1 Institut für Physik, Universität Rostock, Germany
2 CASS and Department of Physics, University of California, San Diego, USA
The high precision spectrometry of galactic cosmic rays (CR), e.g., the Pamela experiment [1],
accurately determined an ≈0.1 difference between the rigidity spectral indices of protons and
helium ions. Similar deviations have been indicated earlier by other experiments [2] and were
confirmed by the recent high-fidelity AMS-02 measurements [3]. These findings may shed light
on the long standing problem of CR origin. While the CR particles are believed to be accelerated
in supernova remnant (SNR) shocks via diffusive shock acceleration (DSA), it is still not under-
stood how different CR elements are extracted from the supernova environments and injected
into the DSA. Comparing the spectra of accelerated particles with different mass-to-charge ra-
tios is a powerful tool for studying the physics of particle injection. Moreover, the similarity of
He/p, C/p, and O/p rigidity spectra demonstrated by AMS-02 has provided new evidence that
injection is a mass-to-charge dependent process. In oder to investigate the elemental selectivity
of the injection mechanism and to determine the injection efficiency of ion species with dif-
ferent mass-to-charge (A/Z) ratio, we performed fully self-consistent hybrid simulations. Our
results confirm the earlier theoretical predictions: the efficiency of injection depends on the
shock Mach number (M) and its increase with A/Z saturates at a level that grows with M. More-
over, our results show that for high A/Z the injection efficiency decreases. By convolving the
time-dependent injection rates of p and He, obtained from the simulations, with a decreasing
shock strength over the active life of SNRs, we generate the integrated SNR spectra for p and
He. These spectra are consistent with the AMS-02 and Pamela data. In particular they correctly
predict the decrease in p/He ratio with increasing rigidity at exactly the rate measured in the
experiments for R > 10 GV. Only at lower rigidities, R . 10 GV, the difference between the
data and our predictions becomes noticeable. Except for this deviation, which might be due to
propagation effects or solar modulation, the suggested mechanism for A/Z-dependence of the
injection fully explains the measured p/He ratio.
References
[1] O. Adriani, et al., Science 332, 69 (2011)
[2] A.D. Panov, et al., Bul. Russian Academy of Sciences: Physics, 73, 564 (2009)
[3] M. Aguilar, et al. (AMS Collaboration), Phys. Rev. Lett., 115, 251101 (2015)
