Cosmic ray spectrum in the energy range 10 15 − 10 18 eV and the second knee according to the small Cherenkov setup at the Yakutsk EAS array

From the data on Cherenkov light from EASs collected over the period of more than 15 years, the spectrum of cosmic rays was obtained in the energy range 1015− 1018 eV. This spectrum has two features: at ∼ 3× 1015 eV (first knee) and at ∼ 1017 eV (second knee). The first knee is characterized by the indexes γ1 = 2.7±0.03 and γ2 = 3.12±0.03 and the second knee — by γ1 = 2.92±0.03 and γ2 = 3.24±0.04. In the second case the difference amounts to ∆γ23 = 0.32± 0.03± 0.05 which is less than the case of the first knee ∆γ12 = 0.42± 0.03± 0.05 (here dual errors represent statistics and systematics correspondingly). The lesser difference ∆γ23 can be explained with the influx of cosmic rays from Meta-galaxy and, hence, with some increase of the cosmic rays intensity in the energy range 5×1016−1018 eV, which compensates the escape of heavier nuclei from the Galaxy. The presence of the second knee could be confirmed by abrupt change in mass composition from from 〈lnA〉 ∼ 3 at ∼ 1017 eV to 〈lnA〉 ∼ 1.5 at 1018 eV found from the analysis of longitudinal development