The trajectories of cosmic rays at the highest energies. III. Applications of predictions to the results from extensive air shower arrays

We have argued (e.g. [1]) that the well-known 'ankle' in the cosmic ray energy spectrum, at logE (eV) ∼ 18.7-19.0, marks the transition from mainly Galactic sources at lower energies to mainly extragalactic above. Recently, however, there have been claims for lower transitional energies, specifically from logE (eV) ∼ 17.0 [2] via 17.2 − 17.8 [3] to 18.0 [4]. In our model the ankle arises naturally from the sum of simple power law-spectra with slopes differing by ∆γ ∼ 1.8; from differential slope γ = −3.8 for Galactic particles (near logE = 19) to γ ∼ −2.0 for extragalactic sources. In the other models, on the other hand, the ankle is intrinsic to the extragalactic component alone, and arises from the shape of the rate of energy loss versus energy for the (assumed) protons interacting with the cosmic microwave background (CMB). Our detailed analysis of the world's data on the ultra-high energy spectrum shows that taken together, or separately, the resulting mean sharpness of the ankle (second difference of the log(intensity×E 3 ) with respect to logE) is consistent with our 'mixed' model. For explanation in terms of extragalactic particles alone, however, the ankle will be at the wrong energy -for reasonable production models and of insufficient magnitude if, as seems likely, there is still a significant fraction of heavy nuclei at the ankle energy.

Section: Discussion Of the Spectral Shapesmentioning

confidence: 99%

“…The results marked 'T' come from our analyses of the b-distribution in the Inner Galaxy using trajectory calculations for particles accelerated in the Galactic Plane [17].…”

Section: The Mass Composition Of the Particles Above Loge (Ev) = 17mentioning

confidence: 99%

Section: The Mass Composition Of the Particles Above Log E (Ev) = 17mentioning

confidence: 99%

See 1 more Smart Citation

At what particle energy do extragalactic cosmic rays start to predominate?

Wibig

Wolfendale

2005

“…Wdowczyk and Wolfendale 1984, Chi et al 1992, and, most recently, Bird et al 1999, their flux appears to be very low. Specifically, from anisotropy studies, Chi et al (1994) estimate a galactic proton fraction of 7% at 10 18 eV, falling to < ∼ 0.3% at 10 19 eV. Their flux is so low that the actual galactic sources have not yet been identified.…”

Section: Introductionmentioning

confidence: 99%

The mass composition of cosmic rays above 10¹⁷eV

Wibig

Wolfendale

1999

Self Cite

A new analysis has been made of the constituent masses of primary cosmic-ray nuclei, using data from the Fly's Eye experiment (Bird et al 1993) and a new air shower analysis by one of the authors (Wibig 1998). It is concluded that below 1018 eV the relative masses are approximately as expected from galactic sources with simple galactic diffusion loss. At higher energies there is increasingly an extragalactic component, a not unusual conclusion, but we argue that it is characterized by a significant fraction of heavy nuclei with probably a variety of masses. The implication is that perhaps as many as 50% of the extragalactic nuclei start their lives as heavy nuclei (probably iron) and fragment on the radiation fields in the universe in the manner described by Tkaczyk et al (1975), Puget et al (1976) and later authors. In this regard, our results are more in accord with those from Akeno (Hayashida et al 1995), who found a much smaller rate of change of composition between 1017.5 - 1018.5 eV than that found by the Fly's Eye experiment. This idea militates against the view, increasingly advanced at present, that the ultra-high energy particles are protons, derived from the decay of exotic massive particles.

“…It was shown earlier, for example, in Chi et al (1993b), that CRs originating in the Galactic disk have two distinctive features in their arrival directions-galactic plane enhancement (GPE) and northsouth asymmetry (NSA)-which can be used to detect the Galactic CR contribution to the primary flux in the transition area. An analysis of the UHE CR Galactic latitude, b, distribution form observed with EAS arrays was used by Chi et al (1994) to estimate the probable fraction of Galactic protons and nuclei in the primary beam. In this paper we use the asymmetry parameters of the b-distribution instead.…”

Section: Introductionmentioning

confidence: 99%

Galactic cosmic rays at

Иванов¹

1998

Self Cite

The arrival direction distribution of the highest-energy cosmic rays with respect to Galactic latitude has been analysed using both the Yakutsk and the available world data from extensive air shower arrays. A north-south asymmetry is indicated in the distribution observed with the Yakutsk array at 10 19 eV in the outer Galaxy direction. A comparison with trajectory calculations for charged particles in the Galactic magnetic field indicates that the observed effect can be explained by a contribution from heavy nuclei originating in the Galactic disk to an extragalactic isotropic primary flux. The mean-mass number of Galactic nuclei estimated using the model is log 10 (A) = 1.37 ± 0.2.