J Szabelski

Origin of cosmic rays of the highest energies

An analysis is made of the current status of the measurement of the energy spectrum and directional anisotropy of cosmic rays of the highest energy, i.e. above about 1018 eV. All the measurements are consistent with cosmic rays below 1019 eV being largely of Galactic origin and having a small excess in the general direction of the Galactic plane, with those of higher energy having come from extragalactic sources. There is evidence that the extra-galactic particles arrive preferentially from the general direction of the centre of the local supercluster and perhaps from directions towards the Galactic South Pole. The latter result is not understood.

Cosmic rays and cosmological microwave background fluctuations

One of the most important topics in modern cosmology concerns the search for anisotropies in the cosmic microwave background radiation. The Galactic synchrotron radiation can mimic or mask a cosmological signal, and the present work examines the extent to which the fluctuations in this local component, a component due to cosmic rays, are understood. It is concluded that at 10 GHz, although the observed fluctuations are of similar magnitude to those predicted for Galactic synchrotron radiation the actual temperature profiles do not agree. Thus, the nature of the detected fluctuations is not understood, although what can be stated is that there is no evidence to prove the existence of cosmic microwave background anisotropies. A prognosis is made for future searches for CMB fluctuations. 17 refs.

The inverse Compton contribution to medium-latitude Galactic gamma-ray emission

The authors present evidence that the inverse Compton contribution to the diffuse gamma-ray emission above 50 MeV is more important than previously thought. They compute the spectrum of the excess gamma -ray emission above the pi 0 and bremsstrahlung components. The calculation shows that the excess emission is substantial, amounting to about 60% of the total emission at intermediate latitudes. In the Galactic plane, from which most of the Galactic gamma -rays are derived, the excess is relatively much smaller. A model in which there is a cosmic-ray halo of total width 10 kpc and radius 20 kpc yields an inverse Compton contribution which accounts for most of the excess.

High-energy cosmic rays and the characteristics of photon-nucleus collisions

One way of explaining the observed excess of cosmic-ray muons in the gamma -ray induced showers from the direction of Cygnus X-3 is to postulate a dramatic increase in the photonuclear cross section at energies above 104 GeV. Such a model is examined here. It is demonstrated that there are apparently no objections to such behaviour, and indeed further anomalies in cosmic-ray physics might be explainable in this way.

Gamma rays and the origin of cosmic rays

It has been pointed out that cosmic γ-rays have something to say about the origin of cosmic-ray particles. Although the statistical precision of the data and the directional accuracy of the satellite-borne detectors operated so far have been poor, useful results have been achieved already.