High Energy Cosmic Ray Events Research Articles

Possible Association of Ultra–High-Energy Cosmic-Ray Events with Strong Gamma-Ray Bursts

We point out that each of the error boxes of the two highest-energy cosmic-ray shower events known, overlaps with that of a strong gamma-ray burst (GRB). The GRBs precede the cosmic rays by 5.5, and 11 months respectively. In one case the strongest known cosmic ray is paired with the strongest gamma-ray burst in the BATSE catalogue. The probability of this to have occurred by chance seems rather small. Without building on post-factum statistics, we think the above is remarkable enough to suggest that the cosmic ray and gamma-ray burst were produced by the same outburst. A time delay (and a small positional disparity) is expected, since the trajectory of a charged cosmic-ray particle is wriggled by intervening magnetic fields. We estimate that the Galaxy's field alone may produce a delay of the order observed. We discuss some of the implications that follow if such an association is confirmed. For example, the upper limit on the distance to the cosmic-ray source, combined with a much-better-determined position of the gamma-ray burst source, narrows greatly the volume in which to look for an optical counterpart. There is also useful information in the time delay regarding, e.g., intergalactic magnetic fields.

On the origin of highest energy cosmic rays

In this paper we show that the conventional diffusive shock acceleration mechanism for cosmic rays associated with relativistic astrophysical shocks in active galactic nuclei (AGNs) has severe difficulties to explain the highest energy cosmic ray events. We show that protons above around 2 x 10 20 eV could have marginally been produced by this mechanism in an AGN or a rich galaxy cluster not further away than around 100 Mpc. However, for the highest energy Fly's Eye and Yakutsk events this is inconsistent with the observed arrival directions. Galactic and intergalactic magnetic fields appear unable to alter the direction of such energetic particles by more than a few degrees. We also discuss some other options for these events associated with relativistic particles including pulsar acceleration of high Z nuclei. At the present stage of knowledge the concept of topological defects left over from the early universe as the source for such events appears to be a promising option. Such sources are discussed and possible tests of this hypothesis are proposed.

First observation of high-energy cosmic-ray events obtained in coincidence between EAS-TOP and LVD at Gran Sasso

We present the first results of the combined measurements of the EAS-TOP (at the surface) and LVD (deep underground) detectors operating as a combined telescope in the study of UHE cosmic rays and their interactions. Examples of different classes of events and their significance in different high-energy and astrophysical studies are discussed.

High energy cosmic ray events of ultra-relativistic nucleus-nucleus collisions

Cosmic ray ultra-relativistic nucleus-nucleus collision events in the TeV/A region are analyzed. The average transverse momentum of non-peripheral events is examined and the breakdown of the limiting behaviour of this quantity is observed in events with high energy density. Close pairing or clustering of tracks is observed in many events. Possible explanations of the phenomena are discussed.

Very high energy cosmic ray events

High energy cosmic rays are reviewed in terms of our present understanding of prominent features in the primary energy spectrum. The spectral change observed around 10 15 eV can be explained either by a change in the primary chemical composition or by a change in the nuclear interaction characteristics. Anomalous interactions are prevalent at about the same energy where galactic propagation effects are expected to lead to the dominance of iron nuclei.

CERENKOV RADIATION OF PIONS

The energy radiated by a nucleon as pions in nuclear reactions is calculated by classical methods in the dipole approximation. This leads to a Cerenkov-type radiation of pions. The results are in good agreement with the measured number and spectra of pions in high-energy cosmic-ray events.