M. Giller

Energy spectra of electrons in the extensive air showers of ultra-high energy

We show that the shape of the energy spectrum of electrons in an extensive air shower with an ultra-high energy (E ≥ 10 19 eV) at a given level in the atmosphere depends only on the shower age at this level. It depends practically neither on the primary particle mass nor on its energy. This fact considerably simplifies interpretation of data from the experiments (e.g., Flys Eye, HiRes and Auger) determining cascade curves of single showers by the fluorescence technique. In particular, the contribution of the scattered Cherenkov light to the total flux produced by a shower can be easily taken into account. Our conclusion has been drawn by analysing results of Monte Carlo simulations of showers with the CORSIKA (Heck et al 1998 Report FZKA 6019) program, using the QGSJet interaction model.

Similarity of extensive air showers with respect to the shower age

Using CORSIKA simulations of the highest energy extensive air showers we show that all showers are similar when described by the shower age parameter: the angular and energy spectra of electrons at a given level in the atmosphere depend only on the shower age at this level. Moreover, electrons with a given energy have the same angular distributions at any level (age) of the shower. We have calculated these distributions and found analytical functions describing them quite well. The total number of particles can also be described in a simple way as a function of age by two halves of a Gaussian function with the widths, however, fluctuating from one shower to another. The description of large showers in terms of age (instead of depth in the atmosphere) is very useful in interpreting data from experiments observing fluorescence light, with admixture of Cherenkov, induced by the showers in the air.

Luminous infrared galaxies as possible sources of UHE cosmic rays

Ultra high energy (UHE) particles coming from discrete extragalactic sources are potential candidates for EAS events above a few tens of EeV. In particular, galaxies with huge infrared luminosity triggered by collision and merging processes are possible sites of UHECR acceleration. Here we check whether this could be the case. Using the PSCz catalogue of IR galaxies we calculate a large scale anisotropy of UHE protons originating in the population of the luminous infrared galaxies (LIRGs). Small angle particle scattering in weak irregular extragalactic magnetic fields as well as deflection by regular galactic field are taken into account. We give analytical formulae for deflection angles with included energy losses on cosmic microwave background (CMB). The hypotheses of the anisotropic and isotropic distributions of the experimental data above 40 EeV from AGASA are checked, using various statistical tests. The tests applied for the large scale data distribution are not conclusive in distinguishing between isotropy and our origin scenario for the available small data sample. However, we show that on the basis of the small scale clustering analysis there is a much better correlation of the UHECRs data below GZK cut-off with the predictions of the LIRG origin than with those of isotropy. We derive analytical formulae for a probability of a given number of doublets, triplets and quadruplets for any density distribution of independent events on the sky. The famous AGASA UHE triple event is found to be very well correlated on the sky with the brightest extragalactic infrared source within 70 Mpc—merger galaxies Arp 299 (NGC 3690 + IC 694).

Galactic pulsar population and the origin of high-energy cosmic rays

We show that assuming a simple cosmic ray (CR) acceleration scenario, where all the pulsar rotational energy is transformed into CR particles of the highest available energy at a given moment, one obtains particle fluxes of the order of the observed ones. We derive the energy spectrum of the produced particles assuming that the pulsar magnetic field decays with time. The slope of the spectrum for E > 1016 eV is determined by a power-law distribution of the pulsar initial periods and the knee in the spectrum at ~3 × 1015 eV by the decay of the pulsar magnetic fields. Moreover, the pulsar parameters at birth, fitted to describe the CR energy spectrum, reconstruct reasonably well their present equilibrium population.

The measurement of isotopic cross sections of 12C beam fragmentation on liquid hydrogen at 3.66 GeV/nucleon

An experiment with 12C beam fragmentation on a liquid hydrogen target has been performed using the magnetic spectrometer, Anomalon, equipped with a Cherenkov charge detector, and the Dubna synchrophasotron at a projectile energy of 3.66 GeV/nucleon. A charge resolution of 0.26e (except for the hydrogen nuclei) and a mass resolution of 0.11-0.18 amu have been achieved. Isotopic and elemental fragmentation cross sections have been obtained for fragments from Z = 1 to 6. Decayed cross sections have also been calculated. We compare the measured cross sections with the results of other experiments and with calculations based on semi-empirical and parametric approaches.

Isotopic cross sections of 12C fragmentation on hydrogen measured at 1.87 and 2.69 GeV/nucleon

We present new results of measurements of the isotopic cross sections of 12C fragmentation in the energy region of a few GeV/n. The experiment has been performed at the Dubna synchrophasotron using the magnetic spectrometer ANOMALON, equipped with Cherenkov counters. In this experiment 12C is the projectile and liquid hydrogen is a target. The isotopic cross sections obtained in the measurement are compared with the values predicted by the models: semi-empirical (Silberberg and Tsao) and parametric (Webber, Kish and Schrier). This work is a continuation of the previous one where similar results, but at 3.66 GeV/n, are presented.

EXTENSIVE AIR SHOWER CHARACTERISTICS AS FUNCTIONS OF SHOWER AGE

We show that extensive air showers (EAS) are all very similar when described by shower age and Moliere length unit. This allows to analyze fluorescence and Cherenkov light emitted by showers in a unified and simple way.

Images of very high energy cosmic ray sources in the Galaxy: I. A source towards the galactic centre

Recent analyses of the anisotropy of cosmic rays at 1018 eV (the AGASA and SUGAR data) show significant excesses from regions close to the galactic centre and Cygnus. Our aim is to check whether such anisotropies can be caused by single sources of charged particles. We investigate propagation of protons in two models of the galactic regular magnetic field (with the irregular component included) assuming that the particles are injected by a short-lived discrete source lying in the direction of the galactic centre. We show that apart from a prompt image of the source, the regular magnetic field may cause delayed images at quite large angular distances from the actual source direction. The image is strongly dependent on the time elapsed after ejection of particles and it is also very sensitive to their energy. For the most favourable conditions for particle acceleration by a young pulsar, the predicted fluxes are two to four orders of magnitude higher than those observed. The particular numbers strongly depend on the galactic magnetic field model adopted but it seems that a single pulsar in the galactic centre could be responsible for the observed excess.

On possibilities of the fluorescence detector to measure the shower light curve

A method to determine the primary energy of very rare big extensive air showers is to measure the fluorescence light flashes induced by them in the atmosphere. From a shower fluorescence image (and its time dependence) it is, in principle, possible to reconstruct the shower cascade curve. The Pierre Auger experiment (in construction) has been using this method (together with measuring the shower charged particles as well) to determine the highest energy part of the cosmic ray spectrum (E J 10 19 eV) and particle arrival directions. Here we analyse which shower parameters affect its image, and, if not taken into account in the reconstruction procedure, may lead to systematic errors in determining its light (cascade) curve, and in consequence, the energy and/or mass of the primary particle. In particular, we analyse the lateral distribution of particles, the thickness and curvature of the shower disk, together with the spherical aberration of the collecting mirror. We show that a non-negligible part of the light flux for showers closer than � 15 km to the detector may be hidden in the non-triggered pixels of the camera. For more distant showers this effect is small, but then the atmospheric attenuation has to be known better. We also derive an analytical solution for a spherical mirror focal plane position and the minimal size of the image (spot size) of a parallel light beam. � 2002 Elsevier Science B.V. All rights reserved.

Status and prospects of the ultrahigh energy cosmic rays

This paper summarizes measurement results of the UHECR energy spectrum and arrival directions. Various scenarios trying to explain the flat AGASA spectrum (no GZK cutoff) are recalled. Recent HiRes data are, however, consistent with the expected GZK cutoff, so that for E > 1020 eV the fluxes measured by the two experiments diverge by more than one order of magnitude. The multiple events, observed by AGASA, seem not to be statistical fluctuations and we analyse the information contained in them. The Pierre Auger Observatory (in construction) is expected to dispel the doubts about existence of the GZK cutoff as well as those about the nature of the multiplets.