Ultrahigh energy nuclei in the turbulent Galactic magnetic field

In this work we study how the turbulent component of the Galactic magnetic field (GMF) affects the propagation of ultrahigh energy heavy nuclei. We investigate first how the images of individual sources and of the supergalactic plane depend on the properties of the turbulent GMF. Then we present a quantitative study of the impact of the turbulent field on (de-)magnification of source fluxes, due to magnetic lensing effects. We also show that it is impossible to explain the Pierre Auger data assuming that all ultrahigh energy nuclei are coming from Cen A, even in the most favorable case of a strong, extended turbulent field in the Galactic halo.     

Using spherical wavelets to search for magnetically-induced alignment in the arrival directions of ultra-high energy cosmic rays

Due to the action of the intervening cosmic magnetic fields, ultra-high energy cosmic rays (UHECRs) can be deflected in such a way as to create clustered energy-ordered filamentary structures in the arrival direction of these particles, the so-called multiplets. In this work we propose a new method based on the spherical wavelet transform to identify multiplets in sky maps containing arrival directions of UHECRs. The method is illustrated in simulations with a multiplet embedded in isotropic backgrounds with different numbers of events. The efficiency of the algorithm is assessed through the calculation of Type I and II errors.     

The dynamical coupling of cosmic rays and magnetic field in galactic disks

In this paper we demonstrate the importance of cosmic rays for the dynamics of the interstellar medium. We present the first 3D-MHD numerical simulations of the Parker instability triggered by cosmic rays accelerated in supernova remnants. We show that in the presence of galactic rotation a net radial magnetic field is produced as a result of the cosmic ray injection. This process provides a very efficient magnetic field amplification within the general frame of so called fast galactic dynamo proposed by Parker (1992). This revised version was published online in September 2006 with corrections to the Cover Date.     

Diffusion tensor for Galactic cosmic rays in the interplanetary medium with a magnetic field

The Boltzmann kinetic equation is analyzed in the MHD approximation. This analysis requires an explicit expression for the collision integral F _c. In the classical theory, F _c=?vf _μ ⁽¹⁾ Ω_μ, where f _μ ⁽¹⁾ is the first spherical harmonic in the Galactic-cosmic-ray (GCR) distribution, Ω_μ are the components of a unit particle velocity vector, and the frequency ν of collisions between GCRs and interplanetary magnetic-field nonuniformities is assumed to be a scalar. The assumption that ν_ij is a tensor (which is the result of anisotropy in the interplanetary medium) distinguishes this study from others. Since the anisotropic GCR effects in the heliomagnetosphere are marginal, the nondiagonal elements of tensor ν_ij were set equal to zero. Our analysis has yielded the diffusion-tensor components D _∥, and D _A, which are expressed in terms of interplanetary parameters. The energy dependencies of D _∥, and D _A are in good agreement with the experimental data and calculations by other authors.     

Detecting filaments in the ultra-high energy cosmic ray distribution

We propose and test new statistical tools to study the distribution of cosmic rays based on the use of the minimal spanning tree. The method described is particularly sensitive to filamentary structures, as those expected to arise from strong sources of charged cosmic rays which get deflected by intervening magnetic fields. We also test the method with data available from the AGASA and SUGAR surface detector arrays.     

Study of dispersion of mass distribution of ultra-high energy cosmic rays using a surface array of muon and electromagnetic detectors

We consider a hypothetical observatory of ultra-high energy cosmic rays consisting of two surface detector arrays that measure independently electromagnetic and muon signals induced by air showers. Using the constant intensity cut method, sets of events ordered according to each of both signal sizes are compared giving the number of matched events. Based on its dependence on the zenith angle, a parameter sensitive to the dispersion of the distribution of the logarithmic mass of cosmic rays is introduced. The results obtained using two post-LHC models of hadronic interactions are very similar and indicate a weak dependence on details of these interactions.     

Primordial black holes as a source of extremely high energy cosmic rays

The origin of observed extremely high energy cosmic rays remains an astrophysical enigma. We show that a single evaporating primordial black hole should produce 8.5·10¹⁴ particles over a 10²⁰ eV threshold. This emission results from direct production of fundamental constituents and from hadronization of quarks and gluons. The induced flux on the Earth is studied as a function of the local density of exploding black holes and compared with experimental data. The discovery potential of future detectors is finally reviewed.     

Influence of solar heliospheric parameters on cosmic rays anisotropy

In the present work the cosmic ray data of three different neutron monitoring stations, Deep River, Inuvik, and Tokyo, located at different geomagnetic cutoff rigidities and altitudes have been harmonically analyzed for the period 1980–95 for a comparative study of diurnal semi-diurnal and tri-diurnal anisotropies in cosmic ray intensity in connection with the change in interplanetary magnetic field Bz component and solar wind velocity on 60 quietest days. It is observed that the amplitudes of all the three harmonics increase during the period 1982–84 at all the stations during the high speed solar wind stream epoch and remain low during the declining phase of the stream. The amplitudes of the three harmonics have no obvious characteristics associated with the time variation of magnitude of the Bz component. The phases of all the three harmonics have no time variation characteristics associated with solar wind velocity and Bz. Published in Astrofizika, Vol. 49, No. 4, pp. 651–664 (August 2006).     

The maximum energy and spectra of cosmic rays accelerated in active galactic nuclei

Astronomy Letters - We computed the energy spectra of the incident (on an air shower array) ultrahigh-energy (E&;gt;4×1019eV) cosmic rays (CRs) that were accelerated in nearby Seyfert...     

Cosmic ray acceleration to very high energy through the non-linear amplification by cosmic rays of the seed magnetic field

The maximum energy for cosmic ray acceleration at supernova shock fronts is usually thought to be limited to around 10¹⁴–10¹⁵ eV by the size of the shock and the time for which it propagates at high velocity. We show that the magnetic field can be amplified non-linearly by the cosmic rays to many times the pre-shock value, thus increasing the acceleration rate and facilitating acceleration to energies well above 10¹⁵ eV. A supernova remnant expanding into a uniform circumstellar medium may accelerate protons to 10¹⁷ eV and heavy ions, with charge Ze , to Z ×10¹⁷ eV. Expansion into a pre-existing stellar wind may increase the maximum cosmic ray energy by a further factor of 10.     

Energy dependence of Ti/Fe ratio in the Galactic cosmic rays measured by the ATIC-2 experiment

Titanium is a rare, secondary nucleus among Galactic cosmic rays. Using the Silicon matrix in the ATIC experiment, Titanium has been separated. The energy dependence of the Ti to Fe flux ratio in the energy region from 5 GeV per nucleon to about 500 GeV per nucleon is presented. The article was translated by the authors.     

A new composition-sensitive parameter for ultra-high energy cosmic rays

A new family of parameters intended for composition studies in cosmic ray surface array detectors is proposed. The application of this technique to different array layout designs has been analyzed. The parameters make exclusive use of surface data combining the information from the total signal at each triggered detector and the array geometry. They are sensitive to the combined effects of the different muon and electromagnetic components on the lateral distribution function of proton and iron initiated showers at any given primary energy. Analytical and numerical studies have been performed in order to assess the reliability, stability and optimization of these parameters. Experimental uncertainties, the underestimation of the muon component in the shower simulation codes, intrinsic fluctuations and reconstruction errors are considered and discussed in a quantitative way. The potential discrimination power of these parameters, under realistic experimental conditions, is compared on a simplified, albeit quantitative way, with that expected from other surface and fluorescence estimators.     

Hard component of ultra-high energy cosmic rays and vortons

Observed events of ultra-high energy cosmic rays may indicate a hard component for the energy spectrum of their flux, which might have origin in the decay of long-lived vortons presumably condensed in the galactic halo. To be consistent with the needed present density, vortons may have been formed during the breaking of an abelian symmetry contained in a large GUT group like E₆ and a part of them could have survived the destabilization caused by the electroweak transition.     

Diurnal variations of cosmic rays during a solar magnetic cycle

We have used data from five neutron monitor stations with primary rigidity (Rm) ranging from 16 GeV to 33 GeV to study the diurnal variations of cosmic rays over the period: 1965–1986 covering one 22-year solar magnetic cycle. The heliosphere interplanetary magnetic field (IMF) and plasma hourly measurements taken near Earth orbit, by a variety of spacecraft, are also used to compare with the results of solar diurnal variation. The local time of maximum of solar diurnal diurnal variations displays a 22-year cycle due to the solar polar magnetic field polarities. In general, the annual mean of solar diurnal amplitudes, magnitude of IMF and plasma parameters are found to show separte solar cycle variations. Moreover, during the declining period of the twenty and twenty-ne solar cycles, large solar diurnal amplitudes are observed which associated with high values of solar wind speed, plasma temperature and interplanetary magnetic field magnitude B3.     

The generation of a large-scale Galactic magnetic field by electric currents of energetic particles

We consider the generation of a magnetic field in the Galaxy by the electric currents excited by cosmic-ray particles in the disk and halo. We assume that the sources of relativistic particles are distributed continuously and uniformly in the Galactic disk, their total power is equal to the observed value, and the particles themselves undergo anisotropic diffusion in a homogeneous medium. We take into account the differential rotation of the Galactic disk but disregard the turbulence gyrotropy (the α effect). The strength of the generated magnetic field in our model is shown to strongly depend on the symmetry of the relativistic proton and thermal electron diffusion tensors, as well as on the relations between the tensor components. In particular, if the diffusion is isotropic, then no magnetic field is generated. For the independent tensor components estimated from observed parameters of the Galactic medium and with a simultaneous allowance made for the turbulent field dissipation processes, the mechanism under consideration can provide an observable magnetic-field strength of the order of several microgauss. This mechanism does not require any seed magnetic field, which leads us to suggest that relativistic particles can give an appreciable and, possibly, determining contribution to the formation of the global Galactic magnetic field. However, a final answer can be obtained only from a nonlinear self-consistent treatment, in which the symmetry and magnitude of the particle diffusion tensor components should be determined together with the calculation of the magnetic field.