Simulation of the temporal variations of the galactic cosmic-ray intensity at neutron monitor energies

We show that the temporal variations of the integrated galactic cosmic-ray intensity at neutron monitor energies (approximately above 3 GeV) can be reproduced applying a semi-empirical 1-D diffusion-convection model for the cosmic-ray transport in interplanetary space. We divide the interplanetary region into `magnetic shells' and find the relative reduction that each shell causes to the cosmic-ray intensity. Then the cosmic-ray intensity at the Earth is reproduced by the successive influence of all shells between the Earth and the heliospheric termination shock. We find that the position of the termination shock does not significantly affect the cosmic-ray intensity although there are some differences between the results for a constant and a variable termination shock radius. We also reproduce the cosmic-ray intensity applying the analytical solution of the force-field approximation (Perko, 1987) and find that the results cannot fit the observed data. Our results are compared with the Climax (geomagnetic cut-off 3 GV) and Huancayo (geomagnetic cut-off 13 GV) neutron monitor measurements for almost two solar cycles (1976–1996).     

Upper limit on the cosmic-ray photon fraction at EeV energies from the Pierre Auger Observatory

From direct observations of the longitudinal development of ultra-high energy air showers performed with the Pierre Auger Observatory, upper limits of 3.8%, 2.4%, 3.5% and 11.7% (at 95% c.l.) are obtained on the fraction of cosmic-ray photons above 2, 3, 5 and 10 EeV , respectively. These are the first experimental limits on ultra-high energy photons at energies below 10 EeV. The results complement previous constraints on top–down models from array data and they reduce systematic uncertainties in the interpretation of shower data in terms of primary flux, nuclear composition and proton-air cross-section.     

The extension of the concept of the cosmic-ray path-length distribution to nonrelativistic energies

The concept of the cosmic-ray path-length distribution is examined. The corresponding cosmic-ray propagation calculational procedure has been justified theoretically at relativistic energies (Ginzburg and Syrovatskii, 1964) where the effects of ionization energy loss are negligible. The present paper extends the use of the path-length distribution concept in cosmic-ray propagation calculations to nonrelativistic energies. Sufficient constraints to effect this extension are presented. The solution of the cosmic-ray propagation equations in terms of a Green's function approach is also investigated and is used to provide a formulation of the path-length distribution at non-relativistic as well as relativistic energies in terms of the cosmic-ray source distribution and the propagation characteristics of the interstellar medium. The leaky-box model of cosmic-ray propagation is also examined.     

Charge composition of medium energy cosmic-ray nuclei from neon to iron

Charge composition of cosmic-ray nuclei from neon to iron has been studied in a stack of cellulose nitrate plastic detectors exposed in a balloon flight over Fort Churchill. 401 cosmic-ray nuclei of 10Z26 stopping in the detector system have been analysed. Fluxes of individual nuclei have been extrapolated to the top of the atmosphere. Relative abundances, obtained from these fluxes, have been compared with those obtained by other investigators.     

Charge transfer processes from low to intermediate energies

The theoretical treatment of charge transfer processes is developed using ab‐initio molecular calculations. Semi‐classical and quantal dynamical approaches are presented for the determination of cross sections and rate constants which are important data for space chemistry models. Accurate cross section values may be determined, taking account of rotational couplings with regard to the collision energy. Such theoretical approaches provide besides an insight into the mechanism of these processes with consideration of anisotropic and vibrational effects for collisions with diatomic molecular targets (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Propagation in 3D spiral-arm cosmic-ray source distribution models and secondary particle production using Picard

We study the impact of possible spiral-arm distributions of Galactic cosmic-ray sources on the flux of various cosmic-ray nuclei throughout our Galaxy. We investigate model cosmic-ray spectra at the nominal position of the sun and at different positions within the Galaxy. The modelling is performed using the recently introduced numerical cosmic ray propagation code Picard. Assuming non-axisymmetric cosmic-ray source distributions yields new insights on the behaviour of primary versus secondary nuclei.We find that primary cosmic rays are more strongly confined to the vicinity of the sources, while the distribution of secondary cosmic rays is much more homogeneous compared to the primaries. This leads to stronger spatial variation in secondary to primary ratios when compared to axisymmetric source distribution models. A good fit to the cosmic-ray data at Earth can be accomplished in different spiral-arm models, although leading to decisively different spatial distributions of the cosmic-ray flux. These lead to different cosmic ray anisotropies, where even reproducing the data becomes possible. Consequently, we advocate directions to seek best fit propagation parameters that take into account the higher complexity introduced by the spiral-arm structure on the cosmic-ray distribution. We specifically investigate whether the flux at Earth is representative for a large fraction of the Galaxy. The variance among possible spiral-arm models allows us to quantify the spatial variation of the cosmic-ray flux within the Galaxy in presence of non-axisymmetric source distributions.     

On the interplanetary cosmic-ray scintillations

The equation for the two-particles cosmic-ray distribution function is derived by means of the Boltzmann kinetic equation averaging. This equation is valid for arbitrary ratio of regular and random parts of the magnetic field. For small energy particles the guiding-center approximation is used. On the basis of the derived equation the dependence between power spectra of cosmic-ray intensity and random magnetic field is obtained. If power spectra are degree functions for high energy particles ( 10 GeV nucleon^–1), then the spectral exponent of magnetic field lies between and –2, where is the spectral exponent of cosmic-ray power spectra. The experimental data concerning moderate energy particles are in accordance with =, which demonstrates that the magnetic fluctuations are isotropic or cosmic-ray space gradient is small near the Earth orbit.     

Aspects of the long-term cosmic-ray modulation

To investigate the long-term modulation of galactic cosmic rays at the ground-based detector energies, the monthly values of the neutron monitor (Climax, Mt. Washington, Deep River, and Huancayo) and ionization chamber (Cheltenham/Fredericksburg, Huancayo, and Yakutsk) intensities have been correlated with the sunspot numbers (used as a proxy index for transient solar activity) for each phase of sunspot cycles 18 to 22. Systematic differences are found for results concerning odd and even sunspot cycles. During odd cycles (19 and 21) the onset time of cosmic-ray modulation is delayed when compared with the onset time of the sunspot cycle, while they are more similar during even (18, 20, and 22) cycles. Checking the green corona data, on a half-year basis, we found typical heliolatitudinal differences during ascending phases of consecutive sunspot cycles. This finding suggests a significant role of the latitudinal coronal behaviour in the heliospherical dynamics during a Hale cycle. Such effectiveness concerns not only the transient interplanetary perturbations but also the recurrent ones. In fact, when lag between cosmic-ray data and sunspot numbers is considered, the anticorrelation between both parameters is very high (correlation coefficient |r| > 0.9) for all the phases considered, except for the declining ones of cycles 20 and 21, when high-speed solar wind streams coming from coronal holes affect the cosmic-ray propagation, and theRz parameter is no longer the right proxy index for solar-induced effects in the interplanetary medium.     

Time-lag of cosmic-ray intensity

The best correlation coefficient between the monthly cosmic-ray intensity of the Inuvik Station and various kinds of solar, interplanetary, and geophysical parameters has been found. It is calculated for different time-lags of cosmic-ray intensity with respect to these parameters. The maximum of these coefficients lead us to a useful empirical model for the 11-year cosmic-ray modulation.     

Observation of MKN 501 at gamma-ray energies

During a balloon flight in September 1979 of the MISO low-energy -ray telescope, the BL Lac-object MkN 501 was studied in the hard X-ray range above 30 keV and in the low energy -ray range up to 19 MeV. No statistically significant X- and -ray fluxes were detected. The implications of the upper limits obtained are discussed in the light of the relativistic jet theories recently proposed.     

Time-evolution of cosmic-ray intensity modulation

Application of analyzing time-series into trigonometric series allows the investigation of cosmic-ray intensity variations in a wide periodicity range from a few months to 10 or even more years. By this technique, the amplitude and the phase of all observed fluctuations can be given. For this purpose, cosmic-ray data of five ground-based neutron-monitor stations for the time interval 1964–1985 have been analyzed.Two kinds of periodicities appeared in these data. The first one includes occurrences at periods greater than two years, as the ones of 10.41, 8.41, and 5.50 yr, which differ very little in amplitude from station to station but are similar in phase, and the second one includes periodicities smaller than two years (24, 12, 8, and 6 months) which are similar in all stations but appeared in variable time intervals.The possible origin of each observed variation due to a contribution either of cosmic-ray interaction in the upper atmosphere or to the solar dynamics is discussed.     

Simulations of cosmic-ray particle diffusion

The diffusion of charged particles in a stochastic magnetic field (strengthB) which is superimposed on a uniform magnetic fieldB ₀ k is studied. A slab model of the stochastic magnetic field is used. Many particles were released into different realizations of the magnetic field and their subsequent displacements z in the direction of the uniform magnetic field numerically computed. The particle trajectories were calculated over periods of many particle scattering times. The ensemble average was then used to find the parallel diffusion coefficient . The simulations were performed for several types of stochastic magnetic fields and for a wide range of particle gyro-radius and the parameterB/B ₀. The calculations have shown that the theory of charged particle diffusion is a good approximation even when the stochastic magnetic field is of the same strength as the uniform magnetic field.     

On the direct observation of cosmic-ray energy losses

During the decay of solar cosmic-ray events cosmic-rays with kinetic energies of about 1 MeV are convected outward with the solar wind. It is shown that, with currently available observations it should be possible to demonstrate directly the energy losses which are occurring. Observations from two spacecraft on the same heliocentric radial line are required. In this paper observations from Venera-4 and Imp-F have been used. A simple and direct demonstration would be provided by the observation of nearly mono-energetic pulses convected between the two spacecraft, but no such pulses were found to be present. A second method depends upon observing the ratio of the integral fluxes at the two spacecraft and comparing this with the value predicted by theory. The relevant theoretical analysis has been given. It is shown that in order to discriminate between energy-loss processes the spacecraft must be well separated. For spacecraft at Earth's orbit and the orbit of Venus the integral-flux ratio predicted with energy loss due to adiabatic deceleration is a factor of three higher than that predicted with no energy loss. Comparisons of integral-flux ratios for two events observed on spacecraft separated by approximately 0.1 AU gave inconclusive results. In view of the importance of energy-loss processes in the propagation of cosmic rays it is suggested that others with access to relevant data might continue this investigation.     

An X-ray telescope sensitive at high energies

A telescope is described which is capable of producing images of point sources of X-rays without recourse to reflection optics. A mathematical approach to the operation and to the signalto-noise properties of the telescope is presented. This is followed by several examples of its response and a discussion of detectors that could be used with the device.     

Heliolatitudinal dependence of cosmic-ray anisotropy

We analyze the heliolatitudinal dependence of the cosmic-ray anisotropy using data from the Yakutsk complex of muon telescopes on the ground and underground at depths of 7, 20, and 60 m w. e. for 1972–2002. The radial cosmic-ray anisotropy component during this period at all recording levels is shown to have been systematically enhanced southward from the helioequator irrespective of the polarity of the general solar magnetic field. The azimuthal anisotropy component depends on heliolatitude only at negative polarity of the general solar magnetic field; it increases northward from the helioequator. Such a situation can take place in the case of interaction of the fast solar wind from coronal holes with the slow wind in the northern part of the heliosphere and continuous particle removal in its southern part.     

Long-term changes in the cosmic-ray diurnal anisotropy

A detailed study has been conducted on the long-term changes in diurnal anisotropy of cosmic rays for the two solar cycles (20 and 21) during the period 1965–1990; this shows that the amplitude of the anisotropy is related to the characteristics of high and low amplitude days. The occurrence of high amplitude days are found to be positively correlated with the sunspot cycle while the low amplitude days are correlated negatively with the sunspot cycle. Further, the variability of the time of maximum of the aniotropy indicates that it essentially is composed of two components; one in the 1800 hours (corotation) direction and the other, an additional component in the 1500 hours direction (45° east of the S-N line) apparently caused by the reversal of the solar polar magnetic field. Our observations also suggest that the direction of the anisotropy of high- and low-amplitude days contribute significantly to the long-term behaviour of the diurnal anisotropy as it produces an additional component of cosmic rays in the radial (1200 hours) direction.     

Photoelectron thermalization and transport in the ionosphere at low energies

The range of applicability of the transport equation for photoelectrons in the ionosphere (Mantas, 1975), is extended to thermal energies. The extension enables one to calculate the photoelectron distribution in the important low energy region (i.e. < 3 eV), where most of the thermal electron gas heating takes place, and thereby to obtain more accurate excitation rates for the low energy: electronic, vibrational and rotational states of the ionospheric constituents, than was formerly possible.     

Metallographic cooling rates of group IIF iron meteorites

Abstract— Metallographic cooling rates have been calculated for all five members of the iron meteorites group IIF using two different techniques. We have determined cooling rates of ～5 °C/Ma based on Ni profiles through the taenite rim enclosing kamacite spindles. Ni profiles through the kamacite phase are less precise cooling rate indicators, but suggest a cooling rate of ～1 °C/Ma within an order of magnitude at lower temperatures (360–400 °C). Based on the kamacite bandwidth and the Ni profiles through the taenite, we estimate that the kamacite nucleated 130–200 °C below the temperature predicted from the phase diagram. The size of and the distance between the large kamacite spindles is found to be consistent with the thermal history that we have determined on the basis of Ni profiles in kamacite and taenite. We find that previously published kamacite bandwidth cooling rates for the five group IIF members are most likely in error because of the presence of large schreibersite spindles in some kamacite spindles and because undercooling of kamacite was ignored. Contrary to previous workers we find that the metallographic cooling rates are consistent with cooling in a common core.     

Thermal instability and the effects of cosmic-ray diffusion

We study the dynamical effects of cosmic rays (CRs) on thermal instability in the linear regime. CRs and the thermal plasma are treated as two different interacting fluids, in which CRs can diffuse along the magnetic field lines. We show that the growth rate of the magnetothermal condensation mode is reduced because of the existence of CRs, and this stabilizing effect depends on the diffusion coefficient and the ratio of CR pressure to gas pressure. Thus, a slower rate of structure formation via thermal instability is predicted when CRs are considered.