A.D. Erlykin

The Anisotropy of Galactic Cosmic Rays as a Product of Stochastic Supernova Explosions

We study the effect of the stochastic character of supernova explosions on the anisotropy of galactic cosmic rays below the knee. We conclude that if the bulk of cosmic rays are produced in supernova explosions the observed small and nearly energy independent amplitude of the anisotropy and its phase are to the large extent determined by the history of these explosions in the vicinity of the solar system, namely by the location and the age of the supernova remnants, within a few kpc, which give the highest contribution to the total intensity at the present epoch. Among the most important factors which result in the small magnitude and the energy independence of the anisotropy amplitude are the mixed primary mass composition, the effect of the Single Source and the Galactic Halo. Special attention is given to the phase of the anisotropy. It is shown that the excessive flux from the Outer Galaxy can be due to the location of the solar system at the inner edge of the Orion Arm which has the enhanced density and rate of supernova explosions.

An all-particle primary energy spectrum in the 3–200 PeV energy range

We present an all-particle primary cosmic-ray energy spectrum in the 3 × 10 6 – 2 × 10 8 GeV energy range obtained by a multi-parametric event-by-event evaluation of the primary energy. The results are obtained on the basis of an expanded EAS data set detected at mountain level (700 g cm −2 )b y the GAMMA experiment. The energy evaluation method has been developed using the EAS simulation with the SIBYLL interaction model taking into account the response of GAMMA detectors and reconstruction uncertainties of EAS parameters. Nearly unbiased (<5%) energy estimations regardless of a primary nuclear mass with an accuracy of about 15–10% in the 3 × 10 6 –2 × 10 8 GeV energy range respectively are attained. An irregularity (‘bump’) in the spectrum is observed at primary energies of ∼7.4 × 10 7 GeV. This bump exceeds a smooth power-law fit to the data by about 4 standard deviations. By not rejecting the stochastic nature of the bump completely, we examined the systematic uncertainties of our methods and conclude that they cannot be responsible for the observed feature.

On the correlation between cosmic ray intensity and cloud cover

Abstract Various aspects of the connection between cloud cover (CC) and cosmic rays (CR) are analyzed. Most features of this connection viz. an altitude dependence of the absolute values of CC and CR intensity, no evidence for the correlation between the ionization of the atmosphere and cloudiness, the absence of correlations in short-term low cloud cover (LCC) and CR variations indicate that there is no direct causal connection between LCC and CR in spite of the evident long-term correlation between them. However, these arguments are indirect. If only some part of the LCC is connected and varies with CR, then its value, obtained from the joint analysis of their 11-year variations and averaged over the Globe, should be most likely less than 20%. The most significant argument against causal connection of CR and LCC is the anticorrelation between LCC and the medium cloud cover (MCC). The scenario of the parallel influence of the solar activity on the Global temperature and CC from one side and CR from the other side, which can lead to the observed correlations, is discussed and advocated.

Time structure of the extensive air shower front

Abstract The GREX/COVER_PLASTEX experiment has measured the temporal and spatial fine structure of the EAS disc at sea level in a new and original way, using resistive plate counter detectors for direct measurements of the arrival time of each particle crossing the detector. Data were taken at EAS core distances up to 100 m for shower size N > 105 (PeV energy range). Arrival times of shower particles were measured with nanosecond accuracy. More than 450000 air shower events have been included in this analysis.

Solar activity and the mean global temperature

The variation with time from 1956 to 2002 of the globally averaged rate of ionization produced by cosmic rays in the atmosphere is deduced and shown to have a cyclic component of period roughly twice the 11 year solar cycle period. Long term variations in the global average surface temperature as a function of time since 1956 are found to have a similar cyclic component. The cyclic variations are also observed in the solar irradiance and in the mean daily sun spot number. The cyclic variation in the cosmic ray rate is observed to be delayed by 2?4 years relative to the temperature, the solar irradiance and daily sun spot variations suggesting that the origin of the correlation is more likely to be direct solar activity than cosmic rays. Assuming that the correlation is caused by such solar activity, we deduce that the maximum recent increase in the mean surface temperature of the Earth which can be ascribed to this activity is of the observed global warming.

Properties of the interstellar medium and the propagation of cosmic rays in the Galaxy

Abstract The problem of the origin of cosmic rays in the shocks produced by supernova explosions at energies below the so-called ‘knee’ (at ∼3×106 GeV) in the energy spectrum is addressed, with special attention to the propagation of the particles through the inhomogeneous interstellar medium (ISM) and the need to explain recent anisotropy results [Proc. 27th Int. Conf. Cosmic Rays, Hamburg 1 (2001) 10]. It is shown that the fractal character of the matter density and magnetic field distribution leads to the likelihood of a substantial increase of spatial fluctuations in the cosmic ray energy spectra. While the spatial distribution of cosmic rays in the vicinity of their sources (e.g. inside the Galactic disk) does not depend much on the character of propagation and is largely determined by the distribution of their sources, the distribution at large distances from the Galactic disk depends strongly on the character of the propagation. In particular, the fractal character of the ISM leads to what is known as ‘anomalous diffusion’ and such diffusion helps us to understand the formation of the cosmic ray halo. Anomalous diffusion allows an explanation of the recent important result from the Chacaltaya extensive air shower experiment [Proc. 27th Int. Conf. Cosmic Rays, Hamburg 1 (2001) 10], viz. a Galactic plane enhancement of cosmic ray intensity in the outer Galaxy, which is otherwise absent for the case of the so-called ‘normal’ diffusion. All these effects are for just one reason: anomalous diffusion emphasizes the role of local phenomena in the formation of cosmic ray characteristics in our Galaxy and elsewhere.

High energy cosmic ray spectroscopy. I. status and prospects

Abstract In a recent paper (Nature, 1996, submitted) we claimed that the ‘bump’ in the extensive air shower size spectrum near 106 particles is due to heavy nuclei from a comparatively local ‘source’. The energy spectrum of this single source is of the shape advocated by Berezhko et al. (JETP 82 (1996) 1) for supernova remnants (SNR) and is characterized by, approximately, an E−2 spectrum up to an energy Emax followed by a rapid fall above. The SNR model makes specific predictions for Emax as a function of nuclear charge. If, as is likely, the CR nuclei are fully ionized, we must identify the ‘bump’ in the paper submitted to Nature with the CNO group of nuclei. We have, accordingly, searched for the corresponding bump due to iron at a bigger shower size. Analysis of the worlds data so far leads us to claim its detection, although not, yet, at as high a level of significance as the first bump. Prospects for augmenting the size spectrum technique, for studying what we call this new branch of spectroscopy, are examined.

High energy cosmic ray spectroscopy. III. Further analyses

Abstract In recent papers (A.D. Erlykin and A.W. Wolfendale, Astropart. Phys. 7 (1997) 1, 203) we presented evidence favouring the identification of “structure” in the size spectrum of cosmic ray electrons and muons with heavy nuclei originating in a single local, recent, supernova. Inevitably, such a claim, in a field that is notoriously difficult, has not met with universal agreement. In the present work we add more recent evidence and address the criticisms. Almot all of the evidence considered appears to support our claim; the remainder is neutral.

High energy cosmic ray spectroscopy. IV. The evidence from direct observations at lower energies and directional anisotropies

Abstract In previous papers (A.D. Erlykin, A.W. Wolfendale, Astropart. Phys. 7 (1997) 1, 203; 8 (1998) 265; J. Phys. G 23 (1997) 979), we presented evidence for structure in the size spectrum of cosmic ray air showers which we interpreted as due to the presence of oxygen and iron nuclei from a local, recent, supernova remnant. Although the energies in question are 3 × 1015 eV and 1.2 × 1016 eV, well above those where direct measurements are possible, the direct measurements are, in fact, relevant. We find that the direct measurements are quite consistent with an extrapolation back of our spectra. Indeed, taken alone, the direct measurements themselves provide strong evidence for the existence of an extra, single source contribution to the total energy spectrum. The paper also includes a discussion of the high energy electron spectrum, anisotropies and the likely site of the local SNR.

Supernova remnants and the origin of the cosmic radiation: II. Spectral variations in space and time

The model described by us earlier (Erlykin and Wolfendale 2001a J. Phys. G: Nucl. Part. Phys. 27 941), which involves Monte Carlo calculations for cosmic rays accelerated by supernova remnants in the interstellar medium, has been used to predict Galactic cosmic ray energy spectra as a function of space and time. Moderate variations of cosmic ray characteristics connected with the random spacetime distribution of supernovae are found to be accompanied by much stronger changes caused by explosions of nearby and recent supernovae. The spatial variations have been compared with results from gamma ray astronomy which relate to possible small variations in spectral shape for the average cosmic ray proton intensity in the energy range 3-100 GeV out to distances of some 100s of pc from the Earth (Fatoohi et al 1995 J. Phys. G: Nucl. Part. Phys. 21 679). Similarly, comparison has been made with results from radio-astronomy, which relate to the electron component. There is found to be no inconsistency with the model predictions in either case. The predicted temporal changes in the cosmic ray intensity at Earth in the range 10-50 GeV, appropriate to cosmogenic nucleus measurements, are, again, not inconsistent with those observed (an upper limit of a few 10s of per cent, with the value depending on the cosmogenic nucleus under study). The amplitude of the anisotropy in arrival directions of cosmic rays predicted by the model is of the order of that observed (typically 1% at 1 PeV) for the situation where there has been a local, recent supernova.