Sporadic emission of ultra high energy gamma rays from crab pulsar

In a further study of sporadic emission from pulsars we find evidence for short lived intense emission from the Crab pulsar.     

Low energy galactic cosmic rays in the heliosphere

The flux of galactic cosmic rays (GCR) extends over a wide range of energies (from 10⁸ to 10²⁰ eV); it has a strong dependence on particle energy. Given the large span of energies the detection techniques, transport mechanisms and other characteristics vary as energy increases. In the low energy region (<10¹² eV) the flux of GCR is modulated by the solar activity. Continuous registers are necessary to study intensity variations that must have their origin in the Sun. Detectors were designed and constructed for the purpose, they operate since the middle of the last century providing valuable information to study recurrent periodicities and their relationship to those of solar phenomena, but also to elucidate whose are the relevant transport mechanisms inside the heliosphere. A brief review of the advancement in the comprehension of these phenomena is presented.     

The composition of cosmic rays at high energies

Measurements of the composition of the cosmic rays at high energies, and of the energy spectra of the individual components provide the basis for the understanding of the sources, of the acceleration mechanism, and of the galactic containment of these particles. We briefly review the presently available information, and we describe a recent measurement on the Space Shuttle that we performed in order to substantially extend the range of energies in which the elemental composition is known. We present and discuss the results, and we also summarize and discuss recent data on the electron component of cosmic rays. The body of data now available contains several features that are difficult to explain within current models of galactic shock acceleration and “leaky box” containment. We emphasize the need for further measurements, and we briefly discuss possible opportunities for future work.     

Primary mass discrimination of high energy cosmic rays using PNN and k-NN methods

Probabilistic neural network (PNN) and k-Nearest Neighbors (k-NN) methods are widely used data classification techniques. In this paper, these two methods have been used to classify the Extensive Air Shower (EAS) data sets which were simulated using the CORSIKA code for three primary cosmic rays. The primaries are proton, oxygen and iron nuclei at energies of 100?TeV–10?PeV. This study is performed in the following of the investigations into the primary cosmic ray mass sensitive observables. We propose a new approach for measuring the mass sensitive observables of EAS in order to improve the primary mass separation. In this work, the EAS observables measurement has performed locally instead of total measurements. Also the relationships between the included number of observables in the classification methods and the prediction accuracy have been investigated. We have shown that the local measurements and inclusion of more mass sensitive observables in the classification processes can improve the classifying quality and also we have shown that muons and electrons energy density can be considered as primary mass sensitive observables in primary mass classification. Also it must be noted that this study is performed for Tehran observation level without considering the details of any certain EAS detection array.     

Trapped antiprotons produced by cosmic rays in the Earth's magnetosphere.

The existence of significant fluxes of antiparticles in the Earth magnetosphere has been predicted on theoretical considerations in this article. These antiparticles (positrons or antiprotons) at several hundred kilometers of altitudes, we believe are not of direct extraterrestrial origin, but are the natural products of nuclear reactions of the high energy primary cosmic rays (CR) and trapped protons (TP) confined in the terrestrial radiation belt, with the constituents of terrestrial atmosphere. Extraterrestrial positrons and antiprotons born in nuclear reactions of the same CR particles passing through only 5-7 g/cm2 of interstellar matter, exhibit lower fluxes compared to the antiprotons born at hundreds of g/cm2 in the atmosphere, which when confined in the magnetic field of the Earth (in any other planet), get accumulated. We present the results of the computations of the antiproton fluxes at 10 MeV to several GeV energies due to CR particle interactions with the matter in the interstellar space, and also with the residual atmosphere at altitudes of approximately 1000 km over the Earth's surface. The estimates show that the magnetospheric antiproton fluxes are greater by two orders of magnitude compared to the extraterrestrial fluxes measured at energies <1-2 GeV.     

On ultra-high energy cosmic rays: Origin in AGN jets and transport in expanding universe

The cosmic ray source spectrum produced by AGN (active galactic nucleus) jets is calculated. A distinctive feature of these calculations is the account for the jet distribution on kinetic energy. The expected cosmic ray spectrum at the Earth is determined with the use of a simple numerical code which takes into account interactions of ultra-high energy protons and nuclei with the background radiation in an expanding universe.     

Propagation of secondary antiprotons and cosmic rays in the Galaxy

Recent measurements of the cosmic ray (CR) antiproton flux have been shown to challenge existing CR propagation models. It was shown that the reacceleration models designed to match secondary to primary nuclei ratios (e.g., B/C) produce too few antiprotons. In the present paper, we discuss one possibility to overcome these difficulties. Using the measured antiproton flux and B/C ratio to fix the diffusion coefficient, we show that the spectra of primary nuclei as measured in the heliosphere may contain a fresh local “unprocessed” component at low energies perhaps associated with the Local Bubble, thus decreasing the measured secondary to primary nuclei ratio. The independent evidence for SN activity in the solar vicinity in the last few Myr supports this idea. The model reproduces antiprotons, B/C ratio, and elemental abundances up to Ni (Z ⩽ 28). Calculated isotopic distributions of Be and B are in perfect agreement with CR data. The abundances of three “radioactive clock” isotopes in CR, ¹⁰Be, ²⁶Al, ³⁶Cl, are all consistent and indicate a halo size z_h ∼ 4 kpc based on the most accurate data taken by the ACE spacecraft.     

A model of galactic cosmic rays for use in calculating linear energy transfer spectra.

The galactic cosmic rays (GCR) contain fully stripped nuclei, from Hydrogen to beyond the Iron group, accelerated to high energies and are a major component of the background radiation encountered by satellites and interplanetary spacecraft. This paper presents a GCR model which is based upon our current understanding of the astrophysics of GCR transport through interstellar and interplanetary space. The model can be used to predict the energy spectra for all stable and long-lived radioactive species from H to Ni over an energy range from 50 to 50,000 MeV/nucleon as a function of a single parameter, the solar modulation level phi. The details of this model are summarized, phi is derived for the period 1974 to present, and results from this model during the 1990/1991 CRRES mission are presented.     

Depth dependency of neutron density produced by cosmic rays in the lunar subsurface

Depth dependency of neutrons produced by cosmic rays (CRs) in the lunar subsurface was estimated using the three-dimensional Monte Carlo particle and heavy ion transport simulation code, PHITS, incorporating the latest high energy nuclear data, JENDL/HE-2007. The PHITS simulations of equilibrium neutron density profiles in the lunar subsurface were compared with the measurement by Apollo 17 Lunar Neutron Probe Experiment (LNPE). Our calculations reproduced the LNPE data except for the 350–400 mg/cm² region under the improved condition using the CR spectra model based on the latest observations, well-tested nuclear interaction models with systematic cross section data, and JENDL/HE-2007.     

On the transport of cosmic rays in the distant heliosheath

This paper discusses the transport of energetic charged particles through a sectored magnetic field in distant regions of the inner heliosheath. As the plasma flow slows down on approach to the stagnation point on the heliopause, the distance between the folds of the current sheet decreases to the point where it becomes comparable to the cyclotron radius of a cosmic ray particle. Under these conditions a particle can effectively drift across the stack of magnetic sectors with a speed comparable with the particle’s velocity. For a random distribution of current sheet separation distances, a diffusive transport across the stack of sectors occurs instead. The proposed mechanism could have contributed to unusually high intensities of galactic cosmic rays measured by Voyager 1 in the heliosheath during 2009–2010.     

Acceleration of interplanetary pick-up ions and anomalous cosmic rays

It may not be doubted anymore that anomalous cosmic rays (ACRs) are produced in the heliosphere from interplanetary pick-up ions through their acceleration at the solar wind termination shock. However, there is no general agreement in the community of heliospheric researchers concerning the mechanism of injection of the pick-up ions into the shock acceleration. We discuss here three possible ways for pick-up ions to be involved into the acceleration process at the termination shock: (1) preacceleration of pick-up ions in the whole region from the Sun up to the termination shock by solar wind turbulences and interplanetary shock waves, (2) local preacceleration of pick-up ions in a vicinity of the termination shock by shock surfing, and (3) formation of high-velocity tails in pick-up ion spectra consisting of secondary pick-up ions which are produced in the supersonic solar wind due to ionization of energetic neutral atoms entering from the inner heliosheath.     

Solar cosmic rays in the near Earth space and the atmosphere

Solar energetic particles (SEPs) constitute a distinct population of energetic charged particles, which can be often observed in the near Earth space. SEP penetration into the Earth’s magnetosphere is a complicated process depending on particle magnetic rigidity and geomagnetic field structure. Particles in the several MeV energy range can only access to periphery of the magnetosphere and the polar cap regions, while the GeV particles can arrive at equatorial latitudes. Solar protons with energies higher than 100 MeV may be observed in the atmosphere above ∼30 km, and those with energies more than 1 GeV may be recorded even at the sea level. There are some observational evidences of SEP influence on atmospheric processes. Intruding into the atmosphere, SEPs affect middle atmosphere odd-nitrogen and ozone chemistry. Since spatial and temporal variations of SEP fluxes in the near Earth space are controlled by solar activity, SEPs may present an important link between solar activity and climate. The paper outlines dynamics of SEP fluxes in the near Earth space during the last decades. This can be useful for tracing relationship between SEPs and atmospheric processes.     

Charging of dust grains by anisotropic solar wind multi-component plasma

In this paper we study the charging process of small grain particles by anisotropic multi-component solar wind plasmas (electrons, protons and heavy ions), versus two-component (electron/proton) plasmas. We are focusing attention on the important characteristics of the charging process, namely the charging time, floating potential and current content as functions of plasma parameters such as He⁺⁺/H⁺ (α/p) number density and T_α/T_p temperature ratios of alpha particles to protons, as well as plasma streaming velocity v₀. Measured statistical properties of solar wind plasma parameters at 1 AU show considerable variations in α/p-temperature ratios from 1 to 10, in α/p-number density ratio from 0.01 to 0.35, as well as in values of streaming velocity v₀ from 200 km/s to 1000 km/s and more. Periods of these variations could last for several days each, leading to significant variability in the charging process, according to newly derived general analytical expressions. Numerical calculations performed for protons/alphas plasmas showed large disparity in the charging characteristics. For example, in anisotropic plasma, grain charging time varies up to 90% depending on α/p-particles temperature and number density ratios, whereas changes in floating potential are up to 40%. In contrast, in isotropic plasma, charging characteristic for grains do not change very much for the same plasma parameters variations, with charging time varying about 12% and floating potential only varying about 4%. It is also shown that in highly anisotropic plasma, with all ballistic electrons and ions, dust grains could not hold their charges, and characteristic discharged time is calculated. We note that the analysis is equally applicable to any sized body immersed in solar wind plasma.     

Fluctuations of cosmic rays and IMF in the vicinity of interplanetary shocks

Fluctuations of cosmic rays and interplanetary magnetic field upstream of interplanetary shocks are studied using data of ground-based polar neutron monitors as well as measurements of energetic particles and solar wind plasma parameters aboard the ACE spacecraft. It is shown that coherent cosmic ray fluctuations in the energy range from 10 keV to 1 GeV are often observed at the Earth’s orbit before the arrival of interplanetary shocks. This corresponds to an increase of solar wind turbulence level by more than the order of magnitude upstream of the shock. We suggest a scenario where the cosmic ray fluctuation spectrum is modulated by fast magnetosonic waves generated by flux of low-energy cosmic rays which are reflected and/or accelerated by an interplanetary shock.     

Uncertainties in the production and propagation of cosmic rays in the Milky Way

We discuss the main sources of uncertainties in the calculation of the positron and antiproton top of the atmosphere spectra using models including diffusion and convection or reacceleration. We show that, even including uncertainties, the models that include diffusion and convection are more consistent with existing measurements. The next generation experiments like PAMELA will help to reduce the uncertainties in the values of the main free parameters of the models, thus improving our knowledge of the origin and propagation of cosmic rays.     

The charge-sign dependent effect in the solar modulation of cosmic rays

The centennial anniversary of the discovery of cosmic rays was in 2012. Since this discovery considerable progress has been made on several aspects related to galactic cosmic rays in the heliosphere. It is known that they encounter a turbulent solar wind with an imbedded heliospheric magnetic field when entering the Sun’s domain. This leads to significant global and temporal changes in their intensity inside the heliosphere, a process known as the solar modulation of cosmic rays. The prediction of a charge-sign dependent effect in solar modulation in the late 1970s and the confirmatory observational discoveries can also be considered as a milestone. A short review is given of these predictions based on theoretical and numerical modelling work, the observational confirmation and related issues.     

Relativistic waves raised by explosions in space as sources of ultra-high-energy cosmic rays

The paper discusses the possibility of particle acceleration up to high energies in relativistic waves generated by various explosive processes in the interstellar medium. We propose to use the surfatron mechanism of acceleration (surfing) of charged particles trapped in the front of relativistic waves as a generator of high-energy cosmic rays (CRs). Conditions under which surfing in the waves under consideration can be made are studied thoroughly. Ultra-high-energy CRs (up to 10²⁰ eV) are shown to be obtained due to the surfing in relativistic plane and spherical waves. Surfing is supposed to take place in nonlinear Langmuir waves excited by powerful electromagnetic radiation or relativistic beams of charged particles, as well as in strong shock waves generated by relativistic jets or spherical formations that expand fast (fireballs).