Time-Dependent Modulation of Cosmic Rays in the Heliosphere

The time-dependent modulation of galactic cosmic rays in the heliosphere is studied by computing intensities using a time-dependent modulation model. By introducing recent theoretical advances in the transport coefficients in the model, computed intensities are compared with Voyager 1, International Monitoring Platform (IMP) 8, and Ulysses proton observations in search of compatibility. The effect of different modulation parameters on computed intensities is also illustrated. It is shown that this approach produces, on a global scale, realistic cosmic-ray proton intensities along the Voyager 1 spacecraft trajectory and at Earth up to ≈?2004, whereafter the computed intensities recover much more slowly towards solar minimum than observed in the inner heliosphere. A modified time dependence in the diffusion coefficients is proposed to improve compatibility with the observations at Earth after ≈?2004. This modified time dependence led to an improved compatibility between computed intensities and the observations along the Voyager 1 trajectory and at Earth even after ≈?2004. An interesting result is that the cosmic-ray modulation during the current polarity cycle is not determined only by changes in the drift coefficient and tilt angle of the wavy current sheet, but is also largely dependent on changes in the diffusion coefficients.     

Is the Highest Cosmic-Ray Flux Yet to Come?

The recent 2009 solar-minimum period was characterized by a record-setting high Galactic cosmic-ray flux observed at Earth. This, along with the unexpected low heliospheric magnetic-field magnitude, caused this period to be characterized as unusual compared with previous minimum epochs. In this work, selected solar-activity proxies and corresponding cosmic-ray observations for the past five solar cycles are compared with each other, and we identify those that showed unusual behaviour during the 2009 solar-minimum modulation period. Using a state-of-the-art numerical-modulation model, the proton-intensity spectra for the past solar minima are reproduced to establish which of the transport processes might be considered the main cause of this unusually high cosmic-ray flux. It is found that diffusion was more prominent during 2009 so that drift effects on the modulation of cosmic rays in the heliosphere were less evident than during previous solar-polarity epochs. However, particle drifts still occurred and because of these drift effects, the proton spectrum is predicted to be even higher during the coming A>0 solar-minimum period.     

Heliospheric modulation of cosmic rays in solar cycles 19–23

The previously developed basic theory of the heliospheric modulation of high-energy cosmic rays is generalized to lower energies. Comparison of the theory with the results of long-term observations of cosmic rays in the stratosphere carried out by the group from the Lebedev Institute of Physics inMoscow andMurmansk shows satisfactory agreement. The cosmic rays are shown to behave quite differently when even and odd solar cycles alternate. Possible causes of the anomalously high cosmic-ray intensity recorded during the last solar activity minimum are discussed.     

Intensity of galactic cosmic rays in the early sun epoch

The process of heliospheric modulation of intensity of galactic cosmic rays is investigated by solving the transport equation. The spatial-energetic distribution of cosmic rays in the present epoch and in the past is analyzed. It is demonstrated that the particle density and the energy density of cosmic rays in the Solar System in the distant past were much lower than the corresponding current values. The cosmic ray intensity modulation in the early heliosphere was especially strong in the case of low-energy particles.     

Anisotropy of high-energy cosmic rays

The anisotropy of high-energy (∼10 GeV and above) cosmic rays is investigated. A simplified model of the heliosphere constructed as a basis for the theory of their long-period variations is investigated for applicability to describing the cosmic-ray anisotropy. This model has been found to need a modification. The necessary changes of the model do not affect the conclusions on the 22-year variations reached on its basis but make it possible to construct a theory of cosmic-ray anisotropy. The theoretical results on the anisotropy are compared with its long-term observations in a wide energy range performed in Yakutsk.     

Cosmic-ray modulation and long-duration solar flare events

The correlation between the long-term intensity variations of cosmic rays at neutron monitor energies and the LDE index measure of solar flares with long-lasting soft X-ray emissions is reported. Three subsequent solar cycles, 20–22, are taken into account and half-monthly data are analyzed. Possible explanation of this correlation is discussed in terms of the recent concepts of cosmic-ray modulation, in particular with merged interaction regions affecting the cosmic-ray intensity.     

Cosmogenic production as a background in searching for rare physics processes

We revisit calculations of the cosmogenic production rates for several long-lived isotopes that are potential sources of background in searching for rare physics processes such as the detection of dark matter and neutrinoless double-beta decay. Using updated cosmic-ray neutron flux measurements, we use TALYS 1.0 to investigate the cosmogenic activation of stable isotopes of several detector targets and find that the cosmogenic isotopes produced inside the target materials and cryostat can result in large backgrounds for dark matter searches and neutrinoless double-beta decay. We use previously published low-background HPGe data to constrain the production of ³H on the surface and the upper limit is consistent with our calculation. We note that cosmogenic production of several isotopes in various targets can generate potential backgrounds for dark matter detection and neutrinoless double-beta decay with a massive detector, thus great care should be taken to limit and/or deal with the cosmogenic activation of the targets.     

Cosmogenic production as a background in searching for rare physics processes

We revisit calculations of the cosmogenic production rates for several long-lived isotopes that are potential sources of background in searching for rare physics processes such as the detection of dark matter and neutrinoless double-beta decay. Using updated cosmic-ray neutron flux measurements, we use TALYS 1.0 to investigate the cosmogenic activation of stable isotopes of several detector targets and find that the cosmogenic isotopes produced inside the target materials and cryostat can result in large backgrounds for dark matter searches and neutrinoless double-beta decay. We use previously published low-background HPGe data to constrain the production of ³H on the surface and the upper limit is consistent with our calculation. We note that cosmogenic production of several isotopes in various targets can generate potential backgrounds for dark matter detection and neutrinoless double-beta decay with a massive detector, thus great care should be taken to limit and/or deal with the cosmogenic activation of the targets.     

The physics of particle acceleration at the heliospheric termination shock

Cosmic rays are ubiquitous in space, and the essential similarity of their energy spectra in many different regions places significant general constraints on the mechanisms for their acceleration and confinement. Diffusive shock acceleration is at present the most successful acceleration mechanism proposed, and, together with transport in Kolmogorov turbulence, can account for the universal specta. A unique laboratory for studying the acceleration and transport of charged particles is the outer heliosphere, including the solar wind termination shock and heliosheath.

A widely accepted paradigm for the transport and acceleration of energetic particles in the heliosphere has evolved over the last few decades. This picture has successfully explained many features of the modulation of galactic cosmic rays and the transport and acceleration of anomalous cosmic rays at the solar-wind termination shock. Recent Voyager observations near and beyond the termination shock have revealed new, and in some cases, unexpected phenomena which have led to questions concerning the established paradigm. The physical interpretation of the observations requires a blunt termination shock, rapid inward motion of the shock and temporal variations over time scales ranging from hours to 22 years. Incorporation of these into the physics has promise of explaining most, if not, all of the observed phenomena while retaining the advantages of the termination shock paradigm for both galactic and anomalous cosmic rays.     

Introduction to Large High Altitude Air Shower Observatory (LHAASO)

Since the century discovery of cosmic ray, the origin of cosmic ray is always a mystery. The study on the origin of high-energy cosmic ray is in an interdiscipline between the very high-energy (VHE) gamma-ray astronomy and the cosmic ray physics. The Large High Altitude Air Shower Observatory (LHAASO) is a unique and new generation cosmic-ray station with the advantages of high altitude, all-weather, and large-scale. It takes the function of hybrid technology to detect cosmic rays and to upgrade greatly the resolving power between gamma rays and cosmic rays. The LHAASO is expected to make the full-sky survey to find new gamma-ray sources, to obtain the highest sensitivity of gamma-ray detection at the high energy band of > 30 TeV, and to make the very high precision measurement on the component energy spectra of cosmic rays in a broad energy range of 5 orders of magnitude, in order to provide the evidence for revealing the mystery of the origin of cosmic ray. This paper describes the detector structure, performance superiority and scientific motivation of the LHAASO.     

GRBs on probation: Testing the UHE CR paradigm with IceCube

Gamma ray burst (GRB) fireballs provide one of very few astrophysical environments where one can contemplate the acceleration of cosmic rays to energies that exceed 10²⁰ eV. The assumption that GRBs are the sources of the observed cosmic rays generates a calculable flux of neutrinos produced when the protons interact with fireball photons. With data taken during construction IceCube has already reached a sensitivity to observe neutrinos produced in temporal coincidence with individual GRBs provided that they are the sources of the observed extra-galactic cosmic rays. We here point out that the GRB origin of cosmic rays is also challenged by the IceCube upper limit on a possible diffuse flux of cosmic neutrinos which should not be exceeded by the flux produced by all GRB over Hubble time. Our alternative approach has the advantage of directly relating the diffuse flux produced by all GRBs to measurements of the cosmic ray flux. It also generates both the neutrino flux produced by the sources and the associated cosmogenic neutrino flux in a synergetic way.     

The influence of the anomalous cosmic-ray component on the dynamics of the solar wind

It is well known that both the galactic and anomalous cosmic rays show positive intensity gradients in the outer heliosphere which are connected with corresponding pressure gradients. Due to an efficient dynamical coupling between the solar wind plasma and these highly energetic media by means of convected MHD turbulences, there exists a mutual interaction between these media. As one consequence of this scenario the enforced pressure gradients influence the distant solar wind expansion. Here we concentrate in our theoretical study on the interaction of the solar wind only with the anomalous cosmic-ray component. We use the standard two-fluid model in which the cosmic-ray fluid modifies the solar wind flow via the cosmic-ray pressure gradient. Then we derive numerical solutions in the following steps: first we calculate an aspherical pressure distribution for the anomalous cosmic rays, describing their diffusion in an unperturbed radial solar wind. Second, we then consider the perturbation of the solar wind flow due to these induced anomalous cosmic-ray pressure gradients. Within this context we especially take account of the action of a non-spherical geometry of the heliospheric shock which may lead to pronounced upwinddownwind asymmetries in the pressures and thereby in the resulting solar wind flows. As we can show in our model, which fits the available observational data, radial decelerations of the distant solar wind by between 5 to 11% are to be expected, however, the deviations of the bulk solar wind flow from the radialdirections are only slightly pronounced.     

Cosmic rays in the heliosphere: Observations

This contribution to the 100th commemoration of the discovery of cosmic rays (6–8 August, 2012 in Bad Saarow, Germany) is about observations of those cosmic rays that are sensitive to the structure and the dynamics of the heliosphere. This places them in the energy range of 10⁷–10¹⁰ eV. For higher energies the heliosphere becomes transparent; below this energy range the particles become strictly locked into the solar wind. Rather than give a strict chronological development, the paper is divided into distinct topics. It starts with the Pioneer/Voyager missions to the outer edges of the heliosphere, because the most recent observations indicate that a distinct boundary of the heliosphere might have been reached at the time of the meeting. Thereafter, the Ulysses mission is described as a unique one because it is still the only spacecraft that has explored the heliosphere at very high latitudes. Next, anomalous cosmic rays, discovered in 1972–1974, constitute a separate component that is ideally suited to study the acceleration and transport of energetic particles in the heliosphere. At this point the history and development of ground-based observations is discussed, with its unique contribution to supply a stable, long-term record. The last topic is about solar energetic particles with energies up to ∼10¹⁰ eV.     

Transient perturbations and their effects in the heliosphere, the geo-magnetosphere, and the Earth’s atmosphere: Space weather perspective

We discuss the effects of certain dynamic features of space environment in the heliosphere, the geo-magnetosphere, and the earth’s atmosphere. In particular, transient perturbations in solar wind plasma, interplanetary magnetic field, and energetic charged particle (cosmic ray) fluxes near 1 AU in the heliosphere have been discussed. Transient variations in magnetic activity in geo-magnetosphere and solar modulation effects in the heliosphere have also been studied. Emphasis is on certain features of transient perturbations related to space weather effects. Relationships between geomagnetic storms and transient modulations in cosmic ray intensity (Forbush decreases), especially those caused by shock-associated interplanetary disturbances, have been studied in detail. We have analysed the cosmic ray, geomagnetic and interplanetary plasma/field data to understand the physical mechanisms of two phenomena namely, Forbush decrease and geomagnetic storms, and to search for precursors to Forbush decrease (and geomagnetic storms) that can be used as a signature to forecast space weather. It is shown that the use of cosmic ray records has practical application for space weather predictions. Enhanced diurnal anisotropy and intensity deficit of cosmic rays have been identified as precursors to Forbush decreases in cosmic ray intensity. It is found that precursor to smaller (less than 5%) amplitude Forbush decrease due to weaker interplanetary shock is enhanced diurnal anisotropy. However, larger amplitude (greater than 5%) Forbush decrease due to stronger interplanetary shock shows loss cone type intensity deficit as precursor in ground based intensity record. These precursors can be used as inputs for space weather forecast.     

Model approximation of cosmic ray spectrum

An analytical model which generalizes the equations describing the intensity of galactic cosmic rays (CR), including both processes, making it applicable in the inner heliosphere (where energy losses dominate) and outer heliosphere (influenced primarily by convection-diffusion processes) is derived. By a suitable choice of a parameter, the proposed model turns into two approximations: solution close to “force-field” model (describing the energy losses of CR in the inner heliosphere) and “convection-diffusion” equation (giving the reduction of CR intensity in the outer heliosphere). A mathematical relation between parameters in the proposed model and the modulation parameter Φ is derived.     

The origin of galactic cosmic rays

One century ago Viktor Hess carried out several balloon flights that led him to conclude that the penetrating radiation responsible for the discharge of electroscopes was of extraterrestrial origin. One century from the discovery of this phenomenon seems to be a good time to stop and think about what we have understood about Cosmic Rays. The aim of this review is to illustrate the ideas that have been and are being explored in order to account for the observable quantities related to cosmic rays and to summarize the numerous new pieces of observation that are becoming available. In fact, despite the possible impression that development in this field is somewhat slow, the rate of new discoveries in the last decade or so has been impressive, and mainly driven by beautiful pieces of observation. At the same time scientists in this field have been able to propose new, fascinating ways to investigate particle acceleration inside the sources, making use of multifrequency observations that range from the radio, to the optical, to X-rays and gamma rays. These ideas can now be confronted with data.I will mostly focus on supernova remnants as the most plausible sources of Galactic cosmic rays, and I will review the main aspects of the modern theory of diffusive particle acceleration at supernova remnant shocks, with special attention for the dynamical reaction of accelerated particles on the shock and the phenomenon of magnetic field amplification at the shock. Cosmic-ray escape from the sources is discussed as a necessary step to determine the spectrum of cosmic rays at the Earth. The discussion of these theoretical ideas will always proceed parallel to an account of the data being collected especially in X-ray and gamma-ray astronomy.In the end of this review I will also discuss the phenomenon of cosmic-ray acceleration at shocks propagating in partially ionized media and the implications of this phenomenon in terms of width of the Balmer line emission. This field of research has recently experienced a remarkable growth, in that Hα lines have been found to bear information on the cosmic-ray acceleration efficiency of supernova shocks.     

Consequences of CP-violation in cosmic-ray sources

In this paper we show that CP-violation is operating in most cosmic-ray sources such as black holes, active galactic nuclei, supernova remnants, and that this leads to the in-equality of the electron—positron component of cosmic rays.Further implications of this result are also discussed.     

Long-Term Modulation of Galactic Cosmic Rays in the Heliosphere by Curvature of the Interplanetary Magnetic Field

Long-term changes of the GCR intensity in the heliosphere were analysed making use of records of cosmogenic isotopes abundances (¹⁰Be and ¹⁴C) in natural archives and neutron monitor data. These data contain information about short-term, 11-year, 22-year, centennial and two-centennial cycles of solar activity. A mechanism to explain the long-term modulation of GCR due to changes in the curvature of the interplanetary magnetic field, resulting from changes in solar activity, is suggested.     

Fluctuations of energetic particle flux during solar cycle based on measurements in the solar wind,in the magnetosphere,and at Earth

We present the results of our studies of the cosmic-ray fluctuations in the frequency range 10⁻⁴−1.67 × 10⁻³ Hz based on energetic particle flux measurements on spacecraft in the solar wind, in the magnetosphere, and at Earth in the 11-year solar cycle. The cosmic-ray fluctuation spectrum is shown to have an 11-year modulation related to the solar cycle. A different behavior of the level of energetic particle fluctuations measured in different regions of space is observed for cosmic rays of different origins. We conclude that the new, previously unknown phenomenon of 11-year modulation of the cosmic-ray fluctuation spectrum has been established. A possible explanation of this phenomenon is given.