Cosmic Ray Gas Research Articles

Surface and underground measurements of long-term changes in the cosmic ray solar diurnal variation

North/south directional telescopes operating at the surface and vertical and inclined telescopes operating at a depth of 60 m.w.e. underground in London have been employed to study changes in the cosmic ray solar diurnal variation over the past few years. In order to extend the study to the low rigidity end of the spectrum, results obtained by the NM64 neutron monitors operating at Deep River and Goose Bay in Canada have also been examined. The surface telescope data require that the full corotation amplitude of 0.59 per cent should have been observed during almost the entire solar cycle with the possible exception of the year 1965 when cosmic ray intensity was a maximum. However, the effective amplitude observed by neutron monitors during most of the solar cycle was only about 0.52 per cent and this reduction has been ascribed to the lower value of the exponent of the energy spectrum which prevails amongst the latitude sensitive primaries. Nevertheless, the upper limiting rigidity was varying during the course of the solar cycle, its value being high when solar activity was high and low when solar activity decreased. During 1965, even though the upper limiting rigidity assumed its lowest value, the free space amplitude was also diminished by a little over 10 per cent. Even though the theory of rigid corotation invoking a purely azimuthal streaming of the cosmic ray gas successfully predicts the free space amplitude, it fails to explain the phase changes observed by both types of monitor and which are quite significant. The underground data require that the component due to atmospheric temperature effects is negligibly small and that throughout the rigidity range covered by the recorder response, there is present an apparent anisotropy due to the orbital motion of the Earth around the Sun. Also the underground data roughly confirm the changes in upper limiting rigidity which were observed by the surface instruments.

An experimental test of the homogeneity of the interstellar medium

Observations of nonthermal continuum radio emission at 750 MHz and hydrogen-line emission at 1420 MHz have been compared in order to test the extent to which cosmic-ray electrons, magnetic fields, and hydrogen gas coexist in the interstellar medium. If the interstellar medium is homogeneous in the sense that its constituents are mixed together and can interact, then regions of line and continuum emission should be spatially correlated. The measurements indicate that at most 28% of continuum emission in the Galaxy comes from such a homogeneous medium. The remaining nonthermal emission agrees in magnitude with the residual emission found by Berkhuijsen after subtraction of the polarized component of nonthermal emission. In addition, the data discussed here show that the major filamentary structures found in the two forms of emission rarely coincide spatially. Consequently, both the average and the exceptional structure in the medium indicate that the synchrotron-radiating magnetoplasma and the neutral hydrogen gas are not closely interacting in the present state of the medium.

Spiral structure and galactic gamma radiation

The intensity of high energy galactic gamma rays is calculated using a model for the distribution of interstellar hydrogen and cosmic ray gas coupled through the interstellar magnetic field. Results are compared with recent empirical data from SAS-2.

Nonlinear mode-mode coupling of Alfven waves in the interstellar medium

A set of differential equations is set up to describe the temporal and spatial evolution of transverse and longitudinal waves under mode-mode coupling in a relativistic plasma embedded in an ambient magnetic field. The plasma consists of immobile protons, thermal electrons and cosmic ray protons. The cosmic rays are assumed to be streaming along the ambient magnetic field direction with a bulk velocity larger than the Alfven velocity. An Alfven wave couples with another transverse and one longitudinal wave. The temporal mode-mode coupling effects on the nonlinear behaviour of the Alfven wave (which is unstable using linear theory in the absence of mode-mode coupling) have been examined. Under certain conditions, it is found that the linear instability of the Alfven wave is 'quenched'. Upon inserting numerical parameters appropriate to the cosmic ray gas in the galactic disk it is shown that when the initial energy of perturbation is 10-2 of the ambient field energy, the rate of quenching is the same order as the linear e-folding time (10 approximately 102 yr when the streaming velocity of the cosmic ray is approximately 108 cm/sec).

The Stability of a Self-Gravitating Nonrotating Gas Layer with Stellar, Magnetic, and Cosmic-Ray Components. 11.

A time-independent linear stability analysis is performed on a self-gravitating, plane-parallel, isothermal layer of nonrotating gas with magnetic and cosmic-ray components. The gas layer is immersed in a rigid plane-stratified isothermal layer of stars which supply a self-consistent gravitational field. The stability analysis is confined to disturbances which propagate along the magnetic field. The principal result to emerge from this study is that the magnetic field and cosmic-ray gas hinder gravitational instability, increasing the minimum length necessary to produce instability approximately by the factor (1 + a + )112, where a is the ratio of magnetic pressure to gas pressure and P is the ratio of cosmic-ray pressure to gas pressure. The author has recently shown that a similar result applies when disturbances propagate across the magnetic field. Subject headings: cosmic rays - hydromagnetics - instabilities

The Origin and Dynamical Effects of the Magnetic Fields and Cosmic Rays in the Disk of the Galaxy

The topic of this presentation is the origin and dynamical behavior of the magnetic field and cosmic-ray gas in the disk of the Galaxy. In the space available I can do no more than mention the ideas that have been developed, with but little explanation and discussion. To make up for this inadequacy I have tried to give a complete list of references in the written text, so that the interested reader can pursue the points in depth (in particular see the review articles Parker, 1968a, 1969a, 1970). My purpose here is twofold, to outline for you the calculations and ideas that have developed thus far, and to indicate the uncertainties that remain. The basic ideas are sound, I think, but, when we come to the details, there are so many theoretical alternatives that need yet to be explored and so much that is not yet made clear by observations.

The Effect of Galactic Cosmic Rays upon the Dynamics of the Solar Wind

view Abstract Citations (16) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Effect of Galactic Cosmic Rays upon the Dynamics of the Solar Wind Sousk, Stephen F. ; Lenchek, Allen M. Abstract The scattering of galactic cosmic rays by the fluctuations in the magnetic field embedded in the solar wind transfers energy and momentum to the cosmic-ray gas. The hydrodynamic equations of the wind, including both these effects, are integrated. The nature of the solutions depends critically on the model chosen for the variation of the diffusion coefficient K with heliocentric distance. It is found that, in order to obtain solutions which give reasonable values for the cosmic-ray pressure at infinity, the diffusion coefficient must vary with heliocentric distance in such a way that, at distances greater than ~-~-`4 au., K increases to a value very much larger than its value at I au. With such models of K(r) the cosmic-ray gas then exerts only a small influence on the wind Publication: The Astrophysical Journal Pub Date: November 1969 DOI: 10.1086/150237 Bibcode: 1969ApJ...158..781S full text sources ADS | Related Materials (1) Erratum: 1970ApJ...159.1133S

Galactic effects of the cosmic-ray gas

On an astronomical scale cosmic rays must be considered a tenuous and extremely hot (relativistic) gas. The pressure of the cosmic-ray gas is comparable to the other gas and field pressures in interstellar space, so that the cosmic-ray pressure must be taken into account in treating the dynamical properties of the gaseous disk of the galaxy. This review begins with a survey of present knowledge of the cosmic-ray gas. Then the kinetic properties of the gas are developed, followed by an exposition of the dynamical effects of the cosmic-ray gas on a large-scale magnetic field embedded in a thermal gas. The propagation of low-frequency hydromagnetic waves is worked out in the fluid approximation. The dynamical properties of the gaseous disk of the galaxy are next considered. The equations for the equilibrium distribution in the direction perpendicular to the disk are worked out. It is shown that a self-consistent equilibrium can be constructed within the range of the observational estimates of the gas density, scale height, turbulent velocity, field strength, cosmic-ray pressure, and galactic gravitational acceleration. Perturbation calculations then show that the equilibrium is unstable, on scales of a few hundred pc and in times of the order 2 × 107 years. The instability is driven about equally by the magnetic field and the cosmic-ray gas and dominates self-gravitation. Hence the instability dominates the dynamics of the interstellar gas and is the major effect in forming interstellar gas clouds. Star formation is the end result of condensation of the interstellar gas into clouds, indicating, then, that cosmic rays play a major role in initiating star formation in the galaxy. The cosmic rays are trapped in the unstable gaseous disk and escape from the disk only in so far as their pressure is able to inflate the magnetic field of the disk. The observed scale height of the galactic disk, the short life (106 years) of cosmic-ray particles in the disk of the galaxy, and their observed quiescent state in the disk, indicate that the galactic magnetic field acts as a safety valve on the cosmic ray pressure P so that P≅B 2/8π. We infer from the observed life and quiescence of the cosmic rays that the mean field strength in the disk of the galaxy is 3–5 × 10−6 gauss.

Solar Diurnal Anisotropy of Cosmic Rays

THE solar diurnal anisotropy of cosmic rays is attributed to the bulk streaming of the cosmic ray gas caused by the corotating interplanetary magnetic field that is “rigidly attached to the Sun”1,2. By analogy with the classical Compton–Getting effect3, a(R), the amplitude of the daily variation at magnetic rigidity R is related to the ratio of particle speed v and the bulk streaming velocity u where γ is the exponent of the differential spectrum. Because, at the orbit of the Earth, u≈450 km s−1 a neutron monitor with mean rigidity of response about 10 GeV and atmospheric threshold 1 GeV should observe an amplitude extrapolated through the atmosphere to free space of about 0.7 per cent.

Pronounced diurnal variation in cosmic-ray intensity

Enhanced diurnal variations during February 1–6, 1967; April 5–14, 1967; and February 22–28, 1968, have been examined by use of data from several super neutron monitors. It is found that during these days, cosmic-ray intensity in a direction 40°–70° west of the sun-earth line was lower with respect to other directions, in particular the polar and antigarden-hose directions. This anisotropy, which resulted from a reduced intensity in the garden-hose direction in the ecliptic plane, suggests that the entire diurnal variation observed in cosmic-ray intensity cannot be attributed to a simple mechanism involving the corotation of cosmic-ray gas, with the interplanetary field. Corotation of cosmic-ray gas implies an enhancement of intensity from a direction roughly 90° east of the sun-earth line (1800 hr direction). Highly variable north-south asymmetries were also present during these periods. These anisotropies occurred without accompanying geomagnetic disturbances or Forbush decreases indicating that they were not due to solar activity on the visible side of the sun.

The equations describing the cosmic-ray gas in the interplanetary region

Beginning with the Boltzmann equation, the continuity and momentum equations for the particles of the cosmic-ray gas which lie within a small energy interval are obtained. These equations are more complete than earlier versions because they include the effects of energy changes due to collisions and electric fields. The main corrections appear as a spectrum dependent factor C(r,T)( r= position vector, T= kinetic energy) which is related to the well known Compton-Getting factor. The correction terms are not negligible and have been evaluated from observational data. The equations have been used to give a more complete development of the theory of the diurnal variation of the cosmic-ray intensity; the essential physical ideas of that theory remain unchanged, but some of the components of the current density are altered and some interpretations are modified.

Quasilinear Theory of Resonant Diffusion in a Magneto-Active, Relativistic Plasma

Equations are set up to describe the quasilinear behavior of a collisionless, relativistic plasma immersed in a uniform, homogeneous magnetic field. Use of the adiabatic assumption, together with an approximation to resonant denominators, enables an estimate to be given of the change of the distribution function due to the turbulent waves. In the particular cases of pure electrostatic waves, magneto-sonic waves, and cyclotron waves, estimates are made of the rate of energy change of resonant particles. It is shown that some modes exhibit resonant diffusion only when relativistic particles are present and for which there is no nonrelativistic counterpart. It is believed that this calculation may be of some interest in situations where relativistic particles play, or are suspected of playing, a major role; for example, the galactic cosmic ray gas and nonthermal radio sources.

Twenty-two-year revolutions in the cosmic-ray diurnal variations

It is shown, from the data obtained during three complete sunspot cycles, that the 22-year variation in the phase of the cosmic-ray diurnal wave is associated with the 11-year revolutions of the diurnal vectors. The revolutions alternate in sense every 11 years. In order to interpret these revolutions, two perpendicular cosmic-ray streamings in interplanetary space are assumed. As both streamings undergo 11-year variations in their velocities, an ellipse is traced out by the termini of the annual vectors; the sense of revolution depends on whether the phase difference between the two is positive or negative. If, on the other hand, their periods are 11 and 22 years and if their phases coincide, the locus is a horseshoelike trajectory, which is traced twice by a to-and-fro motion during 22 years. The observed data available at this stage cannot distinguish between these possibilities. As geomagnetic activity also shows different 11-year variations alternately, its relation to the 22-year revolution in the diurnal variations is discussed. The radial flow of the cosmic-ray particles as well as the rigid rotation of the cosmic-ray gas with the sun suggested by Parker may correspond to the two streamings.

Non-Relativistic Equations of Bulk Motion of a Relativistic Gas. II. Electromagnetic Effects and Superthermal Waves

view Abstract Citations (6) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Non-Relativistic Equations of Bulk Motion of a Relativistic Gas. II. Electromagnetic Effects and Superthermal Waves Lerche, I. Abstract The equations of bulk motion of a gas, in which the pressure cannot be neglected compared to the rest energy of the gas, are deduced by taking moments of the collisionless Boltzmann equation including electromagnetic terms To order u2/c2, where u is the bulk velocity, the derived equations agree with the usual relativistic equations of motion of an ideal fluid. The present analysis relates the mass density and the pressure tensor directly, in terms of integrals over the particles' motions, whereas the standard derivation in terms of the divergence of an energy-stress tensor does not relate the mass density and pressure tensor to the microscopic properties of the fluid. For a particularly simple situation a linearized perturbation analysis yields the modes of oscillation of the gas. An elementary study is made of waves propagating parallel and perpendicular to an ambient magnetic field It is demonstrated that the modes of oscillation differ markedly from those obtained for a non- relativistic gas. The problem is of interest because of its application to the cosmic-ray gas in the Galaxy, non-thermal radio sources emitting radiation by the synchrotron mechanism, and possibly fluctuations in quasi-stellar objects brought about by relativistic particles. Publication: The Astrophysical Journal Pub Date: November 1967 DOI: 10.1086/149365 Bibcode: 1967ApJ...150..651L full text sources ADS |

Energy changes of cosmic rays in the solar system

The energy (in the fixed frame of reference) of a cosmic-ray particle with velocity w in the frame of the solar wind fluctuates between 1 2 M(w + v) 2 and 1 2 M(w − v) 2 as the particle random walks in the magnetic field, where v is the wind velocity. This energy change cannot be treated as a simple Markov process, together with the random walk and adiabatic deceleration, in a fixed frame of reference. To describe the particle motion by a Fokker-Planck differential equation, the energy variable must be the particle energy in a frame of reference moving with the wind. The appropriate transformations of both the solutions and boundary conditions are presented to order v / w . The corrections due to this effect are ∼10% for 1 MeV particles and correspondingly less for higher energy particles. The energy balance between the solar wind and cosmic rays is examined and is shown to depend in a fundamental manner on these energy transformations. Although the solar wind does net work on the cosmic-ray gas, no particle gains more than 2 Mvw kinetic energy and the few particles which penetrate deeply into the solar system suffer a net energy loss because of adiabatic deceleration. Энepгия (B cTaциoнapнoй cиcTeMe кoopдинaT B пpocTpaнcTBe) чacTицы кocMичecкич лyчeй, co cкopocTью w W B cиcTeMe coлнeчнoгo BeTpa, кoлeблeTcя Meждy 1 2 m(w + v) 2 и 1 2 m(w − v) 2 , B To BpeMя кaк чacTицa бpoдиT B MaпниTнoM пoлe, V яBляeTcя cкopocTью BeTpa. Taкyю пepeMeиy эиepгии нe cлeдyeT paccMaTpиBaTь кaк oбыкиoBeииый пpoцecc MapкoBa, BMecTe c бpoжeниeM и aдиaбaTныM зaMeдлeниeM cкopocTи, B cTaциoнapнoй иcTeMe кoopдинaT B пpocTpaнcTBe. чToбы oпиcaTь дBижeниe чacTицы пpи пoMoщи диффepeнциaльнoгo ypaBнeния qFoккepПлaикa, нeoбчoдиMo, чToбы пepeMeннaя энepгии яBянлacь чacTицeй энepгии B пpoдBигaющeйcя BMecTe c BeTpoM cиcTeMe кoopдинaT B пpocTpaнcTBe. BыcTaBляюTcя copaзMepныe пpeBpaщeния кaк peщeний, Taк и гpaничиычycлoBий, cooTBeTcTBeннo пopядкy v / w . ПpoиcTeкaющиe oT эToгo эффeкTa пoпpaBки cocTaBляюT ~10% для чacTиц B 1. Mev и cooTBeTcTBeнныM oбpaзoM Meньщe для чacTиц бoлee Bыcoкoй энepгии. ЙccлeдyeTcя paBнoBecиe зиepгии Meждy coлнeчиыM BeTpoM и кocMичecкиMи лyчaMи, кoTopoe, пoBидиMoMy, элeMeнTapныM oбpaзoM зaBиcиT oT эTич пpeoбpaзoBaний зиepгии. ЧoTя coлиeчный BeTep нe oпepиpyeT нa гaзe кocMичecкич лyчeй, ни oднa чacTицa нe ycилиBaeTcя нa бoлee чeM 2 mvw кинeTичecкoй энepгии и Te нemиoгиe чacTицы, кoTopыe глyбoкo нpoникaюT B coлнeчнyю cиcTey иoдBepгa. oTcн чиcToй иoTepe зиepгии из-зa aдиaбaTнoгo зaMeдлeния cкopocTи.

Non-Relativistic Equations of Bulk Motion of a Relativistic Gas

view Abstract Citations (10) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Non-Relativistic Equations of Bulk Motion of a Relativistic Gas Lerche, I. ; Parker, E. N. Abstract The linearized equations of bulk motion of a gas, in which the pressure cannot be neglected compared to the rest energy of the gas, are deduced by taking moments of the collisionless Boltzmann equation in the absence of external forces. The problem is of interest because of its application to the cosmic-ray gas in the Galaxy. Publication: The Astrophysical Journal Pub Date: July 1966 DOI: 10.1086/148744 Bibcode: 1966ApJ...145..106L full text sources ADS |

The Kinetic Properties of the Galactic Cosmic-Ray Gas

view Abstract Citations (14) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Kinetic Properties of the Galactic Cosmic-Ray Gas Parker, E. N. Abstract The elementary formulae for the pressure and the speed of sound in a statistically isotropic homogeneous cosmic-ray gas are worked out. Cosmic-ray observations near Earth give a cosmic-ray energy density of 1.29 X 10- erg/cm3, a pressure of 0.45 x 1O dyne/cm2, and a compressibility P/ N = 0.66>< 10-li erg/cm3. There is reason to believe that the interstellar values are not significantly higher than near Earth. Publication: The Astrophysical Journal Pub Date: June 1966 DOI: 10.1086/148689 Bibcode: 1966ApJ...144..916P full text sources ADS |

Damping of Interstellar Plasma Waves by the Cosmic-Ray Gas

Damping of interstellar plasma waves by cosmic radiation fluxes due to suprathermal particles - Magnetosonic and Alfven waves

Expanding Supernova Remnants and Galactic Radio Sources

The effect of the expansion of the envelope ejected by a supernova on the interstellar medium is examined. The one-dimensional expansion and hydromagnetic shock propagation is treated first, to investigate the effect of the three constituents (the ordinary “thermal” gas, the cosmic-ray gas and the magnetic field) of the interstellar medium on its compression behind the shock front. A simplification is introduced in the form of an “isothermal” approximation, which is justified a posteriori and this model is generalized for the case of a spherical expansion. It is shown that such an expansion gives rise to a compressed region outside the ejected envelope and that this region acts as a synchrotron radiation source which, in the case of some galactic supernovae, is observable. The theory is applied in some detail to parts of the Cygnus Loop and, less specifically, to IC 443. The results are compared with observations, and satisfactory agreement is found between calculated and measured flux densities. From the applications it is concluded that a significant proportion of the non-thermal radiation from some supernova remnants is emitted in regions formed by the compression process. This process is shown to provide a direct explanation for the well-known near-coincidence of regions of enhanced radio emission with some conspicuous optical features in the Cygnus Loop. The theory predicts a relation between the power frequency spectrum of sources formed by this process and that of the non-thermal galactic background radiation which can be checked by observation.

Origin and Dynamics of Cosmic Rays

As a consequence of the inability to observe directly the origin of a cosmic-ray particle, the development is begun with a discussion of the limitations within which a cosmicray accelerator mechanism can be constructed. Only the betatron effect and the Fermi mechanism can be allowed. Some of the many variations of these mechanisms which are to be found in the literature are reviewed. Then it is shown that trains of oppositely moving hydromagnetic waves of large amplitude and with sharp crests can accomplish large and continued particle accelerations which are adequate to maintain the observed galactic cosmic-ray field. The large acceleration arises as a consequence of the simple fact that each wave tends to sweep up the cosmic-ray particles before it, so that head-on collisions of particles with waves are much more common than overtaking collisions. It is pointed out that the sharp crests of the waves are a natural consequence of the observed supersonic mass motions. Therefore, the acceleration by oppositely moving waves does not depend upon any special wave form, and we suggest that it is the naturally occurring acceleration process. By treating the cosmic rays as a gas with relativistic thermal motions, it is shown that themore » cosmic-ray gas is effectively coupled to the motions of the ordinary matter both parallel and perpendicular to the magnetic field. Thus the effective speed of sound must be computed in the composite cosmic-ray and ordinary gas. It is noted that with this composite speed of sound the irregular mass motions in the gilactic disk and halo are approximately Mach one. It is suggested that this represents a general dynamic balance to be found in all sufficiently active regions of space, and explains how it is that we often observe prolonged mass motions in the galaxy and in stellar atmospheres which would otherwise be computed to be highly supersonic and dissipative. The dynamic balance comes about from the fact that increased cosmicray density would reduce the effective Mach number below one, allowing the sharp crests of the hydromagnetic waves to degenerate, and thereby halting the production of cosmic-ray particles. (auth)« less