Radio-emitting electrons and cosmic ray confinement

The propagation of cosmic ray electrons in the framework of the Disk-Halo diffusion model in which the diffusion coefficientD z E (wherez is the distance from the galactic plane andE is the energy), and the magnetic fieldHz ^– has been examined by making use of the recently available radio data up to 8 GHz toward the Anticenter (A) and Halo Minimum (M). The following inferences are then made. From the difference in the frequency at which steepening occurs in the radio spectra towardA andH, it is found that the observations are consistent with the magnetic field decreasing withz such that =0.24–0.37. An electron injection spectrum with a single power law down to energies well below 1 GeV cannot explain satisfactorily the observed radio spectra. All observations, however, can be understood in a self consistent way if the observed steepening of the radio spectra, and hence the interstellar electron spectrum, is due partly to the deviation in the power law electron injection spectrum below a few GeV and partly to the first break arising from electron energy losses occurring in the same energy region. In this case, using the value of obtained above and a value of =0.3–0.6, it is found that the spectral index ₀ of the injected electrons above a few GeV has a value between 1.9 and 2.3 and the index a value between 0.5 and 1. Further, if the electrons and protons have the same spectral shape at injection, then ₀=2.1–2.3.NASA-NRC, Senior Research Associate on leave from Tata Institute of Fundamental Research, Bombay, India.     

Magnetic field induced metal-insulator transition in a one-dimensional chain: Application to neutron star atmospheres

It is shown that, in the non-interacting limit, a one-dimensional metallic system has a transition to an insulating phase, in presence of external magnetic fieldH, if _B H>E _B where _B is the Bohr magneton andE _Bis the energy band width of the electronic states. Possible realization of this effect in the atmosphere of neutron stars is pointed out.     

Effect of cavitation on spherical blast waves

For spherical blast waves propagating through a self-gravitating gas with an energy inputE =E ₀ t , whereE is the energy released up to timet,E ₀ is a functional constant, and is a constant, kinetic, internal heat, and gravitational potential energies have been computed. Taking the parameterA ², which characterises the gravitational field, equal to 2, variations of the percentages of these energies for =0, 1/2, 4/3, and 3 with shock strength have been presented. For =3, the effect of cavitation on the percentages of kinetic energy and internal heat energies has been explored.     

The possibility of transition radiation in planetary nebulae

A new concept —the Paradox of Nebula IC4997 — is the main subject of the present article. The essence of this paradox arises when the variations of the intensities of forbidden lines 4363 [Oiii] andN ₁+N ₂ [Oiii] take place not in unison as is predicted by the classical theory. An attempt is made to solve this paradox, suggesting the possibility both of spontaneous appearance of relativistic electrons in the nebula and the generation of so-calledtransition radiation as a result of electrodynamic interaction of these electrons with dust particles in nebula. The parameters of relativistic electrons and power of transition radiation are obtained. The problems which need further examination are also enumerated.     

On the abundance of chlorine in the Sun

A low-noise photoelectric scan which includes the predicted position of the Cli transition 4s ⁴ P _5/2-4 _p ⁴ D ⁰ _7/2 provides inconclusive evidence for the presence of the line in the solar photospheric spectrum. An upper limit logN(Cl) 5.5 is derived. It is pointed out that the fundamental vibration rotation band of HC1 at 3.3 should be detectable in the sunspot spectrum unless logN(Cl) < 4.6. Sunspot spectra may also provide the isotopic abundance ratio N(Cl³⁵)/N(Cl³⁷).A new derivation of the chlorine abundance for the Orion nebula is presented: logN(Cl) 5.8. It is suggested that a cosmic abundance logN(Cl) = 5.5 to 5.8 be adopted.Operated by the Association of Universities for Research in Astronomy Inc., under contract with the National Science Foundation.     

Evidence for thin-target X-ray emission in a small solar flare on 26 February 1972

We compare solar X-ray observations from the UCSD experiment aboard OSO-7 with high resolution energetic electron observations from the UCAL experiment on IMP-6 for a small solar flare on 26 February 1972. A proportional counter and NaI scintillator covered the X-ray energy range 5–300 keV, while a semiconductor detector telescope covered electrons from 18 to 400 keV. A series of four non-thermal X-ray spikes were observed from 1805 to 1814 UT with average spectrum dJ/d (hv) (hv)^–4.0 over the 14–64 keV range. The energetic electrons were observed at 1 AU beginning 1840 UT with a spectrum dJ/dE E ^–3.1. If the electrons which produce the X-ray emission and those observed at 1 AU are assumed to originate in a common source, then these observations are consistent with thin target X-ray production at the Sun and inconsistent with thick target production. Under a model consistent with the observed soft X-ray emission, we obtain quantitative estimates of the total energy, total number, escape efficiency, and energy lost in collisions for the energetic electrons.     

Theoretical models of planetary nebulae

Sets of theoretical models of spherically symmetrical gaseous nebulae are calculated for a fixed chemical composition and with central star, energy distributions given by Cassinelli (1971) and by Kunasz, Mihalas and Hummer (1975). A central region of constant densityN _H=100 cm^–3 is surrounded by a broken shell consisting of zones of different density and optical thickness. It is found that for a fixed chemical composition and central star flux, a considerable range can be found in the emitted fluxes of certain lines such as 4686 which are often used to fix the level of excitation of a nebula. Although it is possible to produce models yielding a variety of nebular line ratios in this way, these truncated inhomogeneous shell models have not reproduced the integrated spectra of nebulae that simultaneously show extreme features of high and low excitation with great strength-e.g. [Nii], [Oii] and 4686 Heii.     

Propagation of the cosmic-ray iron group at intermediate energies

Elemental abundances of the VH group of cosmic radiation have been measured in the energy interval 250–550 MeV nucl^–1 in a balloon exposure at Sioux Falls (South Dakota) of a plastic detector LeXAN stack. The so obtained abundances have been extrapolated to the sources in the frame of the homogeneous model correcting for energy loss. After taking into account solar modulation, the best fit to model values has led to a escape mean free path _e = 5E ^–0.4 g cm^–2, whereE is the energy in GeV nucl^–1, forE>1 GeV nucl^–1, and a constant _e = 5 g cm^–2 forE1 GeV nucl^–1. When turning to the diffusion model, also including an energy loss term, a diffusion coefficientD=3×10²⁸ cm² s^–1 has been estimated.     

Ion acoustic instability in the presence of plasma turbulence in the solar wind

The adiabatic theory of interaction between high and low frequency waves has been studied for the case of electron plasma oscillations and ion acoustic waves and the results are applied to the solar wind. The modified dispersion relation for ion acoustic waves has been derived, taking a Gaussian distribution for plasmons. Two limiting cases of the spectrum are studied. For a broad spectrum, the plasma turbulence has a destabilising effect by introducing a growth rate denoted by turbulence, which is positive for k ₀ > (m _e/ m _i )^1/2 _De ^–1 , k ₀ being the central wave numger of the spectrum, _De the electron Debye length. Also, even for v _d(drift velocity between electrons and ions) < c _s, we arrive at unstable ion acoustic modes. For narrow spectrum, the plasma turbulence has a stabilising effect.     

Cosmic neutrinos of ultra-high energies and detection possibility

The fluxes and spectra of galactic and extragalactic neutrinos at energy 10¹¹–10¹⁹ eV are calculated. In particular, the neutrino flux from the normal galaxies is calculated taking into account the spectral index distribution. The only assumption that seriously affects the calculated neutrino flux atE _v 10¹⁷ eV is the power-like generation spectrum of protons in the entire considered energy region.The normal galaxies with the accepted parameters generate the metagalactic equivalent electron component (electrons+their radiation) with energy density _e8.5×10^–7 eV cm^–3, while the density of the observed diffuse X-ray radiation alone is 100 times higher. This requires the existence of other neutrino sources and we found the minimized neutrino flux under two limitations: (1) the power-law generation spectrum of protons and (2) production of the observed energy density of the diffuse X-an -radiation. These requirements are met in the evolutionary model of origin of the metagalactic cosmic rays with modern energy density _M83.6×10^–7 eV cm^–3.The possibility of experiments with cosmic neutrinos of energyE _v 3×10¹⁷ eV is discussed. The upper bound on neutrino-nucleon cross-section <2.2×10^–29 cm² is obtained in evolutionary model from the observed zenith angular distribution of extensive air showers.In Appendix 2 the diffuse X-and -ray flux arising together with neutrino flux is calculated. It agrees with observed flux in the entire energy range from 1 keV up to 100 MeV.     

A reexamination of the Gum nebula

A detailed analysis of interstellar measurements in the direction of the Gum nebula is carried out. The ionized region is shown to have an angular radius of 18° and appears to be bounded by a shell of neutral gas. The mean electron temperature deduced from radio-frequency absorption measurements is found to be 8500K. These parameters suggest that the nebula is the normal and possibly evolved Hii region of Pup and ² Vel, rather than the fossil Strömgren sphere of the Vela supernova as suggested by Brandtet al. (1971).     

Electrical conductivity of neutron star cores in the presence of a magnetic field

General theory of electrical conductivity of a multicomponent mixture of degenerate fermions in a magnetic fieldB, developed in the preceding article (this volume), is applied to a matter in neutron star interiors at densities ₀, where ₀ = 2.8×10¹⁴ g cm^–3 is the standard nuclear matter density. A model of free-particle mixture ofn, p, e is used, with account for appearance of ^–-hyperons at > _c , where _c 4₀. The electric resistivities along and acrossB, and , and the Hall resistivity _H are calculated and fitted by simple analytical formulae at _c and > _c for the cases of normal or superfluid neutrons provided other particles are normal. Charge transport alongB is produced by electrons, due to their Coulombic collisions with other charged particles; is independent ofB and almost independent of the neutron superfluidity. Charge transport acrossB at largeB may be essentially determined by other charged particles. If _c , one has = [1 + (B/B ₀)²] for the normal neutrons, and for the superfluid neutrons, while _H = B/B _e for both cases. HereB _e 10⁹ T ₈ ² G,B ₀10¹¹ T ₈ ² G, andT ₈ is temperature in units of 10⁸ K. Accordingly for the normal neutrons atBB ₀, the transverse resistivity suffers an enhancement, _{1/4 1}. When 5₀ andB varies from 0 toBB _p 10¹³ T ₈ ² G, increases by a factor of about 10³–10⁴ and _H changes sign. WhenBB _p , remains constant for the superfluid neutrons, and _H B ² for the normal neutrons, while _H B for any neutron state. Strong dependence of resistivity onB, T, and may affect evolution of magnetic fields in neutron star cores. In particular, the enhancement of at highB may noticeably speed up the Ohmic decay of those electric currents which are perpendicular toB.     

A generalized method for deriving mass-loss rates: The first order moment of unsaturated P Cygni line profiles

For the case of optically thin lines, we show that the relation existing between the first order momentW ₁ (E()/E _c –1)(–₁₂)d of a P Cygni profile and the quantityMn(level), whereM is the mass-loss rate of the central star andn(level) the fractional abundance of the ion under study, is in fact independent of any Sobolev-type approximations used for the transfer of line radiation, contrary to what has been assumed in some previous works (Castoret al., 1981; Surdej, 1982). Consequently, all results established in the context of very rapidly expanding atmospheres and mainly referring to the non-dependence ofW ₁ vs various physical (underlying photospheric absorption line, limb darkening, etc.) and geometrical (velocity fieldv(r), etc.) effects remain unchanged for arbitrary (e.g non-Sobolev type) outward-accelerating velocity laws.Whenever applied with caution, Equation (50) thus provides a very powerful means of deriving mass-loss rates—with a total uncertainty less than 60 percent—from the measurementW ₁ of unsaturated P Cygni profiles observed in the spectrum of early—as well as late—type stars, quasars, etc.     

Neutrino luminosity by the ordinary URCA process in an intense magnetic field

The neutrino luminosity by the ordinary URCA process in a strongly magnetized electron gas is computed. General formulae are presented for the URCA energy loss rates for an arbitrary degree of degeneracy. Analytic expressions are derived for a completely degenerate, relativistic electron plasma in the special case of neutron-proton conversion. Numerical results are given for more general cases.The main results are as follows: the URCA energy loss rates are drastically reduced for the regime of great degeneracy by a factor up to 10^–3 for 1, andT ₉10, where =H/H _q ,H _q =m ² c ³/eh=4.414×10¹³ G. In the non-degenerate regime the neutrino luminosity is enhanced approximately linearly with for the temperature range 1T ₉10. Possible applications to white dwarfs and neutron stars are briefly discussed.We have been recently informed that in Gamow home-dialect (Odessa dialect) URCA means thief — (Private communication from Prof. G. Wataghin).     

Bipolar outflows from stars and galaxies as a tornado phenomenon

At an early stage in the lives of stars and galaxies when they are surrounded by discs, vorticity in the disc concentrates into a central vortex, thus converting a Keplerian velocity fieldu _ø r ^–1/2 into an irrotational velocity fieldu _ør ^–1, which implies inward transfer of angular momentum. Centrifugal forces due to spin-up of the inner region and gravity dominant in the outer region then squeeze gas at intermediate layers, increasing pressure gradient in the axial direction sufficiently to drive a wide-angle low-velocity bipolar outflow from the disc. A logarithmic singularity of vorticity at the axis implies strong centrifugal forces which expand plasma to radiusR where pressure gradient balances centrifugal force density of ions; the much weaker centrifugal force density of electrons cannot balance pressure gradient, so that electrons are driven inwards relative to ions until charge separation limits the relative displacement. Now the radial gradient ofu _øcauses ions to rotate at a different rate to electrons, generating an azimuthal current densityj _øwhich is the source of an axial magnetic fieldB _zin the core of the central vortex. Centrifuging carries lines of B to the core wall, where they are wound into helical force-free configuration with B j. An annular channel of radiusR and thickness R into which parallel helical lines ofj andB are compressed constitutes a magnetic vortex tube (MVT). An MVT separates an inner high-velocity highly collimated outflow from the outer low-velocity wide-angle outflow, and is responsible for jets. Magnetic pinches in the MVT may constrict the core flow at HH objects.     

Acceleration of ultrarelativistic electrons in the Crab Nebula

Ultrarelativistic electrons must be being accelerated in the Crab Nebula to maintain the synchrotron spectrum. Sufficient power to maintain the synchrotron spectrum is supplied by an observed damping of compressional motions in the central region of the nebula (the wisps of Baade). An acceleration mechanism which involves compressional motions, the gyrorelaxation effect and the removal of pitch angle anisotropies by the generation of hydromagnetic waves is formulated and applied to a model of the Crab Nebula with acceleration confined to a central region. This can account for the power supplied to the electrons, the overall shape of the spectrum and allows acceleration up to energies corresponding to the synchrotron emission of hard X-rays. The acceleration process tends to flatten an initial energy spectrum.     

Cosmic ray origin above 1018 eV: Galactic or extragalactic?

An analysis is made of the implications of assuming that suprathermal dust grains (a3×10⁸ cm) of intergalactic origin may acquire cosmic ray energies as high as 10²⁰ eV. These dust grains may attain suprathermal energy (v _g3×10⁸ cm s^–1) by the Fermi process. Initially the dust grains are accelerated by the radiation pressure against the drag of the ambient gas of the medium, but once these dust grains attain a terminal velocity (U10⁵ cm s^–1), then they may be expelled out of the galactic region into the intergalactic medium and finally acquire high energy     

On the isotropization of electrons in synchrotron sources

Electrons radiating synchrotron radiation develop a pitch angle anisotropy, and so become unstable to the coherent emission of hydromagnetic waves. The evolution of the coupled system of anisotropic electrons and waves is studied in the absence of any dissipation of the waves in the ambient medium. The anisotropy of the electrons approaches a steady state in which the anisotropy is energy independent and of orderv _A/c (v _A=Alfvén speed). The conditions for this small degree of anisotropy to be maintained are examined.Due to this scattering the bend in the synchrotron spectrum, from an inverse power law with index to one with index 4/3+1, due to an initial or recurrent injection of electrons, could only occur at infrared or higher frequencies.     

Positrons and low energy cosmic rays from supernovae

Burgeret al. (1970) calculated the positron flux from the decay of⁵⁶Co⁵⁶Fe from cosmic rays injected from supernovae. The plasma properties of the ejected matter are determined in the present calculation in order to include the ionization loss of the positrons as the matter expands. It is found that using the matter velocity distribution of previous supernova model calculations that roughly 10% of the positrons escape. The average lifetime in the galaxy due to ionization loss is found to be relatively small, 1.5×10⁵ yr, and with the above injection results in ×3, the observed flux. The same matter velocity distribution is subjected to ionization loss in the galaxy and a steady state low energy, 10E200 MeV, differential flux spectrum is found,J(E)E ^–1.2. This removes the difficulty of the high galactic energy density resulting from a steeper spectrum.     

On the role of plasma effects in the cosmic ray propagation and isotropization in the Galaxy

Cosmic ray (c. r.) propagation in interstellar magnetic fields is often considered in the diffusion approximation, i.e. by the diffusion equation in the coordinate space. Cosmic ray momentum distribution in this case is considered isotropic when the space gradients of c.r density are absent. This approach, with the use of an unfixed effective diffusion coefficientD independent of the energyE enables one to describe all the data available However, neither the diffusion mechanism nor the limits of applicability of the diffusion approximation is clear particularly ifD is independent ofE. Furthermore, the diffusion coefficientD must be expressed through the characteristics of the interstellar medium and possibly through the flux velocity and density of c.r. etc. One of the possible approaches for the analysis of the mechanism and characteristic features of c.r. distribution and isotropization is the account taken of the plasma effects and specifically, the study of c.r. flux instability arising when c.r. are moving in the interstellar plasma. As a result of such instability c.r. may generate waves of different types (magnetohydrodynamic, high-frequency plasma and other waves). Generation of waves and scattering on them result in isotropization of cosmic rays while their propagation under certain conditions turns out similar to that under diffusion.An attempt is made here to systematically analyse the avove mentioned plasma effects and to find out to what extent they are responsible for the behaviour of c.r. in the Galaxy. It turns out that c.r. In any case this is true if this mechanism is regarded as the only c.r. isotropization mechanizm within a wide energy range from 1 to 1000 GeV. Isotropization and spatial diffusion of c.r. up toE100–1000 GeV on the waves from external sources (for example, on the waves from the supernova shells) also proved impossible if the diffusion coefficient is assumed to be independent of c.r. energy. Some new possibilities of c.r. isotropization are also considered.A List of Notations D cosmic ray (c.r.) space diffusion coefficient - degree of c.r. anyisotropy - E,E _kin total and kinetic particle energy - p,p particle momentum and its absolute value - angle between the particle momentum direction and the magnetic field direction (z-axis) - cos - v, particle velocity and its absolute value - c light velocity - f(p),f(E) momentum and energy particle distribution function - N( > E) = N( > p) = f(p) dp/(2)³ = _E f dE c.r. particle density - c.r. spectrum index,N(>E)=KE ^–+1 - n _H neutral particle density - n=n _e=n _i ion and electron density - H niagnetic field - T temperature - thermal velocities of electrons and ions - Boltzmann constant - Alfén velocity - M, m proton and electron masses - e electron charge - wave frequency - _H =eH/Mc, = _H (Mc ²/E) gyrofrequency of a plasma proton and relativistic particle - _H =eH/mc gyrofrequency of an electron - plasma frequency - v _ii,v _ei,v _en,v _in collision frequencies between ions, electrons and ions, electrons and neutrals, ions and neutrals - growth rate of wave amplitude - k,k wave vector and its absolute value - angle between the directions of the vectorsk andH - wave energy density