Natural Electromagnetic Radiation Research Articles

High-energy gamma-ray astronomy

All the natural electromagnetic radiation reaching the Earth, whether from nearby or remote parts of the universe, brings with it information on the contents or structure of the region in which it originated. This is true of each part of the spectrum, from radio waves through the visible, ultraviolet and x-ray regions, to the realm of high-energy gamma rays which is our subject here. We will be concentrating on celestial gamma rays, with energies above about 10 MeV, which provide clear and in some respects unique information on the high-energy particles and processes in the universe, both currently and in the remote past.

On the asymmetric nature of micropulsations—I. the spectrum

This paper is based on the postulate that the natural electromagnetic radiation observed in the micropulsation band is accounted for by the eigenmodes of a resonant cavity in the Earth's outer atmosphere, just as the adjacent ELF part of the spectrum is explained by resonances in the Earth-ionosphere cavity. The inner edge of the plasma sheet (the Alfvén layer) forms an effective resonant cavity which we call the Alfvénsphere. Its complex medium is characterized by two parameters, effective conductivity, and effective Alfvén speed: its quasi-stationary states are specified by two state parameters, effective cavity size, and effective time scale for magnetospheric processes, and in principle, they can be evaluated from the power spectra of observed micropulsations. Because of the complex geometry of the cavity and the fact that the vector hydromagnetic wave equation for an asymmetric electric field is not simply separable in spherical and orthogonal dipole coordinates (and the spatial boundary value problem is virtually insoluble), a model is developed which contains the essential physics and admits of tractable equations. A coupling scheme is defined and discussed which permits one to study the eigenvalue equation under conditions of weak and strong coupling as well as the uncoupled case. Emphasis is placed on the most difficult weakly-coupled case because the results can be readily compared with the uncoupled case. The complex dispersion relation-ship is presented and complex eigenvalues are calculated. It is shown that for any mode ( v, i, m), the fundamental ( i = 1) appears at the highest latitude and the highest harmonic ( i = i max) appears at the lowest latitude. Further it is shown that the fundamental and harmonics are split into multiplet frequency states, clustered at different latitudes, and ordered at a particular latitude by the asymmetric label m. This property is used to explain beating and atitudinal and longitudinal variations in pearl pulsations. It is demonstrated that the east-west magnetic component of the perturbed magnetic field (for any mode) has two spatial resonances (logarithmic and asymmetric) and this feature can be used to derive and interpret the T cos 2 Θ = const law. This in turn suggests a method for ordering the east-west component power spectra for a station at any latitude below 70° N mag. in terms of v, and evaluating the corresponding phenomenological state parameters. The inescapable conclusion appears to be that there is no intrinsic difference between the ‘different’ classes of pulsations; they are simply the excited eigenmodes of the Alfvénsphere for different quasi-stationary states.

A Study of Natural Electromagnetic Phenomena for Space Navigation

A study has been carried out for the United States Air Force investigating the use of natural electromagnetic radiation in the space environment for navigational purposes. Radiations from the sun, the stars, and interstellar space in both the visible and RF portions of the spectrum and also cosmic rays have been investigated. Emphasis has been placed on the measurement of velocity in space utilizing the Doppler phenomenon. Equipment and techniques useful in deriving velocity information from Doppler shift measurements are described and figures for expected accuracy are derived. Other passive techniques having possible application to space navigation such as the measurement of total solar radiation and solar diameter are briefly discussed.