Radio Loops Research Articles

High‐Resolution Ultraviolet Observations of the Highly Ionized Interstellar Gas toward Radio Loops I and IV

We present new Goddard High-Resolution Spectrograph (GHRS) echelle observations of the high ionization lines of Si IV, C IV, and N V toward HD 119608, a halo star at d = 4.1 kpc behind the Loop I and IV supernova remnants. Absorption along the path to HD 119608 makes it possible to study energetic processes that may result in the flow of gas into the Galactic halo. The data have a resolution (FWHM) of ≈ 3.5 km s-1 and S/N ratios of 30:1-50:1. The integrated high ion column densities log N = 13.57 ± 0.02, 14.48 ± 0.06, and 13.45 ± 0.07 for Si IV, C IV, and N V, respectively, imply a factor of 2-4 enhancement in the amount of highly ionized gas compared to average sight lines through the Galactic disk and halo. The integrated high ion column density ratios, N(C IV)/N(Si IV) = 8.1 ± 1.1 and N(C IV)/N(N V) = 10.7 ± 2.1, are also several times larger than normal. These high ion results suggest the absorption is influenced by passage of the sight line through the center of Loop IV. The HD 119608 C IV absorption profile has a bimodal velocity structure indicative of an expanding shell; we tentatively derive an expansion velocity of 16 km s-1 for Radio Loop IV. A detailed analysis of the high ion profile structure indicates that multiple types of highly ionized gas with a range of properties exist along this sight line. We also reexamine the high ionization properties of the QSO 3C 273 sight line using new intermediate-resolution (FWHM ≈ 20 km s-1) GHRS data. We obtain log N = 14.49 ± 0.03 and 13.87 ± 0.06 for C IV and N V, respectively. The C IV column density, which is 0.12 dex smaller than earlier estimates, leads to somewhat smaller ionic ratios than previously determined. We find N(C IV)/N(Si IV) = 5.1 ± 0.6 and N(C IV)/N(N V) = 4.2 ± 0.6. However, as for HD 119608, the high ion column densities toward 3C 273 are larger than normal by factors of 2-4. The 3C 273 high ion absorption profiles are much broader than those seen toward HD 119608 and other sight lines near the center of Loop IV. The larger line widths may result because the sight line passes through the turbulent edge of Loop IV as well as the X-ray and radio continuum emission regions of the North Polar Spur. We have compiled a list of the highest quality IUE and GHRS high ion measurements available for interstellar sight lines through the disk and halo and find the following median averaged results: N(C IV)/N(Si IV) = 3.8 ± 1.9 and N(C IV)/N(N V) = 4.0 ± 2.4. These ratios are lower than those found for four Loop IV sight lines. We suggest a model for the production of highly ionized gas in Loop IV in which the contributions from turbulent mixing layers and conductive interfaces/SNR bubbles to the total high ion column densities are approximately equal. Much of the high ion absorption toward HD 119608 and 3C 273 may occur within a highly fragmented medium within the remnant or the outer cavity walls of the remnant.

Interaction of the Local Bubble with its environment

AbstractThe Local Bubble (LB), a volume of roughly 100 pc radius filled with ionized gas of high temperature and low density, is not a unique object. It is obviously surrounded by several interstellar bubbles of similar properties. Some of them are as close as to undergo interaction with the LB. Our most prominent neighbour is the Loop I superbubble formed by the Sco-Cen OB association. It is shown that this huge shell is in collision with our Local Bubble. The product of this interaction is an annular cloud of dense neutral gas at the boundary between the two bubbles. Other examples for close neighbouring bubbles are the Gum nebula, the Eridanus bubble and possibly the two radio loops II and III.

The Morphology and Physics of the Local Interstellar Medium

We are finally on the threshold of obtaining a coherent morphological and physical picture for the local interstellar medium (LISM), especially the region within 300 pc of the Sun. The EUVE is playing a special role in revealing this picture. This instrument can provide direct measurements of the the radiation field that photoionizes both hydrogen and helium. It also can yield direct measurements of the column densities of hydrogen, but especially He I and He II toward nearby white dwarfs. These observations suggest that the ionization in the Local Cloud, the cloud in which the Sun is embedded, is not in equilibrium, but in a recombination phase. Heuristic calculations imply that the the present ionization is due to the passage of shocks, at times greater than 3 × 106 years ago. The origin of these shocks are probably linked to the supernova which was responsible for the expanding nebular complex of clouds know as the Loop I supernova remnant, of which the Local Cloud is a part, extreme- UV radiation field, that which ionizes both hydrogen and helium in the LISM. Of the ISM within 300 pc, the volume appears to be predominantly filled by hot (106 K) coronal gas. This gas is laced with six largescale shell structures with diameters ~100−150 pc including the long-recognized radio loops, Loop I−IV, as well as the Orion-Eridanus and Gum Nebulae are identified. An idea that has evolved in the literature for over two decades is that the kinematically-linked OB associations representing Gould’s Belt, plus the gas and dust of Lindblad’s Ring, require that previous supernova activity and stellar winds carved out a 400–600 pc diameter cavity some 3 to 6 × 107 yr ago. This activity produced a pre-existing low density region, into which the present young loop structures have expanded. The outer boundaries of the identified expanding loop structures, inside this preexisting cavity, delineate the periphery of the the mis-named “local interstellar bubble.” Thus, this picture naturally explains some of the problems often associated with the presence of this low density region exterior to Loop I.

Low-power digital radio as a ubiquitous subscriber loop

The recent growth in the use of digital radio is reviewed. The technology used to implement low-power digital radio in the local exchange loop plant is discussed. The integration of digital radio subscriber loops withnetwork intelligence is explored. The relationship between low-power digital radio loops and broadband fiber loops is briefly examined, and standards and frequency allocation activities are summarized.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

4812761 Electrically parallel equal phase resonant loops for nuclear magnetic resonance surface coils

A nuclear magnetic resonance measurement system is disclosed which includes, in combination, means for generating an applied main magnetic field, and an array of at least two radio frequency current loops. The loops are electrically connected in parallel, and are oriented in a generally planar relationship with respect to each other. The loops are connected in phase with respect to each other so that the component of magnetization generated by the loops which orthogonal to the direction of the applied main magnetic field is in the same general direction. A capacitor is preferably electrically connected in parallel with the loops.

Multiple moving magnetic structures in the solar corona

We report the study of moving magnetic structures inferred from the observations of a moving type IV event with multiple sources. The ejection contains at least two moving radio emitting loops with different relative inclinations. The radio loops are located above multiple Hα flare loops in an active region near the limb. We investigate the relationship between the two systems of loops. The spatial, temporal and geometrical associations between the radio emission and near surface activities suggest a scenario similar to coronal mass ejection (CME) events, although no CME observations exist for the present event. From the observed characteristics, we find that the radio emission can be interpreted as Razin suppressed optically thin gyrosynchrotron emission from nonthermal particles of energy ∼ 100, keV and density ∼ 102–105 cm−3 in a magnetic field ≤ 2 G.

Radio and H-alpha images of the 'figure-8' radio nucleus of the interacting Seyfert galaxy NGC 2992

Synthesis observations at a wavelength of 6 cm of the nuclear region of the Seyfert galaxy NGC 2992 clarify the presence of a striking pair of loops which join at the nuclear point source, forming a figure-8. The radio strands forming the loops are discussed in terms of two possible models: limb-brightened bubbles and magnetic arches. Noting that several examples of radio loops in galactic nuclei have been documented, the frequency of occurrence of galactic center loops is discussed and it is concluded that they may be relatively common. A larger-scale view of the nucleus of NGC 2992 based on a H-alpha image is presented. 22 references.

Soft X-ray emission from radio Loops I and III compared

Soft X-ray emission from radio Loops I and III compared

Radio emission from supernova remnants in a cloudy interstellar medium

The van der Laan (1962) theory of SNR radio emission is modified in light of the inhomogeneity of the interstellar medium, and in order to allow for particle acceleration in shock fronts. It is proposed that most of the radio emission in 10-20 pc radius SNRs originates in cold interstellar clouds that have been crushed by the high pressure hot gas within the expanding remnant. Under these circumstances, simple reacceleration of ambient interstellar cosmic ray electrons can account for the surface brightness-diameter distribution of observed remnants, with the additional, relativistic particle energy compensating for the decreased filling factor of the radio-emitting regions. Warm interstellar gas, at about 8000 K, may also be compressed within very large SNRs (of radius of 30-100 pc) and account for both the giant radio loops, when these SNRs are seen individually, and the anomalously bright galactic nonthermal radio background, which may be the superposition of a number of such features.

A new class of extraordinary HI shell

I consider an ordinary shell to be one which can be produced by ordinary means such as a supernova. Good examples are the HI shells associated with the prominent radio loops, discussed today by Prof. Weaver, and the large HI shell in Eridanus (Heiles, 1976). Figure 1 shows the shell which is associated with radio Loop I, made from a consolidation of data from Martha Cleary of Australia, Raul Colomb and Wolfgang Poppel of Argentina, and myself. It changes size with velocity in the manner expected for an expanding shell. The distance is only 100 pc or so. Similar shells should be easily resolvable in the galactic plane, even with a modest telescope, because differential galactic rotation eliminates the confusing effects of foreground and background gas.

Extensive nebulosity and the giant radio loops

Extensive nebulosity and the giant radio loops

A reappraisal of several extensive phenomena of the high galactic latitudes

This is the first of two papers dealing with the extensive high latitude phenomena. The relationships between the diffuse and filamentary gaseous nebulosity, the giant radio loops and the high, medium and low velocity neutral hydrogen are considered in the light of recent observations. The existence of other giant loops is also suggested. A further article (by K.H.E.) will present some very accurate measurements of the radial velocities of the nebulosities in the vicinity of Loop 2. These will be compared to some neutral hydrogen features in that region.

Filamentary Nebulosity in the Vicinity of Loop III

PROJECTING from the plane of the galaxy are three loops of nonthermal radio emission. Loop I, originally called the North Polar Spur, is 113° in diameter1 and is centred on lII = 330°; bII = 19.5°. The Cetus Arc, now called Loop II, is 92° in diameter2 and is centred at lII = 100; bII = −30°. Loop III is 71° in diameter3 and is centred near the north celestial pole at lII = 124°; bII = 11.5°. It was proposed in ref. 1 that Loop I is the remnant of a supernova close to the Sun, as the radio emission is non-thermal and seems to come from a shell source. If the radio loops are supernova remnants, then we would expect to observe filamentary nebulosity surrounding their radio ridges, as is observed in well known supernova remnants such as the Cygnus Loop.

High-Speed Teleprinter System

A novel printing method is used in a high-speed, fully electronic teleprinter system which is able to transmit, receive, and print-out telegraph and data messages at a maximum speed of 225 characters per second or 1800 bauds, i.e., 20 to 30 times faster than in ordinary teleprinters in use today. The system consists of 1) a photoelectric reader for punched tape and an electronic transmitter, 2) an electronic receiver and high-speed printer, and 3) the necessary equipment to transmit and receive the signals on telephone channels. Main emphasis in this paper is given to the nonpercussive printer, which generates the characters by electrolytical inking of ordinary, untreated teleprinter paper in a 5 by 7 mosaic form. The printing shows good contrast, is fast to wiping, light, and the influence of ordinary chemical fluids, and may be copied by all known office reproduction sets. The system may be used with advantage when: 1) large amounts of information have to be transmitted and printed out, 2) the communication channel is available only for limited time, e.g., in radio satellite communication, and 3) the transmission has to be finished in a short time. The system has been tested with good success on radio satellite communication loops.