Search NASA⌕ Search

SEARCH · Search NASA

Results for “RADIO SOURCE”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Very high resolution observations of the radio source in the supernova remnant G127.1+0.5

The results of recent very long baseline interferometry of G127.11+0.54 at 10.65 GHz reveal a core dual 'jet' structure. The morphology and physical properties of the compact source are similar to those of SS 433. The combined data from various studies of this object suggest that G127.11+0.54 may be the stellar remnant of the supernova event which also produced the supernova remnant G127.1+0.5.

Geldzahler, B. J.↗
NASA NTRS1983

Documentation for the machine-readable version of A Catalogue of Extragalactic Radio Source Identifications (Veron-Cetty and Veron 1983)

Detailed descriptions of the data and reference files of the updated and final version of the machine-readable catalog are given. The computerized catalog has greatly expanded since the original published version (1974), and additional information is given. A separate reference file contains bibliographical citations ordered simultaneously by numerical reference and alphabetically by author.

Warren, W. H., Jr.↗
NASA NTRS1984

Multifrequency light curves of low-frequency variable radio sources

Light curves for the low-frequency variable sources AO 0235 + 16, NRAO 140, PKS 1117 + 14, DA 406, CTA 102, and 3C 454.3, obtained in monthly observations at 318, 430, and 606 MHz using the 305-m telescope at Arecibo and in bimonthly observations at 880 MHz and 1.4 GHz using the 91-m Green Bank transit telescope during 1980-1983, are presented and analyzed. AO 0235 + 16 is found to have basically canonical variability which is attributed to relativistically moving evolving synchrotron components; but in the other sources, strong simultaneous variations at 318, 430, and 606 MHz are observed to be greatly diminished in amplitude at 880 MHz and 1.4 GHz, confirming the existence of the intermediate-frequency gap at about 1 GHz proposed by Spangler and Cotton (1981). The possibility that a second variability mechanism is active in these sources is explored.

Altschuler, D. R.↗
NASA NTRS1986

Polarization distributions in compact radio sources

Intensity and polarization maps of active galactic nuclei, obtained with marcsec resolution at 5 GHz using the Mark III VLBI array during 1981-1982, are presented. The techniques of high-resolution polarization synthesis are described, and maps for the superluminal quasar 3C345, the superluminal galaxy 3C120, and the BL Lac objects 0735 + 178 and OJ287 are characterized, with an emphasis on the relationship between arcsec-scale and marcsec-scale jets.

Roberts, David H.↗
NASA NTRS1989

A method to estimate the motion of unresolved VLBI components in extragalactic radio sources - The case of NRAO 140

A method is proposed for estimating the relative motion of two blended VLBI compact components from measurements of the motion of their brightness centroid. The method requires a priori information about the source components, such as flux densities and separate knowledge of the motion of one of the blended components. Observations of the superluminal quasar NRAO 140 are analyzed to test the technique. Superluminal motion is found for the blended component A2 at 6-cm wavelength with an apparent velocity of about 5c (H0 = 100 km/s/Mpc, q0 = 0.5, z = 1.258).

Charlot, P.↗
NASA NTRS1990

Shock-drift particle acceleration in superluminal shocks - A model for hot spots in extragalactic radio sources

Shock-drift acceleration at relativistic shock fronts is investigated using a fully relativistic treatment of both the microphysics of the shock-drift acceleration and the macrophysics of the shock front. By explicitly tracing particle trajectories across shocks, it is shown how the adiabatic invariance of a particle's magnetic moment breaks down as the upstream shock speed becomes relativistic, and is recovered at subrelativistic velocities. These calculations enable the mean increase in energy of a particle which encounters the shock with a given pitch angle to be calculated. The results are used to construct the downstream electron distribution function in terms of the incident distribution function and the bulk properties of the shock. The synchrotron emissivity of the transmitted distribution is calculated, and it is demonstrated that amplification factors are easily obtained which are more than adequate to explain the observed constrasts in surface brightness between jets and hot spots.

Begelman, Mitchell C.↗
NASA NTRS1990

Phase-referenced VLBI observations of weak radio sources - Milliarcsecond position of Algol

The Fourier inversion of all the delay/rate referenced visibilities of Algol was used to form a 'dirty' map which has dramatically improved VLBI array sensitivity. The Algol system, in a very low state of activity with a total flux density of only 3 mJy, was observed alternatively with the reference source 0309 + 411, about 1 deg away, throughout the 7 hr VLBI experiment. By combining all the individual VLBI observations, the resulting coherent integration time for Algol is 4.2 hr and the corresponding SNR is 12. Internal consistency checks and an analysis of possible systematic astrometric errors indicate that the accuracy of the relative VLBI position of Algol is + or - 0.0005 arcsec in both coordinates and that unknown systematic effects are presently limiting this astrometric measurement.

Lestrade, J.-F.↗
NASA NTRS1992

Gamma rays from extragalactic radio sources

It is proposed that the important connection between 3C 273 and 3C 279, the first two extragalactic sources detected at greater than 100 MeV energies, is their superluminal nature. In support of this conjecture, we propose a radiation mechanism that focuses gamma rays in the superluminal direction, due to Compton scattering of accretion-disk photons by relativistic nonthermal electrons in the jet.

Dermer, Charles D.↗
NASA NTRS1992

Connection between ambient density fluctuations and clumpy Langmuir waves in type III radio sources

A recent stochastic-growth theory of clumpy Langmuir waves in type III sources is shown to imply that the clumps will have the same size distribution as the ambient low-frequency density fluctuations in the solar wind. Spectral analysis of Langmuir-wave time series from the ISEE 3 plasma wave instrument confirms this prediction to within the uncertainties in the spectra. The smallest Langmuir clump size is inferred to be in the range 0.4-30 km in general, and 2-30 km for beam-resonant waves, and it is concluded that the diffusion of waves in the source is anomalous.

Robinson, P. A.↗
NASA NTRS1993

Clumpy Langmuir waves in type III radio sources - Comparison of stochastic-growth theory with observations

Detailed comparisons are made between the Langmuir-wave properties predicted by the recently developed stochastic-growth theory of type III sources and those observed by the plasma wave experiment on ISEE 3, after correcting for the main instrumental and selection effects. Analysis of the observed field-strength distribution confirms the theoretically predicted form and implies that wave growth fluctuates both spatially and temporally in sign and magnitude, leading to an extremely clumpy distribution of fields. A cutoff in the field-strength distribution is seen at a few mV/m, corresponding to saturation via nonlinear effects. Analysis of the size distribution of Langmuir clumps yields results in accord with those obtained in earlier work and with the size distribution of ambient density fluctuations in the solar wind. This confirms that the inhomogeneities in the Langmuir growth rate are determined by the density fluctuations and that these fluctuations persist during type III events.

Robinson, P. A.↗
NASA NTRS1993

Dynamics of Langmuir and ion-sound waves in type III solar radio sources

The study traces the evolution of Langmuir and ion-sound waves in type III sources, incorporating linear growth, linear damping, and nonlinear electrostatic decay. Improved estimates are obtained for the wavenumber range of growing waves and the nonlinear coupling coefficient for the decay process. It is shown that the conditions in the solar wind do not allow a steady state to be attained; instead, bursty linear and nonlinear interactions take place, consistent with the highly inhomogeneous and impulsive waves actually observed. Nonlinear growth is found to be rapid enough to saturate the growth of the parent Langmuir waves in the available interaction time. The competing processes of nonlinear wave collapse and quasi-linear relaxation are discussed, and it is concluded that neither is responsible for the saturation of Langmuir growth.

Robinson, P. A.↗
NASA NTRS1993

Helical jets and the misalignment distribution for core-dominated radio sources

The type of a model which would explain the large population of orthogonally misaligned sources is considered. Two of the best examples of misaligned sources are investigated, namely, the quasar 3C 309.1 (Wilkinson et al., 1986; Kus et al., 1990, 1991) and the BL Lac object 1823 + 568 (Foley, 1982; O'Dea et al., 1988). It is shown that simple bend geometries cannot explain the misaligned sources, and the geometries required to give orthogonal misalignments are explained. A generally applicable model which might explain misaligned sources is proposed.

Conway, J. E.↗