scholarly journals Monitoring source variability with the Fast All Sky Telescope

1991 ◽  
Vol 131 ◽  
pp. 445-448
Author(s):  
Kenneth J. Johnston ◽  
Ralph L. Fiedler ◽  
Richard S. Simon
Keyword(s):  
Interstellar Medium ◽  
Radio Wave ◽  
Wave Scattering ◽  
Study Time ◽  
Time Variability ◽  
Radio Sources ◽  
Limited Sample ◽  
Extragalactic Radio Sources ◽  
Design Goal ◽  
Celestial Sphere

AbstractThe proposed Fast All Sky Telescope (FAST) is an interferometer which is intended to monitor the northern four-fifths of the celestial sphere every two days at 8.1 GHz and daily at 2.7 GHz. The design goal is to have a rms sensitivity of 10 mJy/beam at both frequencies. The array is planned to comprise 20 3-meter diameter antennas with a maximum baseline of 0.7 km. FAST will provide a valuable database that may be used to study time variability in a sensitivity limited sample of radio sources. This will significantly impact on the understanding of active Galactic and extragalactic radio sources, as well as on the understanding of radio wave scattering in the interstellar medium.

scholarly journals The JPL 1986–3 Extragalactic Reference Frame

1988 ◽  
Vol 133 ◽  
pp. 461-464
Author(s):  
O.J. Sovers ◽  
C.D. Edwards ◽  
C.S. Jacobs ◽  
G.E. Lanyi ◽  
R.N. Treuhaft
Keyword(s):  
Rotation Axis ◽  
Time Variability ◽  
Radio Sources ◽  
Dual Frequency ◽  
Deep Space Network ◽  
Space Network ◽  
Celestial Sphere ◽  
Almost All ◽  
Comparable Quality

Intercontinental dual-frequency radio interferometric measurements were carried out during 1978 to 1985 between NASA's Deep Space Network stations in California, Spain, and Australia. Analysis of 6800 pairs of delay and delay rate observations made during 51 sessions produced a catalog of positions of 106 extragalactic radio sources, fairly uniformly distributed over the celestial sphere between −45° and +85° declination. Almost all of the resulting source positions have formal uncertainties between 0.5 and 3 milliarcseconds, with their distributions peaking somewhat below 1 mas. Root-mean-square uncertainties are 2.1 and 2.0 mas for RA and declination, respectively. Evidence is found for a long-term drift of the Earth's rotation axis in inertial space, relative to the 1984 IAU precession and nutation models. Tests for time variability of positions of 32 frequently observed sources place limits at the 1 mas/yr level. Comparisons with independently determined source catalogs of comparable quality show differences of positions of common sources that amount to a few mas, and may indicate the level of systematic errors in VLBI source position measurements.

scholarly journals Non‐Gaussian Radio‐Wave Scattering in the Interstellar Medium

2006 ◽  
Vol 640 (1) ◽  
pp. 344-352 ◽  
Author(s):  
Stanislav Boldyrev ◽  
Arieh Konigl
Keyword(s):  
Interstellar Medium ◽  
Radio Wave ◽  
Wave Scattering ◽  
Non Gaussian

scholarly journals The Galactic Distribution of Electron Density Microstructure Inferred from Radio Scattering Observations

2001 ◽  
Vol 182 ◽  
pp. 11-16
Author(s):  
James Cordes
Keyword(s):  
Interstellar Medium ◽  
Radio Wave ◽  
Electron Density ◽  
Wave Scattering ◽  
Galactic Model ◽  
Dispersion Measures ◽  
Pulse Broadening ◽  
Galactic Distribution

AbstractI first review the observables and optics of interstellar seeing associated with radio wave scattering in the interstellar medium. I then describe the Galactic distribution of electron density and its fluctuations, as inferred from a number of observables, including angular and pulse broadening, diffractive scintillations, and dispersion measures. Propects for improving the Galactic model are outlined.

scholarly journals VLBI Survey of a Complete Sample of Active Nuclei and Quasars

1984 ◽  
Vol 110 ◽  
pp. 15-24 ◽  
Author(s):  
T. J. Pearson ◽  
A.C.S. Readhead
Keyword(s):  
Flux Density ◽  
Radio Sources ◽  
Complete Sample ◽  
Limited Sample ◽  
Extragalactic Radio Sources ◽  
5 Ghz ◽  
Number Of Classes ◽  
Compact Sources ◽  
Continuous Range

We have conducted a VLBI survey of a complete, flux-density limited sample of 65 extragalactic radio sources, selected at 5 GHz. We have made hybrid maps at 5 GHz of all of the sources accessible to the Mark-II system. The sources can be divided provisionally into a number of classes with different properties: central components of extended double sources, steep-spectrum compact sources, very compact (almost unresolved) sources, asymmetric sources (sometimes called “core-jet” sources), and “compact double” sources. It is not yet clear whether any of these classes is physically distinct from the others, or whether there is a continuous range of properties.

scholarly journals Interstellar Scintillation of Radio Sources as a Probe for Investigations of the Local Interstellar Medium

1997 ◽  
Vol 166 ◽  
pp. 215-218
Author(s):  
N. Bochkarev ◽  
M. Ryabov
Keyword(s):  
Interstellar Medium ◽  
Small Scale ◽  
Radio Sources ◽  
Local Interstellar Medium ◽  
Star Formation Region ◽  
X Ray ◽  
Extragalactic Radio Sources ◽  
Hot Gas ◽  
The North ◽  
Scintillation Indices

AbstractA possibility of obtaining information on small scale inhomogeneities of the electron component of the local interstellar medium (LISM) is investigated using interstellar scintillations of extragalactic radio sources. We analyse Culgoora array observational data on variability of 190 extragalactic radio sources, covering most of the sky, at 80 and 160 MHz. The variability at time scales from 1 month to 15 years is interpreted as refractive interstellar scintillations in fast-moving nearby (less than 150 pc) hot gas near shock waves in the LISM. All-sky map of scintillation indices m averaged over 3–5 sources closest to one another shows several m maxima. Two of the 3 most pronounced maxima are probably connected with Loop I; the third one coincides with the soft X-ray (0.1–0.3 keV) background maximum near the South Galactic Pole. Other, less certain, m maxima probably correspond to the Orion star-formation region and to a soft X-ray maximum near the North Galactic Pole. The ”free-of-gas” tunnel in the direction l = 240° corresponds to low values of m. The estimated time scale of interstellar scintillations on the above-mentioned LISM structures is in agreement with that of the observed radio-source variations.

scholarly journals Extreme Scattering Events

1988 ◽  
Vol 129 ◽  
pp. 301-302
Author(s):  
Ralph Fiedler ◽  
Brian Dennison ◽  
Kenneth Johnston
Keyword(s):  
Interstellar Medium ◽  
Flux Density ◽  
Light Curves ◽  
Small Scale ◽  
Radio Sources ◽  
Density Measurements ◽  
Extragalactic Radio Sources ◽  
Scattering Events

Dally flux density measurements of 36 extragalactic radio sources over a seven year period, obtained by the Green Bank interferometer, reveal several unusual minima in the light curves that do not follow typical source variations (Fiedler et al. 1987). The most significant departure from typical source variability occurred at both frequencies in the quasar 0954+658 between 1980.95 and 1981.3. Refractive focussing by small scale inhomogeneities in an ionized structure in the interstellar medium appears to be the most likely explanation.

scholarly journals The Caltech-Jodrell Bank VLBI Surveys

1998 ◽  
Vol 164 ◽  
pp. 17-24
Author(s):  
T.J. Pearson ◽  
I.W.A. Browne ◽  
D.R. Henstock ◽  
A.G. Polatidis ◽  
A.C.S. Readhead ◽  
...  
Keyword(s):  
Flux Density ◽  
Angular Size ◽  
Optical Observations ◽  
Radio Sources ◽  
Limited Sample ◽  
Extragalactic Radio Sources ◽  
Superluminal Motion ◽  
Definition Of ◽  
5 Ghz

AbstractThe Caltech-Jodrell Bank VLBI surveys of bright extragalactic radio sources north of declination 35° were carried out between 1990 and 1995 using the Mark-II system, achieving images with a resolution of about 1 mas at 5 GHz. The CJl survey (together with the older “PR” survey) includes 200 objects with 5 GHz flux density greater than 0.7 Jy; the CJ2 survey includes 193 flat-spectrum sources with 5 GHz flux density greater than 0.35 Jy; and we have defined a complete flux-density limited sample, CJF, of 293 flat-spectrum sources stronger than 0.35 Jy. We summarize the definition of the samples and the VLBI, VLA, MERLIN, and optical observations, and present some highlights of the astrophysical results. These include: (1) superluminal motion and cosmology; (2) morphology and evolution of the “compact symmetric objects” (CSOs); (3) two-sided motion in some CSOs; (4) the angular-size-redshift diagram; (5) misalignment of parsec-scale and kiloparsec-scale jets.

scholarly journals Evolutionary Tracks of Extended Radio Sources

1982 ◽  
Vol 97 ◽  
pp. 21-24 ◽  
Author(s):  
J. E. Baldwin
Keyword(s):  
Flux Density ◽  
Radio Sources ◽  
Radio Luminosity ◽  
Limited Sample ◽  
Physical Size ◽  
Space Density ◽  
Extragalactic Radio Sources ◽  
Extended Radio ◽  
Source Sample ◽  
The Right

We know almost nothing about the evolutionary tracks of extragalactic radio sources but those tracks are, however, strongly constrained by the distribution of sources in the radio luminosity, P, overall physical size, D, diagram. This is the radioastronomer's H-R diagram, an analogy which two lines of algebra shows is exact. Fig. 1 is the P-D diagram for the 3CR 166 source sample of Jenkins et al. (1977) with later additions. Most of the sources are identified and have known redshifts. It is a flux density limited sample so that the numbers at any P are weighted relative to the true space density by P3/2 because of the differing volumes of space sampled. The important feature of the diagram is the lack of sources greater than 1 Mpc in size. Because of doubts about the completeness of the sample in this region, we have made searches in the 6C 151MHz survey for sources having surface brightnesses lying between the two lines of slope 2 on the right of Fig.1. The numbers found to a limiting flux density of 1–2 Jy suggest that there is no serious underestimate of the numbers in the 166 source sample.

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