scholarly journals Bulk Relativistic Motion in a Complete Sample of Flat Spectrum Radio Sources

1988 ◽  
Vol 129 ◽  
pp. 71-72
Author(s):  
C. J. Schalinski ◽  
A. Witzel ◽  
Th.P. Krichbaum ◽  
C. A. Hummel ◽  
P. L. Biermann ◽  
...  
Keyword(s):  
Flux Density ◽  
Status Report ◽  
Radio Sources ◽  
Supporting Evidence ◽  
X Rays ◽  
Relativistic Motion ◽  
Bl Lac Objects ◽  
Vlbi Observations ◽  
Wide Range ◽  
5 Ghz

As part of a multi-epoch and multi-wavelength study of the physics of core dominated radio sources we have investigated the occurrence of apparent superluminal motion and other indications for bulk relativistic motion (b.r.m) in a statistically complete, flux density limited (S5GHz ≥ 1Jy) sample of 13 objects with flat radio spectra These sources come from the S5-survey (Kühr et al., 1981) and are optically identified as 7 quasars and 6 BL-Lac objects. They have been observed over a wide range of frequencies, from radio through X-rays (s. Eckart et al., 1986 and references therein). Radiomaps have been obtained at frequencies from 327 MHz to 22.2 GHz with resolutions from arcseconds to 0.2 mas, using the VLA, MERLIN and telescopes of the US- and European-VLBI networks. A recent status report on the VLBI-observations is given by Witzel (1987). In this paper we summarize the results on the direct evidence for b.r.m. in this sample as derived from repeated VLBI-observations at 5 GHz, as well as supporting evidence from SSC-calculations and flux density variability of the 5GHz VLBI core components (Table 1).

scholarly journals Bulk Relativistic Motion in a Complete Sample of Radio Selected AGN

1987 ◽  
Vol 121 ◽  
pp. 287-293
Author(s):  
C.J. Schalinski ◽  
P. Biermann ◽  
A. Eckart ◽  
K.J. Johnston ◽  
T.Ph. Krichbaum ◽  
...  
Keyword(s):  
Dynamic Range ◽  
Radio Sources ◽  
Relativistic Motion ◽  
Complete Sample ◽  
Superluminal Motion ◽  
Spectrum Radio ◽  
Wide Range ◽  
Show Evidence

A complete sample of 13 flat spectrum radio sources is investigated over a wide range of frequencies and spatial resolutions. SSC-calculations lead to the prediction of bulk relativistic motion in all sources. So far 6 out of 7 sources observed with sufficient dynamic range by means of VLBI show evidence for apparent superluminal motion.

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 Evidence for Relativistic Motion in the Millisecond Structure of BL Lac

1982 ◽  
Vol 97 ◽  
pp. 385-386 ◽  
Author(s):  
R. L. Mutel ◽  
R. B. Phillips
Keyword(s):  
Position Angle ◽  
West Germany ◽  
Relativistic Motion ◽  
Owens Valley ◽  
Vlbi Observations ◽  
Bl Lac ◽  
5 Ghz

After several years of relative quiescence, the flux of BL Lac has increased dramatically at centimeter wavelength, starting about epoch 1979.9 (Fig. 1). We have begun a series of VLBI observations to monitor the milliarcsecond structure at λ6 and λ2.8 cm wavelengths, using a five element VLBI array consisting of telescopes at Bonn, West Germany; Westford, MA; Green Bank, WV; Ft. Davis, TX; and Owens Valley, CA. The first two observations, in 1980 May and September, were at 5 GHz and were not of sufficient resolution to distinguish individual components in the source (Mutel, Phillips and Aller 1981). They did show, however, that the source was highly elongated along position angle ∼ 10° and was expanding that axis with a velocity of ∼4 c. The position angle is the same as several previous VLBI observations of this source, both during quiet periods and during previous flux outbursts (Pearson and Readhead 1981; Shaffer 1978 and references therein).

scholarly journals Unveiling the high-frequency radio source population with the AT20G survey

2013 ◽  
Vol 9 (S304) ◽  
pp. 205-208
Author(s):  
Elizabeth K. Mahony
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
High Frequency ◽  
Gamma Ray ◽  
Low Frequency ◽  
Radio Sources ◽  
Source Population ◽  
Frequency Source ◽  
Galaxy Population ◽  
5 Ghz

AbstractUntil recently, the radio sky above 5 GHz was relatively unexplored. This has changed with the completion of the Australia Telescope 20 GHz survey (AT20G; Murphy et al., 2010); a blind survey of the southern sky down to a limiting flux density of 40 mJy. The AT20G survey provides by far the largest and most complete sample of high-frequency radio sources yet obtained, offering new insights into the nature of the high-frequency active galaxy population. Whilst the radio data provides a unique sample of objects, these data alone are insufficient to completely constrain models of radio source properties and the evolution of radio galaxies. Complementary multiwavelength data is vital in understanding the physical properties of the central black hole.In this talk I will provide a brief overview of the AT20G survey, followed by a discussion of the multiwavelength properties of the high-frequency source population. In particular, I will focus on the optical properties of AT20G sources, which are very different to those of a low-frequency selected sample, along with the gamma-ray properties where we find a correlation between high-frequency radio flux density and gamma-ray flux density. By studying the multiwavelength properties of a large sample of high-frequency radio sources we gain a unique perspective on the inner dynamics of some of the most active AGN.

scholarly journals Surveys of Radio Sources at 5 GHz

1977 ◽  
Vol 74 ◽  
pp. 63-74
Author(s):  
I. I. K. Pauliny-Toth
Keyword(s):  
Flux Density ◽  
Radio Astronomy ◽  
Radio Sources ◽  
Astronomy Observatory ◽  
Max Planck ◽  
Radio Astronomy Observatory ◽  
Density Relation ◽  
Strong Source ◽  
Optical Identifications ◽  
5 Ghz

A number of surveys have been carried out at a frequency of 5 GHz at the National Radio Astronomy Observatory (NRAO) and at the Max-Planck-Institut für Radioastronomie (MPIfR), with the aim of determining the number-flux density relation for the sources detected and also of obtaining their radio spectra and optical identifications. The surveys fall into two categories: first, the strong source (S) surveys, which are intended in due course to cover the whole northern sky and to be complete above a flux density of about 0.6 Jy; second, surveys of limited areas of sky down to lower levels of the flux density.

scholarly journals A VLA Survey of Rich Clusters of Galaxies II. The Stronger Sources: Maps, Polarisations and Identifications

1994 ◽  
Vol 47 (2) ◽  
pp. 145 ◽  
Author(s):  
OB Slee ◽  
AL Roy ◽  
Ann Savage
Keyword(s):  
Flux Density ◽  
Source Parameters ◽  
Angular Size ◽  
Optical Parameters ◽  
Radio Sources ◽  
Very Large Array ◽  
Contour Maps ◽  
Optical Images ◽  
5 Ghz ◽  
Linear Polarisation

We present detailed radio and optical parameters for the stronger radio sources in 58 Abell cluster fields observed with the Very Large Array (VLA) using scaled arrays at 1�5 and 4�9 GHz. These sources comprise a complete sample with 1� 5 GHz flux density :;::20 mJy and cover a combined sky area of 3�5 X 10-5 sr. The cluster fields were distributed over 24 h of RA and between declinations +350 and -300 Contour maps at two frequencies are presented and source parameters such as position, angular size, spectral index, linear polarisation and core flux density are tabulated. We also derive the emitted power and linear size for those sources close to the cluster centres and therefore highly likely to be cluster members. We attempt to identify all these radio sources with optical images on the Palomar and SERC survey plates and give their accurate optical coordinates, morphologies and apparent magnitudes.

scholarly journals Correlated Flux Density Outbursts and Structural Variations in a Sample of Low Frequency Variable Radio Sources

1994 ◽  
Vol 159 ◽  
pp. 420-420
Author(s):  
M. Bondi ◽  
L. Padrielli ◽  
R. Fanti ◽  
L. Gregorini ◽  
F. Mantovani ◽  
...  
Keyword(s):  
Flux Density ◽  
Low Frequency ◽  
Radio Sources ◽  
Structural Variations ◽  
Vlbi Observations ◽  
Variable Radio

Snapshot VLBI observations at 18 cm have been obtained with a global array at three epochs (1980.1, 1981.8, 1987.9) in order to investigate flux density and/or structural variations for a sample of 21 low frequency variable sources (Padrielli et al. 1987 Astron Astrophys. Suppl. Ser., 67, 63; Bondi et al. 1993 in preparation).

scholarly journals Relativistic Beaming Models and VLBI Observations of A Complete Sample of Radio Sources

1988 ◽  
Vol 129 ◽  
pp. 65-70 ◽  
Author(s):  
A. C. S. Readhead ◽  
T. J. Pearson ◽  
P. D. Barthel
Keyword(s):  
Statistical Tests ◽  
Full Range ◽  
Radio Sources ◽  
Complete Sample ◽  
Limited Sample ◽  
Vlbi Observations ◽  
Relativistic Beaming ◽  
Superluminal Motion ◽  
5 Ghz ◽  
Compact Sources

We have conducted a systematic study of the milliarcsecond structure of a complete, flux-density limited sample of strong radio sources selected at 5 GHz. We have made 5 GHz maps at two epochs of the 45 compact sources in the sample, and third-epoch observations are in progress. Our intention was to explore the full range of morphologies exhibited by compact radio sources, to search for new superluminal sources, and to determine how widespread such phenomena as parsec-scale jets, alignment of parsec-scale and kiloparsec-scale jets, and superluminal motion are. In addition, we hoped to use this well-defined sample for statistical tests of the beaming theories.

scholarly journals Distortions in Compact Steep-Spectrum Radio Sources

1984 ◽  
Vol 110 ◽  
pp. 25-28 ◽  
Author(s):  
P. N. Wilkinson ◽  
R. E. Spencer ◽  
A.C.S. Readhead ◽  
T.J. Pearson ◽  
R.S. Simon
Keyword(s):  
Radio Sources ◽  
Spectrum Radio ◽  
Wide Range ◽  
5 Ghz

The size, and therefore the importance, of the population of compact, steep-spectrum, radio sources has only recently been recognised. While it is now clear that the extended steep-spectrum sources are powered by a pair of, originally anti-parallel, beams which transport energy to the outer lobes some 105–106 parcsec away, our understanding of the compact steep-spectrum sources is almost nil. This is largely because our radio maps have not had high enough resolution to show their structures in any detail. However 1.67 and 5 GHz MERLIN observations (resolutions 0″.25 and 0″.1) of the ~20 steep-spectrum 3CR sources whose LAS is ≲2″ have now allowed us to classify their structures, at least in broad terms. These MERLIN maps, and recent VLBI maps, show that while there is a wide range of structures - from colinear doubles to amorphous “blobs” - the “peculiar” structures are strongly concentrated in the objects whose optical counterparts are called QSO's.

scholarly journals X-Ray Properties of Compact Extragalactic Radio Sources

1988 ◽  
Vol 129 ◽  
pp. 109-110 ◽  
Author(s):  
D. M. Worrall
Keyword(s):  
Radio Emission ◽  
Gaussian Distribution ◽  
Radio Sources ◽  
Radio Luminosity ◽  
Bl Lac Objects ◽  
X Ray ◽  
Logarithmic Plot ◽  
Bl Lac ◽  
5 Ghz ◽  
Bl Lacs

A good correlation is known to exist between the X-ray and radio luminosity of flat-spectrum, core-dominated radio sources (e.g., Owen, Helfand and Spangler 1981). Worrall (1987) presents a logarithmic plot of spectral luminosity in the source frame at 2 keV versus that at 5 GHz for a variety of QSOs, Highly Polarized QSOs (HPQs), and BL Lac Objects. Friedmann cosmology with Ho = 100h km s−1 Mpc−1, qo = 0 is assumed. Exclusion of objects which are optically or X-ray selected, or in which the radio emission is not dominated by a flat-spectrum compact core, gives a sub-sample consisting of 50 QSOs, 20 HPQs, and 10 BL Lacs, of which 5,4,3, respectively, are known superluminals. The dispersion of these data about the log-log correlation (assuming a Gaussian distribution), is σobs = 0.44 ± 0.06 (90% confidence errors for one interesting parameter).

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