Shock Models of Time Variability and Superluminal Motion in Compact Extragalactic Radio Sources

1988 ◽  
pp. 81-82
Author(s):  
Philip A. Hughes ◽  
Hugh D. Aller ◽  
Margo F. Aller
Keyword(s):  
Time Variability ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Superluminal Motion ◽  
Shock Models

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 Shock Models of Time Variability and Superluminal Motion in Compact Extragalactic Radio Sources

1988 ◽  
Vol 129 ◽  
pp. 81-82
Author(s):  
Philip A. Hughes ◽  
Hugh D. Aller ◽  
Margo F. Aller
Keyword(s):  
Mode Conversion ◽  
Lorentz Factor ◽  
Time Variability ◽  
Radio Sources ◽  
List Type ◽  
Random Component ◽  
Type Number ◽  
Flow Energy ◽  
Bl Lacertae ◽  
Superluminal Motion

Following the success of a simple shock model for outbursts in BL Lacertae and 3C 279 (see Aller, Aller & Hughes, this meeting) we have constructed computer codes to study in detail the radiation from shocked, relativistic jets. These codes compute the transfer of synchrotron radiation, accounting for polarized emission and absorption, rotation, and mode conversion for a turbulent collimated flow with one or more shocks propagating parallel to the jet axis. We present results for a flow that evolves adiabatically, with the turbulence represented by a random component to the magnetic field within each computational cell, and with the shocks prescribed analytically following Königl (Phys. Fluids, 23, 1083, 1980). From the evolution of the total and polarized fluxes as a function of frequency, and from the corresponding projection of the source structure on the plane of the sky, we see that this type of model a.is capable o f explaining the variability of compact radio sources - see Aller, Aller & Hughes, this meeting,b.highlights the care needed when interpreting VLBI maps, in that i)the component separations are frequency dependent (see Fig. 1)ii)the ‘core’ is not always the brightest component (see Fig. 1)iii)the Doppler boosting factor of the shocked flow is not directly related to the Lorentz factor derived from the apparent superluminal motion of a componentiv)a multiplicity of components can give rise to both apparent contractions and accelerations,c.clearly shows the link between time variability of compact sources and evolving VLBI structure, and suggests that both may be understood in terms of weak shocks that tap a small fraction of a jet's flow energy,d.enables us to probe the physical conditions of the flow and the ambient material.

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 Large Bent Jets in the Inner Region of CSS

1996 ◽  
Vol 175 ◽  
pp. 71-72
Author(s):  
F. Mantovani ◽  
W. Junor ◽  
M. Bondi ◽  
L. Padrielli ◽  
W. Cotton ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Radio Sources ◽  
Ambient Media ◽  
The Core ◽  
Gaseous Environment ◽  
Radio Jets ◽  
Large Size ◽  
Superluminal Motion ◽  
Inner Region ◽  
Quasars And Radio Galaxies

Recently we focussed our attention on a sample of Compact Steep-spectrum Sources (CSSs) selected because of the large bent radio jets seen in the inner region of emission. The largest distortions are often seen in sources dominated by jets, and there are suggestions that this might to some extent be due to projection effects. However, superluminal motion is rare in CSSs. The only case we know of so far is 3C147 (Alef at al. 1990) with a mildly superluminal speed of ≃ 1.3v/c. Moreover, the core fractional luminosity in CSSs is ≃ 3% and ≤ 0.4% for quasars and radio galaxies respectively. Similar values are found for large size radio sources i.e. both boosting and orientations in the sky are similar for the two classes of objects. An alternative possibility is that these bent-jet sources might also be brightened by interactions with the ambient media. There are clear indications that intrinsic distortions due to interactions with a dense inhomogeneous gaseous environment play an important role. Observational support comes from the large RMs found in CSSs (Taylor et al. 1992; Mantovani et al. 1994; Junor et al. these proc.) and often associated with strong depolarization (Garrington & Akujor, t.p.). The CSSs also have very luminous Narrow Line Regions emission, with exceptional velocity structure (Gelderman, t.p.).

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 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.

Super-luminal expansion in extragalactic radio sources

Nature ◽  
1977 ◽  
Vol 267 (5608) ◽  
pp. 211-216 ◽  
Author(s):  
R. D. Blandford ◽  
C. F. McKee ◽  
M. J. Rees
Keyword(s):  
Radio Sources ◽  
Extragalactic Radio Sources

Origin of the central radio gaps in extragalactic radio sources

1992 ◽  
Vol 187 (2) ◽  
pp. 209-214 ◽  
Author(s):  
I. E. Ekejiuba ◽  
P. N. Okeke ◽  
S. E. Okoye
Keyword(s):  
Radio Sources ◽  
Extragalactic Radio Sources
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