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 Extended Structure in High-Redshift Radio Sources

1982 ◽  
Vol 97 ◽  
pp. 59-60
Author(s):  
P. J. Duffett-Smith ◽  
A. Purvis
Keyword(s):  
Radio Source ◽  
High Redshift ◽  
Radio Sources ◽  
List Type ◽  
Type Number ◽  
Extended Structure ◽  
Structure Changes ◽  
Lower Luminosity ◽  
Source Structure

We have compared measurements of several hundred 3C and 4C radio sources at large redshifts to investigate how radio-source structure changes over a factor of 5–10 in luminosity. Our results show that for z ≳ 0.6: (i)most sources (both 3C and 4C) have hotspots about 3.5 kpc in size (Ho = 50 km s−1 Mpc−1, Ω = 1);(ii)lower-luminosity sources (bottom of 4C) have less-extended outer lobes.

scholarly journals Outflow Angles and Bulk Lorentz Factors for Different Categories of AGN

1997 ◽  
Vol 163 ◽  
pp. 695-696 ◽  
Author(s):  
Erick. J. Guerra ◽  
Ruth A. Daly
Keyword(s):  
Lorentz Factor ◽  
Radio Galaxies ◽  
Line Of Sight ◽  
Radio Sources ◽  
Bl Lacertae Objects ◽  
Bl Lacertae ◽  
High Polarization ◽  
Inverse Compton ◽  
Doppler Factor ◽  
Bl Lacs

AbstractRelativistic outflows from AGN can be parameterized by θ, the angle subtended by the direction of the outflow and the line of sight to the observer, and γ, the bulk Lorentz factor of the outflow. The Doppler factor, δ, and the apparent speed in the plane of the sky, βapp, are combinations of θ and γ. The Doppler factor can be estimated using either the equipartition Doppler factor, δeq (Readhead 1994), or the inverse Compton Doppler factor, δIC. These Doppler factor estimates are combined with observed βapp to solve for θ and γ for different categories of AGN.Ghisellini et al. (1993) compute δIC for 105 compact radio sources, and Güijosa & Daly (1996) compute δeq for the same sample. Daly, Guerra, & Güijosa (1996) estimate θ and γ for the 43 sources that have βapp listed by Vermeulen & Cohen (1994) and δeq computed by Güijosa & Daly (1996).Solutions and errors for θ and γ are presented in Figures 1 and 2 using δeq and δIC respectively. Guerra & Daly (1996) discuss these estimates and errors in greater detail. These AGN fall into the following categories: BL Lacertae objects (BL Lacs), core-dominated high-polarization quasars (CDHPQ), core-dominated low-polarization quasars (CDLPQ), core-dominated quasars with no polarization information (CDQ(NPI)), lobe-dominated quasars (LDQ), and radio galaxies (RG).

scholarly journals Interpretation of Cosmological Information on Radio Sources

1977 ◽  
Vol 74 ◽  
pp. 247-257
Author(s):  
G. Burbidge
Keyword(s):  
Radio Astronomy ◽  
Background Radiation ◽  
Radio Galaxies ◽  
Radio Sources ◽  
List Type ◽  
Type Number ◽  
Radio Flux ◽  
Powerful Radio ◽  
Microwave Background ◽  
Microwave Background Radiation

The topic that I have to introduce today is concerned with the question as to whether or not we can obtain any cosmological information from radio astronomy. Alternatively, we may ask “Where does radio astronomy have an impact on cosmology?” There are several areas that must be discussed. They are: 1)The discovery and interpretation of the microwave background radiation.2)The identification of powerful radio sources and the discovery that many of them have large redshifts. If we can prove that the large redshifts mean that the objects are at great distances, then we can use these radio sources as follows:(a)We can attempt to obtain a Hubble relation for the optical objects which are identified with radio galaxies;(b)We can look for a relation between the angular diameters of the radio sources and the redshifts of the optically identified objects and we can also look at relations between the angular diameter and the radio flux;(c)We can construct log N - log S curves and we can carry out luminosity volume tests.

scholarly journals Dust-Embedded AGN in Unusually Warm IRAS Galaxies

1989 ◽  
Vol 134 ◽  
pp. 406-407
Author(s):  
J. P. Vader ◽  
J. A. Frogel ◽  
F. C. Gillett ◽  
M. H. K. de Grijp
Keyword(s):  
Radio Galaxies ◽  
Radio Sources ◽  
List Type ◽  
Broad Line ◽  
Type Number ◽  
Early Type ◽  
Energy Distributions ◽  
Near Ir ◽  
Line Region ◽  
The One

The IRAS Point Source Catalog contains only 61 sources identified as galaxies whose energy distribution peaks at 60 mμ. The scarcity of such galaxies has prompted a search for possible common properties. This sample of ‘60 mμ peakers’, 21 of which are previously identified galaxies, partially overlaps with that of warm IRAS galaxies studied by de Grijp et al. (1987) and contains similar percentages of Seyfert (65%) and starburst galaxies on the one hand, and of strong and weak radio sources on the other hand. A remarkable characteristic is, however, that about half of the 60 mμ peakers seem to be early-type galaxies. The fact that such galaxies are rarely IRAS sources and, if so, have FIR energy distributions peaking at 100 mμ similar to those of spirals, implies that we are sampling active or nuclear starburst early-type galaxies with a very large success rate. The observational data accumulated so far further show that: (i)objects with smaller FIR to near-IR flux ratios have redder J-K colors and warmer 60 to 25 mμ colors, i.e., an infared spectrum dominated by warmer dust and/or a nonthermal source (Figs. 1a,b);(ii)out of 32 objects with radio data, the 5 compact radio sources with luminosities intermediate between those af radio-quiet and radio-loud AGN have among the warmest 60 to 25 mμ colors (Fig. 2). Such warm FIR colors are not a common characteristic of radio galaxies and quasars (Golombek et al. 1987, Neugebauer et al. 1986).(iii)the 60 mμ luminosities range from 109 to 1012 L0, and are largest for Mkn 231, 2306+0505 (Hill et al. 1987) and 2046+1925 (Frogel et al. 1988). The latter 2 objects, along with 0052-7054 (Frogel and Elias 1987) which also belongs to our sample, are Seyfert 2 galaxies with evidence for the presence of a dust-obsured broad line region.

scholarly journals Polarization Variability of Some Compact Radio Sources

1982 ◽  
Vol 97 ◽  
pp. 331-333
Author(s):  
M. M. Komesaroff ◽  
D. K. Milne ◽  
P. T. Rayner ◽  
J. A. Roberts ◽  
D. J. Cooke
Keyword(s):  
Circular Polarization ◽  
Linear Polarization ◽  
Position Angle ◽  
Linear Increase ◽  
Monitoring Programme ◽  
Radio Sources ◽  
List Type ◽  
Type Number ◽  
5 Ghz ◽  
Superluminal Expansion

Figure 1 shows observations for four sample sources from the Parkes 5 GHz polarization monitoring programme. Interesting features illustrated include •Sudden changes of the position angle of the linear polarization by ≳ 70° in PKS 0537-441 and 1253-055 (3C279).•A linear increase in the position angle of the polarization of PKS 2134+004 through 70° over 3/12; years.•Distinct bursts of circular polarization in PKS 0430+052, 0537-441 and 1253-055. In PKS 0430+052 (3C120) such a burst coincides with the possible superluminal expansion (Walker et al., 1981). In PKS 1253-055 (3C279) a burst of circular polarization is currently occurring at a time of very low linear polarization.

scholarly journals A VLBA 15 GHz Small Separation Gravitational Lens Survey

1996 ◽  
Vol 173 ◽  
pp. 405-406
Author(s):  
A.R. Patnaik ◽  
M.A. Garrett ◽  
A. Polatidis ◽  
D. Bagri
Keyword(s):  
High Frequency ◽  
Gravitational Lens ◽  
Radio Sources ◽  
List Type ◽  
Type Number ◽  
Morphological Classification ◽  
Small Separation

We have embarked on a 15 GHz VLBA survey of 1000 flat spectrum sources. We present the results from a 24 hour pilot observing run in which 72 sources were mapped. The primary aims of this project are: –to search for small separation (1-150 mas) gravitational lens systems–to identify targets for current mm and anticipated Space VLBI programs–a morphological classification of compact radio sources at relatively high frequency with sub-mas resolution.

scholarly journals The Angular Diameter-Redshift Relation for Scintillating Radio Sources

1977 ◽  
Vol 74 ◽  
pp. 139-147
Author(s):  
A. Hewish ◽  
A. C. S. Readhead ◽  
P. J. Duffett-Smith
Keyword(s):  
Flux Density ◽  
Hot Spots ◽  
Angular Size ◽  
Observational Evidence ◽  
Angular Diameter ◽  
Radio Sources ◽  
List Type ◽  
Type Number ◽  
Physical Size ◽  
Source Dimensions

Observational evidence on the angular diameter-redshift relation using radio sources has, until recently, been confined to studies of the overall angular size. In this paper a different approach is described in which the very compact hot spots in radio sources are used as standard measuring rods. Such hot spots appear to be especially suitable for cosmological studies for the following reasons. (a)Hot spots which contain one half or more of the total flux density are generally found only in the most powerful sources (P178 ≳ 1027 W Hz−1 sr−1).(b)Hot spots appear to show a smaller dispersion in physical size than the overall source dimensions.

scholarly journals Identifications from the WSRT Deep Surveys

1977 ◽  
Vol 74 ◽  
pp. 165-170
Author(s):  
J. K. Katgert ◽  
H. R. de Ruiter ◽  
A. G. Willis
Keyword(s):  
Surface Density ◽  
Radio Sources ◽  
List Type ◽  
Selection Effects ◽  
Type Number ◽  
Positional Accuracy ◽  
Present Generation ◽  
Systematic Identification ◽  
Optical Telescopes

The WSRT yields samples of radio sources which are well suited for systematic identification work for the following reasons: a)The surface density is high: at 1415 MHz an average of 10 to 30 sources can be detected within 0°.55 from the field centre; at 610 MHz the numbers are 40 to 100 within 1°.0. In any given field, most sources will fall within the boundaries of plates for the present generation of optical telescopes.b)The positional accuracy is, on the whole, rather high. One can thus propose identifications based on positional agreement only, avoiding selection effects present when selecting “on type”.

scholarly journals Superluminal Motion in NRAO 140 and a Possible Future Method for Constraining HO and QO

1982 ◽  
Vol 97 ◽  
pp. 359-360 ◽  
Author(s):  
Alan P. Marscher ◽  
John J. Broderick
Keyword(s):  
Lorentz Factor ◽  
Radio Sources ◽  
Relativistic Motion ◽  
High Brightness ◽  
X Ray ◽  
Vlbi Observations ◽  
Superluminal Motion ◽  
The One ◽  
Superluminal Expansion ◽  
Einstein Observatory

NRAO 140 is a quasar (z = 1.258) which is among only 3 or 4 such objects (and the one with the highest z) which were detected at X-ray energies prior to the operation of the Einstein Observatory (Marscher et al. 1979). We obtained contemporaneous X-ray and radio VLBI observations of the source in early 1980, to determine whether Compton scattering within the radio source is the primary X-ray emission mechanism (Marscher and Broderick 1981b). Instead, we found that the radio parameters predicted more than 103 times more X-ray flux than was observed. Since the Compton calculation is independent of distance, and since the troublesome component was partially resolved (and hence not a high-brightness-temperature emitter), we found that relativistic motion aimed nearly directly toward the observer with Lorentz factor exceeding 4, needed to be invoked in order to bring the predicted Compton flux down to the observed level (Marscher and Broderick 1981a, b). Since relativistic motion is also the preferred explanation for the apparent superluminal expansion seen in some compact radio sources (e.g., M. Cohen, this volume; Marscher and Scott 1980; Kellermann and Pauliny-Toth 1981), we predicted that the compact components in NRAO 140 should appear to separate at a speed exceeding about 4c.

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