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1.
In this paper, we investigate the relativistic beaming effects in a well-defined sample of core-dominated quasars using the correlation between the relative prominence of the core with respect to the extended emission (defined as the ratio of core-to lobe-flux density measured in the rest frame of the source) and the projected linear size as an indicator of relativistic beaming and source orientation. Based on the orientation-dependent relativistic beaming and unification paradigm for high luminosity sources in which the Fanaroff-Riley class-II radio galaxies form the unbeamed parent population of both the lobe- and core-dominated quasars which are expected to lie at successively smaller angles to the line of sight, we find that the flows in the cores of these core-dominated quasars are highly relativistic, with optimum bulk Lorentz factor,γ opt∼ 6–16, and also highly anisotropic, with an average viewing angle, ∼ 9°–16°. Furthermore, the largest boosting occurs within a critical cone angle of ≈ 4°–10°.  相似文献   

2.
We present total-intensity and linear-polarization observations made with the VLA at 5 GHz of 1400+ 162, a BL Lac object in a group of galaxies. It has a misaligned triple structure with a prominent radio jet towards the east. There is evidence of a weak counter-jet towards the western component, which also has the more prominent warm-spot. We discuss possible explanations for some of the observed features of this source. Although interaction with the cluster medium is possibly partly responsible for the observed distortion, we suggest that the large observed misalignment could also be due to amplification of a smaller misalignment by projection effects. In the relativistic beaming model, where BL Lac objects arise when the relativistic jets are seen end-on, we suggest that 1400+ 162 is more oblique to the line of sight than most members of this class.  相似文献   

3.
A list has been compiled of 49 extragalactic sources, most of them identified with quasars, that appear to have a one-sided (D2 type) radio structure characterized by a single outer component displaced from a compact central (nuclear) component coincident with the optical object. The observed properties of a subsample of 28 D2 quasars that have an overall angular size larger than 5 arcsec are briefly discussed and compared with those of normal (D1 type) double quasars. It is found that the central components in most D2 sources account for more than half the total flux density at high frequencies in contrast to the D1 quasars which generally have less than 20 per cent of their total flux density in a central component. This makes it very unlikely that D2 sources are just those D1s in which there is a large intrinsic difference in the flux densities or separations of the two outer components. The observed properties of D2 sources are easier to understand in the relativistic beaming interpretation in which their axes are inclined at smaller angles with the line of sight compared to D1 sources.  相似文献   

4.
We have carried out some statistical tests of relativistic beaming and radio source orientation scenarios using the core dominance parameter Rand linear size D of a recent sample of double-lobed quasars and radio galaxies as orientation indicators. Our results show that the maximum Doppler boosting occurs within a cone angle of ∼ 13°corresponding to an optimum Lorentz factor of ∼ 5. On the average, quasar cores appear to be boosted by a factor of ∼ 10 relative to those of radio galaxies. In general, we found that quasars lie at closer angles to the line of sight than radio galaxies with median values of 28° and 51°respectively, implying a relative foreshortening factor of ∼ 2. These results are consistent with the simple relativistic beaming and orientation-based unification hypotheses in which quasars are the beamed counterparts of powerful radio galaxies which form the isotropic parent population. The results show a strong evidence that orientation of source axis with respect to the line of sight is a crucial parameter in the classification schemes for radio sources. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

5.
As part of our study to understand the nature of extragalactic radio sources which are very asymmetric in the surface brightness of the two lobes, often with radio emission on only one side of the nucleus, we have observed a large number of them with high angular resolution and good surface brightness sensitivity at radio frequencies. In this paper we present VLA and MERLIN observations of 15 such sources. We discuss their observed structures and spectra, and possible explanations for their morphologies. We report evidence of a possible correlation between the hot-spot brightness ratio and the degree of core prominence, used as a Statistical measure of source orientation, suggesting that relativistic beaming of the hot-spot emission does play a significant role in the observed brightness asymmetry. To explain the apparently one-sided sources within the relativistic beaming framework, the velocities required are in the range of 0.2 to 0.8c. We discuss the possibility that the lobe which is seen to the south of the jet in 3C273 is the counter-lobe seen in projection. We also draw-attention to a number of one-sided sources with very weak cores, and discuss their possible nature.  相似文献   

6.
It has become clear in recent years that relativistic beaming is a good explanation for the BL Lac phenomenon. Of studies based on the relativistic beaming model of BL Lac objects, we note that the orientation of jet's axis to the line-of-sight is very small and, therefore, the observed flux emitted from a rapidly moving source is orders of magnitude higher than the flux in its rest-frame:F obs = 3 + F intr, where is the bulk relativistic Doppler factor. Then the observed apparent magnitudem v must be corrected for this effect. For our 39 samples, the corrected apparent magnitudem v corr and logZ have a good correlation.  相似文献   

7.
A new method to estimate the Doppler beaming factor of relativistic large-scale jet regions is presented. It is based on multiwaveband fitting to radio-to-X-ray continua with synchrotron spectrum models. Combining our method with available observational data of proper motions, we derive the intrinsic velocity as well as the viewing angles to the line of sight for eight knotty regions down the M87 jet. The results favour the 'modest beaming' scenario along the jet, with Doppler factors varying between  ∼2–5  . The inner jet of M87 suffers sharp deceleration, and the intrinsic speed remains roughly constant down the outer jet. The orientation of the inner jet regions is fully consistent with the result of 10°–19° to the line of sight suggested by previous Hubble Space Telescope ( HST ) proper motion studies of the M87 jet. The outer jet, however, shows systematic deflection off the inner jet to a much smaller inclination  (θ≪ 10°)  . Further calculation of knot A suggests that this deflection can be regarded as evidence that the outer jet suffers some departure from equipartition. The nucleus region of the M87 jet should have a viewing angle close to its first knot HST-1, i.e.  θ∼ 15°  , which favours the idea that M87 may be a misaligned blazar. This work provides some hints about the overall dynamics of this famous extragalactic jet.  相似文献   

8.
In this paper, we use the distributions of projected linear size (D), core- (P C ) and extended- (P E ) radio luminosities, to investigate a consequence of relativistic beaming and radio source orientation scenario for low-luminosity extragalactic radio sources. In this scenario, BL Lacertae objects (BL Lacs) are believed to be Fanaroff-Riley type I (FR I) radio galaxies, but with radio axes aligned close to the line of sight. At this orientation, the core emission is greatly enhanced by relativistic Doppler boosting and linear size foreshortened due to geometrical projection. A simple outcome of this scenario is that the extended luminosity is expected to be orientation invariant, but a D–P C correlation is envisaged. Results show that both the relative core dominance (R) and linear size are strongly correlated with extended luminosity (r≥ 0.7). Using the R-distribution and R–P E anti-correlation, we show that the difference in radio core-dominance between FR I radio galaxies and X-ray selected BL Lacs can be accounted for by a bulk Lorentz factor γ～5–13 and viewing angle ?～5–15°, which can be understood in terms of the scenario, with relativistic beaming persisting at largest scales.  相似文献   

9.
What we observe as an apparent superluminal motion is the resultant velocity of Hubble flow and a local ejection. Taking Hubble flow into account, one can explain, problems posed for the relativistic beaming model, such as the one-sidedness problem and the untolerable extension of the depromected structure of some superluminal sources; the misalignment of small-and large-scale jets can be analyzed more appropriately. A significant by-product of the present investigation is the initiation to find a new way to determine the value of the Hubble constantH 0, provided that one can observe the superluminal motion at much longer wavelengths, say, meter wavelengths.  相似文献   

10.
We examine a simple statistical consequence of relativistic beaming model using the core-to-lobe flux density ratio (R) and projected linear size (D) as orientation indicators. It is shown that the observed R-D intercept for the 3CRR source sample provides values of the bulk Lorentz factor () which are consistent with the beaming scenario. The result also shows that if the lobe-dominated quasars are to be unified with the core-dominated quasars, they should be oriented at a median angle, _med 40° with respect to the line of sight, but if with powerful radio galaxies, then _med 24°. Application of this result to the quasar-galaxy unification scheme using the observed angular size-redshift relation shows that the scheme is consistent with the observed data.  相似文献   

11.
We here investigate the dispersion properties of radiation in the SS433 relativistic jets. We assume that the jet is composed of cold electron-proton plasma immersed in a predominantly parallel magnetic field to the jet axis. We find that for the mildly relativistic source SS433 (for which 〈ψ〉≃79°), the bulk velocity is too small (v≃0.26c) to produce significant changes in the dispersion properties of the medium. Nonetheless, in the rarefied outer regions of the jets, where radio emission dominates, even a weak magnetic field has some influence on the dispersion properties and there appear two different electromagnetic branches that are slightly sensitive to the bulk relativistic motion. In the inner, X-ray region, the magnetic field is much stronger, but in this region the high electron density preserves the isotropic character of the local plasma and no branch separation occurs. In the region of the jet where the IR and optical emission dominates, the cold plasma may be also considered isotropic, i.e., neither the magnetic field nor the bulk velocity is able to affect the propagation of the radiation. Finally, we find that the Doppler line displacement in SS433 is affected by plasma dispersion only in a narrow frequency range in the far IR. As a consequence, although the shift (z) modulation due to precession of the SS433 jets is well described by previous work, it has to be corrected by plasma dispersion effects in the far-IR range.  相似文献   

12.
《New Astronomy Reviews》2002,46(2-7):405-409
The energy budget of all known optical jets is discussed. It is found that to power the extended radio lobes of radio galaxies, the jet bulk motion on kpc scales must be relativistic, on average. Based on various constraints, a “most probable” region centered around Γbulk∼7.5 and θ∼20° is found. Because of the consequent relativistic beaming, the rest frame magnetic field is lower and electron lifetimes longer. Combining the effects of time dilation and lower emission rate, the electron diffusion length becomes fully consistent with the deprojected jet length, without the need for reacceleration.  相似文献   

13.
Active galactic nuclei(AGNs)have two major classes,namely radio loud AGNs and radio quiet AGNs.A small subset of the radio-loud AGNs is called blazars,which display extreme observational properties,such as rapid variability,high luminosity,high and variable polarization,and superluminal motion.All of those observational properties are probably due to a relativistic beaming effect with the jet pointing close to the line of sight.Observations suggest that the orientation can be expressed by a core-dominance p...  相似文献   

14.
The hypothesis of the relativistic beaming of pulsar emission is discussed in connection with objections advanced by Manchesteret al. (1973). It is shown that the same pulse duration of some pulsars with the non-power-law spectrum over a wide frequency interval may be associated either with large source sizes in longitude, or with location of the emitting source at various distances from the rotation axis of the neutron star (depending on the emission frequency).  相似文献   

15.
We report on centimeter VLA and VLBI observations of the giant, low power radio galaxy 1144+35. On the parsec scale, we see a complex jet component moving away from the center of activity at 2.7h50−1 c. We detect a faint parsec-scale counter-jet and derive a jet velocity of 0.95c and an angle to the line of sight of 25°, consistent with an intrinsically symmetric ejection. These findings lend credence to the claim that even the jets of low-power radio galaxies start out relativistically.  相似文献   

16.
We have examined statistically, structural asymmetries and simple relativistic beaming/source orientation in a sample of Lobe-Dominated Quasars (LDQs) using the source size D as orientation parameter; relative core strength R as beaming parameter; arm-length ratio Q, apparent flux ratio R ?, and bending angle Φ as asymmetric parameters. Our result for Q>1.5, based on the median value data is inconsistent with beaming scenario, where we expect stronger negative correlation for more asymmetric sources, between our beaming parameter R and orientation parameter D than for less asymmetric sources Q≤1.5. This observation indicates that structural asymmetries may depend more on intrinsic factors than beaming. Our kinematic asymmetric model of extra galactic radio sources suggests that larger (possibly older) sources are less asymmetric, which may be interpreted to be indicative of other factors other than beaming as responsible for the observed asymmetries in radio sources.  相似文献   

17.
We have observed emission from the nucleus of the closest radio galaxy, Centaurus A, from the radio to the gamma-ray band. We construct, for the first time, its overall spectral energy distribution (SED) which appears to be intriguingly similar to those of blazars, showing two broad peaks located in the far-infrared band and at ∼0.1 MeV respectively. The whole nuclear emission of Centaurus A is successfully reproduced with a synchrotron self-Compton model. The estimated physical parameters of the emitting source are similar to those of BL Lacs, except for a much smaller beaming factor, as qualitatively expected when a relativistic jet is orientated at a large angle to the line of sight. These results represent strong evidence that Centaurus A is indeed a misoriented BL Lac, and provide strong support in favour of the unification scheme for low-luminosity radio-loud active galactic nuclei. Modelling of the SED of Centaurus A also provides further and independent indications of the presence of velocity structures in sub-parsec-scale jets.  相似文献   

18.
We have investigated the correlations between the asymmetries in depolarization and spectral index in a bright source sample. We find a significant correlation between these asymmetries which can be understood in terms of the relativistic beaming hypothesis in which the counter jet side is steeper and more polarized than the jet side due to the presence of a halo of hot gas surrounding the source and contribution from the beamed jet and hot spot emission to the observed lobe emission. This simple interpretation is however complicated by the presence of a stronger correlation between these parameters and extended luminosity which is expected to be aspect-invariant; suggesting that the observed spectral index – depolarization correlation is an artefact of their being separately correlated with radio luminosity. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
The depolarization asymmetry seen in double-lobed radio sources, referred to as the Laing-Garrington (L-G) effect where more rapid depolarization is seen in the lobe with no visible jet as the wavelength increases, can be explained either by internal differences between the two lobes, or by an external Faraday screen that lies in front of only the depolarized lobe. If the jet one-sidedness is due to relativistic beaming the depolarization asymmetry must be due to an intervening Faraday screen. If it is intrinsic the depolarization asymmetry must be related to internal differences in the lobes. For a random viewing angle distribution, which must be the case here where un-beamed lobe radiation dominates, jet one-sidedness is unrelated to viewing angle and therefore cannot be used either to estimate the viewing angle or to imply beaming. The outflow speed in the kpc jet is notoriously difficult to determine. However, although it has not yet been proven conclusively, we assume in this paper that the speed in the outer jet of several Fanaroff-Riley Class 1 (FRI) sources exhibiting the L-G effect is close to the 0.1c reported by several other investigators. For these sources we find that the jet one-sidedness cannot be explained by beaming and therefore must be intrinsic. In these FRI sources the L-G effect must be due to differences that originate inside the lobes themselves, with the outer regions of the relevant lobe acting as a Faraday screen. Although it is not known if the flow in the outer jets of FRII sources also slows to this speed it is suggested that the explanation of the L-G effect is likely to be the same in both types. This argument is strengthened by the recent evidence that FRII galaxies have very large viewing angles, which in turn implies that the L-G model cannot work regardless of the jet velocity. It may therefore be too soon to completely rule out internal depolarization in the lobes as the true explanation for the L-G effect.  相似文献   

20.
A new general relativistic magnetohydrodynamics (GRMHD) code “RAISHIN” used to simulate jet generation by rotating and non-rotating black holes with a geometrically thin Keplarian accretion disk finds that the jet develops a spine-sheath structure in the rotating black hole case. Spine-sheath structure and strong magnetic fields significantly modify the Kelvin-Helmholtz (KH) velocity shear driven instability. The RAISHIN code has been used in its relativistic magnetohydrodynamic (RMHD) configuration to study the effects of strong magnetic fields and weakly relativistic sheath motion, c/2, on the KH instability associated with a relativistic, γ=2.5, jet spine-sheath interaction. In the simulations sound speeds up to and Alfvén wave speeds up to ∼0.56c are considered. Numerical simulation results are compared to theoretical predictions from a new normal mode analysis of the RMHD equations. Increased stability of a weakly magnetized system resulting from c/2 sheath speeds and stabilization of a strongly magnetized system resulting from c/2 sheath speeds is found.  相似文献   

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