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1.
Internal shocks propagating through an ambient radiation field are subject to a radiative drag that, under certain conditions, can significantly affect their dynamics, and consequently the evolution of the beaming cone of emission produced behind the shocks. The resultant change of the Doppler factor combined with opacity effects leads to a strong dependence on the viewing angle of the variability pattern produced by such systems; specifically, the shape of the light curves and the characteristics of correlated emission. One implication is that objects oriented at relatively large viewing angles to the observer should exhibit a higher level of activity at high synchrotron frequencies (above the self-absorption frequency), and also at gamma-ray energies below the threshold energy of pair production, than at lower (radio/millimetre) frequencies. 相似文献
2.
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
3.
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
4.
A new picture of pulsar high-energy emission is proposed that is different from both the traditional polar cap and outer gap
models, but combines elements of each. The slot gap model is based on electron acceleration along the edge of the open field
region from the neutron star surface to near the light cylinder and thus could form a physical basis for the two-pole caustic
model of Dyks and Rudak (2003). Along the last open field line, the pair formation front rises to very high altitude forming
a slot gap, where the accelerating electric field is unscreened by pairs. The resulting radiation features both hollow cones
from the lower-altitude pair cascades, seen at small viewing angles, as well as caustic emission on the trailing-edge field
lines at high altitude, seen from both poles at large viewing angle. The combination of the small solid angle of slot gap
emission (≪ 1 sr) with a high probability of viewing the emission predicts that more gamma-ray pulsars could be detected at
larger distances. In this picture, many of the positional coincidences of radio pulsars with unidentified EGRET sources become
plausible as real associations, as the flux predicted by the slot gap model for many of the pulsars would provide the observed
EGRET source flux. The expected probability of seeing radio-quiet gamma-ray pulsars in this model will also be discussed. 相似文献
5.
The continuum spectrum of OJ 287, like most other BL Lac objects, is featureless- no emission or absorption lines are observed. However, OJ 287 shows variations at different timescales in flux and polarization at various wavelength bands. Using the available variability data one can estimate the sizes of the emission regions in the source from light travel time arguments. We assume the emission mechanism to be synchrotron radiation by high energy electrons with single power law energy distribution. Theoretical synchrotron spectrum in the frequency range 1011–1017
H
z
is compared with the observed spectral shape, obtained from new multifrequency quasi-simultaneous observations, to estimate the lower and upper cut off frequencies. These frequencies are used to obtain theoretical values of the variability timescales and magnetic field in the emission region. We obtain a value of 0.93 G for the magnetic field and 5.184×104
sec for the cooling time from the quiescent continuum spectrum. The shock-in-jet model explains the spectrum where shocks accelerate the particles and amplify the magnetic field in the jet. This timescale is compared with the one obtained from observed short timescale variability (20 minutes) with proper beaming correction. The short timescale variations (200 minutes in the source frame), possibly caused by an additional, flaring, component of the source, are also used to calculate compressed magnetic field. The observed and theoretically estimated variability timescales and the shape of the spectrum suggest that there are more than one emission components in OJ 287. 相似文献
6.
C.K. Goertz 《Planetary and Space Science》1973,21(8):1431-1445
The (magnetic) amplitude of the Alfvén waves emitted by Io is related to the growth rate of coherent cyclotron radiation. The growth rate is large only in the dense parts of the Jovian ionosphere. The amplitude varies as a function of sub-Io longitude. This together with the beaming of the cyclotron radiation is used to explain the observed emission pattern of Io-controlled decametric radiation from Jupiter. 相似文献
7.
Yong-Xiang Wang Y. Liu Fei-Peng Pi Jiang-He Yang 《Journal of Astrophysics and Astronomy》2011,32(1-2):59-60
In this work, we investigate the correlation between the luminosity and the core-dominance parameter for a sample of X-ray selected BL Lacertae objects (XBLs), and found that the extended luminosity is strongly anti-correlated with the core-dominance parameter while the core (or the total) luminosity is not correlated with the core-dominance parameter. If this is the case, then we can expect that the lower extended luminosity XBLs and their core luminosity is relatively higher. This can be explained by a relativistic beaming model since in this case, the viewing angle is smaller and the emissions dominate the extended emissions. Therefore, the anti-correlation is in fact the result of the relativistic beaming model. 相似文献
8.
Topographic features affect the scattering properties of planetary surfaces by casting shadows and altering the local incidence and emission angles. Measurements of this phenomenon were obtained on the Cornell goniometer for both high and low albedo surfaces. For the low albedo surface, the decrease in reflected radiation due to topography increases sharply with increasing phase angle, whereas for the high albedo sample the effects are approximately constant between phase angles of 30 and 70°. The observations are in good agreement with a theoretical model in the case of the dark surface. However, for the high albedo surface the model overestimates the effects by about a factor of 2, since it does not include the partial illumination of shadows by multiple scattering. For both high and low albedo surfaces, the effects of topography do not become significant until a phase angle of 30–40°. 相似文献
9.
A selected subset of BL Lac objects were monitored with VLBI techniques at multifrequencies. Apparent superluminal motion and X-rays were detected in all of the monitored sources. From the observational data, kinematic parameters, geometric parameters and beaming effects for the core of the selected BL Lac objects have been estimated. Our results indicate that some BL Lacs have large Lorentz factors and small viewing angles; relativistic beaming effects are strongly present in these sources. On the other hand, some BL Lacs have small Lorentz factors; their viewing angles are quite large. It does not seem possible to avoid the fact that some BL Lac objects are not oriented particularly close to the line of sight. It conflicts with the basic assumption of the accepted theories for explaining the characteristics of BL Lac objects at present. Also, it seems that the BL Lac objects in the class I of the Burdige and Hewitt's classification have larger viewing angles than those int he class II. The whole BL Lac classification could be a misnomer: the sources classified as BL Lac objects are a mixture of physically different populations with different parent objects. 相似文献
10.
Existing theory and models suggest that a Type I (merger) GRB should have a larger jet beaming angle than a Type II (collapsar) GRB, but so far no statistical evidence is available to support this suggestion. In this paper, we obtain a sample of 37 beaming angles and calculate the probability that this is true. A correction is also devised to account for the scarcity of Type I GRBs in our sample. The probability is calculated to be 83% without the correction and 71% with it. 相似文献
11.
M. Chiaberge † A. Capetti † A. Celotti † 《Monthly notices of the Royal Astronomical Society》2001,324(4):L33-L37
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
12.
We present a calculation of a three-dimensional pulsar magnetosphere model to explain high-energy emission from the Geminga pulsar with a thick outer gap. High-energy γ -rays are produced by primary accelerated particles with a power-law energy distribution through curvature radiation inside the outer gap. We also calculate the emission pattern, pulse profile and phase-resolved spectra of high-energy γ -rays of the Geminga pulsar, and find that its pulse profile is consistent with the observed one if the magnetic inclination and viewing angle are ∼50° and ∼86° respectively. We describe the relative phases among soft (thermal) X-rays, hard (non-thermal) X-rays, and γ -rays. Our results indicate that X-ray and γ -ray emission from the Geminga pulsar may be explained by the single thick outer gap model. Finally, we discuss the implications of the radio and optical emission of the Geminga pulsar. 相似文献
13.
In unified models of active galaxies the direct line of sight to the nucleus is unobscured only within a certain cone of directions. An opening angle for this cone is usually estimated by methods such as the overall ratio of Seyfert 1s to Seyfert 2s, the latter assumed to be obscured versions of the former. Here we shall show, as has often been suspected, that the opening angle of the cone depends on the luminosity of the central source, with higher luminosities corresponding to larger opening angles. This conclusion depends only on the assumption that the width of the broad emission lines at a given luminosity is a measure of inclination angle, an assumption that is supported by observation in radio-loud systems. On the other hand we show that the scatter in X-ray spectral index is not primarily an effect of viewing angle, in contrast to what might be expected if the scatter on the spectral index versus luminosity relation were a consequence of absorption in the obscuring material. The observed correlation between linewidth and spectral index appears to be a further consequence of the dependence of opening angle on luminosity. 相似文献
14.
E. Belsole D. M. Worrall M. J. Hardcastle 《Monthly notices of the Royal Astronomical Society》2006,366(1):339-352
We present an extensive X-ray spectral analysis of the cores of 19 Faranoff–Riley type II sources in the redshift range 0.5 < z < 1.0 which were selected to be matched in isotropic radio power. The sample consists of 10 radio galaxies (RGs) and nine quasars. We compare our results with the expectations from a unification model that ascribes the difference between these two types of sources to the viewing angle to the line of sight, beaming and the presence of a dust and gas torus. We find that the spectrum of all the quasars can be fitted with a single power law, and that the spectral index flattens with decreasing angle to the line of sight. We interpret this as the effect of increasingly dominant inverse Compton X-ray emission, beamed such that the jet emission outshines other core components. For up to 70 per cent of the RGs we detect intrinsic absorption; their core spectra are best fitted with an unabsorbed steep power law of average spectral index Γ= 2.1 and an absorbed power law of spectral index Γ= 1.6, which is flatter than that observed for radio-quiet quasars (RQQs). We further conclude that the presence of a jet affects the spectral properties of absorbed nuclear emission in active galactic nuclei. In RGs, any steep-spectrum component of nuclear X-ray emission, similar to that seen in RQQs, must be masked by a jet or by jet-related emission. 相似文献
15.
After a silence of some 32 years, the high-mass X-ray binary (HMXB) 4U1901+03 produced an outburst in Feb. 2003. With the observed data of RXTE (Rossi X-ray Timing Explorer) over a 5 month duration, we have made a systematic study of the pulse profile of this source, and obtained its time evolution and its correlation with the photon energy. It is found that the variations of the pulse profile and the pulse fraction with the accretion rate of the binary system exhibit a stepwise evolution, and that the pulse fraction reaches its peak at energies under ten KeV. The complex variation of the pulse profile indicates that the pulse profile can not be explained by a single geometrical or physical model, rather, it must be related with both the viewing angle and the radiation mechanism. The observed features are here discussed in terms of the standard radiation model of pulsars. 相似文献
16.
Donald E. Anderson Jr. 《Planetary and Space Science》1983,31(12):1517-1523
Time-dependent calculations of trace constituent distributions require as input the dissociating radiation field as a function of altitude and solar zenith angle. An isotropic, spherical, multiple scattering model of the radiation field has been developed to determine the radiation field at twilight. Comparison of the spherical model with a plane parallel model at twilight shows that: (1) for solar zenith angles less than 92°, plane parallel solutions for the source function are suitable if the initial deposition of solar energy is calculated for a spherical atmosphere; (2) for solar zenith angles greater than 92°, the plane parallel radiation field can be several orders of magnitude smaller than that calculated with the spherical model; (3) at altitudes above 40 km and at all solar zenith angles, the spherical model predicts 10–20% less radiation than the radiation field calculated with the plane parallel model. Calculations of the rate of photodissociation of NO2 in the troposphere and stratosphere show that the spherical model yields significantly higher values at solar zenith angles greater than 92°. 相似文献
17.
From a detailed analysis of the intensity distribution of Saturn electrostatic discharges (SED) as a function of time during the Voyager 1 encounter with Saturn, the total beaming pattern of the SED source, which is found to be isotropic, is fetermined. This result allows for the derivation of the diurnal variations of the peak electron density over the dayside equatorial ionosphere of Saturn, and thus explains the puzzling features observed during the Voyager 1 encounter with Saturn—the longer extent of the SED visibility after closest approach and the existence of double-humped SED episodes before the encounter—by ionospheric absorption of the SED radio emission. 相似文献
18.
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
19.
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
20.
利用简单的ｔｏｒｎｓ束流模型定量计算Ｓｅｙｆｅｒｔ２型星系的偏振度和散射流量的角分布,在“一次电子散射”的假定下,得到偏振度约为１０％～８０％．而偏振流量的角分布与ｔｏｒｎｓ半张角θｃ和观测角φｏ都有关．特别是当φｏ ５５°时,观测方向的流量和总的散射流量的比值为一定值（０．１６）．用这种纯电子散射模型来解释ＮＧＣ１０６８的光谱偏振更为合适．对于其它一些具有低的偏振度的Ｓｅｙｆｅｒｔ２星系,尘埃的作用则不能忽略． 相似文献