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Zensus J. A. - One of the best experts on this subject based on the ideXlab platform.
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Understanding BL Lacertae objects. Structural and kinematic mode changes in the BL Lac object PKS 0735+178
EDP Sciences, 2010Co-Authors: Britzen S., Witzel A., Gong B. P., Zhang J. W., Aller M. F., Aller H. D., Krishna G., Goyal A., Zensus J. A.Abstract:Context. We present evidence that parsec-scale jets in BL Lac objects may be significantly distinct in kinematics from their counterparts in quasars. We argued this previously for the BL lac sources 1803+784 and 0716+714 and report here a similar pattern for another well-known BL Lac object, PKS 0735+178, whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims. By analyzing the pc-scale jet morphology and its changes in 0735+178 we seek to understand the emission processes in BL Lac objects and to decipher their differences from quasars. A detailed study of the jet components' Motion reveals that the standard AGN paradigm of Apparent Superluminal Motion does not always describe the kinematics in BL Lac objects. We study 0735+178 here to augment and improve the understanding of the peculiar Motions in the jets of BL Lac objects as a class. Methods. We analyzed 15 GHz VLBA (Very Long Baseline Array) observations (2 cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91. Multiple Gaussians were fitted to the derived VLBA data, to trace the kinematical and flux density evolution of the individual VLBI (Very Long Baseline Interferometry) components in the nuclear jet. We then compared the jet kinematics with the optical and radio light curves available for this BL Lac object and point out some striking correlations between the properties of the radio knots and the features in the light curves. Results. We found a drastic structural mode change in the VLBI jet of 0735+178, between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a linear shape. We further found that this jet had undergone a similar transition sometime between December 1981 and June 1983. A mode change, occurring in the reverse direction (between mid-1992 and mid-1995) has already been reported in the literature. These structural mode changes are found to be reflected in changed kinematical behavior of the nuclear jet, manifested as an Apparent Superluminal Motion and stationarity of the radio knots. In addition, we found the individual mode changes to correlate in time with the maxima in the optical light curve. The last two transitions occurred before a (modest) radio flare. The behavior of this pc-scale jet appears to favor a scenario involving non-ballistic Motions of the radio knots, produced by the precession of a continuous jet within the ambient medium. Conclusions. This is the third BL Lac object (after 1803+784 and 0716+714) analyzed by us, which reveals kinematic properties in the parsec-scale radio jet, which are atypical of quasars. For several years, the components in the jet are not found to be separating from the core but instead to be moving perpendicularly to the ridge line of the jet. In 0735+178 this unusual behavior has been particularly conspicuous. Curiously, however, fast Apparent Superluminal Motion characteristic of quasars were present in this jet between the epochs ~1995 and ~2000. Thus we found for this BL Lac object a drastic change in the kinematics of the nuclear jet, i.e, transition from "typical Superluminal" to an unusual "stationary" state. Interestingly, we found that this change is accompanied with a mode change in the nuclear jet's morphology. The long sequences of VLBA images reported here for this BL Lac object do not support the commonly assumed connection between radio flux-density outbursts and the ejection of new VLBI components. In contrast, the two mode changes seem correlated with the radio flares and are more likely an outcome of a changing viewing angle of the same knots. We propose therefore that all these observed features of the nuclear jet of 0735+178 and their correlation with the optical and radio flares might hold significant promise to better understand the basic difference between BL Lac objects and quasars
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Understanding BL Lac objects Structural & kinematic mode changes in the BL Lac object PKS 0735+178
'EDP Sciences', 2010Co-Authors: Britzen S., Witzel A., Gong B. P., Zhang J. W., Goyal Arti, Aller M. F., Aller H. D., Zensus J. A.Abstract:Context. We present evidence that parsec-scale jets in BL Lac objects may be significantly distinct in kinematics from their counterparts in quasars. We argued this previously for the BL lac sources 1803+784 and 0716+714, report here a similar pattern for another well-known BL Lac object, PKS 0735+178, whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims. A detailed study of the jet components' Motion reveals that the standard AGN paradigm of Apparent Superluminal Motion does not always describe the kinematics in BL Lac objects. We study 0735+178 here to augment and improve the understanding of the peculiar Motions in the jets of BL Lac objects as a class. Methods. We analyzed 15 GHz VLBA (Very Long Baseline Array) observations (2cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91. Results. We found a drastic structural mode change in the VLBI jet of 0735+178, between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a linear shape.We further found that this jet had undergone a similar transition sometime between December 1981 and June 1983. A mode change, occurring in the reverse direction (between mid-1992 and mid-1995) has already been reported in the literature. These structural mode changes are found to be reflected in changed kinematical behavior of the nuclear jet, manifested as an Apparent Superluminal Motion and stationarity of the radio knots. In addition, we found the individual mode changes to correlate in time with the maxima in the optical light curve. The last two transitions occurred before a (modest) radio flare. The behavior of this pc-scale jet appears to favor a scenario involving non-ballistic Motions of the radio knots, produced by the precession of a continuous jet within the ambient medium.Comment: Accepted for publication in A&A (Abstract reduced for astro-ph
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Relativistic jet Motion in the core of the radio-loud quasar J1101+7225
2005Co-Authors: Pott J U, Britzen S., Eckart A, Krips M, Krichbaum T P, Alef W, Zensus J. A.Abstract:Multi-epoch GHz Very Long Baseline Interferometry (VLBI) data of the radio-loud quasar J1101+7225 were analyzed to estimate the proper Motion of extended optically thin jet components. Two components separated from the core could be mapped at 1.66 GHz, which is consistent with earlier observations. In one case we found evidence of high Apparent Superluminal Motion (beta_app= 22.5+/-4) at large (deprojected) distances to the core (22 mas ~ 4 kpc at z= 1.46). Typically in other quasars such high separation velocities are only found much closer to the core component. Furthermore the Doppler factor, the magnetic field strength, and the angular size of the optically thick core were derived using published X-ray data. Analysis of 5 GHz VLBI data reveals the existence of further jet components within the central 5 mas. Additionally the data published so far on the GHz-spectrum were discussed at all angular resolutions. J1101+7225 turns out to be a standard quasar for studying different aspects of radio jet kinematics out to kpc-scales
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Relativistic jet Motion in the core of the radio-loud quasar J1101+7225
'EDP Sciences', 2005Co-Authors: Pott J U, Britzen S., Eckart A, Krips M, Krichbaum T P, Alef W, Zensus J. A.Abstract:Multi-epoch GHz Very Long Baseline Interferometry (VLBI) data of the radio-loud quasar J1101+7225 were analyzed to estimate the proper Motion of extended optically thin jet components. Two components separated from the core could be mapped at 1.66 GHz, which is consistent with earlier observations. In one case we found evidence of high Apparent Superluminal Motion (beta_app= 22.5+/-4) at large (deprojected) distances to the core (22 mas ~ 4 kpc at z= 1.46). Typically in other quasars such high separation velocities are only found much closer to the core component. Furthermore the Doppler factor, the magnetic field strength, and the angular size of the optically thick core were derived using published X-ray data. Analysis of 5 GHz VLBI data reveals the existence of further jet components within the central 5 mas. Additionally the data published so far on the GHz-spectrum were discussed at all angular resolutions. J1101+7225 turns out to be a standard quasar for studying different aspects of radio jet kinematics out to kpc-scales.Comment: 8 pages, 5 figures, accepted by A&
Britzen S. - One of the best experts on this subject based on the ideXlab platform.
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A new view on the M87 jet origin: Turbulent loading leading to large-scale episodic wiggling
'EDP Sciences', 2017Co-Authors: Britzen S., Fendt C., Eckart AAbstract:Context. The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for a bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large BH mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. Many kinematic studies have been performed to determine the proper Motions in the jet. Despite M87 providing all proofs of being an active BH, the Apparent jet speed remained puzzling, because proper Motion measurements between 15 and 43 GHz for the same region of 1-10 mas core distance provided largely discrepant results. This source is a prime object to be studied in exquisite detail with the upcoming Event Horizon Telescope (EHT) observations because it promises to allow a direct view on the jet launching process itself. Aims. We aim to decipher some of the kinematic puzzles in the pc-scale jet with the analysis we present here. Methods. We re-modeled and re-analyzed 31 VLBA observations at 15 GHz obtained within the MOJAVE program. The data span a time range between Jul. 1995 and May 2011. We performed a detailed investigation of the pc-scale jet kinematics on different timescales, the shortest periods between the observations beeing 10 and 80 days, and in different jet modes, making use of VLBA observations. In addition, we studied the jet ridge line behavior as a function of time. Special care was taken to analyze the region close to the 15 GHz core, and the dynamics and distribution of newly emerging jet features in the jet. Results. We find an indication for Apparent Superluminal Motion in the jet. Moreover, we present evidence for acceleration between 0.5 and 10 mas of core separation. The data suggest that the central part of M87 at 15 GHz seems to be rotating. Jet components and counter-jet components are ejected in different directions under varying angles, explaining the impression of a broad opening angle. In this paper we present evidence for two different operating modes of the jet of M87. The jet switches between two phases: i) the jet ridge line is at least double or the jet axis is displaced vertically, and ii) an unperturbed phase where the jet ridge line remains almost straight but is smoothly curved and the jet components are aligned along a classical jet axis. The mode change occurs every couple of years. Between the two operating modes, a transition phase is visible. Conclusions. The M87 jet visible at 15 GHz probes a different physical zone compared to the standard blazar-zone we tend to see in AGN jets. The most likely scenario explaining the observed phenomena is a turbulent mass loading into the jet, most probably due to local, fast reconnection processes driven by turbulence of a tangled magnetic field, which is either generated in the accretion disk or the disk corona. In addition, on large scales, a global magnetic structure is required to channel the turbulent flow into what evolves into a large-scale jet. Large-scale jet instabilities may explain the curved pattern of the observed jet flow
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Understanding BL Lacertae objects. Structural and kinematic mode changes in the BL Lac object PKS 0735+178
EDP Sciences, 2010Co-Authors: Britzen S., Witzel A., Gong B. P., Zhang J. W., Aller M. F., Aller H. D., Krishna G., Goyal A., Zensus J. A.Abstract:Context. We present evidence that parsec-scale jets in BL Lac objects may be significantly distinct in kinematics from their counterparts in quasars. We argued this previously for the BL lac sources 1803+784 and 0716+714 and report here a similar pattern for another well-known BL Lac object, PKS 0735+178, whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims. By analyzing the pc-scale jet morphology and its changes in 0735+178 we seek to understand the emission processes in BL Lac objects and to decipher their differences from quasars. A detailed study of the jet components' Motion reveals that the standard AGN paradigm of Apparent Superluminal Motion does not always describe the kinematics in BL Lac objects. We study 0735+178 here to augment and improve the understanding of the peculiar Motions in the jets of BL Lac objects as a class. Methods. We analyzed 15 GHz VLBA (Very Long Baseline Array) observations (2 cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91. Multiple Gaussians were fitted to the derived VLBA data, to trace the kinematical and flux density evolution of the individual VLBI (Very Long Baseline Interferometry) components in the nuclear jet. We then compared the jet kinematics with the optical and radio light curves available for this BL Lac object and point out some striking correlations between the properties of the radio knots and the features in the light curves. Results. We found a drastic structural mode change in the VLBI jet of 0735+178, between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a linear shape. We further found that this jet had undergone a similar transition sometime between December 1981 and June 1983. A mode change, occurring in the reverse direction (between mid-1992 and mid-1995) has already been reported in the literature. These structural mode changes are found to be reflected in changed kinematical behavior of the nuclear jet, manifested as an Apparent Superluminal Motion and stationarity of the radio knots. In addition, we found the individual mode changes to correlate in time with the maxima in the optical light curve. The last two transitions occurred before a (modest) radio flare. The behavior of this pc-scale jet appears to favor a scenario involving non-ballistic Motions of the radio knots, produced by the precession of a continuous jet within the ambient medium. Conclusions. This is the third BL Lac object (after 1803+784 and 0716+714) analyzed by us, which reveals kinematic properties in the parsec-scale radio jet, which are atypical of quasars. For several years, the components in the jet are not found to be separating from the core but instead to be moving perpendicularly to the ridge line of the jet. In 0735+178 this unusual behavior has been particularly conspicuous. Curiously, however, fast Apparent Superluminal Motion characteristic of quasars were present in this jet between the epochs ~1995 and ~2000. Thus we found for this BL Lac object a drastic change in the kinematics of the nuclear jet, i.e, transition from "typical Superluminal" to an unusual "stationary" state. Interestingly, we found that this change is accompanied with a mode change in the nuclear jet's morphology. The long sequences of VLBA images reported here for this BL Lac object do not support the commonly assumed connection between radio flux-density outbursts and the ejection of new VLBI components. In contrast, the two mode changes seem correlated with the radio flares and are more likely an outcome of a changing viewing angle of the same knots. We propose therefore that all these observed features of the nuclear jet of 0735+178 and their correlation with the optical and radio flares might hold significant promise to better understand the basic difference between BL Lac objects and quasars
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Understanding BL Lac objects Structural & kinematic mode changes in the BL Lac object PKS 0735+178
'EDP Sciences', 2010Co-Authors: Britzen S., Witzel A., Gong B. P., Zhang J. W., Goyal Arti, Aller M. F., Aller H. D., Zensus J. A.Abstract:Context. We present evidence that parsec-scale jets in BL Lac objects may be significantly distinct in kinematics from their counterparts in quasars. We argued this previously for the BL lac sources 1803+784 and 0716+714, report here a similar pattern for another well-known BL Lac object, PKS 0735+178, whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims. A detailed study of the jet components' Motion reveals that the standard AGN paradigm of Apparent Superluminal Motion does not always describe the kinematics in BL Lac objects. We study 0735+178 here to augment and improve the understanding of the peculiar Motions in the jets of BL Lac objects as a class. Methods. We analyzed 15 GHz VLBA (Very Long Baseline Array) observations (2cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91. Results. We found a drastic structural mode change in the VLBI jet of 0735+178, between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a linear shape.We further found that this jet had undergone a similar transition sometime between December 1981 and June 1983. A mode change, occurring in the reverse direction (between mid-1992 and mid-1995) has already been reported in the literature. These structural mode changes are found to be reflected in changed kinematical behavior of the nuclear jet, manifested as an Apparent Superluminal Motion and stationarity of the radio knots. In addition, we found the individual mode changes to correlate in time with the maxima in the optical light curve. The last two transitions occurred before a (modest) radio flare. The behavior of this pc-scale jet appears to favor a scenario involving non-ballistic Motions of the radio knots, produced by the precession of a continuous jet within the ambient medium.Comment: Accepted for publication in A&A (Abstract reduced for astro-ph
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Relativistic jet Motion in the core of the radio-loud quasar J1101+7225
2005Co-Authors: Pott J U, Britzen S., Eckart A, Krips M, Krichbaum T P, Alef W, Zensus J. A.Abstract:Multi-epoch GHz Very Long Baseline Interferometry (VLBI) data of the radio-loud quasar J1101+7225 were analyzed to estimate the proper Motion of extended optically thin jet components. Two components separated from the core could be mapped at 1.66 GHz, which is consistent with earlier observations. In one case we found evidence of high Apparent Superluminal Motion (beta_app= 22.5+/-4) at large (deprojected) distances to the core (22 mas ~ 4 kpc at z= 1.46). Typically in other quasars such high separation velocities are only found much closer to the core component. Furthermore the Doppler factor, the magnetic field strength, and the angular size of the optically thick core were derived using published X-ray data. Analysis of 5 GHz VLBI data reveals the existence of further jet components within the central 5 mas. Additionally the data published so far on the GHz-spectrum were discussed at all angular resolutions. J1101+7225 turns out to be a standard quasar for studying different aspects of radio jet kinematics out to kpc-scales
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Relativistic jet Motion in the core of the radio-loud quasar J1101+7225
'EDP Sciences', 2005Co-Authors: Pott J U, Britzen S., Eckart A, Krips M, Krichbaum T P, Alef W, Zensus J. A.Abstract:Multi-epoch GHz Very Long Baseline Interferometry (VLBI) data of the radio-loud quasar J1101+7225 were analyzed to estimate the proper Motion of extended optically thin jet components. Two components separated from the core could be mapped at 1.66 GHz, which is consistent with earlier observations. In one case we found evidence of high Apparent Superluminal Motion (beta_app= 22.5+/-4) at large (deprojected) distances to the core (22 mas ~ 4 kpc at z= 1.46). Typically in other quasars such high separation velocities are only found much closer to the core component. Furthermore the Doppler factor, the magnetic field strength, and the angular size of the optically thick core were derived using published X-ray data. Analysis of 5 GHz VLBI data reveals the existence of further jet components within the central 5 mas. Additionally the data published so far on the GHz-spectrum were discussed at all angular resolutions. J1101+7225 turns out to be a standard quasar for studying different aspects of radio jet kinematics out to kpc-scales.Comment: 8 pages, 5 figures, accepted by A&
Fujisawa K. - One of the best experts on this subject based on the ideXlab platform.
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Milliarcsecond-scale structure in the gamma-ray loud quasar PKS 1622-297
Nihon Tenmon Gakkai, 2006Co-Authors: Wajima K., Bignall Hayley, Kobayashi H., Hirabayashi H., Murata Y., Edwards P., Tsuboi M., Fujisawa K.Abstract:We made a high-resolution VLBI observation of the gamma-ray loud quasar PKS 1622-297 with the HALCA spacecraft and ground radio telescopes at 5 GHz in 1998 February, almost 3 yr after the source exhibited a spectacular GeV gamma-ray flare. The source shows an elongated structure toward the west on the parsec scale. The visibility data are well modeled by three distinct components: a bright core and two weaker jet components. Comparison with previous observations confirms that the jet components have an Apparent Superluminal Motion up to 12.1h-1 c, with the inner jet components having lower Superluminal speeds. We applied the inverse Compton catastrophe model and derived a Doppler factor, d, of 2.45, which is rather lower than those of other gamma-ray loud active galactic nuclei (AGNs), suggesting that the source was in a more quiescent phase at the epoch of our observation. As an alternative probe of the subparsec-scale structure, we also present the results from multiepoch ATCA total flux monitoring, which indicate the presence of persistent intraday variability consistent with refractive interstellar scintillation. We examined the gamma-ray emission mechanism in light of these observations
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Milliarcsecond-Scale Structure in the Gamma-Ray Loud Quasar PKS 1622-297
'Oxford University Press (OUP)', 2005Co-Authors: Wajima K., Kobayashi H., Hirabayashi H., Murata Y., Tsuboi M., Bignall H E, Edwards P G, Fujisawa K.Abstract:We have made a high-resolution VLBI observation of the gamma-ray loud quasar PKS 1622-297 with the HALCA spacecraft and ground radio telescopes at 5 GHz in 1998 February, almost three years after the source exhibited a spectacular GeV gamma-ray flare. The source shows an elongated structure toward the west on the parsec scale. The visibility data are well modeled by three distinct components; a bright core and two weaker jet components. Comparison with previous observations confirms that the jet components have an Apparent Superluminal Motion up to 12.1 h^{-1}c, with the inner jet components having lower Superluminal speeds. We apply the inverse Compton catastrophe model and derive a Doppler factor, \delta, of 2.45, which is somewhat lower than that of other gamma-ray loud active galactic nuclei (AGNs), suggesting the source was in a more quiescent phase at the epoch of our observation. As an alternative probe of the sub-parsec scale structure, we also present the results from multi-epoch ATCA total flux monitoring, which indicate the presence of persistent intraday variability consistent with refractive interstellar scintillation. We examine the gamma-ray emission mechanism in the light of these observations
An T. - One of the best experts on this subject based on the ideXlab platform.
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Gamma-ray-emitting quasar 0202$+$149: a CSS revisited
'American Astronomical Society', 2016Co-Authors: An T., Baan,w. A., Cui Y. -z., Wang W. -h., Mohan P.Abstract:PKS 0202$+$149 is a low-power radio source with blazar-like $\gamma$-ray AGN characteristics and its properties and classification are investigated in relation to its $\gamma$-ray characteristics. It shows a hint of low frequency turnover at about 200 MHz. Radio imaging data of 0202$+$149 at different frequencies show differing morphologies on both kilo-parsec (kpc) and parsec (pc) scales. The overall source shows a triple structure of core and double lobes with a total projected size of $\sim$1.3 kpc. The compact source structure of 0202+149 is reminiscent of a compact steep spectrum (CSS) source. At pc scales a core-jet structure extends $\sim$25 pc (in projection) at a position angle perpendicular to the kpc-scale structure. The curved pc-scale structure with jet and inner lobe suggests that the CSS nuclear activity has recently re-started although its power has been decreasing, while the kpc-scale lobes are relics of earlier activity. A maximum Apparent Superluminal Motion of $\sim16\,c$ is detected in the jet components, indicating a highly relativistic jet flow. The brightness temperature of the core is lower than the average value found for highly-beamed $\gamma$-ray AGN, indicating a lower radio power and a relatively lower Doppler boosting factor. The CSS radio classification indicates that blazar-like $\gamma$-ray properties can also be manifested in low-power CSS radio sources with appropriate jet and beaming properties.Comment: 35 pages, 6 figures, 2 tables, accepted for publication in The Astrophysical Journa
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Kinematics of the parsec-scale radio jet in 3C 48
Royal Astronomical Society, 2010Co-Authors: An T., Venturi T, Hong X. Y., Hardcastle M. J., Worrall D. M., Pearson T. J., Shen Z.-q., Zhao W., Feng W. X.Abstract:We present results on the compact steep-spectrum quasar 3C 48 from observations with the Very Long Baseline Array (VLBA), the Multi-Element Radio Linked Interferometer Network (MERLIN) and the European Very long baseline interferometry (VLBI) Network (EVN) at multiple radio frequencies. In the 1.5-GHz VLBI images, the radio jet is characterized by a series of bright knots. The active nucleus is embedded in the southernmost VLBI component A, which is further resolved into two sub-components A1 and A2 at 4.8 and 8.3 GHz, respectively. A1 shows a flat spectrum and A2 shows a steep spectrum. The most strongly polarized VLBI components are located at component C ~ 0.25 arcsec north of the core, where the jet starts to bend to the north-east. The polarization angles at C show gradual changes across the jet width at all observed frequencies, indicative of a gradient in the emission-weighted intrinsic polarization angle across the jet and possibly a systematic gradient in the rotation measure; moreover, the percentage of polarization increases near the curvature at C, likely consistent with the presence of a local jet–interstellar-medium interaction and/or changing magnetic-field directions. The hot spot B shows a higher rotation measure, and has no detected proper Motion. These facts provide some evidence for a stationary shock in the vicinity of B. Comparison of the present VLBI observations with those made 8.43 yr ago suggests a significant northward Motion for A2 with an Apparent transverse velocity β_(app)= 3.7 ± 0.4c. The Apparent Superluminal Motion suggests that the relativistic jet plasma moves at a velocity of ≳ 0.96c if the jet is viewed at an inclination angle less than 20°. A simple precessing jet model and a hydrodynamical isothermal jet model with helical-mode Kelvin–Helmholtz instabilities are used to fit the oscillatory jet trajectory of 3C 48 defined by the bright knots
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Kinematics of the parsec-scale radio jet in 3C 48
'Wiley', 2010Co-Authors: An T., Venturi T, Hong X. Y., Hardcastle M. J., Worrall D. M., Pearson T. J., Zhao W., Shen Z. -q., Feng W. X.Abstract:We present results on the compact steep-spectrum quasar 3C 48 from observations with the Very Long Baseline Array (VLBA), the Multi-Element Radio Linked Interferometer Network (MERLIN) and the European Very long baseline interferometry (VLBI) Network (EVN) at multiple radio frequencies. In the 1.5-GHz VLBI images, the radio jet is characterized by a series of bright knots. The active nucleus is embedded in the southernmost VLBI component A, which is further resolved into two sub-components A1 and A2 at 4.8 and 8.3 GHz, respectively. A1 shows a flat spectrum and A2 shows a steep spectrum. The most strongly polarized VLBI components are located at component C similar to 0.25 arcsec north of the core, where the jet starts to bend to the north-east. The polarization angles at C show gradual changes across the jet width at all observed frequencies, indicative of a gradient in the emission-weighted intrinsic polarization angle across the jet and possibly a systematic gradient in the rotation measure; moreover, the percentage of polarization increases near the curvature at C, likely consistent with the presence of a local jet-interstellar-medium interaction and/or changing magnetic-field directions. The hot spot B shows a higher rotation measure, and has no detected proper Motion. These facts provide some evidence for a stationary shock in the vicinity of B. Comparison of the present VLBI observations with those made 8.43 yr ago suggests a significant northward Motion for A2 with an Apparent transverse velocity beta(app) = 3.7 +/- 0.4c. The Apparent Superluminal Motion suggests that the relativistic jet plasma moves at a velocity of greater than or similar to 0.96c if the jet is viewed at an inclination angle less than 20 degrees. A simple precessing jet model and a hydrodynamical isothermal jet model with helical-mode Kelvin-Helmholtz instabilities are used to fit the oscillatory jet trajectory of 3C 48 defined by the bright knots
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Kinematics of the parsec-scale radio jet in 3C 48
'Wiley', 2010Co-Authors: An T., Venturi T, Shen Z.-q., Zhao W., Hong X.y., Hardcastle M.j., Worrall D.m., Pearson T.j., Feng W.x.Abstract:‘The definitive version is available at www3.interscience.wiley.com '. Copyright Royal Astronomical SocietyWe present results on the compact steep-spectrum quasar 3C 48 from observations with the Very Long Baseline Array (VLBA), the Multi-Element Radio Linked Interferometer Network (MERLIN) and the European Very long baseline interferometry (VLBI) Network (EVN) at multiple radio frequencies. In the 1.5-GHz VLBI images, the radio jet is characterized by a series of bright knots. The active nucleus is embedded in the southernmost VLBI component A, which is further resolved into two sub-components A1 and A2 at 4.8 and 8.3 GHz, respectively. A1 shows a flat spectrum and A2 shows a steep spectrum. The most strongly polarized VLBI components are located at component C ∼ 0.25 arcsec north of the core, where the jet starts to bend to the north-east. The polarization angles at C show gradual changes across the jet width at all observed frequencies, indicative of a gradient in the emission-weighted intrinsic polarization angle across the jet and possibly a systematic gradient in the rotation measure; moreover, the percentage of polarization increases near the curvature at C, likely consistent with the presence of a local jet–interstellar-medium interaction and/or changing magnetic-field directions. The hot spot B shows a higher rotation measure, and has no detected proper Motion. These facts provide some evidence for a stationary shock in the vicinity of B. Comparison of the present VLBI observations with those made 8.43 yr ago suggests a significant northward Motion for A2 with an Apparent transverse velocity βapp= 3.7 ± 0.4c . The Apparent Superluminal Motion suggests that the relativistic jet plasma moves at a velocity of ≳0.96c if the jet is viewed at an inclination angle less than 20° . A simple precessing jet model and a hydrodynamical isothermal jet model with helical-mode Kelvin–Helmholtz instabilities are used to fit the oscillatory jet trajectory of 3C 48 defined by the bright knotsPeer reviewe
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Kinematics of the parsec-scale radio jet in 3C48
'Wiley', 2009Co-Authors: An T., Venturi T, Hong X. Y., Hardcastle M. J., Worrall D. M., Pearson T. J., Zhao W., Shen Z. -q., Feng W. X.Abstract:We present results on the compact steep-spectrum quasar 3C 48 from observations with the VLBA, MERLIN and EVN at multiple radio frequencies. In the 1.5-GHz VLBI images, the radio jet is characterized by a series of bright knots. The active nucleus is embedded in the southernmost VLBI component A, which is further resolved into two sub-components A1 and A2 at 4.8 and 8.3 GHz. A1 shows a flat spectrum and A2 shows a steep spectrum. The most strongly polarized VLBI components are located at component C $\sim$0.25 arcsec north of the core. The polarization angles at C show gradual changes across the jet width at all observed frequencies, indicative of a gradient in the emission-weighted intrinsic polarization angle across the jet and possibly a systematic gradient in the rotation measure; moreover, the percentage of polarization increases near the curvature at C, likely consistent with the presence of a local jet-ISM interaction and/or changing magnetic-field directions. The hot spot B shows a higher rotation measure, and has no detected proper Motion. These facts provide some evidence for a stationary shock in the vicinity of B. Comparison of the present VLBI observations with those made 8.43 years ago suggests a proper Motion of $\beta_{app}=3.7\pm0.4 c$ for A2 to the north. The Apparent Superluminal Motion suggests that the relativistic jet plasma moves at a velocity of $\gtrsim0.96 c$ if the jet is viewed at an inclination angle less than $20\degr$. A simple precessing jet model and a hydrodynamical isothermal jet model with helical-mode Kelvin-Helmholtz instabilities are used to fit the oscillatory jet trajectory of 3C 48 defined by the bright knots.Comment: 40 pages, 10 figures, accepted for publication in MNRA
Wajima K. - One of the best experts on this subject based on the ideXlab platform.
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Milliarcsecond-scale structure in the gamma-ray loud quasar PKS 1622-297
Nihon Tenmon Gakkai, 2006Co-Authors: Wajima K., Bignall Hayley, Kobayashi H., Hirabayashi H., Murata Y., Edwards P., Tsuboi M., Fujisawa K.Abstract:We made a high-resolution VLBI observation of the gamma-ray loud quasar PKS 1622-297 with the HALCA spacecraft and ground radio telescopes at 5 GHz in 1998 February, almost 3 yr after the source exhibited a spectacular GeV gamma-ray flare. The source shows an elongated structure toward the west on the parsec scale. The visibility data are well modeled by three distinct components: a bright core and two weaker jet components. Comparison with previous observations confirms that the jet components have an Apparent Superluminal Motion up to 12.1h-1 c, with the inner jet components having lower Superluminal speeds. We applied the inverse Compton catastrophe model and derived a Doppler factor, d, of 2.45, which is rather lower than those of other gamma-ray loud active galactic nuclei (AGNs), suggesting that the source was in a more quiescent phase at the epoch of our observation. As an alternative probe of the subparsec-scale structure, we also present the results from multiepoch ATCA total flux monitoring, which indicate the presence of persistent intraday variability consistent with refractive interstellar scintillation. We examined the gamma-ray emission mechanism in light of these observations
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Milliarcsecond-Scale Structure in the Gamma-Ray Loud Quasar PKS 1622-297
'Oxford University Press (OUP)', 2005Co-Authors: Wajima K., Kobayashi H., Hirabayashi H., Murata Y., Tsuboi M., Bignall H E, Edwards P G, Fujisawa K.Abstract:We have made a high-resolution VLBI observation of the gamma-ray loud quasar PKS 1622-297 with the HALCA spacecraft and ground radio telescopes at 5 GHz in 1998 February, almost three years after the source exhibited a spectacular GeV gamma-ray flare. The source shows an elongated structure toward the west on the parsec scale. The visibility data are well modeled by three distinct components; a bright core and two weaker jet components. Comparison with previous observations confirms that the jet components have an Apparent Superluminal Motion up to 12.1 h^{-1}c, with the inner jet components having lower Superluminal speeds. We apply the inverse Compton catastrophe model and derive a Doppler factor, \delta, of 2.45, which is somewhat lower than that of other gamma-ray loud active galactic nuclei (AGNs), suggesting the source was in a more quiescent phase at the epoch of our observation. As an alternative probe of the sub-parsec scale structure, we also present the results from multi-epoch ATCA total flux monitoring, which indicate the presence of persistent intraday variability consistent with refractive interstellar scintillation. We examine the gamma-ray emission mechanism in the light of these observations