| 1. |
- Alberdi, A., et al.
(författare)
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The high-frequency compact radio structure of the peculiar quasar 4C 39.25
- 1997
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Ingår i: Astronomy and Astrophysics. - : Springer-Verlag. - 0004-6361 .- 1432-0746. ; 327:2, s. 513-521
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Tidskriftsartikel (refereegranskat)abstract
- We present new high angular resolution images of the compact non-thermal radio source 4C 39.25 obtained from VLBI observations at λ1.3cm, λ7mm, and λ3mm wavelengths. These maps and Gaussian model-fits show that the milli-arcsecond to sub-milliarcsecond structure of 4C 39.25 consists of a complex bent core-jet structure with embedded moving and stationary VLBI components. Facilitated by the small observing beams and high angular resolutions obtained at mm-wavelengths, we measured the relative positions of the jet components with an accuracy of a few hundred micro-arcseconds. This allows the detailed followup of the ongoing merging process of a westward superluminally moving component (b_) with a stationary component a_, located at ~2.9 mas east of the putative core d_. In contrast to the other components of the structure with steeper spectra, the westernmost component d_ exhibits an inverted spectrum peaking between λ7mm and λ3mm, thus further supporting its identification as the VLBI core, self-absorbed at longer wavelengths. From two VLBI maps obtained nearly simultaneously at λ7mm and λ1.3cm, we made the first spectral index map of 4C 39.25 in this wavelength regime. The main characteristics of the spectral index distribution of the jet are pronounced changes of the spectral index between orientations parallel and transverse to the jet axis. Near the merging components a_ and b_ the spectral index steepens with increasing separation from d_. However, in the bridge of emission c_, which connects d_ with a_ and b_, the spectral index gradient has a direction transverse to the jet axis, suggesting a frequency dependent jet curvature and edge-brightening. A brief discussion of this behaviour within current jet models is presented.
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| 2. |
- Matveenko, L. I., et al.
(författare)
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The injector and variability of the quasar 3C 345
- 1996
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Ingår i: Astronomy letters. - Moscow : MAIK Nauka/Interperiodica. - 1063-7737 .- 1562-6873. ; 22:1, s. 14-23
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Tidskriftsartikel (refereegranskat)abstract
- The VLBI technique is used to study the fine structure of the quasar 3C 345 at = 49 cm. It is shown that the low-frequency radio emission from the core is feeble, whereas the bright compact component corresponds to the jet region adjacent to the core, rather than to the core itself. This region is ~6.4 mas in size, and its brightness temperature, Tb near equal 0.6 1012 K, does not go beyond the Compton limit. The core itself is an injector of relativistic particles surrounded by a wall of thermal plasma. Between 1983.9 and 1990.8, the radio flux density and angular size of the compact component increased by a factor of about 2, while its brightness temperature did not change markedly. During this period, the emission at millimeter wavelengths was reduced about twofold; the UV emission also decreased. The low-frequency variability is shown to be a result of variations in the transparency of the wall of a cocoon—the thermal plasma surrounding the jet. The electron density in the cocoon wall near the bright compact component is Ne near equal 105 cm3 and rises toward the core as ~ r 2. The polarized emission of the quasar originates mainly from the same region, where compact sources are seen athigh frequencies. Its rotation measure is RM near equal 29 rad m–2 and increases toward the core as ~ r 3, reaching 8 104 rad m–2. In the vicinity of the core, the longitudinal component of the magnetic field is ~0.1 mG.
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| 3. |
- Matveenko, L.I., et al.
(författare)
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The structure of the quasar 3C345 at lambda 49cm and its relation to low-frequency variability
- 1996
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Ingår i: Astronomy and Astrophysics. - Berlin : Springer-Verlag. - 0004-6361 .- 1432-0746. ; 312, s. 738-744
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the quasar 3C345 has been studied at lambda 49cm with a global VLBI network. The core has a low-freuqncy cut off in its spectrum, and is very weak at this wavelength. The most compact bright knot is the part of the jet nearest to the nucleus, with a size of about 5x4 mas and a brightness temperature of Tb about 0.6 10^12 K. Its flux density and solid angle increased by a factor of about 2 during the period 1983.9 to 1990.8, but the birghtness temperature did not change significantly. The emission at millimeter wavelengths decreased by a factor of about 2 during the same period, while the UV emission from the nucleus also dcreased. We suggest that variations in the low-frequency emissions are caused by changes in the absorption by a cocoon - the thermal plasma surrounding the jet. The electron density in the region is Ne about 10^5 cm^-3and the longitudal field is about 40 microG. The emission measure and the rotation measure vary with r, the distance from the nucleus as r^-3. The data at lamda 49cm indi´cate several components in and near the "hotspot" at the end of the arcsec jet.
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