| 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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| 4. |
- Bååth, Lars B., et al.
(författare)
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Imaging with Interferometers
- 1998
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Ingår i: Proceedings SSAB Symposium on Image Analysis. ; , s. 4-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A scanning device based on changes in the reflections of an electromagnetic wave for use on wood the image can be calculated.
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| 7. |
- Chu, H.S., et al.
(författare)
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VLBI observations of the puzzling BL Lacertae object 0235+164
- 1996
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Ingår i: Astronomy and Astrophysics. - : Springer. - 0004-6361 .- 1432-0746. ; 307:1, s. 15-20
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Tidskriftsartikel (refereegranskat)abstract
- For over 20 years, many models have been proposed to explain the variability of AO0235+164. Among them, the most favorable has been micro-lensing. We have made a series of VLBI observations on this source in order to better understand its nature. The resultant maps indicate dramatic changes in the position angle of the jet between observations as well as a correlation between the intensity of the VLBI core and flux outbursts which occurred between the observing sessions. These characteristics, in conjunction with other arguments, suggest that the source variability is intrinsic, i.e. microlensing is of minor importance. We suggest two models: 1) a model in which the jet starts at a very small angle to the line of sight and then curves away to become about 6deg at about 1 mas from the core; and 2) a CME (Coronal Mass Ejection) model that also may explain the violent variability in intensity, polarization position angle, and jet direction in AO0235+164.
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| 8. |
- Malmberg, Donald, et al.
(författare)
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Slag level detection in EAFs using microwave technology
- 1999
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Ingår i: Scandinavian journal of metallurgy. - : Blackwell Publishing Ltd.. - 0371-0459 .- 1600-0692. ; 28:6, s. 266-276
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Tidskriftsartikel (refereegranskat)abstract
- Within the metallurgical industry as well as the underground mine industry, there is a need for on-line level detection in the different production processes and their material feeding systems. Microwave technology is a versatile, non-invasive measurement technique, which has a number of advantages compared with penetrating probes, laser and radar technology, and echo sound technique. In its extension, it could also be used for qualitative and quantitative analysis of waste gases due to the presence of specific molecules. This contribution describes the introduction of microwave technology in different metallurgical as well as underground mine production processes with the emphasis on EAF's.
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| 9. |
- 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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| 10. |
- Otarola, A., et al.
(författare)
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Site Survey for a Large Southern Array
- 1996
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Ingår i: Science with large millimetre arrays. - Berlin : Springer. - 3540615822 ; , s. 358-364
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Bokkapitel (refereegranskat)
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