A 20-hour VLBI observation with the NRAO VLBA and GBT in the NOAO Boötes field reaches an rms noise of 9 microJy per beam at 1.4 GHz. Three sources were detected at 10-milliarcsecond resolution within the GBT primary beam of FWHM 8.6, including the 20milliJy calibrator and two sub-milliJy sources. By tapering the visibility data, portions of the VLBA primary beam of FWHM 29 were imaged at poore...

We discuss a technique for mapping the synchrotron turnover frequency distribution using nearly simultaneous, multi–frequency VLBI observations. The limitations of the technique arising from limited spatial sampling and frequency coverage are investigated. The errors caused by uneven spatial sampling of typical multi– frequency VLBA datasets are estimated through numerical simulations, and are ...

We present here two epochs of Space VLBI Observations at 18 cm of the BL-Lac type object Mkn 501. Thanks to the high resolution of these new data we have found that the inner jet is centrally brightened at its beginning but becomes extended and limb brightened at ∼ 8 mas from the core. Moreover a comparison between the two epochs shows the presence of a possible proper motion with apparent velo...

Wide-field very long baseline interferometric (VLBI) imaging can be used to study the compact radio structures in extended extragalactic radio sources such as starburst galaxies and radio galaxies. Recently, compact radio emission has been detected from the southern lobe hotspot in the nearby, powerful radio galaxy PKS B2152 699, using an array of Southern Hemisphere radio telescopes, resulting...

We analyse VLBI data of a sample of radio quasars in order to study the milliarcsecond scale structural properties of quasars in the widest available redshift range of 0:2 < z < 4:5. The statistical study is based on a combination of the 5 GHz Caltech-Jodrell VLBI survey and our data for a set of extremely high redshift sources. We show that the apparently less prominent milliarcsecond scale st...

We present an analysis of new and old high frequency VLBI data collected during the last 10 years at 5– 22 GHz. For the jet components in the mas-VLBI jet, two component identifications are possible. One of them with quasi-stationary components oscillating about their mean positions. Another identification scheme, which formally gives the better expansion fit, yields motion with ∼ 9 c for H0 = ...

We present multi-frequency radio continuum VLBI observations of the gravitational lens system B0218+357 carried out using a global VLBI network and the VLBA. The source has been observed with resolutions from 0.2 mas to 5 mas and displays interesting structure. The spectral properties of various components show that the lensed object is a standard flat spectrum radio source which has many self-...

Abstract. We have obtained mas-scale resolution very long baseline interferometry (VLBI) images of a sample of Seyfert 1 and Seyfert 2 galaxies at 5 GHz (wavelength, λ = 6 cm). The Seyferts of the two types were chosen to be matched in several orientation-independent properties, primarily in order to rigorously test predictions of the unified scheme. We detected all the 15 objects that we obser...

Korean VLBI Network (KVN) is the first dedicated mm-wavelength VLBI Network in East Asia and will be available from the middle of 2008. KVN consists of three stations and has the maximum observation frequency of 129 GHz with the maximum baseline length of 480 km. KVN has unique characteristics in the multifrequency, simultaneous observing system. By taking advantage of this we are considering v...

We present a magnetic field mapping of water maser clouds in the star-forming region W3 IRS 5, which has been made on the basis of the linear polarization VLBI observation. Using the Very Long Baseline Array (VLBA) at 22.2 GHz, 16 of 61 detected water masers were found to be linearly polarized with polarization degrees up to 13 %. Although 10 polarized features were widely distributed in the wh...