Global 6 cm VLBI polarization observations of the intraday variable sources 0716+714, 0917+624, and 0954+658 are analyzed. Integrated VLA measurements during the VLBI observations suggest that although there were no substantial total intensity variations, the polarization for all three sources varied signiicantly during the 24-hour VLBI experiment. The VLBI data were divided into 2{3 hour segme...

We discuss the present performance and the future perspectives of VLBI in the 3 mm to 0.85 mm observing bands (so called mm-VLBI). The availability of new telescopes for mm-VLBI and the recent technical development towards larger observing bandwidth and higher data-rates now allow to image with 3mm-VLBI hundreds of sources with high dynamic range. At 1.3 mm, pilot VLBI studies have proven detec...

We report the results of a successful 12 hour 22 GHz VLBI experiment using a heterogeneous network that includes radio telescopes of the Long Baseline Array (LBA) in Australia and several VLBI stations that regularly observe in geodetic VLBI campaigns. We have determined positions of three VLBI stations, atca-104, ceduna and mopra, with an accuracy of 4–30 mm using a novel technique of data ana...

One important prerequisite for geodetic Very Long Baseline Interferometry (VLBI) is the use of frequency standards with excellent short term stability. This makes VLBI stations, which are often co-located with Global Navigation Satellite System (GNSS) receiving stations, interesting for studies of timeand frequency-transfer techniques. We present an assessment of VLBI time-transfer based on the...

The TeV-emitting BL Lac object Mkn 421 was observed with very long baseline interferometry (VLBI) at three closely-spaced epochs one-month apart in March–April 1998. The source was also monitored at very-high γ-ray energies (TeV measurements) during the same period in an attempt to search for correlations between TeV variability and the evolution of the radio morphology on parsec scales. While ...

[1] The presence of degree-1 deformations in very long baseline interferometry (VLBI) measurements is detected for the first time. We compare VLBI measurements with the deformation field predicted using a GPS-determined load moment. Degree-1 series in the center of figure frame have root mean square values up to 3 and 1.5 mm in the up and horizontal components respectively. The predicted baseli...

Context. The Deep Extragalactic VLBI-Optical Survey (DEVOS) aims at constructing a large sample of compact radio sources up to two orders of magnitude fainter than those studied in other Very Long Baseline Interferometry (VLBI) surveys. Optical identification of the objects is ensured by selecting them from the Sloan Digital Sky Survey (SDSS) list. Aims. While continuing to build up the DEVOS d...

Imaging the vicinity of black hole is one of the ultimate goals of VLBI astronomy. The closest massive black hole, SgrA*, located at Galactic center is the leading candidate for such observations. Combined with recent VLBI recording technique and sub-mm radio engineering, we now have the sufficient sensitivity for the observations. We here show performance simulations of sub-mm VLBI arrays for ...

Advances in VLBI instrumentation now allow wideband recording that significantly increases the sensitivity of short wavelength VLBI observations. Observations of the supermassive black hole candidate at the center of the Milky Way, SgrA*, with short wavelength VLBI reduces the scattering effects of the intervening interstellar medium, allowing observations with angular resolution comparable to ...