We discuss the technique of Wide-field imaging as it applies to Very Long Baseline Interferometry (VLBI). In the past VLBI data sets were usually averaged so severely that the field-of-view was typically restricted to regions extending a few hundred milliarcseconds from the phase centre of the field. Recent advances in data analysis techniques, together with increasing data storage capabilities...

We present and discuss new result from mm-VLBI observations of M 87 and Sgr A*. The imaging of these sources with a spatial resolutions of a few to a few ten Schwarzschild radii offers new possibilities to study the immediate environment of super-massive black holes. 1. Introduction In astronomy, the highest angular resolution is obtained with Very Long Baseline Interferometry (VLBI). VLBI obse...

To locate and image the compact emission regions in quasars, which are closely connected to the phenomenon of IntraDay Variability (IDV), space VLBI observations are of prime importance. Here we report on VSOP observations of two prominent IDV sources, the BL Lac objects S5 0716+714. To monitor their short term variability, these sources were observed with VSOP at 5GHz in several polarisation s...

Systematic differences in the very long baseline interferometry (VLBI) radio polarization structure and average VLBI component speeds of BL Lacertae objects and quasars support the view that the observational distinction between these classes, based in large part on the strength of their optical line emission, is meaningful; in other words, this distinction reflects significant differences in t...

With the establishment of the AUT University 12m radio telescope at Warkworth, New Zealand has now become a part of the international Very Long Baseline Interferometry (VLBI) community. A major product of VLBI observations are images in the radio domain of astronomical objects such as Active Galactic Nuclei (AGN). Using large geographical separations between radio antennas, very high angular re...

The European VLBI Network (EVN) is in the process of establishing an e-VLBI array in which the radio telescopes and the EVN correlator at JIVE are connected in real-time, via high-speed national fibre optic networks and the pan-European research network, GÉANT. This paper reports on recent test results, including the production of the first real-time e-VLBI astronomical image. In a parallel and...

Very long baseline interferometry (VLBI) makes it possible to recover images of astronomical sources with extremely high angular resolution. Most recently, the Event Horizon Telescope (EHT) has extended VLBI to short millimeter wavelengths with a goal of achieving angular resolution sufficient for imaging the event horizons of nearby supermassive black holes. VLBI provides measurements related ...

In 1995, NTT Laboratories have started a joint research project on ultra high-speed communications with public research organizations using a large scale network testbed having the maximum speed of 2.4 Gb/s. Among many applications tried in the first phase of the project, the realtime VLBI (very long baseline interferometry) has proved to be benefited greatly from the high performance communica...

The work presented deals with the determination of sub-daily Earth Rotation Parameters (ERPs) from Very Long Baseline Interferometry (VLBI) observations. Monitoring and interpreting the Earth's rotation variations in general is an important task for Earth sciences, as they provide boundary which support other geophysical investigations. This holds especially for sub-daily variations of the Eart...

Global VLBI imaging at millimeter and sub-millimeter wavelengths overcomes the opacity barrier of synchrotron self-absorption in Active Galactic Nuclei (AGN) and opens the direct view into sub-pc scale regions not accessible before. Since AGN variability is more pronounced at short millimeter wavelength, mm-VLBI can reveal structural changes in very early stages after outbursts. When combined w...