Related papers: Higher Resolution VLBI Imaging with Fast Frequency…
VLBI at millimeter wavelengths (mm-VLBI) allows the detailed imaging of compact galactic and extragalactic radio sources with micro-arcsecond scale resolution, unaccessible by other observing techniques. Here we discuss the scientific…
For Very Long Baseline Interferometry (VLBI), the fringe spacing is extremely narrow compared to the field of view imposed by the primary beam of each element. This means that an extremely large number of resolution units can potentially be…
Radio-loud active galactic nuclei (AGNs), hosting powerful relativistic jet outflows, provide an excellent laboratory for studying jet physics. Very long baseline interferometry (VLBI) enables high-resolution imaging on milli-arcsecond…
In extragalactic jets, the apparent position of the bright/narrow end (the core) depends on the observing frequency, owing to synchrotron self-absorption and external absorption. The effect must be taken into account in order to achieve…
The Global mm-VLBI Array is at present the most sensitive 3 mm-VLBI interferometer and provides images of up to 40 micro-arcsecond resolution. Using this array, we have monitored the rotation of the innermost jet in the quasar NRAO 150,…
Very long baseline interferometry (VLBI) provides the highest-resolution images in astronomy. The sharpest resolution is nominally achieved at the highest frequencies, but as the observing frequency increases so too does the atmospheric…
Extending geodetic and astrometric Very Long Baseline Interferometry (VLBI) observations from traditional centimeter wavebands to millimeter wavebands offers numerous scientific potentials and benefits. However, it was considered quite…
High precision astrometric Space Very Long Baseline Interferometry (S-VLBI) at the low end of the conventional frequency range, i.e. 20cm, is a requirement for a number of high priority science goals. These are headlined by obtaining…
Space Very-Long-Baseline-Interferometry (S-VLBI) observations at high frequencies hold the prospect of achieving the highest angular resolutions and astrometric accuracies, resulting from the long baselines between ground and satellite…
We report results from 3mm-VLBI observations of 3C273 and 3C454.3 during the period 1994-1997. In both sources the images show superluminal motion in feature-rich jets. Due to the improved uv-coverage in the later experiments, the jets can…
From 43GHz VLBA observations of the pair of radio sources 1928+738 and 2007+777 we have demonstrated the feasibility of precision phase-delay differential astrometric techniques at millimeter wavelengths. For a pair of sources with 5…
Context: Phase referencing is a standard calibration technique in radio interferometry, particularly suited for the detection of weak sources close to the sensitivity limits of the interferometers. However, effects from a changing…
(abridged) Very long baseline interferometry (VLBI) observations at 86$\,$GHz (wavelength, $\lambda = 3\,$mm) reach a resolution of about 50 $\mu$as, probing the collimation and acceleration regions of relativistic outflows in active…
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…
Results of a pilot project with the participation of the "Kvazar-KVO" radio interferometry array in observations carried out with the European VLBI Network are presented. The aim of the project was to conduct and analyze multi-frequency…
We report on new developments in VLBI, with emphasis on experiments performed at the highest frequencies possible to date (so called mm-VLBI). We have observed the nucleus of M 87 (Virgo A) with global VLBI at 3 mm. We show a new image of…
Over the past few decades, our knowledge of jets produced by active galactic nuclei (AGN) has greatly progressed thanks to the development of very-long-baseline interferometry (VLBI). Nevertheless, the crucial mechanisms involved in the…
The apparent position of the "core" in a parsec-scale radio jet (a compact, bright emitting region at the narrow end of the jet) depends on the observing frequency, owing to synchrotron self-absorption and external absorption. While…
The 2017 observing campaign of the Event Horizon Telescope (EHT) delivered the first very long baseline interferometry (VLBI) images at the observing frequency of 230 GHz, leading to a number of unique studies on black holes and…
We report on an ongoing effort to image active galactic nuclei simultaneously observed at 2.3 and 8.6 GHz in the framework of a long-term VLBI project RDV (Research and Development - VLBA) started in 1994 aiming to observe compact…