Compact galactic and extragalactic radio sources can be imaged with an unsurpassed angular resolution of a few ten micro-arcseconds, adopting the observing technique of global millimeter VLBI. Here we present the Global Millimeter VLBI Array (GMVA) and discuss its present performance. For individual and partially archetypical radio sources with prominent VLBI jets (e.g. 3C 120, Cygnus A, M 87, ...

A brief Note compiled by: Prof. Madhav N. Kulkarni, IIT Bombay Since the inception of the Very Long Baseline Interferometry (VLBI) system in 1967, this radio interferometry technique has revolutionised the fields of geodesy, geodynamics and astrometry. With the unprecedented precision and resolution made possible by VLBI various tasks such as geodetic positioning, reference frames interconnect...

Very Long Baseline interferometry (VLBI) is a well established technique in radio astronomy for the study of celestial sources at high angular resolution. VLBI is gradually moving to the point where Gbps data rates are becoming routine. A number of experiments have shown that the internet can be used at data rates of several hundred Mbps on production networks. However the use of switched light...

Global Positioning System (GPS) satellites broadcast at frequencies of 1,575.42 MHz (L1) and of 1,227.60 MHz (L2). The dispersive property of the ionosphere can be used to combine independent measurements at the two frequencies to estimate the total electron content (TEC) between a GPS receiver site and a broadcasting satellite. Such measurements, made at sites near to Very Long Baseline Interf...

VLBI is the only technology that will allow sub-milliarcsecond resolution imaging in the near future. As such, it is the only way to image expanding supernovae in nearby galaxies. Such images potentially allow us to study the early evolution of neutron stars or black holes left behind by core-collapse supernovae, the circumstellar wind history of the supernova progenitor stars, the shock accele...

Since one of the main objectives of the Key Stone Project VLBI Network is to measure position changes of four VLBI stations associated with large Earthquakes around Tokyo area, daily observations and fast data processing system are required. To achieve these requirements, highly automated remote operation system and data analysis system have to be developed. The remote operation system of the K...

As part of an ongoing effort to observe high energy γ-ray blazars with VLBI, we have produced 8 and 2 GHz VLBI images, at ten epochs spanning the years 1988 to 1996, of the quasar 1156+295. The VLBI data have been taken from the Washington VLBI correlator’s geodetic database. We have detected four components and have measured their apparent speeds to be 8.8 ± 2.3, 5.3 ± 1.1, 5.5 ± 0.9, and 3.5 ...

Dynamical mass measurements to date have allowed determinations of the mass M and the distance D of a number of nearby supermassive black holes. In the case of Sgr A*, these measurements are limited by a strong correlation between the mass and distance scaling roughly as M ∼ D2. Future very long baseline interferometric (VLBI) observations will image a bright and narrow ring surrounding the sha...

We discuss the opacity in the core regions of active galactic nuclei observed with Very Long Baseline Interferometry (VLBI), and describe a new method for deriving the frequencydependent shifts of the VLBI core from the frequency-dependent time lags of flares observed with single-dish observations. Application of the method to the core shifts of the quasar 3C 345 shows a very good agreement bet...

We present simulated images of Supernova 1993J at 8.4 GHz using Very Long Baseline Interferometry (VLBI) techniques. A spherically symmetric source model is convolved with realistic uv-plane distributions, together with standard imaging procedures, to assess the extent of instrumental effects on the recovered brightness distribution. In order to facilitate direct comparisons between the simulat...