We present pulsar timing results obtained with a new technique that uses standard radioastronomy (VLBI) data recorded on magnetic tape. A special processing system, developed at the Centre National d'Etudes Spatiales in Toulouse, is used to detect the pulsar signal and determine the time of arrival of the pulses. MarkII VLBI data on PSR1937+21 have provided the first timing of a millisecond pulsar at seven participating radio observatories. Data from the Effelsberg (Germany) station form a consistent set of timing observations spanning five years with sub-microsecond measurement uncertainty. This technique offers interesting development prospects, including the possibility of detecting new pulsars using sky survey data.

The temporal evolution of the 5 GHz emission of RS CVn and Algol type binaries is studied. About 70 hours of VLA observations of six systems are used. It is shown that the emission is time variable both during flares and during a significant fraction of the quiescent phases, on time scales ranging from tens of minutes to some hours. Observations of Algol during two successive passages through the quadrature points provide evidence for a recurrent behaviour at these orbital phases. The observed time scales are qualitatively discussed with respect to several possible processes. The directivity of optically thin and thick gyrosynchrotron emission might account for the recurrent phase-dependent behaviour. Variations shorter than ∼1 h are probably related to the evolution of the radiating electrons

AbstractPhase-referencing is a technique used in VLBI to extend the signal coherence time from a few minutes to a few hours in order to enhance significantly its sensitivity. With this technique, VLBI observations of milliJansky radio sources can be conducted for high-accuracy differential astrometry as well as imaging. We describe the technique in some details and present, as an example, a submilliarcsecond differential astrometric experiment design to identify the star responsible for the weak radio emission in the binary system Algol.

An astrometric comparison of the two densest VLBI celestial reference frames produced by the Jet Propulsion Laboratory (JPL) and by the Goddard Space Flight Centre (GSFC) is presented. The comparison indicates that there are global rotations of 0."0015 between these two celestial frames which were produced with independent data and analysis. This comparison reveals also that there are regional deformations less-than-or-equal-to 0."002 in the equatorial band of declination (-30-degrees,30-degrees) whose origins are presently difficult to identify.