Leonid I. Gurvits

Spacecraft VLBI and Doppler tracking: algorithms and implementation

Aims. We present the results of several multi-station Very Long Baseline Interferometry (VLBI) experiments conducted with the ESA spacecraft Venus Express as a target. To determine the true capabilities of VLBI tracking for future planetary missions in the solar system, it is necessary to demonstrate the accuracy of the method for existing operational spacecraft. Methods. We describe the software pipeline for the processing of phase referencing near-field VLBI observations and present results of the ESA Venus Express spacecraft observing campaign conducted in 2010−2011. Results. We show that a highly accurate determination of spacecraft state-vectors is achievable with our method. The consistency of the positions indicates that an internal rms accuracy of 0.1 mas has been achieved. However, systematic effects produce offsets up to 1 mas, but can be reduced by better modelling of the troposphere and ionosphere and closer target-calibrator configurations.

RADIOASTRON OBSERVATIONS OF THE QUASAR 3C273: A CHALLENGE TO THE BRIGHTNESS TEMPERATURE LIMIT

Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of

EXTREME BRIGHTNESS TEMPERATURES AND REFRACTIVE SUBSTRUCTURE IN 3C 273 WITH RADIOASTRON

10^{11.5}

Transient relativistic ejections and stationary core in XTE J1752−223

K. Relativistic boosting can increase its observed value, but apparent brightness temperatures much in excess of

Into the central 10 pc of the most distant known radio quasar

10^{13}

Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique: A test case of the Mars Express Phobos fly-by

K are inaccessible using ground-based very long baseline interferometry (VLBI) at any wavelength. We present observations of the quasar 3C273, made with the space VLBI mission RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as small as 26

VLBI observations of the radio quasar J2228+0110 at z = 5.95 and other field sources in multiple-phase-centre mode

mu

On the Doppler boosting in the compact radio jet of the distant blazar J1026+2542 at z = 5.3

as (2.7 light months) and brightness temperature in excess of

Discovering the sky at the Longest Wavelengths (DSL)

10^{13}

On the nature of bright compact radio sources at z > 4.5

K. These measurements challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive black holes and require a much higher Doppler factor than what is determined from jet apparent kinematics.