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Register a new userFirst results of European VLBI radar observations of space objects
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I. Molotov
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Since 1999 we carried out seven trial VLBI radar experiments under LFVN project. The aim of this work is to adjust new research technique for investigating the Solar system bodies (planets, asteroids, space debris). It is planned to obtain the information on their movement parameters, proper rotation and structure of surface. The transmitter of Evpatoria RT-70 sounded the space objects. Array of Bear Lakes RT-64, Noto RT-32, Urumqi RT-25, Simeiz RT-22 received the echo-signals. The data were processed with NIRFI-3 Mk-2 correlator in N. Novgorod, Russia and NRTV processor in Noto, Italy. The first results of these experiments are presented.
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A crucial part of a space mission for very-long baseline interferometery (VLBI), which is the technique capable of providing the highest resolution images in astronomy, is orbit determination of the missions space radio telescope(s). In order to successfully detect interference fringes that result from correlation of the signals recorded by a ground-based and a space-borne radio telescope, the propagation delays experienced in the near-Earth space by radio waves emitted by the source and the relativity effects on each telescopes clock need to be evaluated, which requires accurate knowledge of position and velocity of the space radio telescope. In this paper we describe our approach to orbit determination (OD) of the RadioAstron spacecraft of the RadioAstron space-VLBI mission. Determining RadioAstrons orbit is complicated due to several factors: strong solar radiation pressure, a highly eccentric orbit, and frequent orbit perturbations caused by the attitude control system. We show that in order to maintain the OD accuracy required for processing space-VLBI observations at cm-wavelengths it is required to take into account the additional data on thruster firings, reaction wheel rotation rates, and attitude of the spacecraft. We also investigate into using the unique orbit data available only for a space-VLBI spacecraft, i.e. the residual delays and delay rates that result from VLBI data processing, as a means to evaluate the achieved OD accuracy. We present the results of the first experience of OD accuracy evaluation of this kind, using more than 5,000 residual values obtained as a result of space-VLBI observations performed over 7 years of the RadioAstron mission operations.
One of our closest neighbours, the Andromeda Galaxy (M31) has been the subject of numerous large area studies across the entire spectrum, but so far full-disk radio surveys have been conducted only at low resolution. The new wide-field capabilities of the DiFX software correlator present the possibility of imaging the entire primary beam of a VLBI array, thus enabling a high resolution wide-field study of the entire galaxy. Using the VLBA and EVN, pilot observations of M31 have been carried out with the aim of using these new wide-field techniques to characterise the population of compact components at VLBI resolution both within and behind one of our nearest neighbours. This contribution describes the observations carried out, the preliminary processing and first results.
According to a generally accepted paradigm, small intrinsic sizes of Compact Steep Spectrum (CSS) radio sources are a direct consequence of their youth, but in later stages of their evolution they are believed to become large-scale sources. However, this notion was established mainly for strong CSS sources. In this series of papers we test this paradigm on 60 weaker objects selected from the VLA FIRST survey. They have 5-GHz flux densities in the range 150 < S_{5GHz} < 550 mJy and steep spectra in the range 0.365 le u le 5 GHz. The present paper is focused on sources that fulfill the above criteria and have angular sizes in the range 0.2arcsec - 1arcsec. Observations of 19 such sources were obtained using MERLIN in snapshot mode at 5 GHz. They are presented along with 1.7-GHz VLBA and 5-GHz EVN follow-up snapshot observations made for the majority of them. For one of the sources in this subsample, 1123+340, a full-track 5-GHz EVN observation was also carried out. This study provides an important element to the standard theory of CSS sources, namely that in a number of them the activity of their host galaxies probably switched off quite recently and their further growth has been stopped because of that. In the case of 1123+340, the relic of a compact dead source is particularly well preserved by the presence of intracluster medium of the putative cluster of galaxies surrounding it. The observed overabundance of compact sources can readily be explained in the framework of the scenario of premature cessation of the activity of the host galaxy nucleus. It could also explain the relatively low radio flux densities of many such sources and, in a few cases, their peculiar, asymmetric morphologies. We propose a new interpretation of such asymmetries based on the light-travel time argument.
Guided by the recently published science case for the future of European VLBI, EVN2015, a roadmap for the future of the EVN is sketched out in this paper. The various desired technical improvements are being discussed with an emphasis on the role of e-VLBI. With this innovation new scientific capabilities are introduced. In this way the EVN is also positioned as an interesting platform for exercising new techniques and operational models, complementary to other SKA pathfinders. In return, the technology development for the SKA can have a positive impact on the scientific capabilities of VLBI, for example on the development of a next generation correlator, capable to process much larger data-rates. The development of cheap, frequency agile antennas can also be of great importance for VLBI. This adds to the potential for maintaining a Northern hemisphere, global VLBI array in the SKA era.
We report the results of the first two 5 GHz e-VLBI observations of the X-ray binary Cygnus X-3 using the European VLBI Network. Two successful observing sessions were held, on 2006 April 20, when the system was in a quasi-quiescent state several weeks after a major flare, and on 2006 May 18, a few days after another flare. At the first epoch we detected faint emission probably associated with a fading jet, spatially separated from the X-ray binary. The second epoch in contrast reveals a bright, curved, relativistic jet more than 40 milliarcseconds in extent. In the first, and probably also second epochs, the X-ray binary core is not detected, which may indicate a temporary suppression of jet production as seen in some black hole X-ray binaries in certain X-ray states. Spatially resolved polarisation maps at the second epoch provide evidence of interaction between the ejecta and the surrounding medium. These results clearly demonstrate the importance of rapid analysis of long-baseline observations of transients, such as facilitated by e-VLBI.
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