Estimation of Orbital Parameters from (u,v)-coverage for a Space Radio Interferometer

Finding a suitable very long baseline (VLBI) interferometer geometry is a key task in planning observations, especially imaging sessions. The main characteristic of the quality of VLBI imaging data is the (u, v)-coverage. In the case when one or more radio telescopes are located in space, this task becomes more complex. This paper presents a method for recovering the optimal orbital parameters of space radio telescopes for a given desired (u, v)-coverage, which in turn is the inverse task of searching for the optimal geometry and orbital configurations of space-ground and pure space VLBI interferometers.Comment: 10 pages, 5 figures, 2 table

On Optimal Geometry for Space Interferometers

This paper examines options for orbit configurations for a space interferometer. In contrast to previously presented concepts for space very long baseline interferometry, we propose a combination of regular and retrograde near-Earth circular orbits in order to achieve a faster filling of $(u,v)$ coverage. With the rapid relative motion of the telescopes, it will be possible to quickly obtain high quality images of supermassive black holes. As a result of such an approach, it will be possible for the first time to conduct high quality studies of the supermassive black hole close surroundings in dynamics.Comment: 9 pages, 6 figure

Lineviewer — program of the astro space locator (asl) package for constructing and processing averaged spectra

Представлены описание и демонстрация работы программы LineViewer, ориентированной на первичную обработку спектров галактических и внегалактических мазеров и визуализацию данных наблюдений, полученных с участием космического радиотелескопа SRT-10 (проект «Радиоастрон»). LineViewer написана на языке C++ и предназначена для корректировки полосы пропускания сигнала, построения и анализа усредненных по времени и частоте интерференции спектров мазерных источников и отождествления мазерных спектральных линий. Программа LineViewer позволяет быстро провести анализ промежуточного результата и его корректировку, чтобы получить релевантные параметры для улучшения или обнаружения корреляции в спектральных линиях.LineViewer program operation a description and demonstration is presented. It is focused on the galactic and extragalactic masers primary spectra processing and visualization of observational data obtained with the SRT-10 space radio telescope (the “Radioastron” project). LineViewer is written in C ++ and is intended for correcting the signal bandwidth, constructing and analyzing the maser sources spectra averaged over time and fringe rate, and identifying maser spectral lines. The LineViewer software allows to analyze quickly the intermediate result and adjust it to obtain the relevant parameters for improving or detecting the correlation in spectral lines

Technical constraints on interstellar interferometry and spatially resolving the pulsar magnetosphere

Scintillation of pulsar radio signals caused by the interstellar medium can in principle be used for interstellar interferometry. Changes of the dynamic spectra as a function of pulsar longitude were in the past interpreted as having spatially resolved the pulsar magnetosphere. Guided by this prospect we used VLBI observations of PSR B1237+25 with the Arecibo and Green Bank radio telescopes at 324 MHz and analyzed such scintillation at separate longitudes of the pulse profile. We found that the fringe phase characteristics of the visibility function changed quasi-sinusoidally as a function of longitude. Also, the dynamic spectra from each of the telescopes shifted in frequency as a function of longitude. Similar effects were found for PSR B1133+16. However, we show that these effects are not signatures of having resolved the pulsar magnetosphere. Instead the changes can be related to the effect of low-level digitizing of the pulsar signal. After correcting for these effects the frequency shifts largely disappeared. Residual effects may be partly due to feed polarization impurities. Upper limits for the pulse emission altitudes of PSR B1237+25 would likely be well below the pulsar light cylinder radius. In view of our analysis we think that observations with the intent of spatially resolving the pulsar magnetosphere need to be critically evaluated in terms of these constraints on interstellar interferometry.Comment: 19 pages, 11 figures, published in The Astrophysical Journa

Simulations of M87 and Sgr A* imaging with the Millimetron Space Observatory on near-Earth orbits

High resolution imaging of supermassive black holes shadows is a direct way to verify the theory of general relativity at extreme gravity conditions. Very Long Baseline Interferometry (VLBI) observations at millimeter/sub-millimeter wavelengths can provide such angular resolution for supermassive black holes, located in Sgr A* and M87. Recent VLBI observations of M87 with the Event Horizon Telescope (EHT) has shown such capabilities. The maximum obtainable spatial resolution of EHT is limited by Earth diameter and atmospheric phase variations. In order to improve the image resolution longer baselines are required. Radioastron space mission has successfully demonstrated the capabilities of Space-Earth VLBI with baselines much larger than Earth diameter. Millimetron is a next space mission of the Russian Space Agency that will operate at millimeter wavelengths. Nominal orbit of the observatory will be located around Lagrangian L2 point of the Sun-Earth system. In order to optimize the VLBI mode, we consider a possible second stage of the mission that could use near-Earth high elliptical orbit (HEO). In this contribution a set of near-Earth orbits is used for the synthetic space-ground VLBI observations of Sgr A* and M87 in joint Millimetron and EHT configuration. General-relativistic magnetohydrodynamic models (GRMHD) for black hole environment of Sgr A* and M87 are used for static and dynamic imaging simulations at 230 GHz. A comparison preformed between ground and space-ground baselines demonstrates that joint observations with Millimetron and EHT significantly improve the image resolution and allow the EHT+Millimetron to obtain snapshot images of Sgr A* probing dynamics at fast timescales.Comment: 12 pages, 6 figure