VLBI2010 Imaging and Structure Corrections

Simulations show that the next generation VLBI system is generally well suited for imaging extragalactic radio sources. In addition to revealing the morphology of the sources, simulated VLBI2010 images may also be used to generate structure correction maps, which characterize the impact of source structure on the VLBI measurements. By comparing structure corrections for a set of simulated images based on Monte-Carlo generated visibilities with theoretical structure corrections derived from the model, we assess the accuracy of VLBI2010 structure corrections. In the most favorable case (32-station network, source at declination +40 deg.), statistics demonstrate that the structure corrections obtained from simulated images are statistically close to the theoretical model ones, which seems very promising for the VLBI2010 system

Report for 2011 from the Bordeaux IVS Analysis Center

This report summarizes the activities of the Bordeaux IVS Analysis Center during the year 2011. The work focused on (i) regular analysis of the IVS-R1 and IVS-R4 sessions with the GINS software package; (ii) systematic VLBI imaging of the RDV sessions and calculation of the corresponding source structure index and compactness values; (iii) imaging of the sources observed during the 2009 International Year of Astronomy IVS observing session; and (iv) continuation of our VLBI observational program to identify optically-bright radio sources suitable for the link with the future Gaia frame. Also of importance is the enhancement of the IVS LiveWeb site which now comprises all IVS sessions back to 2003, allowing one to search past observations for session-specific information (e.g. sources or stations)

Global VLBI Observations of Weak Extragalactic Radio Sources: Imaging Candidates to Align the VLBI and Gaia Frames

The space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the Gaia and VLBI frames (International Celestial Reference Frame) with the highest accuracy. In this respect, it is found that only 10% of the ICRF sources are suitable to establish this link (70 sources), either because most of the ICRF sources are not bright enough at optical wavelengths or because they show extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we initiated a multi-step VLBI observational project, dedicated to finding additional suitable radio sources for aligning the two frames. The sample consists of about 450 optically-bright radio sources, typically 20 times weaker than the ICRF sources, which have been selected by cross-correlating optical and radio catalogs. The initial observations, aimed at checking whether these sources are detectable with VLBI, and conducted with the European VLBI Network (EVN) in 2007, showed an excellent 90% detection rate. This paper reports on global VLBI observations carried out in March 2008 to image 105 from the 398 previously detected sources. All sources were successfully imaged, revealing compact VLBI structure for about half of them, which is very promising for the future

Report for 2012 from the Bordeaux IVS Analysis Center

This report summarizes the activities of the Bordeaux IVS Analysis Center during the year 2012. The work focused on (i) regular analysis of the IVS-R1 and IVS-R4 sessions with the GINS software package; (ii) systematic VLBI imaging of the RDV sessions and calculation of the corresponding source structure index and compactness values; (iii) investigation of the correlation between astrometric position instabilities and source structure variations; and (iv) continuation of our VLBI observational program to identify optically-bright radio sources suitable for the link with the future Gaia frame. Also of importance is the 11th European VLBI Network Symposium, which we organized last October in Bordeaux and which drew much attention from the European and International VLBI communities

Design Aspects of the VLBI2010 System - Progress Report of the IVS VLBI2010 Committee

This report summarizes the progress made in developing the next generation VLBI system, dubbed the VLBI2010 system. The VLBI2010 Committee of the International VLBI Service for Geodesy and Astrometry (IVS) worked on the design aspects of the new system. The report covers Monte Carlo simulations showing the impact of the new operating modes on the final products. A section on system considerations describes the implications for the VLBI2010 system parameters by considering the new modes and system-related issues such as sensitivity, antenna slew rate, delay measurement error. RF1, frequency requirements, antenna deformation, and source structure corrections_ This is followed by a description of all major subsystems and recommendations for the network, station. and antenna. Then aspects of the feed, polarization processing. calibration, digital back end, and correlator subsystems are covered. A section is dedicated to the NASA. proof-of-concept demonstration. Finally, sections tm operational considerations, on risks and fallback options, and on the next steps complete the report

Exploring Source Structure with the Bordeaux VLBI Image Database Comparing Jet Directions with Optical-Radio Offset Vectors

The Bordeaux VLBI Image Database provides to the international VLBI community almost 8,000 VLBI images of radio sources at S and X band and some others at K and Q band. Such images are of interest for astrometric and astrophysical applications, such as the determination of the VLBI jet direction. We developed a fully automatic method to extract this direction from any VLBI image, which we then applied to all BVID images, resulting in the production of 9,215 jet directions for 1,221 sources. Comparing the mean jet directions over all epochs at X band to the Gaia EDR3 (optical) − ICRF3 S/X (radio) offset vector directions indicates that the offset vector is aligned within 30 • of the jet direction in roughly half of the sources, thereby confirming previous studies

Bridging astronomical, astrometric and geodetic scheduling for VGOS

Funding Information: This research has made use of VGOS schedule files provided by the International VLBI Service for Geodesy and Astrometry (IVS) data archives. Publisher Copyright: © 2023, The Author(s).Very Long Baseline Interferometry (VLBI) experiments are organized within the geodetic, astrometric and astronomical communities for different applications, requiring different observation strategies adopted in scheduling. Currently, the next-generation geodetic and astrometric VLBI Global Observing System (VGOS) is being established. Over the last years, evidence was presented that the delays introduced by the angular structure of the geodetic radio sources contribute significantly to the VGOS observable error budget. Consequently, correcting these structure delays through imaging will play an important part in the future, requiring a different scheduling approach. Within this work, a new source-centric VLBI scheduling approach is presented for improved imaging capabilities of geodetic observations. The algorithm is tested for a seven- and nine-station network and compared with classical geodetic schedules. Monte Carlo simulations are utilized to determine the expected geodetic and astrometric parameter precision, and two independent processing pipelines are used to assess the potential for astronomical source imaging. Based on the simulation results, it is revealed that with the new scheduling approach twice as many sources can be properly imaged. Furthermore, the precision of the Earth orientation parameter estimates is improved on average by 15 % , while the source position coordinate estimates are on average improved by 50 %. Tests with two VGOS networks of twelve and 29 antennas further reveal that the scheduling approach is also applicable to future VGOS networks.Peer reviewe

Bridging astronomical, astrometric and geodetic scheduling for VGOS

Very Long Baseline Interferometry (VLBI) experiments are organized within the geodetic, astrometric and astronomical communities for different applications, requiring different observation strategies adopted in scheduling. Currently, the next-generation geodetic and astrometric VLBI Global Observing System (VGOS) is being established. Over the last years, evidence was presented that the delays introduced by the angular structure of the geodetic radio sources contribute significantly to the VGOS observable error budget. Consequently, correcting these structure delays through imaging will play an important part in the future, requiring a different scheduling approach. Within this work, a new source-centric VLBI scheduling approach is presented for improved imaging capabilities of geodetic observations. The algorithm is tested for a seven- and nine-station network and compared with classical geodetic schedules. Monte Carlo simulations are utilized to determine the expected geodetic and astrometric parameter precision, and two independent processing pipelines are used to assess the potential for astronomical source imaging. Based on the simulation results, it is revealed that with the new scheduling approach twice as many sources can be properly imaged. Furthermore, the precision of the Earth orientation parameter estimates is improved on average by 15 % , while the source position coordinate estimates are on average improved by 50 %. Tests with two VGOS networks of twelve and 29 antennas further reveal that the scheduling approach is also applicable to future VGOS networks.ISSN:0949-7714ISSN:1432-139

Enhancing VGOS Operations: Insights from R&D Sessions and Pathways Ahead

The inception of the VGOS R&D program in 2021 marked a pivotal milestone in the evolution of VGOS. This work serves as a catalyst for an interactive discussion, providing a platform to discuss lessons learned from these sessions while charting pathways for future VGOS observations and operational integration.Our focus revolves around the outcomes gleaned from the six VGOS R&D sessions conducted in 2022. These sessions aimed at optimizing the number and distribution of observations and scans, resulting in a significant augmentation, with observations and scans more than doubling compared to conventional VGOS sessions while simultaneously reducing the number of recorded bits. Noteworthy enhancements were observed in Earth orientation parameter estimates, showcasing improved alignment with IERS solutions and SX observations, coupled with bolstered baseline length repeatability and reduced formal errors.Furthermore, our exploration delves into the pioneering two sessions of 2023, trialing source-based VLBI scheduling. This initiative aimed at expanding the VGOS source list through the integration of new ICRF3 sources while amplifying imaging capabilities.Our findings underscore the pivotal advantages of equitably distributing observations among sources, presenting compelling benefits for the VGOS framework.This poster serves as an invitation to engage in a discussion that encapsulates the successes and insights derived from the VGOS R&D sessions. It aims to stimulate discourse on strategies for seamless integration into operational VGOS sessions, fostering a collaborative environment to utilize VGOS capabilities for future scientific endeavors

Design Aspects of the VLBI2010 System

This report summarizes the progress made in developing the next generation VLBI, dubberd the VLBI2010 system. The VLBI2010 Committee of the International Service for Geodesy and Astrometry (IVS) worked on the design aspects of the new system.