ORCID Profile
0000-0002-0694-2459
Current Organisations
Technische Universiteit Delft
,
Joint Institute for VLBI in Europe
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Publisher: American Astronomical Society
Date: 11-2004
DOI: 10.1086/424819
Publisher: Oxford University Press (OUP)
Date: 12-2000
Publisher: Cambridge University Press (CUP)
Date: 08-2006
DOI: 10.1017/S1743921307005431
Abstract: In February 1997 the Japanese radio astronomy satellite HALCA was launched to provide the space-borne element for the VSOP mission. HALCA provided linear baselines three-times greater than that of ground arrays, thus providing higher resolution and higher AGN brightness temperature measurements and limits. Twenty-five percent of the scientific time of the mission was devoted to the “VSOP survey” of bright, compact, extra-galactic radio sources at 5 GHz. A complete list of 294 survey targets were selected from pre-launch surveys, 91% of which were observed during the satellite's lifetime. The major goals of the VSOP Survey are statistical in nature: to determine the brightness temperature and approximate structure, to provide a source list for use with future space VLBI missions, and to compare radio properties with other data throughout the electro-magnetic spectrum. All the data collected have now been analysed and is being prepared for the final image Survey paper. In this paper we present details of the mission, and some statistics of the images and brightness temperatures.
Publisher: Copernicus GmbH
Date: 23-09-2022
DOI: 10.5194/EPSC2022-653
Abstract: & & & strong& JUICE& #8217 s and Europa Clipper& #8217 s synergistic contribution to the Galilean moons& #8217 ephemerides & /strong& & & & & An accurate determination of the ephemerides of natural satellites is critical to our understanding of planetary systems& #8217 evolution, and of tidal dissipation mechanisms in particular. Diverse interior or dissipation-related parameters can be retrieved when reconstructing the moons& #8217 dynamics from space missions& #8217 radiometric data [1,2,3]. For the Galilean moons of Jupiter, unique challenges complicate the estimation of the satellites& #8217 dynamics, as the Laplace resonances between Io, Europa and Ganymede result in a strongly coupled dynamical problem. Efficiently improving the current ephemerides solution would thus ideally require a balanced data distribution between these moons. In this context, the synergy between the upcoming JUICE and Europa Clipper missions is of primary importance. In particular, the ~ 50 flybys at Europa to be performed by the Clipper spacecraft will efficiently supplement JUICE& #8217 s trajectory (2 flybys at Europa, 7 at Ganymede, 21 at Callisto, followed by a long orbital phase around Ganymede), leading to complementary radiometric data sets. Most importantly, in-system concurrent observations will be possible according to current missions& #8217 schedules. Preliminary analyses show that a joint solution from JUICE and Europa Clipper range and Doppler measurements can improve the estimation solution for the Galilean satellites& #8217 ephemerides and related dynamical properties (& em& e.g.& /em& tidal dissipation parameters) [4].& & & & & & & & & & strong& Contribution of PRIDE multi-spacecraft observations& /strong& & & & & The Planetary Radio Interferometry and Doppler Experiment (PRIDE) has been selected as one of the eleven experiments of the JUICE (JUpiter ICy moons Explorer) mission [5]. It relies on Very Long Baseline Interferometry (VLBI) techniques to process radiometric signals used for tracking, communications and/or radioscience. The main PRIDE observables are measurements of the spacecraft& #8217 s lateral position with respect to a phase calibrator (VLBI), expressed in the ICRF (International Celestial Reference Frame) [6], but by-product Doppler observables are also generated [7]. Compared to range and Doppler measurements, which are collected in the line-of-sight direction, PRIDE VLBI data are sensitive to the spacecraft& #8217 s position in the two other directions. They thus provide very complementary information, which could help achieving an improved solution for the spacecraft& #8217 s and moons& #8217 states in particular. A previous analysis has quantified the contribution of PRIDE VLBI observations to the Galilean moons& #8217 ephemerides for the JUICE test case [2], using a simplified non-coupled model [8]. A noticeable improvement was indeed obtained in the out-of-plane direction when including VLBI data, especially for Ganymede and Callisto (more data collected at these two moons).& & & & In addition to these single-spacecraft VLBI measurements, the concurrent in-system tracking of the JUICE and Europa Clipper spacecraft will offer PRIDE a unique opportunity to fully exploit the synergy between the two missions& #8217 trajectories. If the two spacecraft are both visible from a telescope (& em& i.e.& /em& in-beam or within the same telescope beam) and simultaneously transmitting a radio signal, it is possible to realise multi-spacecraft VLBI observations, which will directly provide accurate measurements of the relative lateral position of the two spacecraft (right ascension and declination difference in the ICRF). Such observations were already successfully collected between several Martian orbiters (MRO, MEX, TGO) in 2019 [9], as shown in Figure 1.& & & & & em& & img src=& quot & quot alt=& quot & quot width=& quot & quot height=& quot & quot /& & /em& & & & & & em& Figure 1: Simultaneous detection of the signals transmitted by several Martian orbiters and landers, from [9].& /em& & & & & Given the synergistic nature of the JUICE and Clipper trajectories, the signals of the two spacecraft are expected to be visible in the same beam of ground-based telescopes during a significant fraction of their Jovian tours. Looking in detail at JUICE and Clipper flybys& #8217 sequences displayed in Figure 2, the two spacecraft will occasionally perform near-simultaneous flybys around different moons, with typically only a coupled of days between JUICE& #8217 s and Clipper& #8217 s flybys. The relative angular measurements derived from PRIDE VLBI observations might then translate into direct constraints of the moons& #8217 relative states, expected to be extremely valuable for the ephemerides solutions.& & & & & img src=& quot & quot alt=& quot & quot width=& quot & quot height=& quot & quot /& & & & & & em& Figure 2: JUICE and Europa Clipper trajectories (altitude with respect to the moons)& /em& & & & & & & & & & & strong& Contribution of & /strong& & strong& these& /strong& & strong& observations to the Galilean satellites& #8217 ephemerides & /strong& & & & & Our open-source estimation tool (Tudat(py)& sup& & /sup& ) is now able to concurrently simulate several missions with different trajectories and observation schedules in a single estimation [10]. It is also linked with a VLBI prediction tool allowing to search for suitable phase calibrators close to the spacecraft at any potential observation epoch. Using these functionalities, we perform a simulation study to quantify the potential contribution of multi-spacecraft (in-beam) VLBI observations, also analysing its sensitivity to the observations& #8217 cadence and accuracy.& & & & To this end, we will investigate when multi-spacecraft VLBI observations could be obtained from the JUICE and Clipper spacecraft. This involves searching for suitable phase calibrators and ensuring that both spacecraft are visible from ground telescopes at a given epoch. We will also further investigate promising observation geometries (& em& e.g.& /em& near-simultaneous flybys, see Figure 2). The simulated multi-spacecraft observables will then be added to a joint JUICE & #8211 Clipper estimation, which also includes & em& nominal & /em& & em& (& /em& single-spacecraft) PRIDE VLBI observations for JUICE.& & & & We will then precisely quantify the contribution of these simulated multi-spacecraft VLBI observations to the estimation solution, focusing on the moons& #8217 ephemerides and related dynamical parameters in particular. If proven beneficial, this will motivate the acquisition of such observations during the JUICE and Clipper missions. Additionally, our sensitivity analysis will provide direct recommendations regarding observation scheduling. If need be (& em& i.e.& /em& particularly interesting multi-spacecraft VLBI observation but no phase calibrator in the angular vicinity of the spacecraft), this could also highlight the need to search for yet unknown calibrators in a certain region of the sky.& & & & & & & & & & strong& References& /strong& & & & & [1] Dirkx et al., Planetary and Space Science 134 (2016): 82-95.& & & & [2] Dirkx et al., Planetary and Space Science 147 (2017): 14-27.& & & & [3] Lainey et al., Nature Astronomy 4.11 (2020): 1053-1058.& & & & [4] A. Magnanini et al., in preparation.& & & & [5] Gurvits et al., European Planetary Science Congress (2013).& & & & [6] Duev et al., Astronomy & Astrophysics 541 (2012): A43.& & & & [7] Bocanegra-Bahamon et al., Astronomy & Astrophysics 609 (2018): A59.& & & & [8] Fayolle et al., submitted to Planetary & Space science (under revision)& & & & [9] Molera Calv& #233 s et al., Publications of the Astronomical Society of Australia, 38, E065& & & & [10] Fayolle et al., EGU General Assembly (2022).& & & & & & & & id=& quot sdfootnote1& quot & & / & & id=& quot sdfootnote2& quot & & class=& quot sdfootnote& quot & & em& & sup& & /sup& docs.tudat.space& /em& & & & / & & id=& quot sdfootnote1& quot & & / & & id=& quot sdfootnote2& quot & & class=& quot sdfootnote& quot & & & & & / &
Publisher: American Astronomical Society
Date: 20-11-2004
DOI: 10.1086/424811
Publisher: Springer Science and Business Media LLC
Date: 13-05-2008
Publisher: EDP Sciences
Date: 09-2016
Publisher: Elsevier BV
Date: 08-2018
Publisher: Springer Science and Business Media LLC
Date: 06-2021
DOI: 10.1007/S10686-021-09743-7
Abstract: The Dark Ages and Cosmic Dawn are largely unexplored windows on the infant Universe (z ~ 200–10). Observations of the redshifted 21-cm line of neutral hydrogen can provide valuable new insight into fundamental physics and astrophysics during these eras that no other probe can provide, and drives the design of many future ground-based instruments such as the Square Kilometre Array (SKA) and the Hydrogen Epoch of Reionization Array (HERA). We review progress in the field of high-redshift 21-cm Cosmology, in particular focussing on what questions can be addressed by probing the Dark Ages at z 30. We conclude that only a space- or lunar-based radio telescope, shielded from the Earth’s radio-frequency interference (RFI) signals and its ionosphere, enable the 21-cm signal from the Dark Ages to be detected. We suggest a generic mission design concept, CoDEX, that will enable this in the coming decades.
Publisher: Oxford University Press (OUP)
Date: 21-11-2017
Publisher: EDP Sciences
Date: 10-2021
DOI: 10.1051/0004-6361/202039423
Abstract: We present Space-VLBI RadioAstron observations at 1.6 GHz and 4.8 GHz of the flat spectrum radio quasar 3C 273, with detections on baselines up to 4.5 and 3.3 Earth Diameters, respectively. Achieving the best angular resolution at 1.6 GHz to date, we have imaged limb-brightening in the jet, not previously detected in this source. In contrast, at 4.8 GHz, we detected emission from a central stream of plasma, with a spatial distribution complementary to the limb-brightened emission, indicating an origin in the spine of the jet. While a stratification across the jet width in the flow density, internal energy, magnetic field, or bulk flow velocity are usually invoked to explain the limb-brightening, the different jet structure detected at the two frequencies probably requires a stratification in the emitting electron energy distribution. Future dedicated numerical simulations will allow the determination of which combination of physical parameters are needed to reproduce the spine-sheath structure observed by Space-VLBI with RadioAstron in 3C 273.
Publisher: Cambridge University Press (CUP)
Date: 10-2013
DOI: 10.1017/S174392131400386X
Abstract: We observed an area of sky located within the SDSS Stripe 82 field at 1.6 GHz with the European VLBI Network (EVN). There are fifteen mJy/sub-mJy radio sources within the primary beam of a typical 30-m class EVN radio telescope. Our aim was to obtain information on compact radio structures of all VLBI-detectable sources within this primary beam area. The source of particular interest is the recently identified radio quasar J222843.54+011032.2 (J2228+0110) at z = 5.95. The data correlation was performed at the EVN software correlator at JIVE (SFXC). Three targets (J2228+0110, J222851.45+011203.4, J222941.76+011428.5) were detected, all three with position offsets not exceeding the 3σ accuracy of the original low-resolution radio surveys. The detection rate of 20% is consistent with other wide-field VLBI experiments carried out recently (e.g. Middelberg et al . 2013). The project presented here demonstrates the ability of EVN in multiple-phase-centre experiments and paves the way for future large-scale EVN surveys of compact structures in extragalactic radio sources using the multiple-phase-centre VLBI technique.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 03-2019
Abstract: The binary neutron star merger event GW170817 was observed with gravitational waves and across the electromagnetic spectrum. However, the physical processes that produced that emission remain poorly understood, particularly the late-time x-ray and radio emission. Ghirlanda et al. observed the radio afterglow with an interferometric array of 32 radio telescopes spread across the globe. The size and position of the radio source are not compatible with a uniformly expanding cocoon, as some have suggested. Instead, the data indicate that GW170817 produced a structured jet of material that escaped the surrounding ejecta and is now expanding into the interstellar medium at relativistic speeds. Science , this issue p. 968
Publisher: EDP Sciences
Date: 03-2014
Publisher: Springer Science and Business Media LLC
Date: 05-08-2008
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.56
Abstract: We present a software package for single-dish data processing of spacecraft signals observed with VLBI-equipped radio telescopes. The Spacecraft Doppler tracking (SDtracker) software allows one to obtain topocentric frequency detections with a sub-Hz precision and reconstructed and residual phases of the carrier signal of any spacecraft or landing vehicle at any location in the Solar System. These data products are estimated using the ground-based telescope’s highly stable oscillator as a reference, without requiring an a priori model of the spacecraft dynamics nor the downlink transmission carrier frequency. The software has been extensively validated in multiple observing c aigns of various deep space missions and is compatible with the raw s le data acquired by any standard VLBI radio telescope worldwide. In this paper, we report the numerical methodology of SDtracker, the technical operations for deployment and usage, and a summary of use cases and scientific results produced since its initial release.
Publisher: Oxford University Press (OUP)
Date: 07-04-2016
DOI: 10.1093/MNRAS/STW799
Publisher: WORLD SCIENTIFIC
Date: 16-11-2017
Publisher: Elsevier BV
Date: 11-2017
Publisher: Oxford University Press (OUP)
Date: 12-2000
Publisher: American Astronomical Society
Date: 04-2008
DOI: 10.1086/525025
Publisher: Zenodo
Date: 2021
Publisher: American Astronomical Society
Date: 07-2023
Abstract: We present results from the first 22 GHz space very long baseline interferometric (VLBI) imaging observations of M87 by RadioAstron. As a part of the Nearby AGN Key Science Program, the source was observed in 2014 February at 22 GHz with 21 ground stations, reaching projected ( u , v ) spacings up to ∼11 G λ . The imaging experiment was complemented by snapshot RadioAstron data of M87 obtained during 2013–2016 from the AGN Survey Key Science Program. Their longest baselines extend up to ∼25 G λ . For all of these measurements, fringes are detected only up to ∼2.8 Earth diameter or ∼3 G λ baseline lengths, resulting in a new image with angular resolution of ∼150 μ as or ∼20 Schwarzschild radii spatial resolution. The new image not only shows edge-brightened jet and counterjet structures down to submilliarcsecond scales but also clearly resolves the VLBI core region. While the overall size of the core is comparable to those reported in the literature, the ground-space fringe detection and slightly superresolved RadioAstron image suggest the presence of substructures in the nucleus, whose minimum brightness temperature exceeds T B , min ∼ 10 12 K. It is challenging to explain the origin of this record-high T B , min value for M87 by pure Doppler boosting effect with a simple conical jet geometry and known jet speed. Therefore, this can be evidence for more extreme Doppler boosting due to a blazar-like small jet viewing angle or highly efficient particle acceleration processes occurring already at the base of the outflow.
Publisher: Elsevier BV
Date: 1997
Publisher: Elsevier BV
Date: 11-2021
Publisher: EDP Sciences
Date: 26-04-2012
Publisher: Copernicus GmbH
Date: 23-09-2022
DOI: 10.5194/EPSC2022-342
Abstract: & class=& quot co_mto_htmlabstract mt-3& quot & & class=& quot co_mto_htmlabstract-affilitions& quot & & & The Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique utilize signal recording and processing technology developed originally for Very Long Baseline Interferometry (VLBI) to determine spacecraft lateral position in ICRF, as an extension of conventional radio-tracking techniques [1]. The essence of the PRIDE technique is in observing the spacecraft radio signal with a network of Earth-based radio telescopes. The PRIDE technique, developed at the Joint Institute for VLBI ERIC (JIVE), has been used for numerous experiments with several ESA planetary science missions. PRIDE has been selected by ESA as one of the eleven science experiments of the Jupiter Icy Moons Explorer (JUICE), the L-class mission scheduled for launch in 2023.& & & / & & class=& quot co_mto_htmlabstract-content mt-3& quot & & & & img src=& quot & quot alt=& quot & quot width=& quot & quot height=& quot & quot /& & & & & & strong& Figure 1: PRIDE Experiment for the JUICE Mission& /strong& & & & & The main observables of PRIDE are ultra-precise estimates of spacecraft lateral position based on the phase referenced VLBI tracking and radial Doppler measurements [3,7,8]. The methodology of PRIDE has been proven and validated with the ESA's Venus Express & Mars Express [1,2,4,7,8,9]. PRIDE will contribute to the determination of the JUICE spacecraft state vector and the improvement of the Galilean satellite ephemerides [4,5,10]. It is worth noticing the synergistic nature of PRIDE measurements to other key experiments of the JUICE mission, in particular addressing the major science goals of the mission.& & & & & & & & & & img src=& quot & quot alt=& quot & quot width=& quot & quot height=& quot & quot /& & & & & & strong& Figure 2: PRIDE Experiment Planning chart during the cruise phase of the JUICE Mission. Blue dots indicate celestial positions of radio sources with well-defined coordinates suitable for phase-referencing VLBI [reference on the Petrov's online catalogue]. Red dots show those potential reference sources located within 1 degree to the celestial track of the JUICE spacecraft.& /strong& & & & & The paper will describe the analysis and implementation of system engineering methodologies of the PRIDE inputs into the operational design of the JUICE mission. A particular emphasis will be given on cross instrumental analysis and consolidation of top synergies of PRIDE with other JUICE experiments using the ESA science planning tools. The paper will demonstrate advanced methods of efficient experiment planning and block scheduling. The identification of celestial areas of interest in near-field VLBI (PRIDE) observations of interplanetary spacecraft on all phases of their missions, especially during the cruise phase will also be covered in this paper.& & & & & strong& References& /strong& & & & & ) D. A. Duev. et al.: Spacecraft VLBI and Doppler tracking: algorithms and implementation, Astronomy & Astrophysics, 541, A43, 2012& & & & ) G. Molera Calves. et al.: Observations and analysis of phase scintillation of spacecraft signal on the interplanetary plasma& quot . In: A& A 564, A4, 2014& & & & ) D. A. Duev. et al.: Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique: A test case of the Mars Express Phobos fly-by, Astronomy & Astrophysics, Vol. 593, 2016& & & & ) Dirkx D. et al.: Dynamical modeling of the Galilean moons for the JUICE mission, Planetary and Space Science 134 (2016) 82& #8211 & & & & ) Dirkx D. et al.: On the contribution of PRIDE JUICE to Jovian system ephemerides, Planetary and Space Science, 14& #8211 , 2017& & & & ) G. Molera Calves. et al.: Analysis of an Interplanetary Coronal Mass Ejection by a Spacecraft Radio Signal: A Case Study, Space Weather, 15& & & & ) T. M. Bocanegra-Baham& #243 n. et al.: Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique: A test case of the Mars Express Phobos Flyby II. Doppler tracking: Formulation of observed and computed values, and noise budget, Astronomy & Astrophysics, 609, A59, 2018& & & & ) T. M. Bocanegra-Baham& #243 n. et al.: Venus Express radio occultation observed by PRIDE, Astronomy & Astrophysics, 624, A59, 2019& & & & ) G. Molera Calv& #233 s. Et a.: High spectral resolution multi-tone Spacecraft Doppler tracking software: Algorithms and implementations, Publications of the Astronomical Society of Australia (PASA), 2021& & & & ) Fayolle et al., Decoupled and coupled moons& #8217 ephemerides estimation strategies - Application to the JUICE mission, submitted to Planetary & Space Science, 2022& & & & & & & & & & & & & !-- COMO-HTML-CONTENT-END --& & / & & / &
Publisher: Cambridge University Press (CUP)
Date: 08-2009
DOI: 10.1017/S1743921310001663
Abstract: The presence of water has been considered for a long time as a key condition for life in planetary environments. The Cassini mission discovered water vapour in the Kronian system by detecting absorption of UV emission from a background star (Hansen et al . 2006). Prompted by this discovery, we started an observational c aign for search of another manifestation of the water vapour in the Kronian system, its maser emission at the frequency of 22 GHz (1.35 cm wavelength). Observations with the 32 m Medicina radio telescope (INAF-IRA, Italy) started in 2006 using Mk5A data recording and the JIVE-Huygens software correlator. Later on, an on-line spectrometer was used at Medicina. The 14 m Metsähovi radio telescope (TKK-MRO, Finland) joined the observational c aign in 2008 using a locally developed data capture unit and software spectrometer. More than 300 hours of observations were collected in 2006-2008 c aign with the two radio telescopes. The data were analysed at JIVE using the Doppler tracking technique to compensate the observed spectra for the radial Doppler shift for various bodies in the Kronian system (Pogrebenko et al . 2009). Here we report the observational results for Hyperion, Titan, Enceladus and Atlas, and their physical interpretation. Encouraged by these results we started a c aign of follow up observations including other radio telescopes.
Publisher: IOP Publishing
Date: 27-07-2023
Abstract: The Einstein Equivalence Principle (EEP) is a cornerstone of general relativity and predicts the existence of gravitational redshift. We report on new results of measuring this shift with RadioAstron (RA), a space very long baseline interferometry (VLBI) spacecraft launched into an evolving high eccentricity orbit around Earth with geocentric distances reaching 353 000 km. The spacecraft and ground tracking stations at Pushchino, Russia, and Green Bank, USA, were each equipped with a hydrogen maser frequency standard allowing a possible violation of the predicted gravitational redshift, in the form of a violation parameter ɛ , to be measured. By alternating between RA’s frequency referencing modes during dedicated sessions between 2015 and 2017, the recorded downlink frequencies can essentially be corrected for the non-relativistic Doppler shift. We report on an analysis using the Doppler-tracking frequency measurements made during these sessions and find ε = ( 2.1 ± 3.3 ) × 10 − 4 . We also discuss prospects for measuring ɛ with a significantly smaller uncertainty using instead the time-domain recordings of the spacecraft signals and envision how 10 −7 might be possible for a future space VLBI mission.
Publisher: American Astronomical Society
Date: 11-2004
DOI: 10.1086/424820
Publisher: Oxford University Press (OUP)
Date: 13-06-2011
Publisher: EDP Sciences
Date: 2018
DOI: 10.1051/0004-6361/201731524
Abstract: Context. Closed-loop Doppler data obtained by deep space tracking networks, such as the NASA Deep Space Network (DSN) and the ESA tracking station network (Estrack), are routinely used for navigation and science applications. By shadow tracking the spacecraft signal, Earth-based radio telescopes involved in the Planetary Radio Interferometry and Doppler Experiment (PRIDE) can provide open-loop Doppler tracking data only when the dedicated deep space tracking facilities are operating in closed-loop mode. Aims. We explain the data processing pipeline in detail and discuss the capabilities of the technique and its potential applications in planetary science. Methods. We provide the formulation of the observed and computed values of the Doppler data in PRIDE tracking of spacecraft and demonstrate the quality of the results using an experiment with the ESA Mars Express spacecraft as a test case. Results. We find that the Doppler residuals and the corresponding noise budget of the open-loop Doppler detections obtained with the PRIDE stations compare to the closed-loop Doppler detections obtained with dedicated deep space tracking facilities.
Publisher: EDP Sciences
Date: 2015
Publisher: Cambridge University Press (CUP)
Date: 09-2010
DOI: 10.1017/S1743921310016005
Abstract: The quasar J1819+3845 has shown extreme variability with flux density variations in the radio regime up to 600% in less than one hour. In case of intrinsic high varibility, the short time scale sets a limit on the size of the emitting region and allows to estimate its brightness temperature. This would exceed 10 21 K in the case of J1819+3845. Even an high relativistic jet beamed and doppler boosted in our line of sight cannot explain such an extreme violation of the Inverse Compton limit (10 12 K). The variability of this source has been proven to be due to scattering in the Interstellar medium by a number of different experiments. Such an explanation requires a closeby scattering screen (few parsecs) and it results in a brightness temperature of about 10 14 K. Many observing c aigns have been carried on to map the innermost jet structures of J1819+3845. Here we present the results of a number of VLBI observations, including space VLBI, to search for the missing jet in this puzzling source.
Publisher: EDP Sciences
Date: 04-2019
DOI: 10.1051/0004-6361/201833160
Abstract: Context . Radio occultation is a technique used to study planetary atmospheres by means of the refraction and absorption of a spacecraft carrier signal through the atmosphere of the celestial body of interest, as detected from a ground station on Earth. This technique is usually employed by the deep space tracking and communication facilities (e.g., NASA’s Deep Space Network (DSN), ESA’s Estrack). Aims . We want to characterize the capabilities of the Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique for radio occultation experiments, using radio telescopes equipped with Very Long Baseline Interferometry (VLBI) instrumentation. Methods . We conducted a test with ESA’s Venus Express (VEX), to evaluate the performance of the PRIDE technique for this particular application. We explain in detail the data processing pipeline of radio occultation experiments with PRIDE, based on the collection of so-called open-loop Doppler data with VLBI stations, and perform an error propagation analysis of the technique. Results . With the VEX test case and the corresponding error analysis, we have demonstrated that the PRIDE setup and processing pipeline is suited for radio occultation experiments of planetary bodies. The noise budget of the open-loop Doppler data collected with PRIDE indicated that the uncertainties in the derived density and temperature profiles remain within the range of uncertainties reported in previous Venus’ studies. Open-loop Doppler data can probe deeper layers of thick atmospheres, such as that of Venus, when compared to closed-loop Doppler data. Furthermore, PRIDE through the VLBI networks around the world, provides a wide coverage and range of large antenna dishes, that can be used for this type of experiments.
Publisher: Elsevier BV
Date: 08-2011
Publisher: EDP Sciences
Date: 14-01-2009
Publisher: Elsevier BV
Date: 2020
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-09-1998
DOI: 10.1126/SCIENCE.281.5384.1825
Abstract: High angular resolution images of extragalactic radio sources are being made with the Highly Advanced Laboratory for Communications and Astronomy (HALCA) satellite and ground-based radio telescopes as part of the Very Long Baseline Interferometry (VLBI) Space Observatory Programme (VSOP). VSOP observations at 1.6 and 5 gigahertz of the milli–arc-second–scale structure of radio quasars enable the quasar core size and the corresponding brightness temperature to be determined, and they enable the motions of jet components that are close to the core to be studied. Here, VSOP images of the gamma-ray source 1156+295, the quasar 1548+056, the ultraluminous quasar 0014+813, and the superluminal quasar 0212+735 are presented and discussed.
Publisher: Pleiades Publishing Ltd
Date: 03-2013
No related grants have been discovered for Leonid Gurvits.