RadioAstron as a target and as an instrument: Enhancing the Space VLBI mission’s scientific output

Duev, Dmitry A.; Zakhvatkin, M. V.; Stepanyants, V. A.; Calvés, Guifre Molera; Pogrebenko, S. V.; Gurvits, L. I.; Cimò, G.; Bahamon, T.M. Bocanegra

doi:10.1051/0004-6361/201424940

Cited by 15 publications

(15 citation statements)

References 10 publications

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“…2. These slowly evolving residuals agree well with the expected accuracy of the orbital velocity determination for the SRT (Kardashev et al 2013), but they still should be viewed only as an indicator of the fidelity of the fringe fitted data, while a more detailed discussion of the accuracy of the orbit determination for the SRT is presented elsewhere (Duev et al 2015).…”

Section: Fringe Fittingsupporting

confidence: 76%

“…The accuracy can be further enhanced by simultaneous VLBI measurements performed on the narrow-band downlink signal from the spacecraft (Duev et al 2012). This was demonstrated (Duev et al 2015) using the data from the ESP observations of 0642+449 discussed here.…”

Section: Imaging With Radioastronmentioning

confidence: 85%

“…The main perigee imaging segment, GK047A (raes12a; 10:00 UT/09/03-01:00 UT/10/03) was complemented by VLBI observations of the satellite downlink signal at 8.4 GHz (segment GK047B) made for the purpose of improving the Spektr-R orbit determination (Duev et al 2015). The third segment, GK047C (raes12b; 14:00 UT/10/03-15:00 UT/10/03) was introduced as a long-baseline tracking segment.…”

Section: Radioastron Observation Of 0642+449mentioning

confidence: 99%

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RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

Lobanov

Gómez

Bruni

et al. 2015

A&A

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Context. Polarization of radio emission in extragalactic jets at a sub-milliarcsecond angular resolution holds important clues for understanding the structure of the magnetic field in the inner regions of the jets and in close vicinity of the supermassive black holes in the centers of active galaxies. Aims. Space VLBI observations provide a unique tool for polarimetric imaging at a sub-milliarcsecond angular resolution and studying the properties of magnetic field in active galactic nuclei on scales of less than 10 4 gravitational radii. Methods. A space VLBI observation of high-redshift quasar TXS 0642+449 (OH 471), made at a wavelength of 18 cm (frequency of 1.6 GHz) as part of the early science programme (ESP) of the RadioAstron mission, is used here to test the polarimetric performance of the orbiting Space Radio Telescope (SRT) employed by the mission, to establish a methodology for making full Stokes polarimetry with space VLBI at 1.6 GHz, and to study the polarized emission in the target object on sub-milliarcsecond scales. Results. Polarization leakage of the SRT at 18 cm is found to be within 9% in amplitude, demonstrating the feasibility of high fidelity polarization imaging with RadioAstron at this wavelength. A polarimetric image of 0642+449 with a resolution of 0.8 mas (signifying an ∼4 times improvement over ground VLBI observations at the same wavelength) is obtained. The image shows a compact corejet structure with low (≈2%) polarization and predominantly transverse magnetic field in the nuclear region. The VLBI data also uncover a complex structure of the nuclear region, with two prominent features possibly corresponding to the jet base and a strong recollimation shock. The maximum brightness temperature at the jet base can be as high as 4 × 10 13 K.

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Section: Fringe Fittingsupporting

confidence: 76%

Section: Imaging With Radioastronmentioning

confidence: 85%

Section: Radioastron Observation Of 0642+449mentioning

confidence: 99%

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RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

Lobanov

Gómez

Bruni

et al. 2015

A&A

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“…The solutions are consistent between the two IF bands, and the likely effect of the satellite acceleration is reflected both in the time variations of the fringe delays and in the respective delay rates. The overall behavior of the fringe solutions is in agreement with the expected accuracy of the orbital position and velocity determination (Kardashev et al 2013;Duev et al 2015;Lobanov et al 2015).…”

Section: Fringe Fittingsupporting

confidence: 79%

Multiband RadioAstron space VLBI imaging of the jet in quasar S5 0836+710

Vega-García

Lobanov

Perucho

et al. 2020

A&A

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Context. Detailed studies of relativistic jets in active galactic nuclei (AGN) require high-fidelity imaging at the highest possible resolution. This can be achieved using very long baseline interferometry (VLBI) at radio frequencies, combining worldwide (global) VLBI arrays of radio telescopes with a space-borne antenna on board a satellite. Aims. We present multiwavelength images made of the radio emission in the powerful quasar S5 0836+710, obtained using a global VLBI array and the antenna Spektr-R of the RadioAstron mission of the Russian Space Agency, with the goal of studying the internal structure and physics of the relativistic jet in this object. Methods. The RadioAstron observations at wavelengths of 18 cm, 6 cm, and 1.3 cm are part of the Key Science Program for imaging radio emission in strong AGN. The internal structure of the jet is studied by analyzing transverse intensity profiles and modeling the structural patterns developing in the flow. Results. The RadioAstron images reveal a wealth of structural detail in the jet of S5 0836+710 on angular scales ranging from 0.02 mas to 200 mas. Brightness temperatures in excess of 10 13 K are measured in the jet, requiring Doppler factors of ≥ 100 for reconciling them with the inverse Compton limit. Several oscillatory patterns are identified in the ridge line of the jet and can be explained in terms of the Kelvin-Helmholtz (KH) instability. The oscillatory patterns are interpreted as the surface and body wavelengths of the helical mode of the KH instability. The interpretation provides estimates of the jet Mach number and of the ratio of the jet to the ambient density, which are found to be M j ≈ 12 and η ≈ 0.33. The ratio of the jet to the ambient density should be conservatively considered an upper limit because its estimate relies on approximations.

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“…In the EHI concept we consider a different approach in which the baseline vector and its time derivatives are obtained (measured) directly between the EHI spacecraft in real time. As demonstrated by RadioAstron, orbit determination measurements (not to confuse with orbit reconstruction) are provided by means of radio measurements at the level that correspond to ∼ 20 to 1500 observing wavelengths at 92 to 1.3 cm, respectively, and radial velocity (Doppler) measurements at the mm/s accuracy level (Zakhvatkin et al 2014;Duev et al 2015). Escalating similar requirements for the EHI sub-mm wavelength range leads to the baseline measurement re-quirements at a precision level of ∼ 20 cm for the baseline vector and 0.01 mm/s for its time derivative.…”

Section: Martinmentioning

confidence: 99%

Simulations of imaging the event horizon of Sagittarius A* from space

Roelofs

Falcke

Brinkerink

et al. 2019

A&A

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Context. It has been proposed that Very Long Baseline Interferometry (VLBI) at sub-millimeter waves will allow us to image the shadow of the black hole in the center of our Milky Way, Sagittarius A* (Sgr A*), and thereby test basic predictions of the theory of general relativity. Aims. This paper presents imaging simulations of a new Space VLBI (SVLBI) mission concept. An initial design study of the concept has been presented in the form of the Event Horizon Imager (EHI). The EHI may be suitable for imaging Sgr A* at high frequencies (up to ∼ 690 GHz), which has significant advantages over performing ground-based VLBI at 230 GHz. The concept EHI design consists of two or three satellites in polar or equatorial circular Medium-Earth Orbits (MEOs) with slightly different radii. Due to the relative drift of the satellites along the individual orbits over the course of several weeks, this setup will result in a dense spiral-shaped uv-coverage with long baselines (up to ∼ 60 Gλ), allowing for extremely high-resolution and high-fidelity imaging of radio sources. Methods. We simulate observations of general relativistic magnetohydrodynamics (GRMHD) models of Sgr A* for the proposed configuration and calculate the expected noise based on preliminary system parameters. On long baselines, where the signal-to-noise ratio may be low, fringes could be detected if the system is sufficiently phase stable and the satellite orbits can be reconstructed with sufficient accuracy. Averaging visibilities accumulated over multiple epochs of observations could then help improving the image quality. With three satellites instead of two, closure phases could be used for imaging. Results. Our simulations show that the EHI could be capable of imaging the black hole shadow of Sgr A* with a resolution of 4 µas (about 8 % of the shadow diameter) within several months of observing time. Conclusions. Our preliminary study of the EHI concept shows that it is potentially of high scientific value, as it could be used to measure black hole shadows much more precisely than with ground-based VLBI, allowing for stronger tests of General Relativity and accretion models.

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RadioAstron as a target and as an instrument: Enhancing the Space VLBI mission’s scientific output

Cited by 15 publications

References 10 publications

RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

Multiband RadioAstron space VLBI imaging of the jet in quasar S5 0836+710

Simulations of imaging the event horizon of Sagittarius A* from space

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