arXiv subjects

Manuel Martin-Neira

Publications and source records attributed to Manuel Martin-Neira.

3 recordsLinked to original sources

arXiv2026

Instrument-Level Validation of Upper Sideband Syntonization Concept

Upper Sideband Syntonization (USBS) is a two-way frequency-transfer concept proposed by the European Space Agency for distributed space radio interferometric systems. Previous investigations validated the concept primarily through frequency-stability and phase-transfer measurements. This work demonstrates the first end-to-end instrument-level validation of the USBS concept through coherent W-band cross-correlation measurements and image reconstruction. A P=2 USBS breadboard was integrated with a W-band radio interferometer developed for this test. The synchronized local oscillators (LOs) were evaluated through long-term cross-correlation measurements and coherent imaging of a point-like noise source. The results were compared with those obtained using a conventional common LO as well as two independent free-running LOs. The USBS-derived LOs maintained coherence over 500 s of cumulative effective integration time acquired over approximately five days of elapsed time and preserved inter-session phase stability over measurements spanning 40 days. The reconstructed image is nearly indistinguishable from that obtained with a common LO, whereas independent free-running LOs lead to severe coherence degradation, image distortion, and approximately 38 dB loss of peak response. The results demonstrate that USBS preserves the interferometric coherence required for W-band imaging and present the first end-to-end instrument-level validation of the USBS syntonization concept for future distributed space radio interferometric missions

astro-ph.IM↗

arXiv2020

On the prospects of imaging Sagittarius A* from space

Very Long Baseline Interferometry (VLBI) at sub-millimeter waves has the potential to image the shadow of the black hole in the Galactic Center, Sagittarius A* (Sgr A*), and thereby test basic predictions of the theory of general relativity. We investigate the imaging prospects of a new Space VLBI mission concept. The setup consists of two satellites in polar or equatorial circular Medium-Earth Orbits with slightly different radii, resulting in a dense spiral-shaped uv-coverage with long baselines, allowing for extremely high-resolution and high-fidelity imaging of radio sources. We simulate observations of a general relativistic magnetohydrodynamics model of Sgr A* for this configuration with noise calculated from model system parameters. After gridding the $uv$-plane and averaging visibilities accumulated over multiple months of integration, images of Sgr A* with a resolution of up to 4 $μ$as could be reconstructed, allowing for stronger tests of general relativity and accretion models than with ground-based VLBI.

astro-ph.IM↗

arXiv2019

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

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 general relativity. This paper presents imaging simulations of a new Space VLBI mission concept. An initial design study of the concept has been presented as 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 with slightly different radii. Due to the relative drift of the satellites along the individual orbits, this setup will result in a dense spiral-shaped uv-coverage with long baselines (up to ~60 Glambda), allowing for extremely high-resolution and high-fidelity imaging of radio sources. We simulate EHI observations of general relativistic magnetohydrodynamics models of Sgr A* 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, closure phases could be used for imaging. Our simulations show that the EHI could be capable of imaging the black hole shadow of Sgr A* with a resolution of 4 uas (about 8% of the shadow diameter) within several months of observing time. The EHI concept could thus 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.

astro-ph.HE↗