TY - JOUR
T1 - Simulations of imaging the event horizon of Sagittarius A∗ from space
AU - Roelofs, Freek
AU - Falcke, Heino
AU - Brinkerink, Christiaan
AU - Móscibrodzka, Monika
AU - Gurvits, Leonid I.
AU - Martin-Neira, Manuel
AU - Kudriashov, Volodymyr
AU - Klein-Wolt, Marc
AU - Tilanus, Remo
AU - Kramer, Michael
AU - Rezzolla, Luciano
N1 - Funding Information:
Acknowledgements. This work is supported by the ERC Synergy Grant “Black-HoleCam: Imaging the Event Horizon of Black Holes” (Grant 610058). We thank Andrew Chael and Katie Bouman for making the eht-imaging software publicly available, and for providing the code for regridding and aligning the images and calculating the NRMSE. The design study was the result of a colloquium on space interferometry by H. Falcke at ESTEC on Sep 2, 2015 and an internal ESA study organized by M. Martin-Neira. We are grateful to the anonymous referee for useful and constructive comments. M. Mos´cibrodzka acknowledges H. Shiokawa for providing the HARM3D GRMHD simulation data used in our ray-tracing simulations. We thank Alan Roy, Michael Bremer, Jason Dexter, Itziar Barat, Thijs de Graauw, Vincent Fish, Andrey Baryshev, André Young, and Daniel Palumbo for useful comments and discussions on this work.
Publisher Copyright:
© ESO 2019.
PY - 2019
Y1 - 2019
N2 - Context. It has been proposed that Very Long Baseline Interferometry (VLBI) at submillimeter 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 ∼60Gλ), allowing for extremely high-resolution and high-fidelity imaging of radio sources. Methods. We simulated 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-tonoise ratio may be low, fringes could be detected assuming that 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. Conclusion. Our preliminary study of the EHI concept shows that it is potentially of high scientific value. 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.
AB - Context. It has been proposed that Very Long Baseline Interferometry (VLBI) at submillimeter 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 ∼60Gλ), allowing for extremely high-resolution and high-fidelity imaging of radio sources. Methods. We simulated 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-tonoise ratio may be low, fringes could be detected assuming that 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. Conclusion. Our preliminary study of the EHI concept shows that it is potentially of high scientific value. 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.
KW - Accretion, accretion disks
KW - Galaxy: Center
KW - Techniques: Interferometric
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U2 - 10.1051/0004-6361/201732423
DO - 10.1051/0004-6361/201732423
M3 - Article
AN - SCOPUS:85071294966
VL - 625
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
SN - 0004-6361
M1 - A124
ER -