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Stochastic Optics: A Scattering Mitigation Framework for Radio Interferometric Imaging
Michael D. Johnson
Just as turbulence in the Earth's atmosphere can severely limit the angular resolution of optical telescopes, turbulence in the ionized interstellar medium fundamentally limits the…
Observing---and Imaging---Active Galactic Nuclei with the Event Horizon Telescope
Vincent L. Fish, Kazunori Akiyama, Katherine L. Bouman +7
Originally developed to image the shadow region of the central black hole in Sagittarius A* and in the nearby galaxy M87, the Event Horizon Telescope (EHT) provides deep, very high…
The Optics of Refractive Substructure
Michael D. Johnson, Ramesh Narayan
Newly recognized effects of refractive scattering in the ionized interstellar medium have broad implications for very long baseline interferometry (VLBI) at extreme angular resolut…
High Resolution Linear Polarimetric Imaging for the Event Horizon Telescope
Andrew A. Chael, Michael D. Johnson, Ramesh Narayan +3
Images of the linear polarization of synchrotron radiation around Active Galactic Nuclei (AGN) identify their projected magnetic field lines and provide key data for understanding…
RadioAstron Observations of the Quasar 3C273: a Challenge to the Brightness Temperature Limit
Y. Y. Kovalev, N. S. Kardashev, K. I. Kellermann +17
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of K. Relativistic boosting can increase its observed value, but apparent…
Interstellar Scintillation and the Radio Counterpart of the Fast Radio Burst FRB150418
Kazunori Akiyama, Michael D. Johnson
Keane et al. (2016) have recently reported the discovery of a new fast radio burst, FRB150418, with a promising radio counterpart at 5.5 and 7.5 GHz -- a rapidly decaying source, f…
Modeling Seven Years of Event Horizon Telescope Observations with Radiatively Inefficient Accretion Flow Models
Avery E. Broderick, Vincent L. Fish, Michael D. Johnson +6
An initial three-station version of the Event Horizon Telescope, a millimeter-wavelength very-long baseline interferometer, has observed Sagittarius A* (Sgr A*) repeatedly from 200…
Extreme Brightness Temperatures and Refractive Substructure in 3C273 with RadioAstron
Michael D. Johnson, Yuri Y. Kovalev, Carl R. Gwinn +8
Earth-space interferometry with RadioAstron provides the highest direct angular resolution ever achieved in astronomy at any wavelength. RadioAstron detections of the classic quasa…
Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales
Vincent L. Fish, Michael D. Johnson, Sheperd S. Doeleman +69
The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve the 1.3 mm emission from this source on…
Probing the magnetic field structure in Sgr A* on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations
Roman Gold, Jonathan C. McKinney, Michael D. Johnson +1
Magnetic fields are believed to drive accretion and relativistic jets in black hole accretion systems, but the magnetic-field structure that controls these phenomena remains uncert…
Testing General Relativity with the Shadow Size of Sgr A*
Tim Johannsen, Avery E. Broderick, Philipp M. Plewa +7
In general relativity, the angular radius of the shadow of a black hole is primarily determined by its mass-to-distance ratio and depends only weakly on its spin and inclination. I…
The Intrinsic Shape of Sagittarius A* at 3.5-mm Wavelength
Gisela N. Ortiz-León, Michael D. Johnson, Sheperd S. Doeleman +19
The radio emission from Sgr A is thought to be powered by accretion onto a supermassive black hole of at the Galactic Center. At millimete…