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Resolved Magnetic-Field Structure and Variability Near the Event Horizon of Sagittarius A*
Michael D. Johnson, Vincent L. Fish, Sheperd S. Doeleman +45
Near a black hole, differential rotation of a magnetized accretion disk is thought to produce an instability that amplifies weak magnetic fields, driving accretion and outflow. The…
Limits on Foreground Subtraction from Chromatic Beam Effects in Global Redshifted 21 cm Measurements
Thomas J. Mozdzen, Judd D. Bowman, Raul A. Monsalve +1
Foreground subtraction in global redshifted 21 cm measurements is limited by frequency-dependent (chromatic) structure in antenna beam patterns. Chromatic beams couple angular stru…
Enhancing Low-Cost Ozone Spectrometers to Measure Mesospheric Winds and Tides
O. B. Alam, A. E. E. Rogers
Ground-based spectrometers have been developed to measure the concentration, velocity, and temperature of ozone in the mesosphere and lower thermosphere (MLT) using low-cost satell…
Quantifying ionospheric effects on time-domain astrophysics with the Murchison Widefield Array
Shyeh Tjing Loi, Tara Murphy, Martin E. Bell +39
Refraction and diffraction of incoming radio waves by the ionosphere induce time variability in the angular positions, peak amplitudes and shapes of radio sources, potentially comp…
Ionospheric modelling using GPS to calibrate the MWA. 1: Comparison of first order ionospheric effects between GPS models and MWA observations
B. S. Arora, J. Morgan, S. M. Ord +56
We compare first order (refractive) ionospheric effects seen by the Murchison Widefield Array (MWA) with the ionosphere as inferred from Global Positioning System (GPS) data. The f…
230 GHz VLBI observations of M87: event-horizon-scale structure at the enhanced very-high-energy -ray state in 2012
Kazunori Akiyama, Ru-Sen Lu, Vincent L. Fish +45
We report on 230 GHz (1.3 mm) VLBI observations of M87 with the Event Horizon Telescope using antennas on Mauna Kea in Hawaii, Mt. Graham in Arizona and Cedar Flat in California. F…