Probing Dynamical Activity of Sgr A* Using VLBI Closure Quantities

Abstract

Sagittaruis A* is the name given to the compact radio source at the center of the Milky Way. In 1994 Narayan et al. noted that the source exhibited relatively low luminosity for the large amount of mass it was accreting. They posited that this could be resolved with the black hole model for accretion in which most of the energy was absorbed by the black hole rather than being released as radiation. In 1998, using the Keck 10m telescope to measure the proper motion of stars around the galactic core, Ghez et al. were able to determine constraints for size and mass of the object that aligned with the characteristics of a massive black hole. With more refined calculations, these key observations amongst others provide strong evidence to suggest Sagittarius A* is a supermassive black hole. Given its relative proximity and mass, Sgr A* has the largest angular event horizon of any black hole, making it ideal for further analysis. Millimeter VLBI observations of Sgr A* performed with the Event Horizon Telescope (EHT) demonstrate the existence of structural variation on timescales that correspond to the Schwarzchild radius. The ability to resolve both the spatial and temporal structures on event horizon scales suggests many applications for testing General Relativity in very strong gravitation fields. In preparation for higher-resolution submillimeter VLBI data coming in the next 6 months, we explore closure amplitude and phase signatures of simulated GRMHD movies. These valuable plots allow us to determine important values such as Sag A*?s angle of orientation and the amount of accreted matter there is around. By synthesizing and analyzing data ahead of time, we will be more apt to understand what is going on when the real data comes through. This paper discusses synthesized observations and how to interpret the true VLBI data when it becomes available in early 2015. Research Supervisors: Sheperd Doeleman, Michael Johnson