title: Detection of the intrinsic size of Sagittarius A* through closure amplitude imaging.
abstract: We have detected the intrinsic size of Sagittarius A*, the Galactic center radio source associated with a supermassive black hole, showing that the short-wavelength radio emission arises from very near the event horizon of the black hole. Radio observations with the Very Long Baseline Array show that the source has a size of 24 +/- 2 Schwarzschild radii at 7-millimeter wavelength. In one of eight 7-millimeter epochs, we also detected an increase in the intrinsic size of 60(-17)(+25)%. These observations place a lower limit to the mass density of Sagittarius A* of 1.4 x 10(4) solar masses per cubic astronomical unit.
authors.affiliation: Astronomy Department and Radio Astronomy Laboratory, University of California, Berkeley, CA 94720, USA. gbower@astro.berkeley.edu
authors.forename: Geoffrey C
authors.initials: GC
authors.lastname: Bower
authors.forename: Heino
authors.initials: H
authors.lastname: Falcke
authors.forename: Robeson M
authors.initials: RM
authors.lastname: Herrnstein
authors.forename: Jun-Hui
authors.initials: JH
authors.lastname: Zhao
authors.forename: W M
authors.initials: WM
authors.lastname: Goss
authors.forename: Donald C
authors.initials: DC
authors.lastname: Backer