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 doeleman-astroph.tex ApJ, 2009, 695, 59
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\begin{document}
\slugcomment{Version 4.01: \today}
\shorttitle{Sgr A* Flare Detection with VLBI}
%
\shortauthors{Doeleman et al.}
%
\title{Detecting Flaring Structures in Sagittarius A* with High-Frequency VLBI}
%
\author{
%
Sheperd S.~Doeleman\altaffilmark{1},
%
Avery E.~Broderick\altaffilmark{2},
%
Alan E.~E.~Rogers\altaffilmark{1}}
   Observatory, Route 40, Westford, MA 01886.}
%
\altaffiltext{2}{Canadian Institute for Theoretical Astrophysics,
   University of Toronto, 60 St.\ George St., Toronto, ON, M5S 3H8
   Canada.}
%
\altaffiltext{3}{Institute for Theory and Computation, Harvard
   University, Center for Astrophysics, 60 Garden St., Cambridge, MA
   02138.}

\begin{abstract}
The super-massive black hole candidate, Sagittarius A*, exhibits
variability from radio to X-ray wavelengths on timescales that
correspond to < 10 Schwarzschild radii.  We survey the potential of
millimeter wavelength very long baseline interferometry (VLBI) to
detect and constrain time-variable structures that could give rise to
such variations, focusing on a model in which an orbiting hot spot is
embedded in an accretion disk.  Nonimaging algorithms are developed
that use interferometric closure quantities to test for periodicity,
and applied to an ensemble of hot spot models that sample a range of
parameter space.  We find that structural periodicity in a wide range
of cases can be detected on most potential VLBI arrays using modern
VLBI instrumentation.  Future enhancements of millimeter/submillimeter
VLBI arrays including phased-array processors to aggregate VLBI
station collecting area, increased bandwidth recording, and addition
of new VLBI sites all significantly aid periodicity detection.  The
methods described herein can be applied to other models of
Sagittarius A*, including jet outflows and magnetohydrodynamic
accretion simulations.
\end{abstract}
\keywords{black hole physics --- Galaxy: center --- techniques:
   interferometric --- submillimeter --- accretion, accretion disks}