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 chandra_sgra_02.tex Nature, 413, 45 (2001)
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% astro-ph/0109367
\documentclass[preprint]{aastex}

\begin{document}

\title{Rapid X-ray flaring from the direction of the supermassive
black hole at the Galactic Centre}

\author{F.~K.~Baganoff\altaffilmark{1}, M.~W.~Bautz\altaffilmark{1},
W.~N.~Brandt\altaffilmark{2}, G.~Chartas\altaffilmark{2},
E.~D.~Feigelson\altaffilmark{2}, G.~P.~Garmire\altaffilmark{2},
Y.~Maeda\altaffilmark{2,3}, M.~Morris\altaffilmark{4},
G.~R.~Ricker\altaffilmark{1}, L.~K.~Townsley\altaffilmark{2}, and
F.~Walter\altaffilmark{5}}

\altaffiltext{1}{Center for Space Research, Massachusetts Institute of
  Technology, Cambridge, MA 02139-4307, USA}
\altaffiltext{2}{Department of Astronomy and Astrophysics, Pennsylvania
  State University, University Park, PA 16802-6305, USA}
\altaffiltext{3}{Institute of Space and Astronautical Science, 3-1-1
  Yoshinodai, Sagamihara, 229-8501, Japan}
\altaffiltext{4}{Department of Physics and Astronomy, University of California
  at Los Angeles, Los Angeles, CA 90095-1562, USA}
\altaffiltext{5}{Department of Astronomy, California Institute of
  Technology, Pasadena, CA 91125, USA}

\begin{abstract}

Most galactic nuclei are now believed to harbour supermassive black
holes.  Studies of stellar motions in the central few light-years of
our Milky Way Galaxy indicate the presence of a dark object with a
mass of about 2.6 million solar masses.  This object is spatially
coincident with Sagittarius~A* (Sgr~A*), the unique compact radio
source located at the dynamical centre of our Galaxy.  By analogy with
distant quasars and nearby active galactic nuclei (AGN), Sgr~A* is
thought to be powered by the gravitational potential energy released
by matter as it accretes onto a supermassive black hole.  However,
Sgr~A* is much fainter than expected in all wavebands, especially in
X-rays, casting some doubt on this model.  Recently, we reported the
first strong evidence of X-ray emission from Sgr~A*.  Here we report
the discovery of rapid X-ray flaring from the direction of Sgr~A*.
These data provide compelling evidence that the X-ray emission is
coming from accretion onto a supermassive black hole at the Galactic
Centre, and the nature of the variations provides strong constraints
on the astrophysical processes near the event horizon of the black
hole.

\end{abstract}

\end{document}