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Short-term variability of Sgr A*

Published online by Cambridge University Press:  01 August 2006

M. R. Morris ,
S. D. Hornstein ,
A. M. Ghez ,
J. R. Lu ,
K. Matthews  and
F. K. Baganoff
M. R. Morris
Affiliation:
Dept. of Physics & Astronomy, Univ. of California, Los Angeles, CA 90095-1547, USA email: [email protected]
S. D. Hornstein
Affiliation:
Dept. of Physics & Astronomy, Univ. of California, Los Angeles, CA 90095-1547, USA email: [email protected]
A. M. Ghez
Affiliation:
Dept. of Physics & Astronomy, Univ. of California, Los Angeles, CA 90095-1547, USA email: [email protected]
J. R. Lu
Affiliation:
Dept. of Physics & Astronomy, Univ. of California, Los Angeles, CA 90095-1547, USA email: [email protected]
K. Matthews
Affiliation:
Caltech Optical Observatories, California Institute of Technology, Mail Code 105-24, Pasadena, CA 91125, USA
F. K. Baganoff
Affiliation:
Center for Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Abstract

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Observations of Sgr A* over the past 4 years with the Keck Telescope in the near-infrared, coupled with millimeter and submillimeter observations, show that the 3.7×106M⊙ Galactic Black Hole, Sagittarius A*, displays continuous variability at all these wavelengths, with the variability power concentrated on characteristic time scales of a few hours, and with a variability fraction that increases with wavelength. We review the observations indicating that the few-hour time scale for variability is reproduced at all accessible wavelengths. Interpreted as a dynamical time, this time scale corresponds to a radial distance of 2 AU, or ∼25 Schwarzschild radii. Searches for quasi-periodicities in the near-infrared data from the Keck Telescope have so far been negative. One interpretation of the character of these variations is that they result from a recurring disk instability, rather than from variations in the mass accretion rate flowing through the outer boundary of the emission region. However, neither a variable accretion rate nor a mechanism associated with a jet can presently be ruled out.

Keywords

Galaxy: nucleus – black hole physics – accretion disks
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S238: Black Holes from Stars to Galaxies – Across the Range of Masses , August 2006 , pp. 195 - 200
Copyright
Copyright © International Astronomical Union 2007

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