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H. Bushouse (STScI), F. Yusef-Zadeh, C. Heinke (Northwestern U), D. Roberts (Adler P/Northwestern U), S. Shapiro (UIUC), A. Goldwurm (CEA-Saclay)
While it has been known for a long time that Sgr A* shows variability at radio wavelengths, evidence for near-infrared and X-ray flares has appeared in just the past few years. A five-day monitoring campaign of the Galactic Center region undertaken in Fall 2004, using the Hubble Space Telescope (HST) and its Near Infrared Camera and Multi-Object Spectrometer (NICMOS), has confirmed the variability of Sgr A* at near-IR wavelengths. The photometric stability of the HST/NICMOS platform is ideal for detecting this type of low-level variability. Flare episodes have been detected in all three of the 1.60, 1.87, and 1.90 micron bands that were monitored and occupy 30-50% of the observed time periods, showing increases in emission levels of factors of 2--3 relative to the quiescent state. Individual flares have durations of 20--40 minutes, which is consistent with the near-IR emission being due to synchrotron emission arising from within the inner 10 Schwarzschild radii of Sgr A*. The data from this campaign has also been used to study the light curves of stellar sources within the Galactic Center region, as well as performing detailed measurements of the radial distribution of stellar sources around Sgr A*.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.