An X-ray, IR, and Submillimeter Flare of Sagittarius A*
Abstract
Energetic flares are observed in the Galactic supermassive black hole Sagittarius A* from radio to X-ray wavelengths. On a few occasions, simultaneous flares have been detected in IR and X-ray observations, but clear counterparts at longer wavelengths have not been seen. We present a flare observed over several hours on July 17, 2006 with the Chandra X-ray Observatory, the Keck II telescope, the Caltech Submillimeter Observatory, and the Submillimeter Array. All telescopes observed strong flare events, but the submillimeter peak is found to occur nearly 100 minutes after the X-ray peak. Submillimeter polarization data show a polarization signature in the excess flare emission, increasing from 9% to 17% fractional polarization as the flare passes through its peak, consistent with a transition from optically thick to thin synchrotron emission. The temporal and spectral behavior of the flare requires that the energetic electrons responsible for the emission cool faster than expected from their radiative output. This is consistent with adiabatic cooling in an expanding emission region, with X-rays produced through self-Compton scattering. We also present the submillimeter detection of an IR flare on July 31, 2005, which showed a larger peak IR flux and similar submillimeter flux but did not have measurable X-ray emission. This flare also shows a delay between the IR peak and submillimeter peak, although it is significantly shorter. The submillimeter lag and the variable ratio of IR and X-ray luminosities are related through a synchrotron and self-Compton model.Keywords
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