Far Infrared Variability of Sagittarius A^*: 25.5 Hours of Monitoring with Herschel

Variable emission from Sgr A^*, the luminous counterpart to the super-massive black hole at the center of our Galaxy, arises from the innermost portions of the accretion flow. Better characterization of the variability is important for constraining models of the low-luminosity accretion mode powering Sgr A^*, and could further our ability to use variable emission as a probe of the strong gravitational potential in the vicinity of the 4 x 10^6M_⊙ black hole. We use the Herschel Spectral and Photometric Imaging Receiver (SPIRE) to monitor Sgr A* at wavelengths that are difficult or impossible to observe from the ground. We find highly significant variations at 0.25, 0.35, and 0.5 mm, with temporal structure that is highly correlated across these wavelengths. While the variations correspond to