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5 pags., 7 figs. -- The Universe under the Microscope – Astrophysics at High Angular Resolution, 21–25 April 2008, Bad Honnef, Germany ; We report on recent near-infrared (NIR) and X-ray observations of Sagittarius A* (Sgr A*), the electromagnetic manifestation of the ∼4x106M⊙ super-massive black hole (SMBH) at the Galactic Center. The goal of these coordinated multi-wavelength observations is to investigate the variable emission from Sgr A* in order to obtain a better understanding of the underlying physical processes in the accretion flow/outflow. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope (July 2005, May 2007) and the ACIS-I instrument aboard the Chandra X-ray Observatory (July 2005). We report on a polarized NIR flare synchronous to a 8x1033 erg/s X-ray flare in July 2005, and a further flare in May 2007 that shows the highest sub-flare to flare contrast observed until now. The observations can be interpreted in the framework of a model involving a temporary disk with a short jet. In the disk component flux density variations can be explained due to hot spots on relativistic orbits around the central SMBH. The variations of the sub-structures of the May 2007 flare are interpreted as a variation of the hot spot structure due to differential rotation within the disk. © 2008 IOP Publishing Ltd. ; Part of this work was supported by the German Deutsche Forschungsgemeinschaft, DFG via grant SFB 494. L. Meyer, K. Muzic, M. Zamaninasab, D. Kunneriath, and R.-S. Lu, are members of the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the MPIfR and the Universities of Bonn and Cologne. RS acknowledges support by the Ramon y Cajal programme by the Ministerio de Ciencia y Innovación of the government of Spain.

7 pags., 3 figs. -- The Universe under the Microscope – Astrophysics at High Angular Resolution, 21–25 April 2008, Bad Honnef, Germany ; At the center of the Milky Way, with a distance of 8 kpc, the compact source Sagittarius A* (SgrA*) can be associated with a super massive black hole of 4x 106M⊙. SgrA* shows strong variability from the radio to the X-ray wavelength domains. Here we report on simultaneous NIR/sub-millimeter/X-ray observations from May 2007 that involved the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope, the Australian Telescope Compact Array (ATCA), the US mm-array CARMA, the IRAM 30m mm-telescope, and other telescopes. We concentrate on the time series of mm/sub-mm data from CARMA, ATCA, and the MAMBO bolometer at the IRAM 30m telescope. © 2008 IOP Publishing Ltd. ; Part of this work was supported by the German Deutsche Forschungsgemeinschaft, DFG via grant SFB 494. L. Meyer, K. Muzic, M. Zamaninasab, D. Kunneriath, and R.-S. Lu, are members of the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the MPIfR and the Universities of Bonn and Cologne. RS acknowledges support by the Ramon y Cajal programme by the Ministerio de Ciencia y Innovacion of the government of Spain.