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Abstract: Stellar dynamics indicate the presence of a super massive 3-4x10^6 Msun solmblack hole at the Galactic Center. It is associated with the variable radio,near-infrared, and X-ray counterpart Sagittarius A* SgrA*. The goal is theinvestigation and understanding of the physical processes responsible for thevariable emission from SgrA*. The observations have been carried out using theNACO adaptive optics AO instrument at the European Southern Observatory-sVery Large Telescope July 2005, May 2007 and the ACIS-I instrument aboard theChandra X-ray Observatory July 2005. We find that for the July 2005 flare thevariable and polarized NIR emission of SgrA* occurred synchronous with amoderately bright flare event in the X-ray domain with an excess 2 - 8 keVluminosity of about 8x10^33erg-s. We find no time lag between the flare eventsin the two wavelength bands with a lower limit of less than 10 minutes. The May2007 flare shows the highest sub-flare to flare contrast observed until now. Itprovides evidence for a variation in the profile of consecutive sub-flares. Weconfirm that highly variable and NIR polarized flare emission is non-thermaland that there exists a class of synchronous NIR-X-ray flares. We find that theflaring state can be explained via the synchrotron self-Compton SSC processinvolving up-scattered sub-millimeter photons from a compact source component.The observations can be interpreted in a model involving a temporary disk witha short jet. In the disk component the flux density variations can be explaineddue to spots on relativistic orbits around the central super massive black holeSMBH. The profile variations for the May 2007 flare are interpreted as avariation of the spot structure due to differential rotation within the disk.



Author: A. Eckart, F.K. Baganoff, M. Zamaninasab, M. Morris, R. Schoedel, L. Meyer, K. Muzic, M.W. Bautz, W.N. Brandt, G.P. Garmire, G.R.

Source: https://arxiv.org/







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