The center of the milky way from radio to X-rays

Abstract

We summarize basic observational results on Sagittarius A∗ obtained from the radio, infrared and X-ray domain. Infrared observations have revealed that a dusty S-cluster object (DSO/G2) passes by SgrA within ∼120 AU, the central super-massive black hole of the Milky Way. It is still expected that this event will give rise to exceptionally intense activity in the entire electromagnetic spectrum. Based on February to September 2014 SINFONI observations the detection of a spatially compact and red-shifted hydrogen recombination line emission allowed us to obtain a new estimate of the orbital parameters of the DSO.We have not detected strong pre-peribothron blueshifted nor post-peribothron red-shifted emission above the noise level at the position of SgrA or upstream the orbit. The peribothron position was reached in May 2014. Our 2004-2012 infrared polarization statistics show that SgrA must be a very stable system - both in terms of the geometrical orientation of a jet or accretion disk and in terms of the variability spectrum which must be linked to the accretion rate. Hence, polarization and variability measurements are the ideal tools to probe for any change in the system as a function of the DSO/G2 fly-by. Due to the 2014 fly-by of the DSO, an increased accretion activity of SgrA may still be upcoming. Future observations of bright flares will improve the derivation of the spin and the inclination of the SMBH from NIR/sub-mm observations.