A Detection of Sgr A* in the Far Infrared
This paper reports on the first ever dectection of the variable emission of Sgr A* in the far infrared regime, at wavelengths 160 and 100 microns.
We've used over 40 hours of Herschel Galactic Center observations to obtain these images.
Above: The detection in the differential light curves: as the flare peaks you can see a bright point pop up in the maps above. That's Sgr A*!
Right: With this flux measurement we can constrain the Spectral Energy Distribution (SED) of Sgr A* in the far infrared.
The space craft that took these measurements is decommissioned now, and our measurements will remain the only ones for decades to come!
Scientific Abstract
We report the first detection of the Galactic Center massive black hole, Sgr A*, at 100 μm and 160 μm. Our measurements were obtained with PACS on board the Herschel satellite. While the warm dust in the Galactic Center is too bright to allow for a direct detection of Sgr A*, we measure a significant and simultaneous variation of its flux of and during one observation. The significance level of the variability in the 160 μm band is 4.5σ, and the corresponding variability in the 100 μm band is significant at 1.6σ. We find no example of an equally significant false positive detection. Conservatively assuming a variability of 25% in the FIR, we can provide upper limits to the flux. Comparing the latter with theoretical models, we find that 1D radiatively inefficient accretion flow models have difficulties explaining the observed faintness. However, the upper limits are consistent with modern observations by ALMA and the Very Large Array. Our upper limits provide further evidence for a spectral peak at ∼1012 Hz and constrain the number density of γ ∼ 100 electrons in the accretion disk and/or outflow.