A Detection of Sgr A* in the far infrared

We report the first detection of the Galactic Centre massive black hole, Sgr~A*, in the far infrared. Our measurements were obtained with PACS on board the \emph{Herschel} satellite at $100~\mathrm{\mu m}$ and $160~\mathrm{\mu m}$. While the warm dust in the Galactic Centre is too bright to allow for a direct detection of Sgr~A*, we measure a significant and simultaneous variation of its flux of $\Delta F_{\nu\widehat{=}160 ~\mathrm{\mu m}} = (0.27\pm0.06)~\mathrm{Jy}$ and $\Delta F_{\nu\widehat{=}100 ~\mathrm{\mu m}}= (0.16\pm0.10)~\mathrm{Jy}$ during one observation. The significance level of the $160 ~\mathrm{\mu m}$ band variability is $4.5\sigma$ and the corresponding $100 ~\mathrm{\mu m}$ band variability is significant at $1.6\sigma$. 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 RIAF models have difficulties explaining the observed faintness. However, the upper limits are consistent with modern ALMA and VLA observations. Our upper limits provide further evidence for a spectral peak at $\sim 10^{12} ~ \mathrm{Hz}$ and constrain the number density of $\gamma \sim 100$ electrons in the accretion disk and or outflow.Comment: accepted for publication in AP

The Young Stars in the Galactic Center

[EN] We present a large similar to 30 '' x 30 '' spectroscopic survey of the Galactic Center using the SINFONI IFU at the VLT. Combining observations of the last two decades we compile spectra of over 2800 stars. Using the Bracket-gamma absorption lines, we identify 195 young stars, extending the list of known young stars by 79. In order to explore the angular momentum distribution of the young stars, we introduce an isotropic cluster prior. This prior reproduces an isotropic cluster in a mathematically exact way, which we test through numerical simulations. We calculate the posterior angular momentum space as a function of projected separation from Sgr A*. We find that the observed young star distribution is substantially different from an isotropic cluster. We identify the previously reported feature of the clockwise disk and find that its angular momentum changes as a function of separation from the black hole and thus confirm a warp of the clockwise disk (p similar to 99.2%). At large separations, we discover three prominent overdensities of the angular momentum. One overdensity has been reported previously, the counterclockwise disk. The other two are new. Determining the likely members of these structures, we find that as many as 75% of stars can be associated with one of these features. Stars belonging to the warped clockwise disk show a top-heavy K-band luminosity function, while stars belonging to the larger separation features do not. Our observations are in good agreement with the predictions of simulations of in situ star formation and argue for the common formation of these structures.We thank the referee for a very quick yet thorough report, which helped to improve the paper. A.D., S.V.F., and F.W. acknowledge support from the Max Planck International Research School.Von Fellenberg, SD.; Gillessen, S.; Stadler, J.; Bauböck, M.; Genzel, R.; De Zeeuw, T.; Pfuhl, O.... (2022). The Young Stars in the Galactic Center. The Astrophysical Journal. 932(1):1-29. https://doi.org/10.3847/2041-8213/ac68ef129932

General relativistic effects and the near-infrared and X-ray variability of Sgr A* I

International audienceThe near-infrared (NIR) and X-ray emission of Sagittarius A* shows occasional bright flares that are assumed to originate from the innermost region of the accretion flow. We identified $25$$4.5 \mu m$ and $24$ X-ray flares in archival data obtained with the \textit{Spitzer} and \textit{Chandra} observatories. With the help of general relativistic ray-tracing code, we modeled trajectories of ``hot spots'' and studied the light curves of the flares for signs of the effects of general relativity. Despite their apparent diversity in shape, all flares share a common, exponential impulse response, a characteristic shape that is the building block of the variability. This shape is symmetric, that is, the rise and fall times are the same. Furthermore, the impulse responses in the NIR and X-ray are identical within uncertainties, with an exponential time constant $\tau\sim 15$ minute. The observed characteristic flare shape is inconsistent with hot-spot orbits viewed edge-on. Individually modeling the light curves of the flares, we derived constraints on the inclination of the orbital plane of the hot spots with respect to the observer ($i \sim 30^{\circ} , < 75^{\circ}$) and on the characteristic timescale of the intrinsic variability (tens of minutes)