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Paper: Interpreting Low-Luminosity Accretion From the Extended Quiescent Emission of Sgr A*
Volume: 528, New Horizons in Galactic Center Astronomy and Beyond
Page: 189
Authors: Corrales, L.
Abstract: In quiescence, Sgr A* is surprisingly dim, around 105 times less bright than expected for its environment. This problem has motivated a host of theoretical models to explain radiatively inefficient accretion flows (RIAFs). The unsurpassed imaging resolution of Chandra X-ray Observatory enabled, for the first time, images of X-ray emission from gas within the Bondi radius of Sgr A*. The Galactic Center (GC) X-ray Visionary Project obtained 3 Ms of Chandra observations on the GC, providing an unprecedented look at the quiescent state of Sgr A* and new constraints on RIAF models. This program also provides our only chance to get a high resolution spectrum of quiescent Sgr A* emission, for the next few decades. However, the crowded and hot-plasma suffused GC presents a challenge, as it outshines Sgr A* by an order of magnitude when the entire image is dispersed by the Chandra High Energy Transmission Grating (HETG). The GC is also optically thick to dust scattering, which can lead to dust echoes that affect our interpretation of the Sgr A* image. Fortunately, Chandra-HETG observations employ an order sorting algorithm that reduces these effects. The first high resolution quiescent spectrum of Sgr A* reveals a multi-temperature plasma, and requires modeling the orientation and velocity profile of gas near the Bondi radius. Future examination of Sgr A*, our local supermassive black hole, will need to take into account the effects of local GC environment – such as the dynamics of the stellar winds feeding Sgr A* – in order to fully understand the physics of quiet galactic nuclei.
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