X-ray Polarimetry - a Tool for the Galactic center diagnosis

Abstract

Was the Milky Way galaxy a low-luminosity active galactic nucleus (AGN) in the past? Can we find traces of remnant structures supporting this idea? What is the three-dimensional arrangement of matter around our central supermassive black hole? A number of fundamental questions concerning our own Galactic center remain controversial. To reveal the structure of the high-energy sky around our galactic core, a technique more sensitive to the morphology of the emitters than spectroscopy is needed. In this lecture note, I describe how X-ray polarimetry can open a new observational window by precisely measuring the three-dimensional position of the scattering material in the Galactic center. The observed polarization degree and polarization position angle would also determine unambiguously the primary source of emission and trace the centennial history of our supermassive black hole by detecting echoes of its past activity thanks to astrophysical mirrors. Finally, the synergy between X-ray polarimetry and infrared and radio observations can be used to better constrain the geometry in the first hundred parsecs around the Galactic center.