MSI Seminar

What are the thousands of X-ray emitting point sources in the center of the Milky Way?

Kaya Mori

Columbia University

The Nuclear Spectroscopic Telescope Array (NuSTAR), carrying the first focusing telescopes capable of making sub-arcminute resolution images above 10 keV, conducted a deep survey of the Galactic Center region. One of our primary goals was to identify the origin of the ~9,000 unidentified X-ray sources detected by Chandra in the central ~100 pc of our Galaxy. As a result, NuSTAR discovered the diffuse, central hard X-ray emission (CHXE) over a ~10 pc region centered on the supermassive black hole Sgr A* and detected 70 hard X-ray sources above 10 keV. The CHXE and most of the NuSTAR point sources were attributed to a class of highly magnetized white dwarf binaries called intermediate polars. Their hard X-ray emission (kT ~ 30 keV), in contrast to the softer X-ray emission (kT ~ 15 keV) in the Galactic Ridge detected by Suzaku and INTEGRAL, suggests distinct X-ray source populations between the Galactic Center and Ridge. In the central parsec, NuSTAR detected four X-ray transients including a new magnetar SGR J1745-2900. Our NuSTAR spectral and timing analysis of two new Swift-discovered X-ray transients in 2016 suggests they were outbursting black hole binaries. In addition to an overabundance of transient X-ray binaries observed by Swift and NuSTAR, I present a remarkable cluster of quiescent X-ray binaries in the central parsec, identified with Chandra, and whose properties, numbers and distribution indicate the presence of the long-sought black hole cusp. Throughout my talk, I will present our current understanding of the X-ray source populations in the Galactic Center based on the recent results from NuSTAR, Chandra and other X-ray telescopes.