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Paper: The X-ray Background Emission of the Galactic Center and Bulge with NuSTAR
Volume: 528, New Horizons in Galactic Center Astronomy and Beyond
Page: 371
Authors: Kuznetsova, E.; Krivonos, R.; Perez, K.; Wik, D. R.
Abstract: The Galactic diffuse X-ray emission (GDXE) is believed to arise from unresolved populations of numerous low-luminosity X-ray binary systems that trace stellar mass distribution of the Milky Way. Many dedicated studies carried out over the last decade suggest that a dominant contributor to GDXE is a population of accreting white dwarfs (WDs). The question arises about relative contribution of different subclasses of accreting WD population, namely non-magnetic WD binaries, magnetic intermediate polars (IPs) and polars, in different regions of the Galaxy: the Galactic center, bulge, and ridge. Recent low-energy (E<10 keV) studies indicate that non-magnetic WD binaries, in particular quiescent dwarf novae, provide a major contribution to the diffuse hard X-ray emission of the Galactic bulge. From the other side, previous high energy (E>10 keV) X-ray measurements of the bulge and ridge imply a dominant population of magnetic CVs, in particular intermediate polars. In this work we use side aperture of the NuSTAR to probe the diffuse continuum of the inner ∼1–3° of the Galactic bulge, which allows us to constrain possible mixture of soft and hard populations components of the spectrum. We found that GDXE spectrum is well-described by a single-temperature thermal plasma with kT8 keV, which supports that the bulge is dominated by quiescent dwarf novae with no evidence of a significant intermediate polar population in the hard X-ray band. We also compare this result with previous NuSTAR measurements of the inner 10 pc and inner 100 pc of the Galactic center.
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