NuSTAR's view of the Galactic center diffuse emission

The Galactic diffuse X-ray emission, an unresolved X-ray emission that fills the Galactic center and extends over 100° along the Galactic plane, has been extensively studied since its discovery over 30 years ago. The NuSTAR observatory, due to its angular resolution of 18" for focused photons (< 1 pc at the Galactic center) and its wide aperture for unfocused photons, provides the unique ability to separately measure the diffuse emission of the inner 10 pc, 100 pc, and several hundreds of parsecs of the Galaxy using the same instrument. Conclusions about the dominant underlying stellar remnant populations in the innermost parsecs have already been updated by NuSTAR observations, which indicate that the Galactic center is dominated by intermediate polar systems with heavier white dwarfs than previously assumed. In this contribution, we exploit the wide NuSTAR solid angle aperture for unfocused photons to add to this picture the broad-band measurement of the diffuse emission in the inner ∼1-3° of the Galactic bulge. This allows for a picture of the changing nature of the high-energy X-ray stellar remnant population on various length scales from the Galactic center. In addition, these same NuSTAR observations constrain possible X-ray line signatures from the radiative decay of sterile neutrino dark matter. In most of the mass range 10-50 keV, these (along with those derived from NuSTAR blank-sky observations) are now the strongest limits on this leading dark matter candidate.