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26 April 2024 |
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The Galactic Bulge Diffuse Emission in Broad-Band X-rays with NuSTAR | | Kerstin Perez
; Roman Krivonos
; Daniel R. Wik
; | | Date: |
12 Sep 2019 | | Abstract: | The diffuse hard X-ray emission that fills the Galactic center, bulge, and
ridge is believed to arise from unresolved populations of X-ray binary systems.
However, the identity of the dominant class of accreting objects in each region
remains unclear. Recent studies of Fe line properties and the low-energy (<10
keV) X-ray continuum of the bulge indicate a major population fraction of
non-magnetic cataclysmic variables (CVs), in particular quiescent dwarf novae.
This is in contrast to previous high-energy (>10 keV) X-ray measurements of the
bulge and ridge, which indicate a dominant population of magnetic CVs, in
particular intermediate polars. In addition, NuSTAR broad-band measurements
have uncovered a much heavier intermediate polar population in the central ~100
pc than previously assumed, raising the possibility that some fraction of this
population extends further from the center. Here we use NuSTAR’s large aperture
for unfocused photons and its broad-band X-ray range to probe the diffuse
continuum of the inner ~1-3$^circ$ of the Galactic bulge. This allows us to
constrain possible multi-temperature components of the spectrum, such as could
indicate a mixture of soft and hard populations. Our emissivity is consistent
with previous hard X-ray measurements in the bulge and ridge, with the diffuse
X-ray luminosity tracing the stellar mass. The spectrum is well-described by a
single-temperature thermal plasma with $kT approx 8$ keV, with no significant
emission above 20 keV. This supports that the bulge is dominated by quiescent
dwarf novae; we find no evidence of a significant intermediate polar population
in the hard X-ray band. | | Source: | arXiv, 1909.5916 | | Services: | Forum | Review | PDF | Favorites | |
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