Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Dust Scattering Halo of Cygnus X-3   Dust grains scatter X-ray light through small angles, producing a diffuse
halo image around bright X-ray point sources situated behind a large amount of
interstellar material. We present analytic solutions to the integral for the
dust scattering intensity, which allow for a Bayesian analysis of the
scattering halo around Cygnus X-3. Fitting the optically thin 4-6 keV halo
surface brightness profile yields the dust grain size and spatial distribution.
We assume a power law distribution of grain sizes ($n \propto a^{-p}$) and fit
for $p$, the grain radius cut-off amax, and dust mass column. We find that a $p
\approx 3.5$ dust grain size distribution with amax $\approx 0.2$ um fits the
halo profile relatively well, whether the dust is distributed uniformly along
the line of sight or in clumps. We find that a model consisting of two dust
screens, representative of foreground spiral arms, requires the foreground
Perseus arm to contain 80\% of the total dust mass. The remaining 20\% of the
dust, which may be associated with the outer spiral arm of the Milky Way, is
located within 1 kpc of Cyg X-3. Regardless of which model was used, we found
$\tau_{\rm sca} \sim 2 \ E_{\rm keV}^{-2}$. We examine the energy resolved
halos of Cyg X-3 from 1 - 6 keV and find that there is a sharp drop in
scattering halo intensity when $E < 2-3$ keV, which cannot be explained with
multiple scattering effects. We hypothesize that this may be caused by large
dust grains or material with unique dielectric properties, causing the
scattering cross-section to depart from the Rayleigh-Gans approximation that is
used most often in X-ray scattering studies. The foreground Cyg OB2
association, which contains several evolved stars with large extinction values,
is a likely culprit for grains of unique size or composition.

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The categories of this paper are: physics
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The categories of this paper are: supr-con
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The categories of this paper are: hep-lat
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: nlin
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The categories of this paper are: q-alg
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The categories of this paper are: cmp-lg
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The categories of this paper are: mtrl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: stat
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The categories of this paper are: econ
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The categories of this paper are: chao-dyn