Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Spatially Resolved Study of the Synchrotron Emission and Titanium in
  Tycho's Supernova Remnant with NuSTAR   We report results from deep observations (~750 ks) of Tycho's supernova
remnant (SNR) with NuSTAR. Using these data, we produce narrow-band images over
several energy bands to identify the regions producing the hardest X-rays and
to search for radioactive decay line emission from 44Ti. We find that the
hardest (>10 keV) X-rays are concentrated in the southwest of Tycho, where
recent Chandra observations have revealed high emissivity "stripes" associated
with particles accelerated to the knee of the cosmic-ray spectrum. We do not
find evidence of 44Ti, and we set limits on its presence and distribution
within the SNR. These limits correspond to a upper-limit 44Ti mass of M44 <
2.4x10^-4 M_sun for a distance of 2.3 kpc. We perform spatially resolved
spectroscopic analysis of sixty-six regions across Tycho. We map the best-fit
rolloff frequency of the hard X-ray spectra, and we compare these results to
measurements of the shock expansion and ambient density. We find that the
highest energy electrons are accelerated at the lowest densities and in the
fastest shocks, with a steep dependence of the roll-off frequency with shock
velocity. Such a dependence is predicted by models where the maximum energy of
accelerated electrons is limited by the age of the SNR rather than by
synchrotron losses, but this scenario requires far lower magnetic field
strengths than those derived from observations in Tycho. One way to reconcile
these discrepant findings is through shock obliquity effects, and future
observational work is necessary to explore the role of obliquity in the
particle acceleration process.

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The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
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The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
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The categories of this paper are: atom-ph
33
The categories of this paper are: plasm-ph
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The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
0
The categories of this paper are: hep-ph
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The categories of this paper are: quant-ph
7
The categories of this paper are: hep-th
9
The categories of this paper are: nlin
11
The categories of this paper are: hep-lat
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The categories of this paper are: eess
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The categories of this paper are: alg-geom
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The categories of this paper are: q-bio