Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spectropolarimetric properties of Swift J1818.0$-$1607: a 1.4 s radio
  magnetar   The soft-gamma repeater Swift J1818.0$-$1607 is only the fifth magnetar found
to exhibit pulsed radio emission. Using the Ultra-Wideband Low receiver system
of the Parkes radio telescope, we conducted a 3 h observation of Swift
J1818.0$-$1607. Folding the data at a rotation period of $P = 1.363$ s, we
obtained wideband polarization profiles and flux density measurements covering
radio frequencies between 704-4032 MHz. After measuring, and then correcting
for the pulsar's rotation measure of $1442.0 \pm 0.2$ rad m$^{-2}$, we find the
radio profile is between 80-100 per cent linearly polarized across the wide
observing band, with a small amount of depolarization at low frequencies that
we ascribe to scatter broadening. We also measure a steep spectral index of
$\alpha = -2.26^{+0.02}_{-0.03}$ across our large frequency range, a
significant deviation from the flat or inverted spectra often associated with
radio-loud magnetars. The steep spectrum and temporal rise in flux density
bears some resemblance to the behaviour of the magnetar-like, rotation-powered
pulsar PSR J1119$-$6127. This leads us to speculate that Swift J1818.0$-$1607
may represent an additional link between rotation-powered pulsars and
magnetars.

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The categories of this paper are: hep-th
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The categories of this paper are: nucl-th
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The categories of this paper are: supr-con
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The categories of this paper are: q-alg
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The categories of this paper are: nlin
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The categories of this paper are: chem-ph
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The categories of this paper are: cs
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The categories of this paper are: physics
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The categories of this paper are: alg-geom
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The categories of this paper are: eess
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The categories of this paper are: math
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The categories of this paper are: quant-ph
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The categories of this paper are: stat
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ph
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The categories of this paper are: chao-dyn