Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Remarkable Spin-down and Ultra-fast Outflows of the Highly-Pulsed
  Supersoft Source of Nova Hercules 2021   Nova Her 2021 (V1674 Her), which erupted on 2021 June 12, reached naked-eye
brightness and has been detected from radio to $\gamma$-rays. An extremely fast
optical decline of 2 magnitudes in 1.2 days and strong Ne lines imply a
high-mass white dwarf. The optical pre-outburst detection of a 501.42s
oscillation suggests a magnetic white dwarf. This is the first time that an
oscillation of this magnitude has been detected in a classical nova prior to
outburst. We report X-ray outburst observations from {\it Swift} and {\it
Chandra} which uniquely show: (1) a very strong modulation of super-soft X-rays
at a different period from reported optical periods; (2) strong pulse profile
variations and the possible presence of period variations of the order of
0.1-0.3s; and (3) rich grating spectra that vary with modulation phase and show
P Cygni-type emission lines with two dominant blue-shifted absorption
components at $\sim 3000$ and 9000 km s$^{-1}$ indicating expansion velocities
up to 11000 km s$^{-1}$. X-ray oscillations most likely arise from
inhomogeneous photospheric emission related to the magnetic field. Period
differences between reported pre- and post-outburst optical observations, if
not due to other period drift mechanisms, suggest a large ejected mass for such
a fast nova, in the range $2\times 10^{-5}$-$2\times 10^{-4} M_\odot$. A
difference between the period found in the {\it Chandra} data and a reported
contemporaneous post-outburst optical period, as well as the presence of period
drifts, could be due to weakly non-rigid photospheric rotation.

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The categories of this paper are: quant-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-th
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The categories of this paper are: bayes-an
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The categories of this paper are: acc-phys
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The categories of this paper are: dg-ga
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The categories of this paper are: cs
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The categories of this paper are: econ
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The categories of this paper are: q-alg
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The categories of this paper are: solv-int
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The categories of this paper are: hep-lat
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The categories of this paper are: q-bio
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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: cond-mat