Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Discovery of a New Torque Reversal of the Accreting X-ray Pulsar 4U
  1626-67 by Fermi/GBM   Recent X-ray observations by Fermi/GBM discovered a new torque reversal of 4U
1626-67 after 18 years of steady spinning down. Using Swift/BAT observations we
were able to center this new torque reversal on Feb 4 2008, lasting
approximately 150 days. From 2004 up to the end of 2007, the spin-down rate
averaged at a mean rate of ~dnu/dt=-4.8e-13 Hz s-1 until the torque reversal
reported here. Since then it has been following a steady spin-up at a mean rate
of ~dnu/dt= 4e-13 Hz s-1. The properties of this torque reversal, as well as
the lack of correlation between the X-ray flux and the torque applied to the
neutron star before this transition, challenges our understanding of the
physical mechanisms operating in this system.

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The categories of this paper are: hep-ex
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The categories of this paper are: cond-mat
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The categories of this paper are: chem-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
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The categories of this paper are: q-alg
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The categories of this paper are: dg-ga
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The categories of this paper are: mtrl-th
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The categories of this paper are: eess
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The categories of this paper are: supr-con
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The categories of this paper are: adap-org
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The categories of this paper are: cs
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
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The categories of this paper are: atom-ph