Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Absolute polarisation position angle profiles of southern pulsars at 1.4
  and 3.1 GHz   We present here a direct comparison of the polarisation position angle (PA)
profiles of 17 pulsars, observed at 1.4 and 3.1 GHz. Absolute PAs are obtained
at each frequency, permitting a measurement of the difference in the profiles.
By doing this, we obtain more precise rotation measure (RM) values for some of
the pulsars in the current catalogue. We find that, apart from RM corrections,
there are small, pulse longitude dependent differences in PA with frequency.
Such differences go beyond the interpretation of a geometrical origin. We
describe in detail the PA evolution between the two frequencies and discuss
possible causes, such as orthogonal and non-orthogonal polarisation modes of
emission. We also use the PA and total power profiles to estimate the
difference in emission height at which the two frequencies originate. In our
data sample, there are changes in the relative strengths of different pulse
components, especially overlapping linearly polarised components, which
coincide with intrinsic changes of the PA profile, resulting in interesting PA
differences between the two frequencies.

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The categories of this paper are: funct-an
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-bio
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The categories of this paper are: adap-org
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The categories of this paper are: supr-con
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The categories of this paper are: quant-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-ex
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-lat
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The categories of this paper are: cmp-lg
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The categories of this paper are: nlin
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The categories of this paper are: eess
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The categories of this paper are: patt-sol
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The categories of this paper are: cs
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The categories of this paper are: math-ph