Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Low-frequency pulse profile variation in PSR B2217+47: evidence for
  echoes from the interstellar medium   We have observed a complex and continuous change in the integrated pulse
profile of PSR B2217+47, manifested as additional components trailing the main
peak. These transient components are detected over 6 years at $150$ MHz using
the LOw Frequency ARray (LOFAR), but they are not seen in contemporaneous
Lovell observations at $1.5$ GHz. We argue that propagation effects in the
ionized interstellar medium (IISM) are the most likely cause. The putative
structures in the IISM causing the profile variation are roughly half-way
between the pulsar and the Earth and have transverse radii $R \sim 30$ AU. We
consider different models for the structures. Under the assumption of spherical
symmetry, their implied average electron density is $\overline{n}_e \sim 100$
cm$^{-3}$. Since PSR B2217+47 is more than an order of magnitude brighter than
the average pulsar population visible to LOFAR, similar profile variations
would not have been identified in most pulsars, suggesting that subtle profile
variations in low-frequency profiles might be more common than we have observed
to date. Systematic studies of these variations at low frequencies can provide
a new tool to investigate the proprieties of the IISM and the limits to the
precision of pulsar timing.

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The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph
7
The categories of this paper are: hep-th
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: comp-gas
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The categories of this paper are: stat
31
The categories of this paper are: ao-sci
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat