Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Plasma Prism Model for an Anomalous Dispersion Event in the Crab
  Pulsar   In 1997 October daily monitoring observations of the Crab pulsar at 327 MHz
and 610 MHz with an 85ft telescope in Green Bank, WV showed a jump in the
dispersion measure by 0.1 cm$^{-3}$ pc. Pulses were seen simultaneously at both
old and new dispersions over the course of several days. During the dispersion
jump the pulsed flux diminished by an order of magnitude. In the months before
this event the average pulse profiles contained faint ``ghost'' pulse
components offset in phase from the regular main pulse and interpulse
components by a nearly frequency independent time delay that quadratically
diminished to zero over a month. After the dispersion event there was an order
of magnitude increase in the level of scattering, as measured by pulse
broadening at 327 MHz. There was also a curious shift in the rotational phase,
a slowing down, at both frequencies at the time of the dispersion jump which we
associate with intrinsic timing noise. All of the observed phenomena except
this slowing down can be explained by the variable perturbing optics of a
triangular plasma prism that is located in the filamentary interface between
the synchrotron nebula and the supernova ejecta and which crosses the line of
sight over a period of months. The required density, scale length and velocity
are reasonable given previous observations and analysis of these filaments. Our
study thus provides a probe of the plasma column on scales of 30 microarcsecond
to 3 milliarcsecond ($10^{12-14}$ cm) which complements scales accessible to
optical emission line studies with HST resolution ($10^{16-18}$ cm). In
combination both observations provide a detailed look at a sample of the
interface region that can be matched statistically to the results of numerical
simulations.

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The categories of this paper are: dg-ga
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The categories of this paper are: hep-lat
29
The categories of this paper are: funct-an
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
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The categories of this paper are: atom-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: cmp-lg
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The categories of this paper are: adap-org
2
The categories of this paper are: math
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
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The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc