Radio Sounding of the NearSun Plasma Using Polarized Pulsar Pulses

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Radio Sounding of the Near-Sun Plasma Using
Polarized Pulsar Pulses

• I.V.Chashei, T.V.Smirnova, V.I.Shishov
• Pushchino Radio Astronomy Obsertvatory,
  Astrospace Center, Lebedev Physical Institute

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ABSTRACT
The results are presented of radio sounding
observations probing the inner solar wind near
the minimum of solar activity cycle using
polarized pulsar pulses from PRS B052521 and PSR
B053121 received when the lines of sight toward
these pulsars was close to the Sun. The
observations were obtained in June 2005 and June
2007 on the Large Phased Array of Lebedev
Physical Institute at 111 MHz. An upper limit for
the scattering of giant pulses from PSR B053121
due to their passage through the turbulent solar
wind plasma is determined. The arrival-time
delays for pulses from PSR B053121 are used to
derive the radial dependence of the mean density
of the circumsolar plasma. The resulting density
distribution indicates that the acceleration of
fast high latitude solar wind outflows continues
to heliocentric distances of 5-10 RS, where RS
is the solar radius. The mean plasma density at
heliocentric distances of about 5 RS is 1.4 ? 104
cm-3 , substantially lower than at solar
activity maximum. This is associated with the
presence of polar coronal holes. The Faraday
rotation measure at heliocentric distances of 6-7
RS is estimated. Deviation of the spatial
distribution of the magnetic field from spherical
symmetry are comparatively modest in the studied
range of heliocentric distances.
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Propagation effects of pulsed signals in the
solar wind

• Dispersion delay of pulses
• Scattering of pulses on electron density
  fluctuations
• Faraday rotation of polarization plane

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Dispersion delay of pulses

• ?t A? ?2 ? DM , A const
• DM ? N dz

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Scattering of pulses on electron density
fluctuations

• Structure function of radio wave phase
  fluctuations
• DS(?) 2?(?re)2 lt?Nl2(R0)gt (?/l)2 l?Reff
• l turbulence inner scale
• Wave field coherence scale ?0
• DS(?0) 1
• Scattering angle ?sc
• ?sc ? / 2? ?0
• Pulse broadening by scattering
• ?sc z ?sc2 / 2 c

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Scattering of pulses on electron density
fluctuations

• t
• I(t) I0 ? exp ( - t?2 / ?02 ) exp ( t - t?) /
  ?sc dt?
• -?
• I(t) I0 exp (?02/4 ?sc2 t/ ?sc) 1 - ? (?0/2
  ?sc t/ ?0 )
• Max. at t ? ?0

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Faraday rotation of polarization plane

• ? C ? ?2 ? RM , C const
• RM ? N Bz dz

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Observations

• Radio telescope BSA LPI geometric area 70 000
  ?2,
• operation frequency 111 ?Hz
• Receiver 96 channels ? 20 ???, whole bandwidth
  1.92 ?Hz, integration time 2.68 ?s
• Pulsar ? 052521 period 3,74 s, two components,
  polarization degree 40-50 yy 2005, 2007.
• Pulsar in the Crab nebula ? 053121 period 33
  ?s, giant pulses, polarization degree10 y
  2007 .

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Antenna BSA LPI
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(No Transcript)
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Pulsars coronal occultation
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Example of pulsar ? 0525 record
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Dispersion delay for pulsar PSR ? 0525, 2005,
2007
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Pulse delay and ambient plasma density

• Dispersion delay upper estimate
• ?t lt 2 ms ? DM lt 2 ? 1016 cm-2 ?
• N (5.5 R?) lt 2 ?104 cm-3 (2005)
• ?t lt 4 ms ? DM lt 4 ? 1016 cm-2 ?
• N (5.5 R?) lt 4 ?104 cm-3 (2007)
• Counselman Rankin, 1969-1970 observations ,
  111-430 ???
• ?t ? 5 ms, N (10 R?) ? 7 ?103 cm-3, N (5.5
  R?) ? 6 ?104 cm-3

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Dispersion delay for PRS B 0531, 2007
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Density dependence on the distance from the Sun,
PSR B 0531, 2007
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Giant pulses of PSR ? 0531
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PSR ? 0531scattering
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Scattering and density fluctuations

• Upper estimate of pulse broadening (B 0531)
• ?sc lt 2 ms ? scattering angle ?sc lt 3
  10-3 rad ? 10?
• Counselman Rankin, 1969-1970 observations,
  111-430 ?Hz
• ?sc ? 6 ms

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PSR ? 0525 Faraday rotation
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Rotation measure radial profile ? 0525
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Rotation measure

• Rotation measure upper estimate at R 7 R?
• RM lt 6 rad/m2 (2005 y.)
• RM lt 3 rad/m2 (2007 y.)
• Bird et al., observations 1978-1979 y. RM lt 10
  rad/m2

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Conclusions

• Our estimates of ?t, ?sc show, that in the years
  2005-2007 mean density, as well density
  fluctuations were several times (2-3) lower, than
  in observations 1969-1970 ?. (Counselman
  Rankin).
• During period of closest approach solar offset
  point of radio path was located at high
  heliolatitudes, about 80?. Possible explanation
  polar coronal hole with low plasma density at
  solar activity minimum.
• Our estimates of rotation measure are in
  agreement with the results of Bird et al.,
  (1978-1979?.). The deviations in spatial
  magnetic field distribution from spherically
  symmetric are modest Bns lt 6?10-3 G, Brgt 2?10-2
  G .
• Radial density profile ( B 0531, 2007) show that
  the acceleration of fast solar wind continues up
  to the distances about 5 10 RS .