George Gloeckler

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George Gloeckler IBEX Team Meeting Sheraton
Moana Surfrider Hotel, Honolulu, Hawaii March
10 2006
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Suprathermal tails throughout the heliosphere
f(w)fow 5 tails are observed at all levels of
disturbance throughout the heliosphere A roll
over or cutoff is observed at W 50-70 ( 2.5-5
MeV)
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Low-energy particles accelerated at the
termination shock
Anomalous Cosmic Rays are not accelerated at the
Termination shock where Voyager 1 crossed it
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How and where are the Anomalous Cosmic Rays
accelerated?
Possibly by second order Fermi acceleration in
the heliosheath by the same process that produces
power law tails with index -5 in the
heliosphere In the heliosheath pickup ions
continue to be produced in the heliosheath with
pressure fluctuations The magnetic field
strength may increase, causing the rollover in
spectrum to move to higher energies as is
observed This mechanism should be even more
efficient in the heliosheath than in the
heliosphere because of smaller adiabatic energy
losses
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What are the upstream solar wind and pickup ion
densities?

• Solar wind density at 94 AU is obtained by
  extrapolating (with appropriate time delay) 1 AU
  ACE observations of speed, proton density and
  He/H ratio. The solar wind is assumed to slow
  down as shown in the figure
• The distribution functions and the resulting
  densities of interstellar pickup protons and
  helium at 94 AU are determined by standard hot
  models for the ionization of interstellar neutral
  gas in the solar wind
• The resulting total density of solar wind protons
  and helium, and interstellar protons and helium
  is found to be 0.001 cm-3, which is consistent
  with the electron density upstream of the
  Termination Shock, inferred from the measured
  plasma frequency on Voyager 1
• Solar wind number density 0.000727 cm-3
• Pickup ion number density 0.000259 cm-3

Solar wind speed slows down (due to mass loading)
from 550 km/s at 1 AU to 265 km/s at 94 AU as
observed with Voyager 2 and inferred from Voyager
1 LECP measurements
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Voyager 1 LECP Observation Upstream of the
Termination Shock and Estimated Proton Velocity
Distributions below 40 keV
Pickup ions carry almost all of the pressure as
well as a large fraction of the density.
Differential intensity spectrum of suprathermal
(tail) protons in the heliosphere upstream of
the termination shock is a power law with index g
-1.5
Measurements of lt 40 keV particles are not
available on Voyager 1
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Estimate Mach number and shock speed from jump of
pickup ion tail particles across the termination
shock and downstream solar wind speed
Mu1 (4fsth,d/fsth,d 1)/51/2 Mu2
(3ruuu2/5Pu )1/2
ru 1.7610-27 gm/cm3 Pu 1.4210-13
dyne/cm2
At 1 AU nSW 3.76 cm-3 VSW 547 km/s
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Upstream and downstream proton velocity
distributions in the spacecraft frame of
reference

• The Rankine-Hugoniot relationship with a Mach
  number of 3.82 is applied to the solar wind and
  core pickup ion component of the gas
• The average speed of the downstream solar wind is
  taken to be 22 km/s as suggested by Voyager 1
  LECP measurements

2VSW
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Pickup Ion Tails Will IBEX see tails at the TS
and Heliosheath? Any chance to measure spectral
shape? (would require increasing upper energy
limit IBEX-HI) Pickup Ion Core IBEX will see
tails at the TS and Heliosheath Can we untangle
contributions from the TS and Heliosheath? -
In Heliosheath pickup ions will be continuously
produced - Pickup ions will be continuously
heated rather than cooled - Tails will be
generated and will probably grow
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VENAVION - Vd
Vd ud- Vsh
uu udr
uu udr
r 4Mu2/(3Mu2)
uu Mu(5Pu/3ru)
Vu uu- Vsh