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Galactic and Anomalous Cosmic Rays in the Heliosheath

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Galactic and Anomalous Cosmic Rays in the Heliosheath. J zsef ... Diffusive Shock Acceleration: 1st order Fermi. Energy gain from crossing the shock many times ... – PowerPoint PPT presentation

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Title: Galactic and Anomalous Cosmic Rays in the Heliosheath


1
Galactic and Anomalous Cosmic Rays in the
Heliosheath
? V-1
21st ECRS, Košice, September 2008
? V-2
  • József K?ta
  • University of Arizona
  • Tucson, AZ 85721-0092, USA
  • Thanks to J.R. Jokipii, J. Giacalone

kota_at_lpl.arizona.edu
2
Motivation where is the source?is history
repeating itself ??
ACR fluxes continued to increase beyond TS

Source outside
Shock
V. Hess 1912
Voyager-1 December 2004 Similar result from V-2
(2007)
3
? Are Anomalous Cosmic Rays (ACRs) indeed
accelerated at the solar wind termination shock
(TS) ? Likely yes but ? Bluntness of TS
counts ? Topology between Shock Field lines
counts
4
Heliosphere our cosmic environment
lt 1000 AU (10 lightdays) gt
Pristine ISM
? V1
TS
Solar material
Perturbed ISM
26 km/s
5
Global structure of Heliosphere
VLISM partially ionized H,He 0.1/cc µG B ?
ACR
SEP
GCR
6
ACRs are accelerated at the solar wind
Termination Shock Same Physics as SNR
ACRs
SNR
Diffusive Shock Acceleration 1st order Fermi
Energy gain from crossing the shock many times
7
LECP Low energy charged particles (Decker
JHU-APL)
8
Voyager-1 after crossing the TS
ACR fluxes continued to increase into
the Heliosheath ? Temporal variaton (Florinski
Zank,2006) ? Magnetic topology (McComas
Schwadron, K?ta Jokipii) ? Combination of the
two?
9
First Signature of Blunt Shock
  • Voyager-1 observed large beaming anisotropies
    seemingly from the sunward direction.
  • Interpreted in terms of multiple intersection
    between the Parker spiral field and the blunt TS
  • Hint for a deformation of the shock (likely due
    to interstellar B).

10
How do we understand anti-sunward
anisotropies?Magnetic field line may intersect
the TS multiple times.
Jokipii, Giacalone, and Kota 2004, Kóta and
Jokipii 2004 Multiple intersection also explains
the two population spectrum
V-2
V-1
Displacement of the nose helps
11
McComas and Schwadron (2006) Blunt Shock
acceleration at Flanks ?
Short time for acceleration
12
Topological effects on ACR spectrum
  • Acceleration ineffective at the nose due to lack
    of time fof acceleration.
  • ACR spectrum does not unfold at the TS
  • ACR flux continues to increase into the
    heliosheath
  • Could have been anticipated

13
2-D Model TS Offset Circle
  • In the modeling we select an offset sphere for
    the TS
  • Another possibility is bullet shape (McComas
    Schwadron, 2006)
  • Nose region (V1 and V2) is similar in either case
  • Differences can be expected for the tail region.
    Tail region turn effective for sphere and
    probably less effective for bullet shape.
  • Consider preferential injection at flanks

14
Blunt Shock (offset circle)perpendicular
diffusion included (?0.02)
Polar contours of simulated 200keV fluxes
spectrum along the TS
15
2-DSimulation Blunt shock
Model 2-D plane, TS offset circle, uniform
injection at 10 keV, ?0.02
V-2
Radial variation at fixed azimuth fluxes
continue increase beyond TS
V2
V1
V-1
16
Larger perpendicular diffusion ?0.05 effect
smaller but still there
17
Summary
?V-1
?V-2
? Magnetic field lines cross the blunt TS
multiple times. This explains
? Upstream field-aligned anisotropies - away
from the Sun (V-1) TS offset helps - toward
the Sun (V-2) if TS is offset
? Two-population spectrum low energy particles
are accelerated at nearby fresh shock. ACRs
are accelerated farther away are still modulated
at the TS, and continue to increase into the
heliosheath. ? 2-D Shock differs from 1-D shock
(topology) Think in 2 D (at least) ? Topology
may be important at other shocks too.
18
Motto
  • ? Make everything as simple as possible, but not
    simpler

Topology counts
19
Voyager-1 in the Heliosheath
  • ? V-1 crossed the Termination Shock on December
    16, 2004

After Crossing ?small anisotropies ? small
day-to-day variability ? ACRs still modulated ?
Double power law spectra with break around few
MeV/n (HeH110)
Before Crossing ? large beaming anisotropies
from sunward direction ? large day-to-day
variability ? ACRs still modulated
two-population!?
? Voyager-2 crossed the TS on DOY 244, 2007
20
Voyager -1 -2 reached the TS 2004/2007
SW Plasma
LECP
CRS
radio
Launched in 1977
B
Interestingly in the same year as the theory of
shock acceleration
21
Where is the Termination Shock ?
Very different methods all predict 100 AU range
Shock is not steady but moves in response of
solar input
E.C. Stone 2001
22
Uneven injection preferential injection at flanks
Injection at 10 keV, qsin(?)2
23
Preferential injection at flanks contnd
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