galactic and anomalous cosmic rays in the heliosheath józsef kόta university of arizona tucson, az...
TRANSCRIPT
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Galactic and Anomalous Cosmic Rays in the Heliosheath
József Kόta University of Arizona
Tucson, AZ 85721-0092, USAThanks to : J.R. Jokipii, J. Giacalone
21st ECRS, Košice, September 2008
● V-1
● V-2
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Motivation: where is the source?is history repeating itself ??
ACR fluxes continued to increase beyond TS
V. Hess 1912
Voyager-1 December 2004 Similar result from V-2 (2007)
Source outside
Shock
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● 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
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Heliosphere: our cosmic environment
Pristine ISM
Solar material
Perturbed ISM
TS
26 km/s
< 1000 AU (10 lightdays) >
● V1
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Global structure of Heliosphere
GCR
ACR SEP
VLISM: partially ionizedH,He0.1/cc μG B ?
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ACRs are accelerated at the solar wind
Termination Shock Same Physics as SNR
Diffusive Shock Acceleration: 1st order Fermi Energy gain from crossing the shock many times
ACRs SNR
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LECP Low energy charged particles (Decker JHU-APL)
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Voyager-1 after crossing the TS
ACR fluxes continuedto increase into theHeliosheath
● Temporal variaton(Florinski Zank,2006)
● Magnetic topology(McComas & Schwadron,Kόta & Jokipii)
● Combination of the two?
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First Signature of Blunt Shock
o Voyager-1 observed large beaming anisotropies seemingly from the sunward direction.
o Interpreted in terms of multiple intersection between the Parker spiral field and the blunt TS
o Hint for a deformation of the shock (likely due to interstellar B).
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How do we understand “anti-sunward” anisotropies?Magnetic field line may intersect the TS multiple times.
V-2
V-1
Jokipii, Giacalone, and Kota 2004, Kóta and Jokipii 2004Multiple intersection also explains the two population spectrum
Displacement of the ‘nose’ helps
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McComas and Schwadron (2006) Blunt Shock: acceleration at Flanks ?
Short time foracceleration
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Topological effects on ACR spectrum
o Acceleration ineffective at the nose due to lack of time fof acceleration.
o ACR spectrum does not unfold at the TS
o ACR flux continues to increase into the heliosheath
o Could have been anticipated
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2-D Model: TS = Offset Circle
o In the modeling we select an offset sphere for the TS Another possibility is bullet shape (McComas &
Schwadron, 2006)
o Nose region (V1 and V2) is similar in either case
o Differences can be expected for the tail region. Tail region turn effective for sphere and probably less effective for bullet shape.
o Consider preferential injection at flanks
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Blunt Shock (offset circle)perpendicular diffusion included (η=0.02)
Polar contours of simulated 200keV fluxes & spectrum along the TS
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2-DSimulation – Blunt shock
Model: 2-D plane, TS offset circle,uniform injection at 10 keV, η=0.02
Radial variation at fixedazimuth:fluxes continue increase beyond TS
V2
V1
V-2
V-1
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Larger perpendicular diffusion: η=0.05 effect smaller but still there
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Summary: ●V-1
● 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.
●V-2
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Motto:
● “Make everything as simple as possible, but not simpler “
“Topology counts”
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Voyager-1 in the Heliosheath
● V-1 crossed the Termination Shock on December 16, 2004
Before Crossing:
● large beaming anisotropies from sunward direction● large day-to-day variability● ACRs still modulated – two-population!?
After Crossing:
●small anisotropies● small day-to-day variability● ACRs still modulated● Double power law spectra with break around few MeV/n (He:H=1:10)
● Voyager-2 crossed the TS on DOY 244, 2007
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Voyager -1 & -2 reached the TS 2004/2007
Launched in 1977
B
LECP
CRS
SW Plasma
radio
Interestingly in the same year as the theory of shock acceleration
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Where is the Termination Shock ?
E.C. Stone 2001
Very different methods all predict ~100 AU range
Shock is not steady but moves in response of solar input
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Uneven injection: preferential injection at flanks
Injection at 10 keV, q~sin(θ)**2
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Preferential injection at flanks contn’d