galactic and anomalous c osmic r a ys in the heliosheath

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

kota@lpl.arizona.edu

● V-1

● V-2

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

● 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

Heliosphere: our cosmic environment

Pristine ISM

Solar material

Perturbed ISM

TS

26 km/s

< 1000 AU (10 lightdays) >

● V1

Global structure of Heliosphere

GCR

ACR SEP

VLISM: partially ionizedH,He0.1/cc μG B ?

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

LECP Low energy charged particles (Decker JHU-APL)

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?

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).

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

McComas and Schwadron (2006) Blunt Shock: acceleration at Flanks ?

Short time foracceleration

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

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

Blunt Shock (offset circle)perpendicular diffusion included (η=0.02)

Polar contours of simulated 200keV fluxes & spectrum along the TS

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

Larger perpendicular diffusion: η=0.05 effect smaller but still there

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

Motto:

● “Make everything as simple as possible, but not simpler “

“Topology counts”

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

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

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

Uneven injection: preferential injection at flanks

Injection at 10 keV, q~sin(θ)**2

Preferential injection at flanks contn’d