observational evidences of CR acceleration at shocks

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observational evidences of CR acceleration at
shocks

• chung-ming ko
• institute of astronomy and
• department of physics, national central
  university, taiwan

KAW4, KASI, Daejeon, Korea, 2006.05.17
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shocks, shocks everywhere

• from interplanetary shocks to stellar wind
  termination shocks to supernova remnant shocks to
  merger shocks to

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what I want to talk

• SNR shocks has been discussed by Peter and Aya
• DSA has been discussed by Hyesung
• those are the things I know better than what I am
  going to discuss, so bear with me if I say
  something trivial or stupid
• I will concentrate on heliospheric shocks
• the particles are low energy (low energy
  energetic particles?), in MeV or even sub-MeV
  range

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interplanetary or heliospheric shocks
(collisionless)

• CME driven shocks
• planetary and cometary bow shocks
• CIR and MIR
• termination shock

• in situ measurements
• energy spectrum
• composition
• temporal variation
• magnetic field
• Waves
• plasma properties
• seed

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Voyager 1 has crossed the solar termination shock
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Voyager 1 2 (Voyager Interstellar Mission,VIM)
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voyage to the edge of heliosphere
counterclockwise from top right Frisch et al.
APOD20020624 Fisk (2005) Decker et al. (2005)
APOD20020624
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heliosphere is just one more bubble in the sky
but smaller
bow shock near young star
wind bubble from hot star
planetary nebula
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how do we know Voyager 1 have crossed the
termination shock?

• magnetic field strength and its fluctuations
• 3 times increase in magnitude right across the
  shock
• field in heliosheath is 2.4 times the average
  upstream field
• larger fluctuations after shock crossing

Burlaga et al. 2005
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together with

• abrupt increase in low-energy particle intensity
• electron plasma oscillations
• detected upstream and not detectable downstream
• inferred solar wind speed
• reduce solar wind speed

Fisk 2005 Stone et al. 2005 Decker et al. 2005
Gurnett Kurth 2005 Burlaga et al. 2005
termination shock (TS) is a reverse
quasi-perpendicular pickup ion-dominated
shock now it is at 94 AU and is moving inward (gt
90 km s-1?) compression ratio between 2.4 and 3.0
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how about energetic particles?

• besides SEPs, ACRs, GCRs there are TSPs recently
• TSPs are energetic termination shock particles
  (e.g., protons at several MeV)
• strongly affected by heliospheric disturbances
  such as MIRs

Stone et al. 2005
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TSPs

• mysterious streaming outward along B field
  upstream of TS
• source located several AU closer to the sun and
  closer to the pole than Voyager 1
• TS distorted by LISM B field or interstellar wind

Decker et al. 2005
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TSPs before and after TS

• upstream
• field-align beaming
• large intensity variation
• large spectral slope variation (-1 to -2)
• heliosheath
• reduced anisotropy
• less intensity variation
• less spectral slope variation (-1.26 to -1.56)
• spectral break varies very little ( 3.5 MeV)
• same source for upstream and heliosheath (steady
  source from TS)
• reason of break unknown (cf., spectral break in
  ACR comes from adiabatic deceleration)

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ACRs

• anomalous CRs are
• interstellar neutrals ionized by UVpickup by
  solar wind at around 1 KeV/nucleonthen
  accelerated by TS to gt 10 MeV/nucleon
• ACRs are substantially modulated in the
  heliosheath
• source is somewhere beyond (may still be TS but
  at a distance from the region where Voyager 1
  crossed)

Stone et al. 2005
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ACR spectrum

• diffusive shock acceleration is alright
• however, 0.0420 MeV can also be explained by
  solar wind ram pressure heating at TS(Gloecker
  et al. 2005)

Decker et al. 2005
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ACR acceleration
further into heliosheath

• not quite what is expected
• the spectrum does not change and the intensity
  does not increase cross the shock
• low energy ions (lt 3 MeV per nucleon) are rapidly
  accelerated, while high energy ions are not
  affected by shock
• TS is a shock but not an efficient accelerator
• new physics is needed?some say yes and some say
  no, of course!

immediate downstream
Stone et al. 2005
immediate upstream
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TSPs and ACRs

• both ACRs and TSPs are accelerated pickup ions
  (e.g., both are deficient in carbon ions)
• two stagess acceleration first accelerate TSPs,
  then accelerate ACRs later (but further
  fractionation of H is needed in the second stage
  as H/He ratios are different)

Stone et al. 2005
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interplanetaryshocks
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connection to earth
magnetic field
energized particles
adapted from Lee 1983
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typical IP shock
ACE measurements 2000.06.202000.06.26

• most interplanetary shocks are CME driven shocks
• in situ measurements by ACE, SOHO, WIND, Ulysess,
  Voyagers, IMP8, ISEE3, Goes, etc.
• particles are energized, but
• seed population?
• location?
• self-excited waves?
• modified-shock?

Desai et al. 2003
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SEPs (solar energetic particles)
two types gradual and impulsivedifferent
isotopic compositions
associated with CMEs?
associated with flares?
Reames 1999
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spectrum from solar wind to CR energies
seed? high energy tail of solar wind? or
pre-accelerated suprathermal ions?
Mewaldt et al. 2001
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seed population

• solar wind ions or suprathermal ions?
• observation of IP shocks at 1 AU indicates seeds
  come from suprathermal ions pre-accelerated by
  solar flares or other IP shocks
• 3He rich events associated with solar flares

Desai et al. 2003
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acceleration sites for SEPs

• solar flares or CME driven shocks
• common view (but not all) is CME driven shocks
• how do we know
• timing
• spectrum and intensity of anisotropic
  ground-level events (GLEs)
• GLE-associated with CMEs
• solar gamma ray line flares has little
  correlation with SEPs

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self-excited waves

• the idea is waves excited upstream of the shock
  by energetic particles trap the particles for
  further acceleration
• the breaks in these spectra may be an indication
  of proton-excited Alfven waves (e.g., due to
  saturation)

Mewaldt et al. 2005
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direct measurement

• Bastille 2000 event (2000.07.15)
• self-excited Alfven waves by protons
• weakly super-Alfvenic ions generates ion whistler
  waves
• ions are trapped by these waves near shock and
  thus increasing the efficiency of shock
  acceleration

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2000.07.15 event (Bastile day event)
Terasawa et al. 2006
ACE news 91, 2005.08.30 (Kallenbach Bamert)
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modified shock?

• at strong shock, when accelerated particles gain
  enough energy, backreaction will take place
• SEPs suck up 10 of CMEs energy (dissipation of
  CME, modified shock?)

Mewaldt et al. 2005
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1994.02.21 event
2003.10.29 event (Halloween event)
Terasawa et al. 2006
shock precursor?
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complications

• both 3He and 4He intensities are increased at CME
  magnetic compression region (C) and CME fast
  forward shock (S)
• 3He/4He enhancement with respect to solar wind
• ion intensities at (C) is larger than at (S)
  indicates shocks are not the only acceleration
  mechanism in interplanetary space

ACE news 44, 2000.04.25 (Desai et al.)
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complications

• 2005.01.20 event pushes the shock model to its
  extreme parameters regime
• because of the fast rise time and intensity

Ryan et al. 2005
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factors affecting IP shock acc

• shock strength, velocity, size and curvature,
  lifetime, etc.
• quasi-parallel and quasi-perpendicular
• seed populations
• solar wind suprathermal
• solar flare suprathermal
• CMEs may or may not have associated shocks
• direction of CMEs propagation and connectivity
• a lot of things needs to be disentangled

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complicated business
Mason 2001
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some statistics
354 shocks

• how does energetic particle relate to shock
  parameter?
• no apparent trend from shock angle and speed
  (except maybe shock speed has to be large enough
  for large increase in intensity)

Cohen et al. 2005
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162 fast forward IP shocks (CME related)
ACE news 44, 2000.04.25 (Lario et al.)

• shock parameters may not govern the associated
  energetic particle event
• maybe the energetic particle event is a history
  of injections and accelerations (by other shocks
  or accelerators), while the shock is measured
  locally
• about half of the shocks do not affect
  pre-existing particle intensities, i.e., no shock
  acceleration (even for a few strong shocks)

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its goodstill lots of things to do
are you hungry for some?
to be contd
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the end