Observational evidences of CR acceleration at shocks chung-ming ko institute of astronomy and department of physics, national central university, taiwan.

observational evidences of CR acceleration at shocks

chung-ming koinstitute of astronomy and

department of physics, national central university, taiwan

KAW4, KASI, Daejeon, Korea, 2006.05.17

shocks, shocks everywhere

from interplanetary shocks to stellar wind termination

shocks to supernova remnant shocks to merger shocks to …

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

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 …

Voyager 1 has crossed the solar termination shock

Voyager 1 & 2 (Voyager Interstellar Mission,VIM)

launch outward directiontermination Shock

heliopause

Voyager 11997.09.05

35.55o ecliptic latitude260.78o ecliptic longitudeat 3.50 AU/year

cross on 2006.12.16at 94 AU

expect to reach in 2015

Voyager 21997.08.20

47.46o ecliptic latitude, 310.89o ecliptic longitudeat 3.13 AU/year

could cross between 2008 and 2010

reach in 10 years after crossing TS

voyage to the edge of heliosphere

counterclockwise from top right Frisch et al. APOD20020624Fisk (2005)Decker et al. (2005)

heliosphere is just one more bubble in the sky but smaller

bow shock near young star

planetary nebulawind bubble from hot star

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

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 (> 90 km s-1?)compression ratio: between 2.4 and 3.0

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

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

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)

ACRs

anomalous CRs are interstellar neutrals

ionized by UVpickup by solar wind at around 1 KeV/nucleonthen accelerated by TS to > 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

ACR spectrum

diffusive shock acceleration is alright however, 0.04~20

MeV can also be explained by solar wind ram pressure heating at TS(Gloecker et al. 2005)

Decker et al. 2005

ACR acceleration

not quite what is expected the spectrum does not

change and the intensity does not increase cross the shock

low energy ions (< 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!

Stone et al. 2005

further into heliosheath

immediate upstream

immediate downstream

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

interplanetaryshocks

adapted from Lee 1983

energized particles

connection to earth

magnetic field

typical IP shock

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? …

ACE measurements2000.06.20~2000.06.26

Desai et al. 2003

SEPs (solar energetic particles)

Reames 1999

two types: gradual and impulsivedifferent isotopic compositions

associated with

flares?

associated with

CMEs?

spectrum from solar wind to CR energies

seed?high energy tail of solar wind? or pre-accelerated suprathermal ions?

Mewaldt et al. 2001

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

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 …

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

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

ACE news #91, 2005.08.30 (Kallenbach & Bamert)

Terasawa et al. 2006

2000.07.15 event (Bastile day event)

modified shock?

at strong shock, when accelerated particles gain enough energy, backreaction will take place

SEPs suck up ~10% of CME’s energy (dissipation of CME, modified shock?) Mewaldt et al. 2005

Terasawa et al. 2006

shock precursor?

1994.02.21 event 2003.10.29 event (Halloween event)

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.)

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

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

complicated business

Mason 2001

some statistics

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

354 shocks

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)

162 fast forward IP shocks (CME related)

ACE news #44, 2000.04.25 (Lario et al.)

it’s goodstill lots of things to do

to be cont’dare you hungryfor some?

the end