Recent developments in our understanding of solar energetic particles

Recent developments in our understanding of solar energetic particles

Karl-Ludwig Klein ([email protected])

SoHO/EIT

• Before the discovery of CMEs (1971-73), flares and filament eruptions were the only form of prominent transient activity. All other time-coincident activity (e.g. SEP events) was related to them.

• Since 1980s CMEs appeared as a new candidate particle accelerator, through the shock the fastest of them are expected to drive.

Flares, CMEs, and the acceleration of solar energetic particle (SEP) events

• Reames 1999 SSR 90, 413 : claims a neat separation of ‘impulsive’ (flare-accelerated) and ‘gradual’ (CME shock accelerated) SEP events :

Flares, CMEs, and the acceleration of SEP events : the view of the 1990s

C.M

.S. C

ohen

, 200

3 IC

RC

Rap

port

eur

pape

r

But :• flares/CMEs in both types of events• abundances and charge states are energy-dependent

‘impulsive’‘gradual’

SEP acceleration : which role do flares and CME play ?

Event-integrated energy spectra during two large SEP events (ACE & Wind; Tylka et al 2005 ApJ 625, 474)

• Two large SEP events : similar solar activity, but marked differences in abundances, E >10 MeV /n

• Tylka et al 2005 : shock acceleration in both events, but

– different geometries– different seed populations

(quiet corona vs flare suprathermals)

• Alternative : contribution of different acceleration processes (flare, CME-shock) at different E ?

Gop

alswam

y et al.

2004 JG

R 109, A

12105Flares, CMEs, SEP - statistical relationship

• All large SEP events (GOES) are accompanied by fast/broad CMEs and flares

• There is some correlation - with considerable scatter - between SEP intensity (p>10 MeV) and

– CME speed– Soft X-ray peak flux

Gop

alswam

y et al.

2004 JG

R 109, A

12105Flares, CMEs, SEP - statistical relationship

• All large SEP events (GOES) are accompanied by fast/broad CMEs and flares

• There is some correlation - with considerable scatter - between SEP intensity (p>10 MeV) and– CME speed– Soft X-ray peak flux– Gamma-ray peak flux (Chertok

1990)

• Are there ‘pure CME’ or ‘pure flare’ SEP ?

Chertok 1

990, A

stron. Nachr.. 311

, 379

Do fast CMEs produce SEP in the absence of ‘flares’ ?

Marqué et al. 2006 ApJ 642, 1222

• Attempt to isolate pure CME-shock-events :– Fast (>700 km/s) west-limb CME

(SoHO) : likely to drive shock.– EUV manifestations on disk, but no

metric radio emission : no evidence for particle acceleration related to a flare (3 events 1996-98).

• SEP from the CME shock ?

Do fast CMEs produce SEP in the absence of ‘flares’ ?

Marqué et al. 2006 ApJ 642, 1222

• Attempt to isolate pure CME-shock-events :– Fast (>700 km/s) west-limb CME

(SoHO) : likely to drive shock.– EUV manifestations on disk, but no

metric radio emission : no evidence for particle acceleration related to a flare (3 events 1996-98).

• SEP from the CME shock ? – None detected at GOES.– SoHO/COSTEP & ACE/EPAM: weak

or 0 (deka-MeV protons, hecto-keV electrons).

• Indication that CME shock alone is NOT an efficient SEP accelerator at these energies !

Do ‘confined’ flares produce SEP in the absence of CMEs ?

X class

Ada

pted from

Gopalsw

amy et al. 2

004

2

• Identify flares without CME (LASCO/SoHO or EIT/SoHO : no CME, no dimmings; Wang & Zhang 2007 ApJ 665, 1428) : – 11/104 X-class flares without CME

(1996-2004)– Confined / eruptive may depend

on location of energy release w/r

to the centre of the flaring AR;

higher magnetic flux above energy

release site in confined flares

• 4/11 confined flares in W solar

hemisphere : none has SEP

event detected by GOES; flux <1 pfu

X 1.4N14 W64

Do ‘confined’ flares produce SEP in the absence of CMEs ?

X 1.4N14 W64

Confined flare :• no SEP• no type III (no eIP space)

GOES (Yashiro, CME catalog)

WIND/WAVES

• It is difficult to identify ‘pure’ flares or ‘pure’ CMEs.• But : flares and CMEs appear necessary conditions for SEP

events :– no conspicuous SEP event without particle acceleration signatures in

the corona (radio), even when fast CME is observed;– no SEP event even with X class flares when they lack CME.

• Particle numbers in space and in the corona (EM radiation) :– A minor fraction of electrons escape to space (Ramaty et al. 1993 ASR

13(9), 275; Krucker et al. 2007 ApJ 663, L109)

– The ratio of escaping to interacting protons (>30 MeV) >1 or <1, depending on the event (Ramaty et al. 1993)

• Acceleration process during flares capable of accounting also for escaping SEP. There is no reason to suspect that flare-accelerated particles cannot contribute to large SEP events !

Flares, CMEs and SEP events : a statistical view

Masson et al. 2008, work in progress

Particle acceleration in reconnecting current sheets : observational evidence

RHESSI / Krucker et al. 2008 ApJ 678, L63http://cse.ssl.berkeley.edu/hessi_epo

• Hard X-ray sources : simultaneous double footpoints • Rapidly varying source positions (fragmented acceleration region)• Complex acceleration time history. Reconnection in the corona.


• Hard X-ray sources : simultaneous double footpoints • Rapidly varying source positions (fragmented acceleration region)• Complex acceleration time history. Reconnection in the corona.

Release of relativistic p


SXR, EUV

B=0

HXR, RH, Ly, FIR



• Hard X-ray sources : simultaneous double footpoints • Rapidly varying source positions (fragmented acceleration region)• Complex acceleration time history. Reconnection in the corona. • Closely related acceleration of interacting and escaping relativistic p

(Simnett 2006 A&A, Grechnev et al 2008 SP, McCracken et al. 2008 JGR, Masson et al. 2008)

Release of relativistic p

1.4-1.5 AU

ACE/EPAM

Particle acceleration in reconnecting current sheets : CME and SEP

• SoHO/LASCO : fast CME• Nançay RH : synchrotron

emission from relativistic electrons (behind CME front when bwd extrapolated; acceleration in the pertubed corona).

• + transport modelling (adiabatic focussing + PA scattering)

Maia, Gama, Mercier, Pick, Kerdraon, Karlicky 2007 ApJ 660, 874

• Particle acceleration in the magnetically stressed corona in the aftermath of a CME

Inj. time profile

Radio time profile

(see also Akimov et al. 1996 SP 166, 107; Klein et al 1999 AA 348, 271; Laitinen et al 2000 AA 360, 729; Klein & Trottet 2001, Spa Sci Rev 95, 215).

• How are CMEs and flares related (how do large scales and small scales couple in solar eruptions) ?

• What are the respective roles of the CME and the flare in particle acceleration & transport during large SEP events (how does the answer depend on SEP species and energy):

– SEP acceleration at the CME shock– SEP acceleration in the flaring AR / the relaxing post-CME corona

(« post » flare loops, arcade formation) : magnetic reconnection– Large-scale B field reconfiguration in the course of a CME

• Need for new coronagraphic & disk observations (SMESE), and for in situ measurements from a near-solar vantage point : Solar Orbiter !

Perspectives for understanding SEP acceleration and propagation

• A common idea since 1990 (cf. Reames 1999 SSR 90, 413) : – numerous small (« impulsive ») SEP are flare-accelerated particles

(magnetic reconnection)– ALL large (« gradual ») SEP events are accelerated at CME shocks

• From the report Managing Space Radiation Risk in the New Era of Space Exploration (Committee on the Evaluation of Radiation Shielding for Space Exploration, Nat. Res. Council, USA) : « In gradual SPEs, which have large intensities at energies relevant to astronaut radiation safety, shocks driven by fast CMEs are the dominant accelerator. »

• Present talk : this may be oversimplified.

Flares, CMEs, and the acceleration of solar energetic particle (SEP) events

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Recent developments in our understanding of solar energetic particles