Recent developments in our understanding of solar energetic particles
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Transcript of 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.
Particle acceleration in reconnecting current sheets : observational evidence
• 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
Masson et al. 2008, work in progress
SXR, EUV
B=0
HXR, RH, Ly, FIR
Masson et al. 2008, work in progress
Particle acceleration in reconnecting current sheets : observational evidence
• 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