Recent developments in our understanding of solar energetic particles

1. SoHO/EIT Recent developments in our understanding of solar energetic particles Karl-Ludwig Klein (ludwig.klein@obspm.fr)

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

3. Flares, CMEs, and the acceleration of SEP events : the view of the 1990s • Reames 1999 SSR 90, 413 : claims a neat separation of ‘impulsive’ (flare-accelerated) and ‘gradual’ (CME shock accelerated) SEP events : ‘gradual’ ‘impulsive’ C.M.S. Cohen, 2003 ICRC Rapporteur paper • But : • flares/CMEs in both types of events • abundances and charge states are energy-dependent

4. SEP acceleration : which role do flares and CME play ? • 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 ? Event-integrated energy spectra during two large SEP events (ACE & Wind; Tylka et al 2005 ApJ 625, 474)

5. Flares, 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 Gopalswamy et al. 2004 JGR 109, A12105

6. Flares, 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 1990, Astron. Nachr.. 311, 379 Gopalswamy et al. 2004 JGR 109, A12105

7. Do fast CMEs produce SEP in the absence of ‘flares’ ? • 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 ? Marqué et al. 2006 ApJ 642, 1222

8. Do fast CMEs produce SEP in the absence of ‘flares’ ? • 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 ! Marqué et al. 2006 ApJ 642, 1222

9. Do ‘confined’ flares produce SEP in the absence of CMEs ? • 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 Adapted from Gopalswamy et al. 2004 X class 2

10. Do ‘confined’ flares produce SEP in the absence of CMEs ? X 1.4 N14 W64 X 1.4 N14 W64 GOES (Yashiro, CME catalog) • Confined flare : • no SEP • no type III (no eIP space) WIND/WAVES

11. Flares, CMEs and SEP events : a statistical view • 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 !

12. Particle acceleration in reconnecting current sheets : observational evidence Masson et al. 2008, work in progress • Hard X-ray sources : simultaneous double footpoints • Rapidly varying source positions (fragmented acceleration region) • Complex acceleration time history. Reconnection in the corona. RHESSI / Krucker et al. 2008 ApJ 678, L63 http://cse.ssl.berkeley.edu/hessi_epo

13. Particle acceleration in reconnecting current sheets : observational evidence Masson et al. 2008, work in progress Release of relativistic p • Hard X-ray sources : simultaneous double footpoints • Rapidly varying source positions (fragmented acceleration region) • Complex acceleration time history. Reconnection in the corona.

14. Particle acceleration in reconnecting current sheets : observational evidence Masson et al. 2008, work in progress Release of relativistic p 1.4-1.5 AU SXR, EUV HXR, R H, Ly, FIR B=0 • 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)

15. Inj. time profile Radio time profile ACE/EPAM • Particle acceleration in the magnetically stressed corona in the aftermath of a CME  Particle acceleration in reconnecting current sheets : CME and SEP Maia, Gama, Mercier, Pick, Kerdraon, Karlicky 2007 ApJ 660, 874 • 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) (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).

16. Perspectives for understanding SEP acceleration and propagation • 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 !

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