Recent developments in our understanding of solar energetic particles Karl-Ludwig Klein SoHO/EIT

Before the discovery of CMEs ( ), 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. Cohen, 2003 ICRC Rapporteur paper 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 ?

Gopalswamy et al JGR 109, A12105 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 JGR 109, A12105 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

Do fast CMEs produce SEP in the absence of ‘flares’ ? Marqué et al 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 ). SEP from the CME shock ?

Do fast CMEs produce SEP in the absence of ‘flares’ ? Marqué et al 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 ). 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 Adapted from Gopalswamy et al 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 ( ) –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 1.4 N14 W64 Do ‘confined’ flares produce SEP in the absence of CMEs ? X 1.4 N14 W64 Confined flare : no SEP no type III (no e  IP 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 ASR 13(9), 275; Krucker et al 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 ApJ 678, L63 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,  R H , 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 JGR, Masson et al. 2008) Release of relativistic p 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 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