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Group V: Report

Group V: Report. Regular Members : K. Arzner, A. Benz, C. Dauphin, G. Emslie, M. Onofri, N. Vilmer, L. Vlahos Visitors: E. Kontar , G. Mann, R. Lin, V. Zharkova. Main Goals.

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Group V: Report

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  1. Group V: Report Regular Members: K. Arzner, A. Benz, C. Dauphin, G. Emslie, M. Onofri, N. Vilmer, L. Vlahos Visitors: E. Kontar, G. Mann,R. Lin, V. Zharkova

  2. Main Goals • Constrains on particle acceleration from the RHESSI data (close collaboration with all WGs) and other available sources of information on high energy particles • Discuss new theories on particle acceleration • Connecting theories on particle acceleration with the global magnetic topologies hosting flares and CMEs

  3. Constraints on Acceleration/Transport(Electrons) • Must produce an electron flux of at least 1037 electrons per second • Must be able to accelerate electrons on time scales at most 10 milliseconds • Must sometimes produce electron energies greater than at least 10’s of GeV • Mechanism must be able to produce a flattening of the electron distribution at energies on the order of 500 keV • Higher nonthermal hard X-ray flux statistically associated with harder spectra

  4. The Electron “Problem” • Efficiency of bremsstrahlung production ~ 10-5 (ergs of X-rays per erg of electrons) Electron flux ~ 105 hard X-ray flux • Electron energy can be 1032 – 1033 ergs in large events • Total number of accelerated electrons up to 1040 (cf. number of electrons in loop ~1038). • replenishment and current closure necessary

  5. Revised Numbers

  6. X/ -ray spectrum Thermal components T= 2 10 7 K T= 4 10 7 K Electron bremsstrahlung Ultrarelativistic Electron Bremsstrahlung -ray lines (ions > 3 MeV/nuc) SMM/GRS Phebus/Granat Observations GAMMA1 GRO GONG Pion decay radiation (ions > 100 MeV/nuc) sometimes with neutrons RHESSI Energy range

  7. Electron-Dominated Events • First observed with SMM (Rieger et al, 1993) • Short duration (s to 10 s) high energy (> 10 MeV) bremsstrahlung emission • No detectable GRL flux • Photon spectrum > 1 MeV (X-1.5—2.0) • For 2 PHEBUS events • if Wi>1MeV/nuc  We>20 keV • No detectable GRL above continuum • Weak GRL flares? Vilmer et al (1999) BATSE PHEBUS

  8. non-thermal thermal RHESSI two component fits: T, EM γ, F35

  9. spectral index flux Grigis & B.

  10. Energy dependent photon spectral index Interval 3 (peak of the flare) Spectral index evolution:

  11. Mean Electron Spectrum: Temporal evolution 1 3 5 RHESSI Lightcurves 3-12keV; 12-25keV; 25-50keV; 50-300keV 2 4 Temporal evolution of the Regularized Mean Electron Spectrum (20s time intervals) 3 1 2 4 5

  12. GOES 1-8 A DERIVATIVE Non-thermal preflare coronal sources

  13. RHESSI SPECTRA 5-50 keV Thermal+broken powerlaw Preflare period: 01:02:00-01:11:00 Broken powerlaw extends down to 5 keV Thermal component never dominates EM and T are poorly determined Chisquare ~ 1 if EM=0 (NB similar source in July 23rd 2002 event) White = photons, Green = thermal model, Red = broken powerlaw, Purple = background

  14. Electron spectrum at 1AU Typical electron spectrum can be fitted with broken power law: Break around: 30-100 keV Steeper at higher energies Oakley, Krucker, & Lin 2004

  15. Ions • Tens of MeV ions and hundreds of MeV particles can be accelerated at the same time; • We also see cases where we see a stage when hundreds of MeV ions are primarily accelerated.

  16. g-ray line emission can be delayed from hard X-rays from <2 to 10’s of sec. 50- 180 keV 275- 325 keV 4 – 6.4 MeV |-----20 sec----| 50- 180 keV 275- 325 keV 4 – 6.4 MeV |------100 sec------|

  17. June 3, 1982 - Evidence for delayed high-energy emission

  18. Constraints for Theory Radio spectral features and flares • Connection between hard X-ray features and spikes in the range 300-3000 MHz, corresponding to densities of 109 -1011, has always been a promising diagnostic of energy release • But there are some aspects hard to understand: frequently the spikes occur in a narrow frequency range for 10s of seconds, implying a fixed density in the energy release site. Energy release widespread over a large volume would produce spikes over a wide frequency (i.e. density) range • Wide range of burst types in this frequency range is hard to understand: what controls frequency drift rates of different features?

  19. Radio Emission at Decimetric Wavelengths

  20. Constraints for Theory Magnetic configuration of flares in the low corona • See configurations of all types in radio images: single “loops”, double “loops”, complex configurations • Frequently see magnetic connections over very large spatial scales • Magnetic field strength: spectra typically imply 500-1000 G in the radio source • But radio spectra are frequently flat-topped: hard to model, range of fields in the source (need FASR) • See both prompt precipitation, implying either rapid scattering of electron pitch angles or loops with little height dependence for B, and trapping, where radio is strong but X-rays are weak, implying little pitch angle scattering.

  21. Radio Flare Loop

  22. Geometry The MHD incompressible equations are solved to study magnetic reconnection in a current layer in slab geometry: Periodic boundary conditions along y and z directions Dimensions of the domain: -lx < x < lx, 0 < y < 2ly, 0 < z < 2lz

  23. Description of the simulations: equations and geometry Incompressible, viscous, dimensionless MHD equations: B is the magnetic field, V the plasma velocity and P the kinetic pressure. and are the magnetic and kinetic Reynolds numbers.

  24. Time evolution of the electric field The surfaces are drawn for E=0.005 from t=200 to t=300

  25. Kinetic energy as a function of time <E> (erg) t=400 t=300 Magnetic energy: Total final energy of particles: t (s)

  26. Energy spectra: e (blue) and p (black)upper panel – neutral, middle – semi-neutral,lower – fully separated beams 1.8 for p 2.2 for e 1.8 for p 2.2 for e 1.7 for p 4-5 for e 4-5 for p 2.0 for e 1.5 for p 1.8 for e

  27. Proton beam compensated by proton-energised electrons precipitate about 10s Pure electron beams, compensated by return current, precipitate in 1s The suggested scheme of proton/electron acceleration and precipitation

  28. Electron Acceleration in Solar Flares basic question: particle acceleration in the solar corona energetic electrons  non-thermal radio and X-ray radiation electron acceleration mechanisms:  direct electric field acceleration (DC acceleration) (Holman, 1985; Benz, 1987; Litvinenko, 2000; Zaitsev et al., 2000)  stochastic acceleration via wave-particle interaction (Melrose, 1994; Miller et al., 1997) shock waves (Holman & Pesses,1983; Schlickeiser, 1984; Mann & Claßen, 1995; Mann et al., 2001)  outflow from the reconnection site (termination shock) (Forbes, 1986; Tsuneta & Naito, 1998; Aurass, Vrsnak & Mann, 2002) radio observations of termination shock signatures HXR looptop HXR footpoints

  29. Outflow Shock Signatures During the Impulsive Phase Solar Event of October 28, 2003: • • X17.2 flare • RHESSI & INTEGRAL data (Gros et al. 2004) • • termination shock radio signatures start • at the time of impulsive HXR rise • • signatures end when impulsive • HXR burst drops off The event was able to produce electrons up to 10 MeV.

  30. Discussion I basic coronal parameters at 150 MHz ( 160 Mm for 2 x Newkirk (1961)) (Dulk & McLean, 1978) (flare plasma) shock parameter total electron flux through the shock

  31. Summary •  The termination shock is able to efficiently generate energetic electrons • up to 10 MeV.  Electrons accelerated at the termination shock could be the source of • nonthermal hard X- and -ray radiation in chromospheric footpoints • as well as incoronal loop topsources. • The same mechanism also allows to produceenergetic protons (< 16 GeV).

  32. Summary • The constrains on the acceleration are becoming so many and the ability of a single acceleration to handle all this become impossible- No unique acceleration • Shocks, stochastic E-Fields and turbulent acceleration enters into the picture • Synchronized from photosheric motions complex magnetic topologies maybe be the answer

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