Energy Release and Particle Acceleration in Solar Flares Nicole Vilmer LESIA-Observatoire de Paris VII COLAGE-Atibaia 01/04/04

Magnetic energy release in the solar corona: CME’s (see previous talks) But ALSO EFFICIENT PARTICLE ACCELERATION

Flare Accelerated Particles  Particle acceleration (Where, How Fast? How Many? Which Ones?)  Injection in the interplanetary medium (Where? When? Relation with flare particles?)

Hard X-ray/  -ray continuum (HXR/GR): ~ 10 keV-~100 Mev (up to GeV) electrons (acceleration time scales, energy spectra, number)  -ray line radiation (GRL) : a few MeV/nuc-a few GeV/nuc ions (acceleration time scales, energy spectra, abundances…) High energy (~75 MeV)  -ray continuum and neutrons: > 100 MeV/nuc ions (acceleration time scales, energy spectra, numbers) Observations of several thousands of X-ray flares 30 GRL flares on 3 solar activity cycles Main scientific goal of RHESSI Direct diagnostics of accelerated particles interacting in the solar atmosphere

RHESSI observations SXR emission Hot plasma (a few MK ) HXR emission Bremsstrahlung from non Thermal electrons Prompt  -ray lines: Deexcitation lines from C and 0 (60%) due to interactions from > Mev Protons and alphas Neutron capture line: p on heavy ions produce neutrons Neutrons are slowed down and captured by ambient hydrogen  deuterium MeV.

X/  -ray spectrum RHESSI Energy range Pion decay radiation (ions > 100 MeV/nuc) sometimes with neutrons Ultrarelativistic Electron Bremsstrahlung Thermal components Electron bremsstrahlung  -ray lines (ions > 3 MeV/nuc) T= K T= K Phebus/Granat observations

Energetic Ions   -ray line spectroscopy   ions in the 1MeV/nuc -100 MeV/nuc range   narrow deexcitation  -ray line fluences  ion energy spectrum and target abundances (i.e. solar atmosphere)  Broad  -ray lines  abundances of accelerated ions  2.2 MeV deuterium line: capture line after thermalization from neutrons from nuclear reactions (Share & Murphy,2000)

Decimetric/metric emissions Non thermal electrons Propagating in the corona Plasma emissions Cm/mm radio emissions Gyrosynchrotron emissions from >100 keV-1 MeV electrons In the corona HXR emissions Bremsstrahlung radiation from >10 keV- 10 MeV electrons in the chromosphere

Particle acceleration associated with solar flares in active regions  Electrons from 10 keV to GeV  électrons > 25 keV  ergs > 25 keV  Ions from 10 MeV to GeV  > 30 MeV  ergs > 1 MeV From many flares observed by SMM YOHKOH-GRANAT-CGRO (with limited spectral resolution) to ergs released timescales from a second to tens of minutes

Principal Investigator: Robert Lin UCB Project Manager: Peter Harvey UCB Lead System Engineer: David CurtisUCB Lead Co-Investigator: Brian Dennis GSFC Co-Investigators: Arnold Benz ETHZ Patricia Bornmann NOAA John Brown U. of Glasgow Richard Canfield Montana State U. Carol CrannellGSFC Gordon EmslieU. Alabama Huntsville Shinzo Enome Gordon HolmanGSFC, Code 682 Hugh Hudson UCB Gordon HurfordGSFC,Code 682 Takeo KosugiNAOJ Norman Madden LBNL Reuven RamatyGSFC, Code 661 Frank van BeekDelft U. Nicole VilmerParis Observatory Tycho von RosenvingeGSFC, Code 66 Alex ZehnderPSI

RHESSI Characteristics  Imaging  Angular resolution  Field of View  Spectroscopy  Energy range  Energy resolution  Fourier-transform imaging with 9 bi-grid rotating modulation collimators  2.3  to 36  depending on energy  HXR 2.3  ; GRL /GR 36   Full Sun  Tens of ms for basic image  (near future)  2s for detailed image  3 keV to 10 MeV  < 1 keV 5 20 MeV

 First RHESSI observations of a solar  -ray line flare : images and spectra at high resolution (23/07/02 event)  Electron & Ion interaction sites: First images at gamma-ray energies  Electron & Ion production time profiles: effects of transport in the solar atmosphere?  Some preliminary observations of the gamma-ray flares in October/November 2003  Relationship between cm/mm emitting electrons and HXR/gamma-ray ones: towards higher frequencies: Evidence of flat energetic electron components above 1 MeV

23/07/2002 X4.8 GOES: RHESSI  -ray line flare Lin et al, 2003 (ApJ, October 2003) Images:64’’ wide At the time of flare maximum

Early phase: evidence of production of non Thermal electrons in the corona From Lin et al, keV contours with TRACE 195 A Thermal + steep double Law components : E >20 keV > ergs in this phase Mostly released in the corona (compared to total energy :10 31 ergs above 30 KeV

First impulsive peak 40 MK + 2 power laws Lin et al, 2003, Krucker et al, 2003

Second impulsive peak Apparent movement of northern footpoint and Coronal source // ribbon (  50 km/s) No systematic motion of southern footpoint Reconnection in highly sheared region?

Halpha-HXR movie Courtesy S. Krucker)

Spectral evolution movie Holman et al 2003

X4.8 flare : 23/07/2002 Imaging spectroscopy with RHESSI Emslie et al, 2003 N M x0.1 Sx0.01 Photon spectrum

Lin et al, MeV line Nuclear Prompt lines Electron bremsstrahlung

Electron & Ion Production Time Profiles Spectral analysis 6 narrow lines Broken electron power law Broad nuclear line component 511 keV and 2.2 MeV lines Share et al, 2003 Radiation from electrons Radiation from ions (delay of ~ 10s: transport Effects) E >2.5 MeV  ergs

Smith et al, 2003 Redshift ( %)larger than expected for a limb flare if Downward isotropic distribution if Radial B field! SMM 5 flares Same longitude Broadening % FWHM No redshift (light curve) Redshift (Heavy curve)

First gamma-ray images of a flare! Gamma-ray line image displaced from 20 ’’ from electron emission site!!! Interpretation? Hurford et al, TRACE post flare loop

X/  -ray spectrum RHESSI Energy range Pion decay radiation (ions > 100 MeV/nuc) sometimes with neutrons Ultrarelativistic Electron Bremsstrahlung Thermal components Electron bremsstrahlung  -ray lines (ions > 3 MeV/nuc) T= K T= K Phebus/Granat observations

Bremsstrahlung and Synchrotron Emitting Electrons (I): Electron « broken » energy spectra  Many evidence from HXR/GR observations that hardening of electron spectra above a few hundred keV (i.e. electron dominated disk event but also GRL events)  Evolution of the break energy in the course of the event  Relation between mm/cm emitting electrons and electrons above Eb PHEBUS& Bern Trottet et al (1998)

Bremsstrahlung and Synchrotron Emitting Electrons (II): Production of submm emissions by ultrarelativistic electrons? First detection at 212 GHz Now also at 405 GHZ (Kaufman et al, 2002,2004) From Trottet, Raulin, Kaufman et al, 2002 Gyrosynchrotron emission From power law energy distribution with  = 2.7 Corresponding to a mid size electron-dominated event above > 100 kev (no observations)

The Sun is an efficient particle accelerator  First observations of a solar  -ray line flare with high spectral and spatial resolutions: HXR imaging spectroscopy: variations of photon (electron) spectra from one HXR source to the other (e- transport in loops…) HXR images: spatial distribution and movements of footpoint sources consistent with magnetic reconnection scenarios? HXR spectroscopy: precise determination of the electron spectrum from photon spectrum at high resolution GRL spectroscopy : measurements of redshifts  emissions by ions in tilted B fields GRL images: unexpected displacement between electron and ion interaction sites (acceleration? propagation and injection in  B fields? Other  -ray line observations in October/November ???

The Sun: an efficient particle accelerator  Bremsstrahlung and synchrotron emitting electrons Relationship between cm/mm and a few MeV electrons is it still true for ultrarelativistic electrons and for the production of submillimeter emissions?? Gamma-ray observations from 1 to 10 MeV (even > 10 MeV) with observations >100 GHz needed to conclude…