5 th RHESSI workshop, Locarno. WG 4 Report Participants: Steven ChristeSäm Krucker Brian DennisMonique Pick Lyndsay FletcherEd Schmahl Peter GallagherManuela Temmer Jean-Claude HénouxMikko Vaananen Hugh HudsonAstrid Veronig Haishen Ji

Programme Overview: (1) Presentations by each participant (2 by Brian) (2) Joint discussions with: WG3 on coronal sources WG5 on (new) observations for focus of theory group WG2 on annihilation line, FIP effect, atmospheric structure (3) Small group discussions and planning.

RHESSI Fe & Fe/Ni complex (6.7keV) Dennis Centroid energy varies with T & count rate. Equivalent width varies with T – But does not agree with current theoretical predictions Fe to Fe/Ni ratio varies with T. –Different dependence for different flares. Fe/Ni feature is a reliable indicator of presence of thermal plasma. Feature parameters determined by T, abundance

19-sep :39 Multi-instrument DEM McTiernan GOES+RHESSI differential emission measure calculations done for first time. An example 3 components – worrying large systematic errors between peaks Lowest T peak drops below significance early Position of peaks does not seem to vary through flare Will be extended to include CDS and XRM data

Update on the SMART-1 X-ray Solar Monitor Vaananen XRM measures 1-20 keV with energy resolution of 0.34 keV. Especially interesting for comparison with Fe/Ni complex. A number of flares observed: RHESSI/XSM inter-calibration work is proceeding.

Average Temperature : 10 MK (detector limited) Average Gamma : 5-7 Broad range of break energies: peak ~ 10 keV. RHESSI microflare statisticsChriste 8500 RHESSI microflares from A1 to C1 analysed. Spectrum fitted with thermal+power law NB – interpreting power-law section as thick target gives total non-thermal energies – ergs.

keV (dashed line) 25 – 50 keV (solid line) Chromospheric Evaporation Gallagher Electron energy flux and plasma flows measured as function of temperature in CDS/RHESSI impulsive phase. upflows downflows Consistent with gentle evaporation - assuming target area cm 2

Preflare (pre-impulsive) phenomena Schmahl Coronal source RHESSI imaging shows hard coronal source 10 mins before impulsive phase onset Spectrum well-fitted by broken powerlaw down to 5 keV Thermal component never dominates – like July 23 rd 2002 Flare related to nice CME in MLSO

E 20keV the emission is faint, with fast time variations Nov 18, 2003: GOES M4 >20 keV emission above thermal emission Upwards motion ~5-40 km/s HXR emission from 18-Nov-03 occulted flare Krucker

600 km/s + Rapidly moving Type III burst sourcesPick Series of Type III bursts, with sources moving outwards in corona along path of CME (temporal relation not clear) Potential reconstruction  Type IIIs, CME moving along open field

Impulsive phase:  Kinematics of LT & FPs is consistent  LT: higher energies at higher heights Altitude decrease of 3-Nov-2003 looptop source ~ 45 km/s „downward“. Simultaneous with change in spectrum Kinematics of RHESSI sources Veronig Spectral change corresponds to a) increase of T (thermal emission) and/or b) spectral hardening (non-thermal)

H  footpoint separation HXR source ‘height’ Motion of H  kernels and coronal sources Ji H  flare footpoint separation decreases along with projected HXR source height at impulsive onset – 4 examples

HXR footpoints and flare ribbons 17-Jan-05 Temmer HXR footpoints tracked and ‘reconnection rate’ (vB) measured. Tracks HXR flux well for one footpoint, but not the other

RHESSI keV RHESSI keV 07:01:31 – 07:02:01 07:02:01 – 07:02:30 07:02:30 – 07:03: Rate of change of ‘magnetic flux’, d  /dt, calculated from UV footpoint motions. HXR sources tend to be where d  dt highest UV footpoint motions and RHESSI sourcesFletcher

RHESSI and white light observations Hudson WL coincides with HXR source locations, but WL source sizes consistent with TRACE PSF (3-4 px = ~ 1000 km  area ~ cm 2 )

Pol. Levels: H  5.0, 6.0 % H  : 5.0, 6.0 % THEMIS flare spectropolarimetryHénoux HaHa 10:07 June radial tangential H  Int. H , H  and NaD2 lines linearly polarized in impulsive phase (1 flare). Polarization patches at the outer edge of the kernels. Polarization properties consistent with electron beams and their associated return current HbHb radial tangential H  Int. 10:07 June

WG4 Presentations - Wednesday 8 th June 10: :00 Introduction + preliminaries 11: :30 Dennis - Separation of Thermal and Nonthermal Emissions 11: :00 McTiernan - Multi-Instrument Differential Emission Measure Lunch 14: :30 Vaananen – XSM: A stellar X-ray Spectroscope for the Sun 14:30 – 15:00 Christe - Microflare Statistics and Frequency Distribution 15: :30 Schmahl - Hard & soft X-ray and EUV pre-flare phenomena Coffee break 16: :30 Gallagher - Chromospheric and Transition Region Response 16:30 – 17:00 Temmer - Hard X-ray emission & flare ribbon expansion 17: :30 Ji - Converging motion of solar flare kernels

Joint session with WG – Bone – multiwavelength observations of a partially occulted flare Krucker – Coronal HXR sources in partly occulted flares Dauphin - Veronig – X-ray looptop altitude decrease in an X-class flare Coffee 10:45 – 11:15 Hudson - Implications of compact footpoints 11:15 – 11:45 Henoux - Flare impact polarization observed with THEMIS 11:45 – 12:15 Fletcher - UV ribbons and Hard X-ray footpoints Lunch 14:00 – 14:30 Pick – Evidence for magnetic reconnection 14:30 – 15:30 All - Discussion with WG5 Friday 10 th June Dennis – Flare vs. CME energy WG 4 presentations - Thursday 9 th June