Cristina Chifor SESI Student Intern 2005 Solar Physics, Code 612 NASA/Goddard Space Flight Center Mentors: Dr. Ken Phillips & Dr. Brian Dennis FE AND FE/NI SPECTRAL LINE COMPLEXES IN RHESSI SOFT X-RAYS

SOLAR FLARE X-RAYS 1. Non-Thermal   Synchrotron radiation   Electron kinetic energy higher than average thermal energy of plasma ELECTRONPROTONPHOTON BREMSSTRAHLUNG Thermal  Depends on the random thermal motion of the heated electrons  Maxwellian distribution of electron velocities

REUVEN RAMATY HIGH ENERGY SOLAR SPECTROSCOPIC IMAGER  X-ray/gamma-ray spectrometer : 3 keV – 17 MeV  9 Ge detectors  ~ 1 keV resolution  Images through modulation collimators (~2 arcsec resolution)  Movable shutters control high photon fluxes

SPECTRAL MODELLING “ One spectrum is worth a thousand images”…. A. Dupree.   Thermal component of flare X-rays ( 3 keV -20 keV )   Physical plasma properties: T, emission measure, elemental abundances etc.

Analyze the Fe (~6.7 keV) and Fe/Ni (~8 keV) line complexes in the soft X-ray part of the solar flare spectra from RHESSI. MAIN PROJECT GOAL : Why bother ? 1.Valuable diagnostic information about emitting plasma (e.g. T dependent) 2.Can determine the origin of flare plasma (since coronal Fe abundances ~ 4 x photospheric Fe abundances) 3.Better understand the RHESSI transmission as a function of energy in different attenuator states and the effects of increased count rates

FLARE SAMPLING FLARE SAMPLING   Isothermal approximation OK in the late decay stages   So, hunt for long duration, slowly decaying flares   IDL GUI to make quick plots of monthly GOES data   Any RHESSI data for the selected times (no data gaps, particle precipitation events, SAA) ? Using the Geostationary Operational Environmental Satellites (GOES).

METHOD Count rate spectrum file + response matrix file   s time bins   0.3 keV energy bins   1 isothermal component + 2 Gaussian lines (1 keV FWHM) centered at ~ 6.7 and 8 keV  Reduce chi-squared 2. Background subtraction 3.Choose model functions to fit ~ 5 – 15 keV 4.Fit model to data: In total, this summer: > 2000 spectra for > 30 flares 5. Calculate complexes EQW + plot vs. T

THE BULK OF RESULTS:

COMPLICATIONS : MULTI-THERMAL FLARE PLASMAS COMPLICATIONS : MULTI-THERMAL FLARE PLASMAS  Most evident during flare rise, peak, soon after peak.  Each T component in a multi-thermal plasma contribute to the fluxes in the Fe and Fe/Ni complexes ! To help with DEM analysis, we had guests this summer !   Dr. Janusz Sylwester (Polish Academy of Sciences)  RESIK (soft X-ray Bragg crystal spectrometer)  DEM – onology  RESIK vs RHESSI cross-calibrations  LiWei Lin (Harvard – Smithsonian Astrophysical Observatory)  Pint Of Ale

MORE COMPLICATIONS: INSTRUMENTAL High count rates in RHESSI detectors decrease energy resolution in the soft X-ray range and increase calculated T.   Line complexes difficult to detect. Fitting Gaussians vary in width.   Does this mean that results from lowest count rates (both sets of shutters in ) are most reliable ?

  RHESSI instrumental effects are important (e.g. high count rates decrease energy resolution in the soft X-ray range).   Multi – thermal flare plasma calls for DEM techniques. However, ok results where isothermal approximation appropriate.   Coronal origin of flare plasma (from calculated Fe abundances).   Fe and Fe/Ni EQWs vs. T follow theoretical diagnostic curves.   But, there may be a need for improved theoretical atomic calculations. “RHESSI Observations of the Solar Flare Fe and Fe/Ni Lines” : paper to be submitted to the Astrophysical Journal soon. CONCLUSIONS

SPECIAL THANK YOU: Dr. Ken Phillips Dr. Brian Dennis Ana Rosas Merrick Berg CUA International Office

END OF PRESENTATION

Count rate spectral fit in OSPEX

RHESSI count flux vs. time

Ingredients% by number of atoms% by mass Hydrogen - H Helium - He Oxygen - O Carbon - C Nitrogen - N Neon - Ne Silicon - Si Iron - Fe Magnesium - Mg Sulfur - S Argon - Ar Aluminum - Al Calcium - Ca Sodium - Na Nickel - Ni SUN RECIPE