Presentation on theme: "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."— Presentation transcript:
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 2. 2. 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 1. 1. Count rate spectrum file + response matrix file 20 - 60 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: http://hesperia.gsfc.nasa.gov/hessi/chifor
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 ? http://hesperia.gsfc.nasa.gov/hessi/chifor/may072002_html/feqw.htm http://hesperia.gsfc.nasa.gov/hessi/chifor/nov112003_html/nov112003.htm
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