Hard X-Ray Imaging of Solar Flares

Foreword
Preface
Contents
Acronyms
1 Hard X-Ray Emission in Solar Flares
	1.1 A Brief Overview of Solar Flares
	1.2 Hard X-Ray Emission from Flares
		1.2.1 Acceleration of Nonthermal Electrons
		1.2.2 Hard X-Ray Production by Accelerated Electrons: The Bremsstrahlung Process
		1.2.3 Relation of the Mean Source Electron Spectrum to the Accelerated Spectrum
	1.3 History of Solar Hard X-Ray Imaging Observations
2 X-Ray Imaging Methods
	2.1 Medical Imaging
	2.2 Solar and Astrophysical X-Ray Imaging
	2.3 X-Ray Imaging Techniques
		2.3.1 Absorption
			2.3.1.1 Collimation
			2.3.1.2 Coded-Aperture Techniques
			2.3.1.3 Modulation-Collimator Techniques
		2.3.2 Scattering
		2.3.3 Reflection
		2.3.4 Diffraction
			2.3.4.1 Bragg Diffraction
			2.3.4.2 Fresnel Zone Plates
3 RHESSI and STIX
	3.1 RHESSI Design/Brief History of Concept Development
	3.2 The RHESSI Imaging Concept
	3.3 Strengths and Limitations of the RHESSI RMC Imaging Technique
	3.4 RHESSI Imaging Example
	3.5 SSW and the RHESSI GUIs
	3.6 STIX Design/Brief History of Concept Development
	3.7 The STIX Imaging Concept
	3.8 STIX Software
	3.9 RHESSI vs. STIX: A Comparison of Strengths and Limitations
4 Image Reconstruction Methods
	4.1 The Essence of the Image Reconstruction Problem
		4.1.1 Count-Based Versus Visibility-Based Imaging
		4.1.2 Point Spread Functions
	4.2 The Ill-posedness of the Image Reconstruction Problem
	4.3 The Regularization Concept
	4.4 Numerical Optimization
5 Count-Based Imaging Methods
	5.1 Back-Projection
	5.2 CLEAN
		5.2.1 Two-Step CLEAN Method
	5.3 Forward Fit
	5.4 Pixon
		5.4.1 Maximum Entropy Methods
		5.4.2 The Pixon Method
	5.5 Expectation Maximization
6 Visibility-Based Imaging Methods
	6.1 Visibilities
	6.2 Visibility-Based Methods
	6.3 VIS_FWDFIT
	6.4 Bayesian Optimization
	6.5 MEM_NJIT and MEM_GE
	6.6 uv_smooth
	6.7 VIS_CLEAN and Multi-Scale CLEAN
	6.8 Compressed Sensing: VIS_CS and VIS_WV
	6.9 Electron Flux Maps
7 Application to Solar Flares
	7.1 Number and Nature of Hard X-Ray Sources in the 2002 February 20 Event
	7.2 The Physical Nature of Multiple Hard X-Ray Sources in the 2002 July 23 Event
	7.3 Properties of the Electron Acceleration Region
		7.3.1 Using the VIS_FWDFIT Method to Estimate the Acceleration Region Length and Density
		7.3.2 Using the MEM_NJIT Method to Revisit Earlier Results
	7.4 Empirical Determination of the Electron Energy Loss Rate
	7.5 Hard X-Ray Imaging and the Global Energetics of Solar Flares
8 Future Possibilities
	8.1 STIX
	8.2 NuSTAR
	8.3 FOXSI
	8.4 Advanced Spaced-Based Solar Observatory
	8.5 GRIPS
	8.6 Hard X-ray Polarimetry
	8.7 Conclusion
References
Index