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Yang Su NASA,CUA,PMO young.su@yahoo Gordon D. Holman NASA Brian R. Dennis NASA

Spectral Breaks in Flare HXR Spectra A Test of Thick-Target Nonuniform Ionization as an Explanation. Yang Su NASA,CUA,PMO young.su@yahoo.com Gordon D. Holman NASA Brian R. Dennis NASA Napa, CA Dec.10.0 8. 1/2 Nonuniform Ionization 1/3-1/2: Introduction 2/3-1/2: Models

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Yang Su NASA,CUA,PMO young.su@yahoo Gordon D. Holman NASA Brian R. Dennis NASA

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  1. Spectral Breaks in Flare HXR SpectraA Test of Thick-Target Nonuniform Ionization as an Explanation Yang Su NASA,CUA,PMO young.su@yahoo.com Gordon D. Holman NASA Brian R. Dennis NASA Napa, CA Dec.10.08

  2. 1/2 Nonuniform Ionization • 1/3-1/2: Introduction • 2/3-1/2: Models • 3/3-1/2: RHESSI Observation • 2/2 Time evolution and Imaging spectroscopy • Flux of one source from Clean, Pixon • time evolution of spectral breaks • Image Spectroscopy, spectra from footpoints (spectral breaks)

  3. 1/3-1/2 Introduction • Solar flare HXR spectra • single / double power-law • time evolution (Dulk et al. 1992; Lin & Schwartz 1987) • break energy: typically between ~50 and 100 keV • Spectral breaks is important • acceleration mechanisms • electron propagation and energy losses • relationships between flare X-ray sources, radio sources, and particles

  4. 1/3-1/2 Introduction • For the count and photon spectra • Instrumental effects, such as pulse pile-up (Smith et al. 2002) • Additional components, such as: • Albedo (Kontar et al. 2006; Kontar & Brown 2006; Zhang & Huang 2004) • emission from thermal plasma

  5. 1/3-1/2 Introduction • For the accelerated electrons • Non-power-law electron distribution from the acceleration process, e.g. • a double power-law electron distribution • a low-energy cutoff (Gan et al. 2002; Sui et al. 2007) • a high-energy cutoff (Holman 2003) • An anisotropic electron pitch-angle distribution (Petrosian 1973; Massone et al. 2004) • Beam-plasma instability (Holman et al. 1982; Melrose 1990) • Return current energy losses (Knight & Sturrock 1977; Zharkova & Gordovskyy 2006) • Nonuniform target ionization (Brown 1973; Brown et al. 1998; Kontar et al. 2002)

  6. 1/3-1/2 Introduction • Aims • Spectrum from nonuniform ionization thick-target with full cross section • Can nonuniform ionization model explain the spectral breaks in observations? • And how many?

  7. 2/3-1/2 Model • Nonuniform target ionization • Electron energy losses lower in un-ionized or partially ionized plasma than in fully ionized plasma • Brown et al. 1998, x(N) is the ionization level effective column density M

  8. 2/3-1/2 Model • linear-function • the atmospheric ionization • When N0 = N1=N*, step function • full relativistic cross section of Bethe and Heitler • step-function • Brown 1973, Kontar et al. (2002) • the atmospheric ionization • the Kramers approximation of the cross section, q=1

  9. 2/3-1/2 Model N step linear E*=E1=30 keV 1 1 N1 0 N0 0 0 Ee=60 keV stops here (M0)

  10. 2/3-1/2 Model δ=4.5 (best fit γ=3) (Brown 1973)

  11. 2/3-1/2 Model Fc=1035 electrons s-1; Ec= 1 keV Relation between N and E Photon flux from linear-function model (=0 for N1=N0)

  12. Photon spectra and photon spectral index γ from the four models with δ=4 Arrows: upward knee, downward knee and γ(ε) for fully ionized model (not constant)

  13. 2/3-1/2 Model Spectra from linear-function model with fixed E1 and increasing E0

  14. 3/3-1/2 RHESSI Observation • RHESSI flare sample • 2002 February 12 - 2004 December 31. Non-solar and particle events were excluded. • 12-25 keV count rate > 300 counts s-1 detector-1. the 50-100 keV count rate to be at least 3σabove the background count rate. (F50) • Radial distance > 927” from disk center (>~ 75 degrees longitude at the solar equator) • This minimizes the impact of albedo on the X-ray spectrum (Kontar et al. 2006) • Detectorcorrected count rate live times> 90%. This gave a final sample size of 20 flares. • This minimizes the impact of pulse pile-up (Smith et al. 2002; Ka·sparov¶a et al. 2007).

  15. 3/3-1/2 RHESSI Observation • 1/3 keV bins from 3 to 15 keV and 1 keVbins above 15 keV • All RHESSI front detectors • no 2 and 7 -- poor energy resolution • no 5 for the 30 Nov 2003 flare -- unusually low livetime • no 8 for some flares -- interference from RHESSI's communication antenna • One spin period, mostly at the HXR peak time • Full RHESSI response matrix, instrumental systematic uncertainty: zero (Sui et al. 2007) • Isothermal + three spectral lines+ nonthermal models • Two steps for fit, first fit above 6 keV, then fix thermal comp. then fit above 15 keV • the ion line complex at ~6.7 keV • the ion/nickel line complex at ~8 keV (Phillips 2004) • and a nonsolar line at ~10.5 keV • CLEAN Images : 40-60 keV for same time interval

  16. Examples for poor fit (left) and good fit (right)

  17. 3/3-1/2 RHESSI Observation fit results from: Bpow fit F_ion fit (Kramers) N_ion fit (full cs)

  18. 3/3-1/2 RHESSI Observation ∆γ VS δ ∆γ from bpow fit δ from step-function fit

  19. -1/2 Summary • full cs and Kramers (up to 36% on flux and 6.8% on γ) • step and linear • upper limit on ∆γ of spectra from nonuniform ionization model • In 20 F50 flares (around peak) • 5 with single , 15 with broken • 10 out of 15 F50 flares can not be explained by nonuniform ionization alone • All the 5 that can be explained by non-ion have DF sources

  20. 2/2 Time evolution and Imaging spectroscopy • Aims: • spectral breaks VS time • How HXR sources change when the spectra change from single to b-pow • spectrum from each footpoint • relation between spectral breaks for footpoints and total spectrum

  21. 2/2 Time evolution and Imaging spectroscopy • Flux from single source of one image: • flare id: 4010604, 22:32 • energy range: 40-60 keV

  22. 2/2 Time evolution and Imaging spectroscopy pixon D2-D8, -973.855, 75.125, 9 32.147 pixon D2-D8, including background model , 32.106 Clean D2-D8, different iterations, 300, stop if, 46.290 Normal, no stopMM=Media Mode 50: 51.356 50: 30.223 100: 43.952 100: 33.154 300: 37.070 300: 34.189 500: 35.290 500: 34.456 700: 34.434 700: 34.529 1000: 33.751 1000: 34.667 Clean D2-D8, 4.06s 100: 43.996 100: 33.311 300: 37.001 300: 34.196 1000: 33.477 1000: 34.514

  23. 2/2 Time evolution and Imaging spectroscopy 150-250 keV Pixon: center -972.855, 73.125, circle:9, 2.4521 Flux Area Centroid (X,Y) Peak (X,Y) St Dev (X,Y) Peak 2.4521 290.00 -973.92 72.75 -973.28 73.15 3.94 3.95 0.026954 Clean D2-D9, different iterations 300, stop if, 6.5105 MM: 4.0746 Normal, MM 50: 5.3177 50: 4.2477 100: 3.9565 100: 4.4367 300: 1.8182 300: 4.5518 500: 1.1578 500: 4.5647 700: 0.9261700: 4.5654

  24. 2/2 Time evolution and Imaging spectroscopy

  25. 2/2 Time evolution and Imaging spectroscopy

  26. 2/2 Time evolution and Imaging spectroscopy

  27. 2/2 Time evolution and Imaging spectroscopy

  28. 2/2 Time evolution and Imaging spectroscopy

  29. 2/2 Time evolution and Imaging spectroscopy

  30. 2/2 Time evolution and Imaging spectroscopy

  31. 2/2 Time evolution and Imaging spectroscopy

  32. ?/? The highest HXR source???

  33. ?/? Direct observation of reconnection??? To be continued

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