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H α and hard X-ray observations of solar white-light flares

H α and hard X-ray observations of solar white-light flares. M. D. Ding Department of Astronomy, Nanjing University. A brief review. WLFs originate from deeper layers than ordinary flares Many examples support a relationship between WL emission and energetic electrons

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H α and hard X-ray observations of solar white-light flares

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  1. Hαand hard X-ray observations of solar white-light flares M. D. Ding Department of Astronomy, Nanjing University

  2. A brief review • WLFs originate from deeper layers than ordinary flares • Many examples support a relationship between WL emission and energetic electrons • Heating in the lower layers in WLFs remains unsettled

  3. Previous radiation and heating mechanisms • Hydrogen recombinations (free-bound transition) in chromosphere and negative hydrogen emission in photoshphere • Heating mechanisms: electron beam(Aboudarham & Henoux 1986) proton beam(Machado et al. 1978) soft-X-ray irradiation(Henoux & Nakagawa 1977) EUV irradiation (Poland et al. 1988) Alfvén wave dissipation (Emslie & Sturrock 1982) Backwarming (Machado et al. 1989)

  4. Electron beam＋Backwarming（Ding et al. 2003)

  5. Example I • The X10 WLF of 2003 October 29 (S15 W02) by BBSO at 1.56 μm (Xu et al. 2004) • Blue: RHESSI HXR 50-100 keV Red: NIR continuum

  6. Example II • The X5.3 WLF of 2001 August 25 (S17 E34) observed by TRACE (Metcalf et al. 2003) • Gray images: TRACE WL White contours: YOHKOH HXR at 33-53 keV

  7. There are, however, examples showing the WL and HXR kernels are not cospatial • The X2.2 WLF of 1991 December 3 (N17 E72) observed by YOHKOH (Sylwester & Sylwester 2000) • Gray images: WL Solid contours: HXR 33-53 keV

  8. Multi-wavelength observations of white-light flare • The M2.6/2B WLF of 2002 September 29 (N12 E21) • The M2.1/1B WLF of 2002 September 30 (N13 E10) • Simultaneously observed by the imaging spectrograph of the Solar Tower of NanjingUniversity and by RHESSI

  9. The 2002 September 29 WLF A • Black contours: 15-50 keV HXR (06:36:00—06:36:30 UT) • White contours: WL emission (06:36:16 UT) • White-dashed line: MDI magnetic neutral line B

  10. General features • The RHESSI images resolve two conjugate footpoints (A and B) • The continuum emission and the HXR emission are basically cospatial • The magnitude of continuum emission is not simply related to the electron beam flux

  11. A • RHESSI HXR images showing that FP A is harder than B B

  12. Power-law fitting of the HXR spectra for kernels A and B A B

  13. Comparison of Kernels A and B

  14. Continuum Contrast

  15. FP A: higher coronal pressure • FP B: lower coronal pressure

  16. The 2002 September 30 WLF • Black contours: 12-25 keV HXR • White contours: WL emission • White-dashed line: MDI magnetic neutral line

  17. Motion of the flare footpoint in the continuum White-light & 12-25 keV HXR

  18. Conclusions • The WLF is basically consistent with the electron beam heating model • First detection of a WL footpoint motion • Heating in the lower atmosphere responsible for the WL emission is achieved through backwarming • The energy flux of the electron beam derived from the HXR spectra can explain the WL enhancement • The coronal pressure is crutial to the response of the flare footpoints subject to electron beam heating

  19. Thank You!

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