HHαα and hard X-ray observations and hard X-ray observations of solar white-light flaresof solar white-light flares

M. D. DingM. D. Ding

Department of Astronomy, Nanjing Department of Astronomy, Nanjing UniversityUniversity

A brief reviewA brief review

WLFs originate from WLFs originate from deeper layersdeeper layers than o than ordinary flaresrdinary flares

Many examples support a relationship bMany examples support a relationship between etween WL emissionWL emission and and energetic electrenergetic electronsons

Heating in the lower layers in WLFs remaiHeating in the lower layers in WLFs remains ns unsettledunsettled

Previous radiation and heating Previous radiation and heating mechanismsmechanisms

Hydrogen recombinationsHydrogen recombinations (free-bound transitio (free-bound transition) in chromosphere and n) in chromosphere and negative hydrogen emisnegative hydrogen emissionsion in photoshphere in photoshphere

Heating mechanisms:Heating mechanisms: electron beamelectron beam (Aboudarham & Henoux 1986)(Aboudarham & Henoux 1986) proton beamproton beam (Machado et al. 1978)(Machado et al. 1978) soft-X-ray irradiationsoft-X-ray irradiation (Henoux & Nakagawa 1977)(Henoux & Nakagawa 1977) EUV irradiationEUV irradiation (Poland et al. 1988) (Poland et al. 1988) Alfvén wave dissipationAlfvén wave dissipation (Emslie & Sturrock 1982) (Emslie & Sturrock 1982) BackwarmingBackwarming (Machado et al. 1989) (Machado et al. 1989)

Electron beamElectron beam ＋＋ BackwarmingBackwarming （（ Ding et al. 20Ding et al. 200303))

Example IExample I

The X10 WLF of 2003 October 29 (S15 W02) by The X10 WLF of 2003 October 29 (S15 W02) by BBSOBBSO at at 1.56 1.56 μμm m (Xu et al. 2004) (Xu et al. 2004)

Blue: RHESSI HXR 50-100 keV Blue: RHESSI HXR 50-100 keV Red: NIR continuumRed: NIR continuum

Example IIExample II

The X5.3 WLF of 2001 August 25 (S17 E34) observed by The X5.3 WLF of 2001 August 25 (S17 E34) observed by TRACETRACE (Metcalf et al. 2003) (Metcalf et al. 2003)

Gray images: TRACE WL White contours: YOHKOH HXGray images: TRACE WL White contours: YOHKOH HXR at 33-53 keV R at 33-53 keV

There are, however, examples showing the There are, however, examples showing the WL and HXR kernels are not cospatialWL and HXR kernels are not cospatial

The X2.2 WLF of 1991 DecThe X2.2 WLF of 1991 December 3 (N17 E72) obserember 3 (N17 E72) observed by ved by YOHKOHYOHKOH (Sylwest (Sylwester & Sylwester 2000)er & Sylwester 2000)

Gray images: WLGray images: WL Solid contours: HXR 33-53 Solid contours: HXR 33-53

keVkeV

Multi-wavelength observations of Multi-wavelength observations of white-light flarewhite-light flare

The M2.6/2B WLF of 2002 September 29 (N12 E21)The M2.6/2B WLF of 2002 September 29 (N12 E21)

The M2.1/1B WLF of 2002 September 30 (N13 E10)The M2.1/1B WLF of 2002 September 30 (N13 E10)

Simultaneously observed by Simultaneously observed by the imaging the imaging

spectrograph of the Solar Tower of Nanjingspectrograph of the Solar Tower of Nanjing

UniversityUniversity and by and by RHESSIRHESSI

The 2002 September 29 WLFThe 2002 September 29 WLF

Black contours: 15-50 keV HXR (06:36:00Black contours: 15-50 keV HXR (06:36:00——06:36:30 UT)06:36:30 UT) White contours: WL emission (06:36:16 UT)White contours: WL emission (06:36:16 UT) White-dashed line: MDI magnetic neutral lineWhite-dashed line: MDI magnetic neutral line

General featuresGeneral features

The RHESSI images resolve two conjugaThe RHESSI images resolve two conjugate footpoints (A and B)te footpoints (A and B)

The continuum emission and the HXR eThe continuum emission and the HXR emission are basically cospatialmission are basically cospatial

The magnitude of continuum emission iThe magnitude of continuum emission is not simply related to the electron beas not simply related to the electron beam flux m flux

RHESSI HXR images showing that FP A is harder than BRHESSI HXR images showing that FP A is harder than B

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

Comparison of Kernels A and BComparison of Kernels A and B

Kernel AKernel A Kernel BKernel B

Energy flux of Energy flux of electron beamelectron beam

11×10×1010 10

ergs cmergs cm-2 -2 ss-1-1

0.80.8×10×1010 10

ergs cmergs cm-2 -2 ss-1-1

Continuum Continuum enhancementenhancement ~4%~4% ~8%~8%

HHααline profileline profileStrong,Strong,

no central no central reversalreversal

Relatively Relatively weak, centrally weak, centrally reversedreversed

Continuum Continuum ContrastContrast

FP A: FP A: higherhigher coronal coronal pressurepressure

FP B: FP B: lowerlower coronal coronal pressurepressure

The 2002 September 30 WLFThe 2002 September 30 WLF

Black contours: 12-25 keV HXRBlack contours: 12-25 keV HXR White contours: WL emissionWhite contours: WL emission White-dashed line: MDI magnetic neutral lineWhite-dashed line: MDI magnetic neutral line

Motion of the flare footpoint in the continuuMotion of the flare footpoint in the continuumm

White-light & 12-25 keV HXR

ConclusionsConclusions The WLF is basically consistent with the The WLF is basically consistent with the electroelectro

n beam heatingn beam heating model model First detection of a WL First detection of a WL footpoint motionfootpoint motion Heating in the lower atmosphere responsible foHeating in the lower atmosphere responsible fo

r the WL emission is achieved through r the WL emission is achieved through backwarbackwarmingming

The The energy fluxenergy flux of the electron beam derived fr of the electron beam derived from the HXR spectra can explain the WL enhancom the HXR spectra can explain the WL enhancementement

The The coronal pressurecoronal pressure is crutial to the response is crutial to the response of the flare footpoints subject to electron beam of the flare footpoints subject to electron beam heatingheating