I. Evidence of Rapid Flux　Emergence Associated with the

M8.7 Flare on 2002 July 26

Wang H. et al. 2004, ApJ, 605, 931

--using high temporal resolution BBSO vector magnetograms

Liu 2004-04-26 Kyoto Univ.

Introduction

• Flare-associated phenomena, e.g., emergence of magnetic flux and enhancement of magnetic shear, are undoubtedly important for understanding the basic physical process during solar flares. However, results from many previous studies are inconclusive or contrary

• For example, some people thought that rapid flux increase might be a common property of major solar flares (Kosovichev & Zharkova 2001; Spirock et al. 2002, Wang et al. 2002). However, Green et al. (2003) pointed out that no systematical or permanent magnetic changes associated with flares.

• Studies on relationship between flares and the magnetic nonpotentiality (e.g., magnetic shear) also present different results (decrease, increase or unchange)

In the present work, comprehensive coordinated observations supplied for an M-class flare, clearly showing an emerging flux as a trigger or a participant for the reconnection, associated with obvious enhancement of Bz, Bt and shear angle

Observations

• BBSO 19:00-24:00 UT

Hα (1”, 1min; 300”X300”)

magnetogram(0.6”, 1min; 2G - Bz, 20 G-Bt)• TRACE

1600 Å and 171 Å ( 0.5” )• SOHO

MDI ( 2”, 1min )• RHESSI

HXR images• SOHO

LASCO/C2 ( halo-CME )

RHESSI 5-10 keV

post-flare loops in EUV

northern footpoint

southern footpoint

All the observations suggest the fast emergence of new fluxes. It will be interesting to demonstrate in detail the evolution of some important parameters, e.g., Bz, Bt, shear angle, for the emerging flux region

• MDI magnetic flux evolution in the field of view

positive negative

GOES SXR flux

M8.7

M4.6

M5.3

parameters

BBSO - Bz

weighted mean shear angle (Wang,H., 1992)

unbalanced

Spirock et al. 2002

Hα 21:01 Hα 22:30

stable filament

TRACE images showing slowly rising post-flare loops which are very flat

evolution of the flare and the filament

Estimation of Erecin the corona

ribbon separating speed

electric current deduced

(Qiu, J., 2002)

Main Conclusions1.Both rapid increase of transverse fields an

d longitudinal fields are observed following the flare, showing a inclined loop emergence

2.Unbalanced Bz flux evolution observed for the two foot points, also complying the emergence of the low-lying loop deviated from solar center

3.This rising loop must has a close relationship to the trigger of the CME associated

II. Observations of Nonthermal and Thermal Hard X-Ray Spikes in an M

-class Flare

Ji, H. et al. 2004, ApJ, 605, 938

-- for the first time to study whether a HXR spike is thermal or nonthermal, with the aid of RHESSI data

Introduction

• Research of solar flares information of release of free energy and acceleration of particles

• Chromosphere brightening may be caused by nonthermal ionization Hα blue-wing increased emission, highly correlated with HXR sources both in locations and time profiles)

• Another heating mechanism is by conduction time delay between HXR and Hα

• Maybe both of them can operate in a same flare process

• Simultaneous Hα and HXR observations are expected

Introduction

• To identify whether it is thermal or nonthermal for a HXR emission is necessary

• Two ways : (1) examine the time delay between HXR and Hα emissions (2) study the HXR spectra to give electron distribution

• Until the launch of RHESSI is it possible to verify the claims of thermal and nonthermal heating mechanisms

• RHESSI is able to provide HXR/γ-ray image and spectrum with spatical resolution (2.3“, full-disk mode), spectral resolution of 1-10 keV and several seconds time resolution, for accurate position information

Observations

• BBSO Hα-1.3 Å, 40ms cadence, 0.5” resolution,

256X256 CCD. AR 0105 (2002 Sep 9, S07 E53). M2.3-class flare

• RHESSI, 4s time cadence, calibrated light curves and maps, co-aligned with Hα-blue data with an accuracy better than 1”

M2.3 flare (17:40-18:30 UT) 50 mins in SXRs and Ha center. About 20 mins in HXR and Ha blue wing

Flare time profiles

GOES8 0.5-4.0 Å

HXR 15-25 keV

25-50 keV

Hαcenter

Hαcenter

a1a2

db c+d

c

started 2 mins later from softer HXR

these spiky structures may be discrete impulsive energy release process and represent nonthermal HXR emissions

then our basic goals is to find HXR-associated peaks in Ha blue-wing kernels

quite different ?

Five flare ribbons in Ha center, three shown in Ha-1.3Å image (a1, a2, b)

EIT 195Å observation showing a flaring loop, which is thought to be a magnetic loop

EIT loop (bright part)

RHESSI 12-25 keV

(loop-top source) Ha -1.3Å

a2a1

b

a1 and a2 are conjugate kernels

a2-a1 Ha blue-wing curves are closely correlated with 25-50 keV HXR curve

a2

b

corresponding Ha-1.3Å spikes are found. their life time is 10-20 s

b does not resemble HXR profile, but its spikes 6-8 is obvious

40 s delay

loop-top source HXR spikes

a1

Image X-ray spectra of loop-top source for a number of time periods (I-VI), construct in 6 energy bands (10-12, 12-14, 14-17, 17-20, 20-28, 28-45 keV)

integrated flux in a box around the loop-top source

The spectra fits are constructed by minimum 2 fitting method (Lampton et al. 1976)

period I: heat conduction

period II: nonthermal electrons

period III: weaker nonthermal

In a conclusion: thermalnonthermal hard nonthermal soft, for the impulsive phase of the flare, unlike the usual soft hard soft process

=-5.6

-7.0

-7.3 -7.4

for comparison, 12-25 keV contours and 25-50 keV contours are overlaid on Ha blue-wing image (period II)

nonthermal heating

Simultaneously rising

for comparison, 12-25 keV contours and 25-50 keV contours are overlaid on Ha blue-wing image (period IV)

10s

the time delay 10s gives a speed of energy transport to be ~1500 km/s, suggesting a heating mechanism by thermal conduction

no detectable footpoint HXR sources

for comparison, 12-25 keV contours and 25-50 keV contours are overlaid on Ha blue-wing image (period V,VI)

weak footpoint HXR emissions

no time delay

period V VI

both of them are nonthermal heating

some discussion about the other ribbons b, c and d

kernel b, c and d may be conjugate and should have no direct relation to a1 and a2 for the following reasons:

• Kernel b shows poorer temporal correlations with HXR emissions ( e.g., 90 s time lagged for initiation, obviously moving away while a1 and a2 are stably compact, no HXR source associated, bright kernal ended much earlier)

• Summed light curve of c and d seems similar to that of b• Their Ha line-center profiles are different from a1 and a2• c and d in same magnetic polarity of positive, b in negative, so they

may be conjugate footpoints. Their brightening may be “remote brightenings” by interaction of flaring loops and preexisting higher loops (Wang H. et al., 2002) or triggered by magnetic instabilities resulted by the M-class flare

Possible reasons why there is no HXR emissions from b

(1) There were no accelerated electrons to this site, heated by thermal conduction

(2) The electron density was too low for the production of HXRs

(3) The dynamic range of HXR maps is relatively low (at present, ~10:1)

observed and predicted nonthermal heating

Estimation of excess flare emission in Ha blue wing ( Canfield & Gary, 1987)

Nearby continuum – constant

Residual intensity in blue wing

: electron beam spectral index

Nc: cutoff stopping depth -- constant

H: pre-flare scale height

q: characteristic heating per

hydrogen nucleus

K: a factor weakly dependent on the

beam parameters, -- constant (assuming 10keV for cutoff energy)

i, j : spike number, and

Predicted ratio:

Two other relations found for and q, therefore, the theoretic ratios of residual intensity for the spikes in H blue wing can be obtained

Results

predicted

observed

observed

1/0.13

1/0.371/0.59

1/0.14

1/0.391/0.60

Obviously, the first spike (spike 1) did not produce the predicted Ha blue-wing intensity

Summary and Conclusion

• In this flare, both nonthermal and thermal heating are revealed by their different properties (HXR emission source, spectral spikes, time delay, et al.)

• The thermal heating spike can be fitted by a double-temperature model, with a low energy transportation speed (1500km/s)

• It is also found non-HXR emission associated some Ha ribbons, which could be caused by several reasons (remote brightening; flaring loops interaction)

• According a comparison between theory and observation for excess flare emission in the Ha blue wing, it is found the first spike did not produce the predicted Ha intensity, which is probably attributed to the delay to ionization of cool chromosphere at the beginning of the flare.