High Resolution Imaging and EUV spectroscopy for RHESSI Microflares

S. Berkebile-Stoiser1, P. Gömöry1,2, J. Rybák2, A.M. Veronig1, M. Temmer1, P. Sütterlin3

1 IGAM/Institute for Physics, University of Graz, Austria2 Astronomical Institute, Slovak Academy of Sciences, Slovakia3 Institute for Solar Physics, The Royal Swedish Academy of Sciences, Sweden

Microflare observation campaign 2006Initiators: Jan Rybàk, Peter Gömory (AI/Slovak Academy of Sciences),

Astrid Veronig, Manuela Temmer, Sigrid Stoiser, IGAM/Institute of Physics, Uni Graz

Campaign Duration: June 28 – July 12, 2006

Goals: - study of the dynamics and fine structure of microflares

- Energy transfer and dynamics of waves in the chromospheric network

Instruments:• Dutch Open Telescope (DOT)• Coronal Diagnostic Spectrometer (SOHO/CDS)• Extreme Violet Imaging Telescope (SOHO/EIT)• Michelson Doppler Interferometer (SOHO/MDI)• Transition Region and Coronal Explorer (TRACE)• Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)• Kanzelhöhe Solar Observatory (KSO), Hvar Observatory

Data Description

Best Data Set: July 4, 2006 07:44 – 10:09 UT, Target: AR 10898

• DOT: H (656.3 nm, ± 0.35 Å), Ca II H (396.8 nm), G-Band (430.5 nm), blue and red continuum (432 and 651 nm) FoV: 85“ x 65“ Time Cadence : < 30 s Spatial Resolution: 0.2“ (speckled)

• CDS: He I (58.43 nm, T ~ 4x 104 K), O III (59.96 nm, T ~ 105 K), O V (62.97 nm, T ~ 2.5x 105 K), Ne VI (56.28 nm, T ~ 4x 105), Mg IX (38.6 nm, T ~ 1 MK), Si XII (52.07 nm, T ~ 2 MK) FoV: 2“x240“, sit and stare mode; rasters each ~5.5 hours for co-alignment Time cadence: 15 s Spatial resolution: 2“ x 1.6“ pixels

• MDI: high resolution white light images and magnetograms FoV: 614“ x 300“ Time cadence: 1 min Spatial Resolution: 0.6“/pixel

• TRACE: 17.1 nm, ~1 MK FoV: 511“ x 511“ Time Cadence: < 90 s Spatial Resolution: 0.5“/pixel

• RHESSI: > 3 keV FoV: full disk Time cadence: ~ 4 s Spatial resolution: ~ down to 2“ Spectral resolution: 1 keV no attenuation

SOHO/MDI White Light

Target AR 10898

3 RHESSI microflares observed by DOT and CDS (plus other instruments):

RHESSI peak times: ~08:26 UT, ~08:38 UT, ~08:45 UTGOES classification: < A9/A1 with/without background

Coronal appearance 08:26 UT event

RHESSI 3-8 keV

−1500, −600, −200 G

+70, +200 G

Contours:MDI Magnetic Field(~ 45 min earlier )

Images: TRACE 17.1 nm, T≈1 MK

jet

Coronal appearance 08:45 UT event

Images: EIT 19.5 nm, T≈1.5 MK

RHESSI 3-8 keV

DOT – Chromospheric Response

Chromospheric signatures 08:26 UT event

Hα velocity scale: [-5,5] km s-1

Chromospheric signatures 08:38 UT event

Chromospheric signatures 08:45 UT event

CDS spectrogram chromosphere

T≈ 40 000 K

CDS lightcurves 1st event

Log

In

ten

sit

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erg

s c

m-2 s

-1 s

tera

d-1

Å-1]

Velo

citie

s [k

m s

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1]

Northern footpoin

t

Southern

footpoint

CDS lightcurves 2nd event

Log

In

ten

sit

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erg

s c

m-2 s

-1 s

tera

d-1 Å

-

1]

Velo

citie

s [k

m s

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1]

CDS lightcurves 3rd event

Log

In

ten

sit

ies [

erg

s c

m-2 s

-1 s

tera

d-1 Å

-

1]

Velo

citie

s [k

m s

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1]

CDS Flows at the flare peak

08:26 UT event, southern brightening

-> such two-component profiles are observed at and between the both CDS brightenings

Velocities He I line

CDS spectrogram chromosphere

CDS spectrogram corona

T≈ 2 MK

CDS velocities - summary

• 1st event: downflows ∼10–40 km s−1 in He I, O V, Ne VI (Chromosphere, TR)• 2nd event: upflows ∼10–50 km s−1 in He I, O V, Ne VI

• 3rd event: - southern brightening: downflows ∼ 20 km s−1 in

He I and O V

• no clear velocity signal in the coronal Si XII line

• oppositely directed, high velocity flows at the flare peaks (spatially unresolved) in several lines: upflows: up to 80 km s−1 , downflows: up to 190 km s−1

• strong downflows (supersonic) into the penumbra in He I, O V -> consistent with plasma in free fall

Non-Thermal Electron Flux Density

Energy Flux Density: Energy flux/ Impact Area -> determines if evaporation is `gentle‘ or `explosive‘

Electron energy flux -> RHESSI, Impact area-> DOT (5∙1015 – 4 ∙ 1016 cm2)

Result: - high Energy Flux Density found: F ≈ 1.1 - 1.4 ∙ 1010 erg cm-2 s-1

- threshold from gentle to explosive evap.: ≈1010 erg cm-2 s-1

Conclusions• Imaging:

- Multi-wavelength appearance and magnetic field environment in basic agreement with the standard flare model

- finely structured brightenings (DOT, TRACE)

-DOT HDoppler maps: loop-shaped fibrils with enhanced

velocity between brightening -> twisting motions?

- Timing of the DOT and CDS emission follows RHESSI X-ray light curve

Conclusions

EUV Spectroscopy:

- comparison with flare simulations (e.g. Fisher et al. 1984): 1st event: explosive evaporation , 2nd event: gentle evaporation

- indications of twisting motions

- strong downflows into the penumbra -> plasma in free fall?

RHESSI Spectroscopy: - evidence for non-thermal e-

- non-th. energy flux density at the threshold between gentle and explosive evaporation

Fisher, G. H., Canfield, R. C., & McClymont, A. N. 1984, ApJ, 289, 414