High Resolution Imaging and EUV spectroscopy for RHESSI Microflares S. Berkebile-Stoiser 1, P. Gömöry 1,2, J. Rybák 2, A.M. Veronig 1, M. Temmer 1, P. Sütterlin 3 1 IGAM/Institute for Physics, University of Graz, Austria 2 Astronomical Institute, Slovak Academy of Sciences, Slovakia 3 Institute for Solar Physics, The Royal Swedish Academy of Sciences, Sweden

Microflare observation campaign 2006 Initiators: 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, :44 – 10:09 UT, Target: AR 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 10 4 K), O III (59.96 nm, T ~ 10 5 K), O V (62.97 nm, T ~ 2.5x 10 5 K), Ne VI (56.28 nm, T ~ 4x 10 5 ), 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 RHESSI microflares observed by DOT and CDS (plus other instruments): RHESSI peak times: ~08:26 UT, ~08:38 UT, ~08:45 UT GOES 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≈ K

CDS lightcurves 1 st event Log Intensities [ergs cm -2 s -1 sterad -1 Å -1 ] Velocities [km s -1 ] Northern footpoint Southern footpoint

CDS lightcurves 2 nd event Log Intensities [ergs cm -2 s -1 sterad -1 Å -1 ] Velocities [km s -1 ]

CDS lightcurves 3 rd event Log Intensities [ergs cm -2 s -1 sterad -1 Å -1 ] Velocities [km s -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 1 st event: downflows ∼ 10–40 km s −1 in He I, O V, Ne VI (Chromosphere, TR) 2 nd event: upflows ∼ 10–50 km s −1 in He I, O V, Ne VI 3 rd 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∙10 15 – 4 ∙ cm 2 ) Result: - high Energy Flux Density found: F ≈ ∙ erg cm -2 s -1 - threshold from gentle to explosive evap.: ≈10 10 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 H  Doppler 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): 1 st event: explosive evaporation, 2 nd 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