Source sizes and energy partition from RHESSI imaging and spectroscopy Alexander Warmuth Astrophysikalisches Institut Potsdam

Thermal vs. nonthermal energy content What is the energy partition (thermal vs. nonthermal) in solar flares? How do these quantities change with flare importance? Consequences of energy partition: is it consistent with the standard picture (heating by nonthermal electron beams driving evaporation)?

Parameters from HXR spectral fits: - emission measure - temperature Parameters from HXR imaging: - thermal source area  thermal volume (direct) - footpoint area - footpoint separation  thermal energy: Thermal component: thermal volume (indirect) Parameters from HXR spectral fits: - total injected electron flux above low-energy cutoff  nonthermal energy Nonthermal component:

18 flares (from C5.5 to X17.2) Time series of HXR spectral fits: - VTH + THICK - corrected for decimation, albedo & pile-up  physical parameters Time series of HXR images: - images at thermal energies: thermal areas - images at nonthermal energies: footpoint areas & sep.  geometric parameters Method

HXR spectroscopy: Spectral time series

Area measurements Imaging algorithms used: CLEAN uniform weighting CLEAN natural weighting MEM_NJIT VIS_FWD Area measurements: CLEAN: gaussian fit to sources, FWHM, quadratic subtraction of CLEAN beam MEM_NJIT: area inside 50% contour VIS_FWD: area directly obtained from fit Volumes: direct: V dir = 4  /3 A th 3/2 indirect: V ind = A FP * l

Time series of an M-class flare: FWHM, area & volume CLEAN uniformVIS_FWD CLEAN naturalMEM_NJIT

Thermal volumes – direct & indirect method (cotemporal)

Thermal and nonthermal total energies

Radiative losses: after Cox & Tucker (1969) Conductive losses: approximation by Veronig et al. (2005) Losses from the thermal plasma

Radiative & conductive losses vs. nontherm. energy

Losses Conductive losses on the order of 1E32 erg in large flares But: simple model may be not applicable However: from SORCE observations: total radiative energy in 2003 Oct 28 flare: 4E32 erg (Kopp et al. (2004), Woods et al. (2004), Emslie et al. (2005)) are high conductive losses real after all?

Conclusions using several imaging algorithms gives error estimation on source areas & volumes good correlation between thermal & nonthermal energies strong radiative and conductive losses consistent with total radiated energy conduction could heat dense lower atmosphere which radiates in UV & WL Consequence: either low cutoff energy of nonthermal electrons or additional heating mechanisms