1. FLARE ENERGETICS:TRACE WHITE LIGHT AND RHESSI HARD X-RAYS* L. Fletcher (U. Glasgow), J. C. Allred (GSFC), I. G. Hannah (UCB), H. S. Hudson (UCB), T. R. Metcalf (CoRA) Overview: In this poster, we investigate the formation of the white light (WL) continuum during solar flares, and its relationship energy deposition by electron beams. We compare the beam power necessary to produce HXR and WL signatures Conclusion: We find insufficient power in electrons above 50keV to account for the WL continuum, but lower-energy electrons do contain enough power. This is consistent with overonisation of the chromosphere as a mechanism for continuum formation. Introduction: The earliest observation of a solar flare was of its white light signature. Because the WL continuum originates in the photospere, it has been argued that only the most energetic events produce a detectable WL signature. It has also been supposed by various authors that generation of a WL signature requires excitation of deep layers of the solar atmosphere by electron beams, and hence high fluxes of very energetic (E > 50keV) electrons. We have previously had no means of assessing the total WL (continuum) energy in the absence of UV observations. TRACE data now make that possible and with RHESSI data we can direct comparisons of these major energetic components of a solar flare. Spatial Relationship We have reconstructed RHESSI images at 25-50keV energies for 9 of the 11 events in Table 1 (two events could not be imaged) and overlaid them on TRACE WL or WL difference images. In seven of the nine cases we are able to confirm that, to within observational uncertainties, the HXR sources and TRACE WL footpoint sources, coincide. In the cases of 12-Nov-2002 and 12-Jun-2003 the main HXR sources are not cospatial with WL footpoints, and may be coronal sources. These are not used in our further energy analysis. White Light Energetics The flares in our sample have TRACE WL and 1700Å counts. These can be compared with model counts. HXR energetics We make a spectral fit (thermal plus power-law components) to each HXR source, and from the parameters of the non-thermal component we calculate the beam power above 20 and 50 keV. The total power (ergs s -1 ) above energy E o (keV) is TRACE WL or WL difference images, with RHESSI contours overlaid (0.2, 0.4, 0.8 of max) Time-series development of UV/WL spectral ratios in three different models: F10, F11, and one derived from Holman et al.’s fits to the RHESSI July 23, 2002 flare. DATE HXR PEAK GOES CLASS Beam power WL (ergs s -1 ) Beam power >20keV (erg s -1 ) Beam Power > 50keV (erg s -1 )  EbEb COMMENT 25-JUL-0203:59:04C2.7 4.7  10 25 6.4  10 22 7.2  1.0 14.7No HXR imaging 26-JUL-0319:00:35M1.0 2.2  10 27 2.7  10 24 7.3  0.1 14.2 04-OCT-0205:35:49M4.0 6.1  10 28 1.6  10 27 1.2  10 25 5.2  0.2 16.6 05-OCT-0210:41:58M1.2 1.8  10 27 2.7  10 27 2.6  10 25 5.1  0.1 14.5 12-NOV-0218:16:04C9.9 4.9  10 27 5.1  10 24 7.5  0.2 16.2coronal HXRs 12-JUN-0301:27:01M7.3 4.8  10 28 2.2  10 25 8.4  0.2 17.7coronal HXRs 23-OCT-0302:39:49M2.4 4.0  10 28 3.9  10 28 3.3  10 26 5.2  0.1 15.2 09-JAN-0401:40:17M3.2 3.8  10 28 8.4  10 25 6.7  0.1 14.9 22-JUL-0400:29:56M9.1 3.2  10 26 3.3  10 24 5.0  0.3 16.6 24-JUL-0400:35:30C1.6 5.0  10 26 7.9  10 24 4.5  0.2 16.4No HXR imaging 24-JUL-0413:34:38C4.8 3.4  10 30 1.5  10 28 2.8  10 26 4.4  0.1 14.6 The TRACE continuum data determine a power that we compare below with that inferred from the hard X-rays (see Table). The UV/WL model ratios (left) agree approximately with the observations, with the F11 model (beam power 10 11 erg cm -2 sec -1 ) coming closest. where B is the beta function, and  the photon spectral index (Brown. 1971) Results: The table shows the inferred beam parameters, with highlighted rows indicating those events for which we also have a white-light estimate. In these cases, the power needed for the WL exceeds that available in electrons > 50keV by an order of magnitude or more, but may be provided by a beam with cut-off between 10 and 20keV *This work uses the TRACE WL flares surveyed in Hudson et al. (2006), a sample of flares in the C1.6-M9.1 range with complete TRACE and RHESSI coverage.