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RHESSI Microflare Statistics

RHESSI Microflare Statistics. Steven Christe 1,2 , Iain Hannah 2 , Säm Krucker 2 , J. McTiernan 2 , R. P. Lin 1,2 1 Physics Department, University of California at Berkeley 2 Space Sciences Lab, University of California at Berkeley. Past Work. HXR Slope : 1.5-1.7 SXR Slope : 1.7

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RHESSI Microflare Statistics

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  1. RHESSI Microflare Statistics Steven Christe1,2, Iain Hannah2, Säm Krucker2, J. McTiernan2, R. P. Lin1,2 1Physics Department, University of California at Berkeley 2Space Sciences Lab, University of California at Berkeley

  2. Past Work • HXR Slope : 1.5-1.7 • SXR Slope : 1.7 • EUV Slope : 1.7-2.5 • Magic Slope : 2

  3. Enter RHESSI • Provides unique sensitivity in the 3-15 keV energy range. • Effective area ~100 times larger than HXIS (SMM) at 10 keV. • Spectral resolution 1 keV. • Imaging down to 2 arcseconds.

  4. The Flare List • Created using the standard, time-tested, flare finding algorithm (by J. McTiernan) applied to the 6-12 keV channel. • Time period : Jan - Jun 2004 • Number of Flares : 8500 analyzed (1500) • Flare Frequency : 2 per hour • Flare sizes : A1 < GOES CLASS < C1

  5. The Flare List

  6. Flare Statistics • Min. Peak count rate - ~100/s (GOES CLASS A1) • Average Duration : ~ 2 minutes (4 s. resolution)

  7. Spectral Fitting - OSPEX Light curve Photon Spectrum

  8. Auto Flare Spectra - OSPEX • Created spectrum files for all times during the time period considered. • Night-time backgrounds were chosen for each flare. • Flares were split into 16 s intervals and fit automatically with a thermal continuum and a broken power law. • The total (thick target) nonthermal power is calculated for each interval and added to get the total nonthermal energy.

  9. Parameter Distributions • Average Temperature : 10 MK (detector limited) • Average Gamma : 5-7 • Broad Range of break of energies with some bias to 10 keV. NOTE : Red lines represent an imposed cutoff.

  10. Energy Distribution

  11. Region of Validity • Large flares (~105 peak count rate) are excluded. • Flares with less than ~100 peak count rate were not easily imaged. • Trusted energy range ~ 1029- 1030 erg.

  12. Past Work • HXR Slope : 1.5-1.7 • SXR Slope : 1.7 • EUV Slope : 1.7-2.5 • Magic Slope : 2 • RHESSI Slope : ~1.4 in 1029-1030 erg range.

  13. Some Questions Marks Instrument sensitivity? ???

  14. Conclusions • A typical microflare : • last a ~2 minutes • Temperature of 10 MK • Power law index ~ 6 • Low Energy Cutoff ~ 7-10 keV • Total Energy ~ 1029 erg • Down to 1029 erg, • the energy contained in microflares seems insufficient to heat the Corona. • There is no evidence of a break to a steeper slope.

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