preflare physical conditions inferred from hinode hugh hudson (uc berkeley) and ed deluca (cfa)
Post on 22-Dec-2015
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TRANSCRIPT
Comments
• Theorists want to know what conditions prevail when a flare happens
• Hinode has the best resolution ever• We reconnoiter the XRT data• EIS data are in principle much more
powerful for this purpose
Methods
• Identify flares/microflares in XRT movies
• Try to identify common footpoints• Do RTV-based analysis to get limits
C-class flare of 2007 June 5
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Analysis for preflare (T, n)
S = n2f(T)V XRT responseT ~ (pL)1/3 RTV law
=> S ~ T4f(T)
Tf(T)1/4 = Tref f(Tref)1/4
* (S/Sref)1/4
Solve for T = T(Tref, S)
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The pre-event density n follows fromthe RTV scaling since n ~ T2 for a fixedreference geometry (nearby loop)
Results of RTV-based analysis
Temperature: < 1MKDensity: < 1 x 108 cgsPlasma beta: < 1 x 10-4
Alfvén speed: > 0.1 c (100 G)
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Brosius & Phillips, ApJ 613, 580 (2004):TRACE/SOHO/Yohkoh comparisons;
a possible counterexample?
Conclusions
• In several microflares and one C-class event, XRT usually sees an “empty corona” prior to the flare (at least 3/4 cases)
• Using RTV scaling to compare with similar AR loops, we find low temperatures and densities
• These imply low plasma beta and high Alfvén speeds (> 0.1c)
What is there before the flare?
W hat is there before the flare?Hinode can tell us whereMagnetic heating's brought to bearUpon coronal plasma rare
An X-ray image just before Shows the active-region coreTo have some loops, and rather moreEmptiness, void loops in store
Does a flare loop coincideWith preflare loop, or lie beside?The blink technique that we've appliedAllows us quickly to decide.
And thus we set an upper limit.We must now interpret it; To get a pre-flare pressure fitRTV can help a bit
Conclusions we can now unfold:The pre-flare plasma's thin and cold,Do not believe the textbooks oldHinode's worth its weight in gold
A curiosity indeed!That flare occurrence seems to needCold voids to be there as a seedFlare instability to breed.
Without loop interactionCan we trust in reconnection?Or can our (TBD) theory section
Invoke some brilliant new direction?