Preflare physical conditions

inferred from HinodeHugh Hudson (UC Berkeley)

and Ed DeLuca (CfA)

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

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B3.2

Three Microflares

Microflare #1

Microflare #1: New features flare

Microflare #2

Microflare #2: Could be pre-existing

Microflare #3

Microflare #3: New features flare

Preflare (log) Flare (log) Difference

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?

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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?