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Conjugate Hard X-ray Footpoints in the ‘03/10/29 X10 Flare: Unshearing Motions, Asymmetries, and Correlations. Wei Liu 1 , Vahé Petrosian 2 , Brian Dennis 1 , & Gordon Holman 1 1 NASA Goddard Space Flight Center 2 Stanford University. 1. Introduction - PowerPoint PPT Presentation
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Wei Liu1, Vahé Petrosian2, Brian Dennis1, & Gordon Holman1
1 NASA Goddard Space Flight Center2 Stanford University
Conjugate Hard X-ray Footpoints in the ‘03/10/29 X10 Flare: Unshearing Motions,
Asymmetries, and Correlations
Contents1. Introduction
2. RHESSI observations of the hard X-ray footpoints in the 2003/10/29 X10 flare (a million $ event: Xu+04, Metcalf+04, Liu,C.+05, Krucker+05, Ji+08,…)
2.1 Source motions – footpoint unshearing & loop-top downward motion
2.2 Asymmetries – hard X-ray flux, magnetic field
2.3 Correlation – between hard X-ray flux and magnetic field strength
3. Summary and discussion
surface
corona
surface(movie courtesy of T. Forbes)
Original models:
Sturrock (1966), Hirayama (1974), Kopp & Pneuman (1976)
1. Introduction: Classic picture of two-ribbon flares (pre-RHESSI)
Loop-top X-rays
Footpoint X-rays
Loop-Top: red cntr, +’sFootPoints: cyan cntr, trianglesbkgrd: TRACE 195
Footpoint migration (on MDI)
2.1 Source motions
Source motions in detail
Anti-parallel (to N.L.) motion early on (also
Sakao+98, Masuda+’00)
Note the rotated “L” shape.
(Liu, Petrosian, Dennis, & Holman, ApJ, 2009 March, in press)
Source motions (vs. time)
Rapid decrease of footpoint shear cotemporary w/ loop-top downward motion
(see also Ji, H. et al. 2008)
(Liu et al. 2004; see also Sui & Holman 2003, Sui et al. 2004, Holman et al. 2005)
More loop-top downward motion: 2003/11/03 X3.9 flare
Downward motion
Cotemporary Footpoint unshearing & loop-top downward motions – interpretation & Discussion
* Ji et al (‘07): lower-lying, less sheared field lines=> less free-energy. Can such topological transition actually take place?
* Hudson (‘00): Implosion;
* Loop-top downward motion:
Longcope, Guidoni, & Linton (’08): gas-dynamic shock heating.
c.f. Forbes & Acton (’96): Yohkoh SXR loop shrinkage;
Veronig et al. (‘06): Betatron acceleration, don’t expect footpoints to move.
No clear explanation yet.
2.2 Asymmetric footpoint hard X-ray fluxes & magnetic field strengths
(Cartoon – courtesy of L. Fletcher)
slow motion fast motion
Strong HXR
Weak HXR
Different field convergence
Different loss-cones
Different electron precipitating rates & HXR fluxes, I1/I2~B2/B1
Hard X-rays & magnetic field strengths
E-FP X-ray brighter and B-field weaker than W-FP –
Consistent with asymmetric mirroring,
but not all the time!
Alternative – asymmetric column densities to footpoints?
Need spectral info
Spectral index evolution of footpoints – E-FP: consistently harder spectrum, smaller column density from loop-top
Effects of asymmetric column densities alone on HXR flux and spectral index –> contradiction (c.f, Falewicz & Siarkowski ‘07)
Consistent w/ Saint-Hilaire et al. (‘08)
Footpoint Asymmetry: Discussion
Mirroring or column density alone – inconsistent w/ data
… combined – possible
Other transport effects:
Non-uniform target ionization (Brown; Kontar) – Yes (E-FP: brighter, harder)
Photospheric albedo (Langer & Petrosian, Bai & Ramaty) – No (E-FP: softer)
Relativistic beaming (McTiernan & Petrosian) – No (E-FP: softer)
Return current – ?
Acceleration, asymmetric (McClements & Alexander ‘05) – ?
Final answer yet to come from detailed modeling.
2.3 Correlation between hard X-ray flux (log) & magnetic field strength
Implications:
• Stochastic acceleration – particle acceleration rate strongly depends on B;
• Electric field acceleration – larger electric field => larger electron flux and harder spectrum
3. Summary & Discussion
1. Footpoints unshearing motion & simultaneous loop-top downward motion – c.f, classic flare model.
2. Asymmetric hard X-ray footpoints – asymmetric magnetic mirroring, column densities, and other transport effects.
3. Correlation between hard X-ray flux and magnetic field strength – implication for particle acceleration mechanisms.
Preprints (hardcopy & pdf) available here