1. Observations and NLFFF Modeling of AR 10953 Yingna Su 1,2 Collaborators: A. A. Van Ballegooijen 1, E. E. Deluca 1, Leon Golub 1 P. Grigis 1, B. Lites 3, G. L. Huang 2 1. Harvard-Smithsonian Center for Astrophysics, USA 1. Harvard-Smithsonian Center for Astrophysics, USA 2. Purple Mountain Observatory, China 2. Purple Mountain Observatory, China 3. High Altitude Observatory, USA 3. High Altitude Observatory, USA AGU/SPD, Fort Lauderdale, 05/29/2008

2. Outline  Background  NLFFF Modeling of (pre-flare) AR 10953 Flux Rope Insertion Method Data: SOHO/MDI, Hinode/SOT, KSO/H-alpha, Hinode/XRT  Observations of a C8.5 Flare in AR 10953 Data: Hinode/XRT, TRACE, RHESSI, MLSO/H-alpha  Interpretations and Conclusions

3. Background  Existing methods for constructing NLFFFs (non-linear force free fields) Most methods : extrapolating photospheric vector fields to the corona (Schijver et al. 2006). The method we adopted : “flux rope insertion method” (van Ballegooijen 2004; Bobra etal. 2008) which requires line of sight magnetograms. This method was tested by Bobra et al. (2008), and the model was constrained by TRACE observations.  What is the 3D pre-flare magnetic configuration? Where and how is the flare initiated?  In this work, we construct NLFFF models for the pre-flare state of AR 10953, and the model is constrained by multiple non-potential X-ray loops observed by XRT.

4. Flux Rope Insertion Method PF modelInsert Flux RopeNLFFF Model MDI+SOT/SP 2007-May-02 17:30 UT KSO/H-alpha 2007-May-02 11:31 UT2007-May-02 14:59 UT XRT MDI+SOT/SP Magneto Friction Van Ballegooijen 2004; Bobra et al. 2008

5. Model Constraint: X-ray Loops Best fit model field lines for four non-potential X-ray loops Model Free Parameters: Axial flux and Poloidal flux of the flux rope

6. Model Axial Flux (Mx) Loop 1 14:49:09 UT Loop 2 15:17:04 UT Loop 3 22:58:20 UT Loop 4 18:17:27 UT NLFFF 5e200.00170.00350.00390.0067Y 7e200.00200.00220.00180.0047Y 9e200.00250.00240.00130.0034Y 12e200.00310.00260.00180.0020Y 15e200.00560.00310.00240.0012? Table 1 The Average Distance (in solar radii) of the projected best-fit model field lines from the observed X-ray loops for various models with fixed Poloidal Flux (1e10 Mx/cm). Calculation Solution Set  Best Fit Model: Axial Flux=7e20±2e20 Mx, Poloidal Flux ~ 1e9 to 1e11 Mx/cm (larger range); Eruption for Axial Flux~ 15e20 Mx  Loop 4 may be in a non-stable state.

7. Comparison with SOT/SP Vector Magnetogram Best Fit Model: Axial Flux=7e20 and 9e20 Mx Blue Vector: Observation Black Vector: Model

8. Vector Magnetogram: Obs. Versus Mod. Best Fit Model: Axial Flux=7e20 and 9e20 Mx Blue Vector: Observation Black Vector: Model worst fit good fit worse fit

9. Observations of C8.5 Flare MLSO/H-alpha TRACE/171 XRT/Ti_poly  Filament activation (23:30 UT) associated with the flare was seen in H-alpha and EUV, not X-ray.  Two-ribbon flare: unsheared-sheared-unsheared.  Not associated with filament eruption and CME.

10. Light Curves of C8.5 Flare EUV flare starts about 20 minutes later than the X-ray (XRT and RHESSI) flare, Why?

11. Pre-EUV flare X-ray brightenings XRT RHESSI XRT TRACE RHESSI Spectral fitting suggests that the pre-EUV flare X-ray sources are mainly caused by thermal bremsstrahlung emission.

12. Where Does the Flare Start? At flare onset, the flare loop is unsheared. This suggests the flare starts near the outer edge of the flux rope. XRT 2007-May-02 23:09:24 UT Z=14 flare loop Current layer * Reconnection site?

13. Conclusions (I)  Comparison of modeled and observed X-ray loops for pre-flare (C8.5) state of AR 10953 Axial Flux: 7e20±2e20 Mx (good constraints from X-ray loops) Poloidal Flux: 1e9-1e11 Mx/cm (wide range) Upper limit: Axial Flux~15e20 Mx Free Energy: ~0.85e32 erg, Potential Energy: 9.62e32 erg Similar result obtained by comparisons of observed and modeled photospheric vector magnetograms.  The axial flux ( 7e20±2e20 Mx ) in the flux rope is far away from the upper limit (15e20 Mx) for eruption, which is consistent with the fact that no successful filament eruption occurred in this active region.

14. Conclusions (II)  The X-ray brightenings appear about 20 minutes earlier than the EUV flare associated with a filament activation, which may be caused by the localized coronal heating. Open question: Why does the heating not propagate to the chromosphere where EUV flare occurs?  This flare starts from unsheared brightenings, unlike most two-ribbon flares (Su et al. 2007).  Interpretation: the flare starts near the outer edge of the flux rope, Not at the inner side or at the bottom as suggested in the standard flare model (e.g., Moore et al. 2001).

15. Thank you for your attention !