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Loop-top altitude decrease in an X-class flare

Loop-top altitude decrease in an X-class flare. A.M. Veronig 1 , M. Karlick ý 2 ,B. Vršnak 3 , M. Temmer 1 , J. Magdalenić 3 , B.R. Dennis 4 , W. Otruba 5 , W. Pötzi 5 1 Institute of Physics/IGAM, University of Graz, A-8010 Graz, Austria

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Loop-top altitude decrease in an X-class flare

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  1. Loop-top altitude decrease in an X-class flare A.M. Veronig1,M. Karlický2,B. Vršnak3,M. Temmer1, J. Magdalenić3, B.R. Dennis4, W. Otruba5, W. Pötzi5 1 Institute of Physics/IGAM, University of Graz, A-8010 Graz, Austria 2 Ondřejov Observatory, Czech Academy of Sciences, Czech Republic 3 Hvar Observatory, Faculty of Geodesy, HR-10000 Zagreb, Croatia 4 NASA Goddard Space Flight Center, MD 20771, U.S.A.5 Kanzelhöhe Solar Observatory, University of Graz, A-9521 Treffen, Austria

  2. Introduction • Recent RHESSI X-ray observations provided evidence for a loop-top altitude decrease during the early phase of a flare Sui & Holman 2003, Sui et al. 2004, Krucker et al. 2003, Liu et al. 2004 Afterwards the behavior changed to the generally observed upward growth of the flare loop system. • Here: Analysis of the flare loop system of the X3.9 flare on 2003 November 3 Aim: Extract further observational details (LT kinematics; LT plasmaevolution) during the time of altitude decrease & Modelling in the frame of a collapsing magnetic trap • Data: RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) • GOES-12/SXI (Soft X-ray Imager) • SoHO/EIT (Extreme-ultraviolet Imaging Telescope) • Kanzelhöhe H

  3. X4 flare from NOAA 10488 GOES 3-day plot: 2003 November 2–5

  4. Magnetic evolution of NOAA 10488 21 Oct – 4 Nov 2003 MDI Magnetograms + Flare locations Courtesy of Peter T. Gallagher

  5. RHESSI soft and hard X-ray lightcurves

  6. RHESSI image sequence Impulsive Phase: 09:47 UT – 10:01 UT Images: 12–15 keV Contours: 70–100 keV  2 footpoints at high energies + Loop-top source at low energies

  7. KanzelhöheH image sequence Preflare, main & decay phase: 9 – 13 UT

  8. H loops in flare decay phase H images from Public Observatory Rimavska Sobota (Slovakia) 12:46 UT 14:55 UT

  9. GOES-12 SXI image time series Full day 2003 Nov 3: 2 X-class flares from same AR 10488

  10. Evolution of flare and post-flare loop system Loop Height vs. Time

  11. Evolution of RHESSI footpoints and loop-top Centroids of RHESSI FPs and LT source on MDI continuum image

  12. Time of LT altitude decrease: • Spectral change • a) increase of T (thermal em) and/or • b) spectral hardening (non-th) Kinematics of RHESSI sources Impulsive phase: • Kinematics of LT & FPs • is consistent • LT: higher energies at higher heights

  13. Kinematics of RHESSI & SXI loop-top source

  14. Results from linear fits: EnergyInitial Altitude Final Altitude Downward velocity (keV) (Mm) (Mm) (km/s) RHESSI 25-30 13.8 7.3 45 RHESSI 20-25 12.1 7.7 30 RHESSI 15-20 11.7 7.5 29 RHESSI 10-15 10.1 8.2 14 SXI 8.6 7.0 12  Distinct relation with X-ray energy (consistent with results of Sui et al.) Loop-top altitude decrease: Kinematics

  15. RHESSI spatially integrated spectra

  16. Summary of observational results • Impulsive phase: LT source moved upward and FPs separated. At higher energies the LT source is located at higher altitudes. Consistent with the standard reconnection model in which the energy release occurs higher and higher in the corona. • At the very beginning the LT altitude decreased. The effect is stronger for higher X-ray energies (cf. Sui & Holman 2003, Sui et al. 2004). Decrease up to 50% of the initial height, mean „downward“ velocities up to 45 km/s. • Simultaneously the LT spectrum changes.RHESSI spectra indicate thermal emission of a „superhot“ (Lin et al. 1981)plasma (3545 MK) before the acceleration of fast particles! • X-ray and H observations are indicative of very high densities in LT. Hot LT plasma at time of LT altitude decrease: n  1010 cm3 Hot LT plasma peak density: n  3·1011 cm3H post-flare LT plasma density: n  1012 cm3(H loop in emission against the solar disk: Heinzel & Karlický 1987, Švestka et al. 1987)

  17. Discussion LT altitude decrease:Intrinsic process of magnetic reconnection? • Relaxation of newly reconnected field lines („field line shrinkage“) to form closed loops(Švestka et al. 1987, Lin et al. 1995, Forbes & Acton 1996, Lin 2004) • Push down of the lower bound of the current sheetduring the change from slow X-point to fast Petschek reconnection(Sui et al. 2004) • Plasma processes in a collapsing magnetic trap configuration (Somov & Kosugi, 1997, Karlický et al.) • Plasma processes in a collapsing magnetic trap configuration (Somov & Kosugi, 1997, Karlický et al.)

  18. Betatron mechanism: acceleration & heating (Brown & Hoyng 1975, Emslie 1981, Karlický & Kosugi 2004) Farady‘s law Collapsing magnetic trap: Model Model based onKarlický and Kosugi (2004)

  19. Collapsing magnetic trap (1-D): Results X-ray Intensity for thermal bremsstrahlung as function of height at 3 times

  20. Collapsing magnetic trap (1-D): Results Height (t) Velocity (t) Time evolution of emission centroid (for thermal bremsstrahlung)

  21. Comparison of model results & observations • Collapsing magnetic trap model can account for: • Altitude decrease of emission centroid (for thermal and nonthermal X-rays) • Structuring of X-rays with energies: Emission source of higher energy X-rays are located above lower energies – works only for the thermal case!For 2003 Nov 3 flare this is in agreement with RHESSI spectra • Higher downward „velocities“ for higher X-ray energies

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