Loop-top altitude decrease Loop-top altitude decrease in an X-class flarein 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, Austria2 Ondřejov Observatory, Czech Academy of Sciences, Czech Republic

3 Hvar Observatory, Faculty of Geodesy, HR-10000 Zagreb, Croatia4 NASA Goddard Space Flight Center, MD 20771, U.S.A.

5 Kanzelhöhe Solar Observatory, University of Graz, A-9521 Treffen, Austria

IntroductionIntroduction

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 plasma

evolution) 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

GOES 3-day plot: 2003 November 2GOES 3-day plot: 2003 November 2––55

X4 flare fromNOAA 10488

Magnetic evolution of NOAA 10488Magnetic evolution of NOAA 10488

21 Oct – 4 Nov 2003

MDI Magnetograms+ Flare locations

Courtesy of Peter T. Gallagher

RHESSI soft and hard X-ray lightcurvesRHESSI soft and hard X-ray lightcurves

RHESSI image sequenceRHESSI 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

KanzelhöheKanzelhöhe HH image sequence image sequence

Preflare, main & decay phase:

9 – 13 UT

HH loops in flare decay phase loops in flare decay phase

H images from Public Observatory Rimavska Sobota (Slovakia)

12:46 UT 14:55 UT

GOES-12 SXI image time seriesGOES-12 SXI image time series

Full day 2003 Nov 3:

2 X-class flares fromsame AR 10488

Evolution of flare and post-flare loop system Evolution of flare and post-flare loop system

Loop Height vs. Time

Centroids of RHESSI

FPs and LT source on

MDI continuum image

Evolution of RHESSI footpoints and loop-topEvolution of RHESSI footpoints and loop-top

Kinematics of RHESSI sourcesKinematics of RHESSI sources

Impulsive phase:

Kinematics of LT & FPs is consistent LT: higher energies at higher heights

Time of LT altitude decrease: Spectral change a) increase of T (thermal em) and/or b) spectral hardening (non-th)

Kinematics of RHESSI & SXI loop-top sourceKinematics of RHESSI & SXI loop-top source

Loop-top altitude decrease: KinematicsLoop-top altitude decrease: Kinematics

Results from linear fits:

Energy Initial 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.)

RHESSI spatially integrated spectraRHESSI spatially integrated spectra

Summary of observational resultsSummary of observational results

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.

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.

Simultaneously the LT spectrum changes. RHESSI spectra indicate thermal emission of a „superhot“ (Lin et al. 1981) plasma (3545 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 cm3

Hot LT plasma peak density: n 3·1011 cm3

H post-flare LT plasma density: n 1012 cm3

(H loop in emission against the solar disk: Heinzel & Karlický 1987, Švestka et al. 1987)

DiscussionDiscussion

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)

Plasma processes in a collapsing magnetic trap configuration (Somov & Kosugi, 1997, Karlický et al.)

Push down of the lower bound of the current sheet during 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.)

Collapsing magnetic trap: ModelCollapsing magnetic trap: Model

Model based on Karlický and Kosugi (2004)

Betatron mechanism: acceleration & heating

(Brown & Hoyng 1975, Emslie 1981, Karlický & Kosugi 2004)

Farady‘s law

t

BE

Collapsing magnetic trap (1-D): ResultsCollapsing magnetic trap (1-D): Results

X-ray Intensity for thermal bremsstrahlung as function of height at 3 times

Collapsing magnetic trap (1-D): ResultsCollapsing magnetic trap (1-D): Results

Time evolution of emission centroid (for thermal bremsstrahlung)

Height (t)

Velocity (t)

Comparison of model results & observationsComparison 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