On the Upward Motion of the Coronal HXR Sources in Solar Flares: Observational and Interpretation Problems

2 We selected flares according to the following criteria The peak count rate in the Yohkoh M2- band ( keV) is greater than 1000 counts per second per subcollimator The heliocentric longitude of an active region is greater than 80 degree

3 The Study of Coronal HXR Sources Removing a background from the HXT images Selection of the most important sources and determination of their coordinates Identification of the positions of a source in the successive images The least-square analysis to obtain the average velocity V and its dispersion sigma

4 Upward motion of the coronal HXR source in the Masuda flare HXT M2-band images of the flare. The arrows show the direction of the HXR source motions Height of the source centroid as a function of time

5 The M3.6 flare on 1991 December 2 The flare was particularly occulted by the solar limb The average upward velocity of the upper HXR source was 23 km/sec

6 For 5 of 20 selected flares, the average velocity V > 3 sigma The upward component of average velocity is of about km/sec The effect should be studied statistically better by using the RHESSI high- resolution HXR and gamma- imaging data

7 Particle Acceleration in a Collapsing Trap A magnetic trap between the Super-Hot Turbulent-Current Layer (SHTCL) and a Fast Oblique Collisionless Shock (FOCS) above magnetic obstacle (MO) Ref.: Somov, B.V. and Kosugi, T., ApJ, 485, 859, 1997

8 The First-order Fermi-type Acceleration as the Second-step Mechanism Decrease of the field line length (collapse of the trap) provides an increase of the longitudinal momentum of a particle Ref.: Somov, B.V. and Kosugi, T., ApJ, 485, 859, 1997

9 Acceleration of Electrons

10 Acceleration of Ions Each reflection of an ion on a moving mirror leads to a jumpy increase of the parallel velocity Protons are easily accelerated from thermal to MeV energies Ref.: Somov, B.V., Henoux, J.C., Bogachev, S.A., Adv. Space Res., 30, No. 1, 55, 2002 Acceleration of protons

11 Two Effects in Collapsing Trap Decrease of the field line length provides the first-order Fermi acceleration Compression of the magnetic field lines provides betatron acceleration

12 The Betatron Effect in a Collapsing Trap As the trap is compressed, the loss cone becomes larger Particles escape from the trap earlier An additional energy increase by betatron acceleration is exactly offset by the decrease in a confinement time Ref.: Somov, B.V. and Bogachev, S.A., Astronomy Letters, 29, 621, 2003

13 Both Effects Together Ref.: Somov, B.V. and Bogachev, S.A., Astronomy Letters, 29, 621, 2003

14 Conclusions The betatron effect significantly increases the efficiency of the first-order Fermi-type acceleration Collapsing traps with a residual length (without shock) accelerate protons and ions well Ref.: Somov, B.V. and Bogachev, S.A., Astronomy Letters, 29, 621, 2003

15 Collapsing Trap Model: Predictions Two components: the non-thermal (N) and quasi-thermal (T) coronal HXRs The upward motion of the coronal HXR source Ref.: Somov, B.V. and Kosugi, T., ApJ, 485, 859, 1997