On the Upward Motion of the Coronal HXR Sources in Solar Flares:

Observational and Interpretation Problems

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We selected flares according tothe following criteria

• The peak count rate in the Yohkoh M2-band (33--53 keV) is greater than 1000 counts per second per subcollimator

• The heliocentric longitude of an active region is greater than 80 degree

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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

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Upward motion of the coronal HXR sourcein 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

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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

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For 5 of 20 selected flares, the average velocity V > 3 sigma

• The upward component of average velocity is of about 10 - 30 km/sec

• The effect should be studied statistically better by using the RHESSI high-resolution HXR and gamma- imaging data

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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

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The First-order Fermi-type Accelerationas 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

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Acceleration of Electrons

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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

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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

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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

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Both Effects Together

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

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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

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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