Decay Phase of Proton and Electron SEP Events

1
Decay Phase of Proton and Electron SEP Events
E.I. Daibog1, K.
Kecskemйty2, Yu.I. Logachev1 1
Skobeltsyn Inst. of Nuclear Physics, Moscow State
Univ., Russia 2 KFKI RMKI, Budapest, Hungary
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• Why decays?
• the features and conditions in a source of SEPs
  at the Sun become unessential during decay phase
  and effects and peculiarities of particle
  acceleration and losses in interplanetary space
  become more important.
• - rising phase and maximum origin and
  propagation mechanism
• - decay phase - propagation mechanism and
  interplanetary medium conditions

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Decay phase

• Observed flux profile a mixture of temporal and
  spatial variations
• Functional form of the particle flux decline
• power-law predominantly diffusive
  propagation
• exponential adiabatic deceleration and
  convection
• Statistical investigation (Daibog et al. 2003)
• 700 events of 1-5 MeV proton fluxes (3
  solar cycles, at 1 AU) IMP 8 (CPME)
• 90 of SEP decays are exponential
• power-law mostly at high energies
• Exponential decays longer than 24 hrs. gt4 MeV
  flux gt 1-2 p/cm2ssr
• Background instrumental remnants of preceding
  events

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• Exponential form J ? exp(-t/?)
• dN/dt N. Neglecting diffusion
• Lupton and Stone, 1971. Model with absorbing
  boundary and
• Burlaga, 1967. Spherically-symmetric diffusion.
  The volume limited by a boundary outside of which
  particles fly away freely.
• ?
  R2abs/p2?
• Owens,1979. Convection
• ? 9?/4V2 (2
  a ?)2
• Contrary ? and E dependence
• Ng and Gleeson, 1976. ????0(1r3). Gradual
  transition to free particle escape. Nearly
  exponential solution .

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• Forman, 1970 Jokipii, 1971. Convection and
  adiabatic deceleration dominate over gradients,
  scattering, and drift
• t 3r / 2V (2 a ?),
• a T2mc2/(Tmc2)