Mostly Electron Acceleration and Hard Xrays

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Mostly Electron Acceleration and Hard X-rays

• Gordon Emslie

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Magnetic Reconnection

• Are multiple structures necessary?
• Renounce simple dipole models (Zirin, Doschek,
  Trottet)
• Required energy release rates achievable
• Detailed mode by which flux unfreezes not
  critical (Drake)
• Still not clear how energy buildup occurs without
  flaring (Longcope)

3
Particle Acceleration - General

• ALL acceleration is by electric fields (Coulomb,
  Newton)
• j and E are secondary quantities (Priest)
• very large E (1000 V/m 105 ED) on very short
  scales ubiquitous (Priest, Drake)
• smaller E on larger scales more commonly invoked
  (Holman)
• Timing of e/p acceleration? (Arndt, Muraki,
  Hénoux)

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Large-Scale Electric Field Acceleration

• Ampère, Faraday constraints
• large (107 - 1014 !!) number of acceleration
  regions, depending on geometry
• Current closure - where? how?
• Flat energy spectrum?
• Time-of-flight arguments (Aschwanden) argue
  against extended acceleration region

5
Stochastic Acceleration

• Need for continual, large-scale disturbance in
  magnetic field (Miller)
• Naturally occurring in CMEs (Simnett) and in
  reconnection models (Drake)
• Wave energy densities depend on type of waves
  used (Miller, Petrosian)
• Needs to be prompt to maintain FIP differentials
  (Reames)

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Interesting Acceleration Mechanisms

• Neutral beam (waterskier glider-towing)
  model (Brown)
• Betatron acceleration in collapsing reconnected
  loops (Priest)
• Is this related to uniform, slow, downward speed
  of reconnected loops (Simnett)?
• Solar wind-type acceleration in expanding
  magnetic geometry (Shimizu)

7
Was John Brown right after all?

• Thick-target electron model
• explains synchronous footpoints (Sakao)
• supports Neupert effect (Hudson)
• but
• power in lt 1 MeV ions may dominate (Ramaty,
  Murphy, Share)
• hydrodynamic response (in simple loop models) not
  consistent with observations

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Low Energy Diagnostics of Particle Beams

• Polarization in H? (Hénoux)
• tangential in impulsive phase - vertical beam of
  high-energy electrons
• radial in main phase - vertical beam of
  low-energy (lt 200 keV) protons
• implies long delay in proton acceleration
• Optical Line Profiles (Canfield)
• Redshifted L? (Brosius)

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Critical HESSI Observations I

• Spatial Imaging of Hard X-ray Spectra
• Injected vs. footpoint vs. trapped spectra
  (Metcalf)
• Extent of acceleration site (Holman)
• Comparison with radio (Gary)
• Forward modeling
• Fokker-Planck (Petrosian)
• Ito Calculus (Conway)
• Empirical Modeling (Emslie)

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Empirical Energy Loss Determination
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Critical HESSI Observations II

• Low-energy cutoffs in e and p spectra (Brown,
  Sato)
• Resolution of Acceleration Process(es)
• spatially (probably not the site of most intense
  hard X-ray emission Simnett)
• temporally (Petrosian, Miller)
• Hard X-ray polarization (McConnell)

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Interpretation of HESSI Observations

• HESSI observes photons, emitted when particles
  interact with a target
• Target is
• optically thin ? line-of-sight integration
• collisionally thin/thick depending on energy
• nonuniform in temperature and ionization level
• affects relationship between hard X-ray and
  electron spectra (Barrett) and beam energy
  deposition rate

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Complementary Observations

• Radio (Microwave/millimeter)
• complementary in energy and pitch angle (Gary)
• Vector Magnetographs
• Other High-Energy
• CGRO, Yohkoh
• Context
• SoHO, TRACE

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Important things I have learned

• Timing analysis is a profitable business
• Finding out that Im wrong can be a good thing
• This is a lot more fun than rewriting the UAH
  Graduate Handbook
• Reuven Puts on a Helluva Good Meeting