# Presentation: 502886

## Mostly Electron Acceleration and Hard X-rays

- Gordon Emslie

## 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)

## 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)

## 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

## 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)

## 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)

## Was John Brown right after all?

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

## “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 (< 200 keV) protons
- implies long delay in proton acceleration
- Optical Line Profiles (Canfield)
- Redshifted L (Brosius)

## 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)

## Empirical Energy Loss Determination

## 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)

## 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

## Complementary Observations

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

## Important things I have learned

- Timing analysis is a “profitable business”
- Finding out that I’m 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***