A Local Reacceleration Thick Target Model (LRTTM) A Local Reacceleration Thick Target Model (LRTTM) (a modification of the Collisional Thick Target Model CTTM -Brown 1971)(a modification of the Collisional Thick Target Model CTTM -Brown 1971)Brown, Turkmani, Kontar, MacKinnon and Vlahos AA submittedBrown, Turkmani, Kontar, MacKinnon and Vlahos AA submitted

Collisional TTMCollisional TTM

Acceleration

Radiation onlyNo accln

Collisional TransportNOAcceleration

The The CCollisional ollisional TThick hick TTarget arget MModel CTTM odel CTTM Brown 71, 73 etc Hudson 72 etcBrown 71, 73 etc Hudson 72 etc

MERITS OF CTTMMERITS OF CTTM Provides a ‘cartoon’ scenario for flare Provides a ‘cartoon’ scenario for flare

impulsive phase emissions roughly fitting impulsive phase emissions roughly fitting observationsobservations

Collisional transport is easy to work with even Collisional transport is easy to work with even though we know it cannot really be valid!though we know it cannot really be valid!

Separates acceleration site from HXR (TT Separates acceleration site from HXR (TT Injection) source – ie no acceleration in Injection) source – ie no acceleration in HXR source. Simple but v restrictiveHXR source. Simple but v restrictive

PROBLEMS WITH CTTMPROBLEMS WITH CTTM Inefficiency of bremss => Inefficiency of bremss =>

1. Beam density ~ coronal loop density1. Beam density ~ coronal loop density unless loop area there >> footpoint areaunless loop area there >> footpoint area2. Very large no. Ne of e’s accelerated >> IP & radio Ne2. Very large no. Ne of e’s accelerated >> IP & radio Ne

Downward beaming => Downward beaming =>

Strong albedo bumps in HXR spectra - not observed. Strong albedo bumps in HXR spectra - not observed. Data => comparable upward and downward fluxes Data => comparable upward and downward fluxes (Kontar and Brown 2006)(Kontar and Brown 2006)

Does not really tally with EM(t) and T(t) dataDoes not really tally with EM(t) and T(t) data

Beam driven evaporation does not work – self chokingBeam driven evaporation does not work – self choking

HXR Source RequirementsHXR Source Requirements

Regardless of model, observed HXR flux fixes Regardless of model, observed HXR flux fixes required value of source nonthermal EMrequired value of source nonthermal EM

For a large HXR event

For any thick target model the For any thick target model the NN11 source source

electrons of life electrons of life need ‘replenished’ at a rate need ‘replenished’ at a rate

brem

Et

brem nvQdtnvQ )(

brem

Et

brem nvQdtnvQ )(

brems

Et

brems nvQdtnvQ )(

For the CTTM collisional case For the CTTM collisional case =tcoll ~ =tcoll ~ 1/n and 1/n and F F 11 is independent of n is independent of n

If there is If there is LLOCAL OCAL RREACCELERATION EACCELERATION inside the HXR source inside the HXR source is increased is increased and and FF11 reduced. In other words the reduced. In other words the

photon yield per electron is increased photon yield per electron is increased

brems

Et

brems nvQdtnvQ )(

Bremss

Et

Bremss nvQdtnvQ )(

ONE CANDIDATE FOR THEONE CANDIDATE FOR THELOCAL REACCELERATION –LOCAL REACCELERATION –

ELECTRIC FIELDS IN CURRENT SHEET ELECTRIC FIELDS IN CURRENT SHEET CASCADE OF DISTRIBUTED ENERGY CASCADE OF DISTRIBUTED ENERGY RELEASERELEASE (Galsgaard…. Vlahos… (Galsgaard…. Vlahos… Turkmani…..)Turkmani…..)

MHD defines stochastic electric fieldsMHD defines stochastic electric fields

Test particle acceleration occurs in these in Test particle acceleration occurs in these in both the corona and then after injection to both the corona and then after injection to the chromospherethe chromosphere

CSC E fields

electron motion

Corona

Chromosphere

A Local Reacceleration A Local Reacceleration Thick Target Model (LRTTM)Thick Target Model (LRTTM)

E(t) for 10 test electronsE(t) for 10 test electrons1 CTTM & 9 LRTTM1 CTTM & 9 LRTTM

E(t)

t/tcollCTTM

LRTTM

Photon emission rate for test electronsPhoton emission rate for test electrons

LRTTM

CTTM

Cumulative photon emission of test electronsCumulative photon emission of test electronsover lifetime in thick targetover lifetime in thick target

CTTM

LRTTM

SOME LRTTM vs CTTM SOME LRTTM vs CTTM PROPERTIESPROPERTIES

Needs Needs lower electron flux and numberlower electron flux and number (but as much (but as much beam power) as CTTM. How much lower depends on beam power) as CTTM. How much lower depends on uncertain parameter values (resistivity etc). More uncertain parameter values (resistivity etc). More consistent with radio and IP values.consistent with radio and IP values.

Electrons much Electrons much less anisotropicless anisotropic (less albedo) (less albedo) Like CTTM, predicts HXR Like CTTM, predicts HXR footpointsfootpoints displaying rapid displaying rapid

structure, syhnchronism and structure, syhnchronism and time of flight delaystime of flight delaysBUTBUT Footpoint/coronal contrast higher than CTTMFootpoint/coronal contrast higher than CTTM MUCH MUCH higher proportion of beam power goes into higher proportion of beam power goes into

chromosphere, and deeperchromosphere, and deeper – may help with – may help with evaporation and WLF problemsevaporation and WLF problems

OVER TO RIM FOR OVER TO RIM FOR CSC DETAILS !CSC DETAILS !