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 !
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