A Local Reacceleration Thick Target Model (LRTTM)
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A Local Reacceleration Thick Target Model (LRTTM) (a modification of the Collisional Thick Target Model CTTM -Brown 1971) Brown, Turkmani, Kontar, MacKinnon and Vlahos AA submitted. Collisional TTM. Acceleration. Collisional Transport NO Acceleration. Radiation only No accln.

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A Local Reacceleration Thick Target Model (LRTTM)

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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)

Brown, Turkmani, Kontar, MacKinnon and Vlahos AA submitted


Collisional ttm

Collisional TTM

Acceleration

Collisional

Transport

NOAcceleration

Radiation

only

No accln


The c ollisional t hick t arget m odel cttm brown 71 73 etc hudson 72 etc

The Collisional Thick Target Model CTTM Brown 71, 73 etc Hudson 72 etc

MERITS OF CTTM

Provides a ‘cartoon’ scenario for flare impulsive phase emissions roughly fitting observations

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

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


Problems with cttm

PROBLEMS WITH CTTM

  • Inefficiency of bremss =>

    1. Beam density ~ coronal loop density

    unless loop area there >> footpoint area

    2. Very large no. Ne of e’s accelerated >> IP & radio Ne

  • Downward beaming =>

    Strong albedo bumps in HXR spectra - not observed.

    Data => comparable upward and downward fluxes

    (Kontar and Brown 2006)

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

  • Beam driven evaporation does not work – self choking


Hxr source requirements

HXR Source Requirements

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

For a large HXR event


For any thick target model the n 1 source electrons of life t need replenished at a rate

For any thick target model the N1 source electrons of life t need ‘replenished’ at a rate

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

If there is LOCAL REACCELERATION inside the HXR source t is increased and F1reduced. In other words the photon yield per electron is increased


One candidate for the local reacceleration

ONE CANDIDATE FOR THELOCAL REACCELERATION –

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

MHD defines stochastic electric fields

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


A local reacceleration thick target model lrttm

CSC E fields

Corona

Chromosphere

electron motion


A local reacceleration thick target model lrttm

A Local Reacceleration

Thick Target Model (LRTTM)


E t for 10 test electrons 1 cttm 9 lrttm

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

E(t)

LRTTM

CTTM

t/tcoll


Photon emission rate for test electrons

Photon emission rate for test electrons

LRTTM

CTTM


Cumulative photon emission of test electrons over lifetime in thick target

Cumulative photon emission of test electronsover lifetime in thick target

LRTTM

CTTM


Some lrttm vs cttm properties

SOME LRTTM vs CTTM PROPERTIES

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

  • Electrons much less anisotropic (less albedo)

  • Like CTTM, predicts HXR footpoints displaying rapid structure, syhnchronism and time of flight delays

    BUT

  • Footpoint/coronal contrast higher than CTTM

  • MUCH higher proportion of beam power goes into chromosphere, and deeper – may help with evaporation and WLF problems


A local reacceleration thick target model lrttm

OVER TO RIM FOR CSC DETAILS !


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