2nd RHESSI/NESSI

WORKSHOP -Distribution Functions of

Energetic Flare Particles -

Glasgow, Scotland,  

March 24-26, 2004

How far can we go in quantitative determination (inference) of the (spectral, space, time) distribution functions of energetic flare electrons and ions from Hard X-Ray,  gamma-ray, and other data, starting from raw observations. Pure theory, model fitting, flare phases and such data morphology, are discouraged.

Team 1: FROM RAW DATA TO PHOTON DISTRIBUTIONS (led by Richard Schwartz,TBC) counts=> photons (detector response)

- Instrumental calibration and background effects. - Line and continuum issues - Images, spectra and spectral images, bearing in mind temporal    variation/modulation - Direct use of modulation data as opposed to reconstructions

Team 2: FROM PHOTONS TO RADIATION SOURCE STRUCTURE (led by Chris Johns-Krull) photons to particles (inversion of the photon spectra)- Photon spectra and images -> radiation source (volume or line of sight    integrated) particle distributions. - Inversion and forward fitting approaches. - Effects of method and cross section  and albedo.

Team 3: FROM SITES OF RADIATION TO PARTICLE SOURCES (led by Hugh Hudson) the rest of the problem- Particle energy loss, pitch angle scattering and dispersion, drifts - Mapping through realistic coronal magnetic models - Particle "escape" onto open magnetic lines

- Energy and particle transport

• Team 1: FROM RAW DATA TO PHOTON DISTRIBUTIONS (led by Richard Schwartz,TBC)

Progress since May 2003:

roll database; aspect gaps; livetime corrections; pixon& forward fitting; provision for image with weighting (especially useful for 2.2 MeV imaging); SPEX; pile-up correction for spectroscopy; decimation correction; response matrix improvement; quick look lightcurve & image with decimation & attenuator correction; 相对转动轴位置的谱定标校正；两种 方法获得光变…… .. Near term / intermediate term: livetime correction in back projection; estimation of source size; improving image evaluation; harmonics; stacker; Fourier-based imaging algorithm; implement visibility………

Imaging / Spectroscopy overview: livetime & pile-up (Sam Krucker) 日冕强源产生 pile-up 如何影响足点源？ (1) 仅考虑 livetime is high( 比如 80%) (2) 仅考虑日冕源被 grid masked

以 7 月 23 日耀斑为例，不同的 grid ~40keV pile-up peak 一系列成像比较，选择不同的 livetime 和不同的 grid 另也进行理论模拟，假设源，使用不同的 grid 调制曲线 结论：只选高 livetimeless pile-up ；无助于在强源边的弱源。 ( 系统性开展成像校正，时机还不成熟）

Improving Imaging / Spectroscopy (Golden Hurford) 近中远期需要解决的问题： resolve subcollimators’ difference; improving forward

fitting; stacker; implement visibility; implement algorithm;

MEM…….

imaging  (eg source sizes, photometry, algorithms) 哪种情况下能够测定源大小？ FWHM / resolution < 0.5 relative visibility > 0.8 FWHM / resolution > 1.3 relative visibility < 0.2 0.5 < FWHM / resolution < 1.3 sensitive to source size 目前情况： no friendly tools MEM-SATO: overestimated MEM-VIS: underestimated CLEAN: ?? Forward fitting / PIXON: is an option 此外的复杂性： Albedo; multi-component source

 Demodulation: 如何获得高时间分辨光变曲线？ remove 调制影响 , summed 光变曲线。两种算法： Arzner; Hurford. 不同时间分辨下 RHESSI 与 HXRS 比较很好

Continuum spectroscopy & gamma-ray issues Share, G.:

temporal variation (1 min for Oct. 28 flare; 2 min. for Nov. 2

flare) of 200 keV, nuclear lines ( 最大达 10 ） , 511 keV

line （极大小于 3 ） , 511 keV line width （小于 10keV, 6

keV9 keV2 keV)

energy spectrum: 11:08:04—11:16:20 for Oct. 28 flare

?? for Nov. 2 flare. Bgd 前后两天，大于 300keV 双幂律谱，仪器位移可达 10- 15keV,10.30 大气伽玛射线明显 explanation on 511 keV line:

constitute: solar emission, bremsstrahlung, nuclear lines,

2.223 MeV line

line width: to use 6000 K fitting while the predicted 3g/2g

too strong. The conclusion seems that it

needs a higher density region at round 104 K;

while previous result (for July 23 flare) is that

it needs a higher density region at round 105 K

Gan, W.Q.: see separate ppt file fluences are generally consistent with those of Share; the spectrum is more or less the same （ fluctuation above 8 MeV; flux depends on time interval selected) complementary each other Trottet, G.: Aug. 30, 2002, observed with both CORNAS and RHESSI. 511 keV is seen in count spectrum but it is in fact no gamma-ray line flare, if the photon spectrum is seen Oct. 28, 2003, observed with 210GHz, CORONAS, & RHESSI, lightcurve comparisons Highlight: presented the gamma-ray line spectrum of Oct. 28, observed with INTEGRAL. The C line and O line are very obvious, dissimilar to RHESSI observation! The analysis is being undertaken

Hurford, G.: 2.223 MeV images for other 3 flares are available! (but at the workshop he did not show his results, ???) Oct. 28: double source, similar to hard X-ray sources

Oct. 29: single source, just between double hard X-ray sources

Nov. 2: single source(?), between double hard X-ray sources(?)

It seems that there are still not any definite conclusions between the gamma-ray sources and hard X-ray sources. It is especially stressed the difficulty for comparisons, like different time interval, detectors, movement, angular resolution, and so on

• Team 2: FROM PHOTONS TO RADIATION SOURCE STRUCTURE (led by Chris Johns-Krull)

photons to particles (inversion of the photon spectra)

Inverting photon spectra to recover electron spectra

- Regularization Methods forward method 结果不同

5.5 difference

July 23, 2003 Holman et al.

Piana et al.

- Regularization Methods 与早期 Johns & Lin 方法基本一致

• White: Johns & Lin (1992)

• Red: Piana et al. 0th order

regularization

- Pile-up correction plus Albedo effect

to use only livetime > 80%, with or without Albedo

( 与以前 power-law 电子谱不是一回事）

With albedo

No albedo

- Kontar: 光子谱 == 》

Regularization Methods 与 forward fitting 存在gap

电子谱

20-30keV

Aug.20, 2002

Forward-fitting and the use of models to look for specific X-ray

diagnostics (Brown, Holman, Kasparova, Massone, Zharkova):

-Very flat X-ray spectrum (gamma <= 2 below 80 keV) was

detected at the burst maximum of 20 Aug 2002 flare. Fitting of an

isothermal component plus a double power-law electron flux

distribution function in the thick target model revealed the low

energy cutoff of 80 keV. Assuming different shapes of electron

flux distribution below the low energy cutoff we investigate their

influence on the photon spectrum.

-ANISOTROPIC BREMSSTTRAHLUNG EMISSION FOR THE

FLARE OF AUGUST 21, 2002

Effects of albedo (C. Alexander, Brown, Johns-Krull, Schmahl)

- 利用 Bai & Ramaty (1978) 结果， 看含与不含的区别

- 在 regularization 方法基础上校正很厉害

- 非自洽计算，假设 a power-law, 实际非单幂律谱

- Albedo patch (Schmal)

Goodness of fit criteria for derived electron spectra

Methods to perform imaging spectroscopy (Lin, Schmahl):

- Imaging spectroscopy of the 2002 Mar 14 flare with two different

ways: parametric fits to photon spectra and forward fits from

electron thick-target parameters

Team 3: FROM SITES OF RADIATION TO PARTICLE SOURCES (led by Hugh Hudson)

Focus area #1: “Realistic” magnetic fields: drifts, scattering, energy losses, trapping, Neupert effect

Focus area #2(radiation): “Realistic” magnetic fields: Microwave and X-ray luminosity, coronal emission, Alfven speeds, “cornucopia effect”

Focus area #3: Footpoint physics

Focus area #4: radiative hydrodynamics

Observations: Mainly (double) footpoint sources(Hoyng et al. 1981, Sakao 1994)

Sometimes faint above the loop-top source(Masuda et al. 1994)

Theory: Modelling expected source height structure for thick-targetHXR emission confirms predominance of footpoint emission(Brown & McClymont 1975, Emslie 1981, Brown et al. 2002)

Hard X-ray source structure

Microwave brightness distribution along flaring loops (f = 34 GHz).

We consider that the most probable explanation of the loop-top source is a strong concentration of mildly relativistic electrons in the upper part of a flaring loop.

This strong concentration can occur if there exists a strong pitch-angle anisotropy of high energy electrons perpendicular to magnetic field lines.

A loss cone anisotropy produced by the simple cut of the initial isotropic pitch-angle distribution is not enough to explain the observed microwave brightness distribution.

To obtain such a strong pitch-angle anisotropy, we need either some specific anisotropic acceleration/ injection of mildly relativistic electrons, or a specific transport effect producing highly anisotropic distributions of trapped mildly relativistic electrons.

So, these findings put important new constraints on the particle acceleration/ injection mechanisms and the kinetics of high energy electrons in flaring magnetic loops

What is the physical reason for the existence of loop-top sources?

Color Image: 6 12 keVContour lines: 25 50 keV

Integration time / image: 21 sTime range: 00:01 00:16 UT FoV: 64 64 arcsec

Veronig et al.

Observations: EIT/RHESSI at last peak

EIT 195 Å image near RHESSI highest peak (00:10 – 00:11 UT).

RHESSI 25 – 50 keV image at highest peak and EIT overlay.

Interpretation II: Origin of high coronal N

Theoretically beam driven column density: 1.3 1020 cm2f ( P(25), A, )

Theoretically conduction driven column density: f ( T ) 4.9 1020 cm2

Observationally: f ( n, L )

N conductively driven

4.5 1020 cm2

Conclusions (for now)

14 April 2002, 23:55 UT flare:HXR source in which the HXR emission is almost entirely in a coronal loop so dense as to be collisionally thick at electron energies up to 60 keV.

•L1) Loop column density N observed is consistent with the coronal thick-target interpretation of the HXR image.

2)This N is consistent with chromospheric evaporation by thermal conduction flux from the hot coronal plasma rather than by electron beam heating.

3)T of the hot loop plasma (and hence the conductively driven N value) is consistent with thick-target collisional heating by electrons.

Petrosian

Emslie: e, p 加热动力学模型 区别：均出现 condensation, 前者低温高密度； 后者高温高密度。 原因是靶是热的

Allred: 一维辐射动力学程序 RADYN （ Carlsson 1997 ）

解 H 、 He 、 CaII 、 MgII 线，包括光球、色球、

过渡区、日冕；叠代法求解 非热电子加热： Emslie(1978)+ 双幂律改正 初始大气： Vernazza et al. (1981)

结果：与通常不同， T<107 K

Propagation Questions

• To what extent are electron footpoints smeared out by drift motions? Being studied… maybe?

• To what extent can ions and electrons be separated spatially? Considerably

• Do separatrices correspond to ribbons, or (Metcalf et al, 2003) are they intriguingly related? Being studied

• Does trapping and Coulomb loss explain 34-GHz looptop sources? Being studied… probably?!

• At what time scale does the steady-state approximation break down? Experts discussing

Radiation Questions

• Does trapping and Coulomb loss explain 34-GHz looptop sources? Being studied… probably?!

• Can a coronal loop be dense enough to stop 60 keV electrons? Yes; new input to models

• Do RHESSI observatinos suggest a coronal current sheet? Yes… being studied

• Can “realistic” field extrapolations help to understand flare X-ray sources? Being studied

Footpoint Questions

• Do electron-heated atmospheres produce thick enough transition regions to explain the 511-keV line width? No

• Do proton-heated atmospheres produce thick enough transition-region material to explain the 511-keV line width? Being studied

• Do we understand footpoint DEMs well enough to explain ribbon radiation? Being studied

• Do we understand why hard X-ray footpoint structures are so concentrated in the ribbons? Being studied