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How big are Hard X-ray Sources ---- Really?. Brian Dennis GSFC. Objectives. Determine real HXR source sizes Compare image reconstruction algorithms Establish objective procedures Analyze many flares Obtain source size distributions vs. Energy Flare intensity. Motivation. SCIENTIFIC

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How big are hard x ray sources really

How big are Hard X-ray Sources----Really?

Brian Dennis

GSFC


Objectives
Objectives

  • Determine real HXR source sizes

  • Compare image reconstruction algorithms

  • Establish objective procedures

  • Analyze many flares

  • Obtain source size distributions vs.

    • Energy

    • Flare intensity

Brian Dennis

GSFC


Motivation
Motivation

SCIENTIFIC

  • Thermal SXR source area  volume

    volume + EM  density

    density + T + filling factor  thermal energy

  • HXR footpoint area + spectrum  electron flux density

  • Footpoint asymmetry  magnetic field asymmetry

    INSTRUMENTAL

  • Refine RHESSI imaging capabilities

  • Establish requirements for future HXR imagers:

    • STIX on Solar Orbiter

    • XRI on Solar Sentinels

Brian Dennis

GSFC


METHOD FOR DETERMINING

SIZES, POSITIONS & FLUXES

Thanks to Ed Schmahl

Don't use CLEAN OR MEM or PIXON

Use FORWARD FIT with VISIBILITIES

REASONS: Old algorithms don't weight size sensitivity properly Better to find the closest fit to the calibrated visibilities of a specific model (e.g. Gaussians + albedo)

Select energy and time range with good S/N

Compute visibility using SSW tools

Run vis_fwdfit with 8-10 parameters

Brian Dennis

GSFC

RHESSI WORKSHOP, MEUDON, 2006 APRIL 5-8


WHAT DOES VIS_FWDFIT DO?

Visibility

amplitudes

(crosses)

are fit by a

model

black curve)

Residuals

(squares)

Brian Dennis

GSFC

RHESSI WORKSHOP, MEUDON, 2006 APRIL 5-8


RESULTS (1)

FWHM=

4.1,3.6

FLUX=

21.4, 20.9

Brian Dennis

GSFC

RHESSI WORKSHOP, MEUDON, 2006 APRIL 5-8


Source sizes vs energy thanks to rick pernak http hesperia gsfc nasa gov pernak
Source Sizes vs. EnergyThanks to Rick Pernakhttp://hesperia.gsfc.nasa.gov/~pernak/

Brian Dennis

GSFC


Image comparisons pernak et al 2006 poster
Image ComparisonsPernak et al. (2006) poster

Brian Dennis

GSFC


30 october 2004 16 23 48 to 16 24 48 ut

MEM_NJIT

CLEAN (d4 – 8)

PIXON

30 October 200416:23:48 to 16:24:48 UT

CLEAN images

Natural weighting

Detectors 1 - 9

TF = 1

D3 - 9

TF = 2

Brian Dennis

GSFC


30 oct 2004 forward fit with stacker thanks to richard schwartz
30 Oct. 2004Forward-Fitwith stackerThanks to Richard Schwartz

Source sigmas: 1.1 & 1.0 arcsec.

Brian Dennis

GSFC


30 october 2004 16 23 48 to 16 24 48 ut1
30 October 200416:23:48 to 16:24:48 UT

MEM_NJIT

VIS_FF

Brian Dennis

GSFC


Vis ff 30 october 2004 16 23 48 to 16 24 48 ut
VIS_FF30 October 200416:23:48 to 16:24:48 UT

RChisq = 15

Brian Dennis

GSFC




Clean images

CLEAN Image, TF = 1

6 - 12 & 30 – 40 keVNatural weightingTF = 2

CLEAN Images

Brian Dennis

GSFC


Clean pixon images

30 – 40 keVUniform weightingTF = 23x3 boxcar smoothed

CLEAN & Pixon Images

Pixon ImageColor stretched

Brian Dennis

GSFC


Clean pixon images1
Clean & Pixon Images

Brian Dennis

GSFC


Pixon images
Pixon Images

Unsmoothed

Boxcar smoothed3x3 pixels

Brian Dennis

GSFC


VIS_FF

2 circular sources

Brian Dennis

GSFC


Peak roll angles for grid 4

30”

2xFWHM = 24”

Brian Dennis

GSFC


Ellipse fwhm 14 eccentricity 0 97 circle fwhm 6 8
Ellipse - FWHM = 14” eccentricity = 0.97 Circle – FWHM = 6.8”

Brian Dennis

GSFC


Ellipse fwhm 15 eccentricity 0 75 pa 110 circle fwhm 4 3
Ellipse – FWHM = 15” eccentricity = 0.75, PA = 110Circle – FWHM = 4.3”

Brian Dennis

GSFC


Ellipse fwhm 5 6 eccentricity 0 75 pa 110 circle fwhm 4 5
Ellipse – FWHM = 5.6”, eccentricity 0.75, PA = 110Circle – FWHM = 4.5”

Brian Dennis

GSFC


Conclusions
Conclusions

  • Always make CLEAN images first

    • Detectors 1 – 9 above ~25 keV

    • Natural weighting, test factor = 1, 2 or ∞

    • Uniform weighting for compact sources

    • Use “media mode” - don’t add residuals

  • Use Pixon for extended sources

    • Boxcar smooth image

  • Use VIS_FF

    • Only if one or two clear compact sources

    • Use elliptical sources

    • Check chi-squared values for each detector

    • Include albedo

    • Investigate poor fits to detector 1 & 2 visibilities

Brian Dennis

GSFC


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