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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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Presentation Transcript
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

slide4

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

slide5

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

slide6

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

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

clean images

CLEAN Image, TF = 1

6 - 12 & 30 – 40 keVNatural weightingTF = 2

CLEAN Images

Brian Dennis

GSFC

clean pixon images1
Clean & Pixon Images

Brian Dennis

GSFC

pixon images
Pixon Images

Unsmoothed

Boxcar smoothed3x3 pixels

Brian Dennis

GSFC

slide19

VIS_FF

2 circular sources

Brian Dennis

GSFC

slide20

Peak roll angles for grid 4

30”

2xFWHM = 24”

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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