RHESSI Studies of Solar Flare Hard X-Ray Polarization Mark L. McConnell 1, David M. Smith 2, A. Gordon Emslie 4, Martin Fivian 3, Gordon J. Hurford 3,

RHESSI Studies of Solar Flare RHESSI Studies of Solar Flare Hard X-Ray PolarizationHard X-Ray Polarization

Mark L. McConnell1, David M. Smith2, A. Gordon Emslie4, Martin Fivian3, Gordon J. Hurford3,

Robert P. Lin3, and James M. Ryan1

1Space Science Center, University of New Hampshire, Durham, NH2Dept. Of Physics, U.C. Santa Cruz, Santa Cruz, CA

3Space Sciences Laboratory, U.C. Berkeley, Berkeley, CA4Physics Department, University of Alabama, Huntsville, AL

Polarization in Solar FlaresPolarization in Solar Flares

The hard X-ray continuum is dominated by electron bremsstrahlung emission.

Measurements of hard X-ray polarization can shed light on the geometry of the acceleration process.

Models predict polarization levels as high as 20 or 30%.

Model parameters include :

1) pitch angle distribution

2) B-field geometry

3) viewing angle

4) atm density profile

The Polarization SignatureThe Polarization Signature

For a fixed Compton scatter angle (), the azimuthal distribution of scattered photons contains the polarization signature.

The amplitude of the modulation defines the level of polarization.

The scattering angle corresponding to the minimum of the distribution defines the plane of polarization.

2000

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0

Counts

350300250200150100500

Azimuthal Scatter Angle (degs)

C-max

C-min

polarization angle

€

C η( ) = A cos2(η−ϕ)+B

1

10

100

Asymmetry Ratio

1201008060Scattering Angle (degrees)

50 keV

100 keV

250 keV

500 keV

1 MeV

Asymmetry Ratio

RHESSI as a Polarimeter (20 – 100 keV)RHESSI as a Polarimeter (20 – 100 keV)

A small (3 cm diam by 3.5 cm high) cylinder of Be serves as a Compton scattering element.

The Ge detectors measure the distribution of the scattered radiation.

The rotation of the spacecraft rotation provides an effective method for fine sampling of the scatter distribution.

RHESSI as a Polarimeter (20 – 100 keV)RHESSI as a Polarimeter (20 – 100 keV)

Complications :

Varying background as a function of spacecraft spin angle.

Scattering of solar flux from parts of the spacecraft other than the Be block.

Scattering of solar flux off atmosphere (spin-dependent).

The Polarization Signal - Simulated ResultsThe Polarization Signal - Simulated Results

40 keV

40 keV

80 keV

80 keV

Top row shows results for narrow incident beam (no

spacecraft scattering).

Bottom row shows results for wide

incident beam (with spacecraft scattering).

Note the significant degradation of signal

at 80 keV.

Polarimeter Mode – Effective AreaPolarimeter Mode – Effective Area

The effective area is defined for both a narrow beam and a broad beam.

The broad beam simulation incorporates the effects of scattering of solar flux into

the rear Ge segments, which leads to an increase in effective area at higher

energies .0.01

0.1

1

10

10 100

Energy (keV)

RHESSI Polarimeter ModeEffective Area

Narrow Beam

Broad Beam

Polarimeter Mode – Modulation FactorPolarimeter Mode – Modulation Factor

The modulation factor is a measure of the quality of the polarization signal.

Scattering of incident solar flux reduces the quality of the polarization signal. (The scattered flux is not

modulated.)

1.0

0.8

0.6

0.4

0.2

0.010 100

Energy (keV)

RHESSI Polarimeter ModeModulation Factor

Narrow Beam

Broad Beam

Polarimeter Mode – Figure of MeritPolarimeter Mode – Figure of Merit

The figure-of-merit is a measure of the intrinsic capability to measure

polarization.

Here, it is defined as the product of (effective area)1/2 and the modulation factor.

As defined here, it does not incorporate the effects of

detector background.

0.6

0.5

0.4

0.3

0.2

0.1

0.010 100

Energy (keV)

RHESSI Polarimeter ModeFigure of Merit

Narrow Beam

Broad Beam

Nature of the RHESSI DataNature of the RHESSI Data

Rear Segment Data(20 – 40 keV)

X4.8 Flare - 23 July 2002

00:27 – 00:43 UT

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BGD Counts

360°300°240°180°120°60°0°

Detector Roll Angle

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FLR Counts

FLR interval BGD interval

Ge112000

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BGD Counts

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Detector Roll Angle

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FLR Counts


Ge3

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BGD Counts

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Detector Roll Angle

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FLR Counts


Ge412000

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BGD Counts

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FLR Counts


Ge5

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BGD Counts

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Detector Roll Angle

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FLR Counts


Ge6

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BGD Counts

360°300°240°180°120°60°0°

Detector Roll Angle

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FLR Counts


Ge7

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BGD Counts

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Detector Roll Angle

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FLR Counts


Ge812000

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FLR Counts

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Detector Roll Angle

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BGD Counts


Ge9

An Initial Approach to RHESSI AnalysisAn Initial Approach to RHESSI Analysis

Three pairs of detectors with similar background : detectors 8/9, detectors 3/5 and detectors 4/6.

The data from detectors 3-6 can be used as background estimate for the polarimeter mode detectors 8/9.

Limitations :

• Does not use detector #1

• Assumes symmetric geometry

• No modeling of Earth albedo

Nature of the RHESSI DataNature of the RHESSI Data

Rear Segment Data(20 – 40 keV)

X4.8 Flare - 23 July 2002

00:27 – 00:43 UT

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BGD Counts

360°300°240°180°120°60°0°

Detector Roll Angle

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FLR Counts


Ge112000

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BGD Counts

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Detector Roll Angle

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FLR Counts


Ge3

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BGD Counts

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Detector Roll Angle

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FLR Counts


Ge412000

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BGD Counts

360°300°240°180°120°60°0°

Detector Roll Angle

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FLR Counts


Ge5

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BGD Counts

360°300°240°180°120°60°0°

Detector Roll Angle

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FLR Counts


Ge6

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BGD Counts

360°300°240°180°120°60°0°

Detector Roll Angle

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FLR Counts


Ge7

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BGD Counts

360°300°240°180°120°60°0°

Detector Roll Angle

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FLR Counts


Ge812000

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FLR Counts

360°300°240°180°120°60°0°

Detector Roll Angle

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BGD Counts


Ge9

X4.8 Flare of 23-July-2002X4.8 Flare of 23-July-200225000

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Counts per 5 sec Time Bin

00:20 00:30 00:40 00:50

Time (UT)

FLR207230120 - 40 keV

FLR BGD1 (24 hrs before) BGD2 (24 hrs after)

25000

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15000

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0


00:20 00:30 00:40 00:50

Time (UT)

FLR207230140 - 60 keV


25000

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0


00:20 00:30 00:40 00:50

Time (UT)

FLR207230160 - 80 keV


25000

20000

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0


00:20 00:30 00:40 00:50

Time (UT)

FLR207230180 - 100 keV


Analysis Interval : 00:27 – 00:43 UT


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Counts per 15°

360°300°240°180°120°60°0°

Azimuthal Scatter Angle

20 – 40 keV

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Counts per 15°

360°300°240°180°120°60°0°


20 – 40 keV

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Counts per 15°

360°300°240°180°120°60°0°


40 - 60 keV

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Counts per 15°

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40 - 60 keV

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Counts per 15°

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60 - 80 keV

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Counts per 15°

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60 - 80 keV

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Counts per 15°

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80 - 100 keV

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Counts per 15°

360°300°240°180°120°60°0°


80 - 100 keV

“Background”-subtracted data

An Initial Approach to RHESSI AnalysisAn Initial Approach to RHESSI Analysis

Two Component Analysis

1. Systematic Component:• Single sinusoid component.

2. Polarization Signal• Double sinusoid component.

€

f (η ) = A + B sin2(η −ϕ ) + C sinα (η −ψ )

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Counts per 15°

360°300°240°180°120°60°0°


20 – 40 keV

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Counts per 15°

360°300°240°180°120°60°0°


20 – 40 keV

Background SystematicsBackground Systematics

-4000

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0

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FLR Counts

360°300°240°180°120°60°0°

Detector Roll Angle

Ge4/6 - Ge5/3


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Counts per 15°

360°300°240°180°120°60°0°


20 – 40 keV

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Counts per 15°

360°300°240°180°120°60°0°


20 – 40 keV

10000

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0

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Counts per 15°

360°300°240°180°120°60°0°


40 - 60 keV

10000

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Counts per 15°

360°300°240°180°120°60°0°


40 - 60 keV

10000

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Counts per 15°

360°300°240°180°120°60°0°


60 - 80 keV

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0

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Counts per 15°

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60 - 80 keV

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Counts per 15°

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80 - 100 keV

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Counts per 15°

360°300°240°180°120°60°0°


80 - 100 keV

“Background”-subtracted data


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Counts

360°300°240°180°120°60°0°


FLR2072301 : 20 - 40 keV

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0

Counts

360°300°240°180°120°60°0°


FLR2072301 : 20 - 40 keV

-2000

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0

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2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 60 - 80 keV

-2000

-1000

0

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2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 60 - 80 keV

-2000

-1000

0

1000

2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 40 - 60 keV

-2000

-1000

0

1000

2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 40 - 60 keV

-2000

-1000

0

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2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 80 - 100 keV

-2000

-1000

0

1000

2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 80 - 100 keV

Residual Polarization Signal


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Counts

360°300°240°180°120°60°0°


FLR2072301 : 20 - 40 keV

χν2 ( ) = 3.32polar

χν2 ( ) = 9.46line

6000

4000

2000

0

Counts

360°300°240°180°120°60°0°


FLR2072301 : 20 - 40 keV

χν2 ( ) = 3.32polar

χν2 ( ) = 9.46line

-2000

-1000

0

1000

2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 40 - 60 keV

χν2 ( ) = 3.90polar

χν2 ( ) = 3.88line

-2000

-1000

0

1000

2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 40 - 60 keV

χν2 ( ) = 3.90polar

χν2 ( ) = 3.88line

-2000

-1000

0

1000

2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 60 - 80 keV

χν2 ( ) = 1.72polar

χν2 ( ) = 1.67line

-2000

-1000

0

1000

2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 60 - 80 keV

χν2 ( ) = 1.72polar

χν2 ( ) = 1.67line

-2000

-1000

0

1000

2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 80 - 100 keV

χν2 ( ) = 0.62polar

χν2 ( ) = 0.92line

-2000

-1000

0

1000

2000

Counts

360°300°240°180°120°60°0°


FLR2072301 : 80 - 100 keV

χν2 ( ) = 0.62polar

χν2 ( ) = 0.92line


X1.5 Flare of 21-April-2002X1.5 Flare of 21-April-2002

3000

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0


01:05 01:10 01:15 01:20 01:25

Time (UT)

FLR204210120 - 40 keV


3000

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01:05 01:10 01:15 01:20 01:25

Time (UT)

FLR204210140 - 60 keV


3000

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0


01:05 01:10 01:15 01:20 01:25

Time (UT)


FLR204210160 - 80 keV

3000

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01:05 01:10 01:15 01:20 01:25

Time (UT)

FLR204210180 - 100 keV




400

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0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 20 - 40 keV

400

300

200

100

0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 40 - 60 keV

400

300

200

100

0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 60 - 80 keV

400

300

200

100

0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 80 - 100 keV



400

300

200

100

0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 20 - 40 keV

χν2 ( ) = 0.42polar

χν2 ( ) = 0.37const

400

300

200

100

0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 20 - 40 keV

χν2 ( ) = 0.42polar

χν2 ( ) = 0.37const

400

300

200

100

0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 40 - 60 keV

χν2 ( ) = 0.77polar

χν2 ( ) = 0.60const

400

300

200

100

0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 40 - 60 keV

χν2 ( ) = 0.77polar

χν2 ( ) = 0.60const

400

300

200

100

0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 60 - 80 keV

χν2 ( ) = 0.99polar

χν2 ( ) = 1.05const

400

300

200

100

0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 60 - 80 keV

χν2 ( ) = 0.99polar

χν2 ( ) = 1.05const

400

300

200

100

0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 80 - 100 keV

χν2 ( ) = 2.09polar

χν2 ( ) = 1.58const

400

300

200

100

0

-100

-200

Counts

360°300°240°180°120°60°0°


FLR2042101 : 80 - 100 keV

χν2 ( ) = 2.09polar

χν2 ( ) = 1.58const


X3.9 Flare of 03-November-2003X3.9 Flare of 03-November-200335000

30000

25000

20000

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0

Counts per Time Bin

09:45 09:50 09:55 10:00

Time (UT)

FLR311031620 - 40 keV


35000

30000

25000

20000

15000

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0

Counts per Time Bin

09:45 09:50 09:55 10:00

Time (UT)

FLR311031640 - 60 keV


35000

30000

25000

20000

15000

10000

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0

Counts per Time Bin

09:45 09:50 09:55 10:00

Time (UT)

FLR311031660 - 80 keV


35000

30000

25000

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Counts per Time Bin

09:45 09:50 09:55 10:00

Time (UT)

FLR311031680 - 100 keV




6000

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2000

0

Counts

360300240180120600


FLR3110316 : 20 - 40 keV

6000

4000

2000

0

Counts

360300240180120600


FLR3110316 : 20 - 40 keV

1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 40 - 60 keV1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 40 - 60 keV

1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 60 -80 keV1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 60 -80 keV

1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 80 - 100 keV1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 80 - 100 keV



6000

4000

2000

0

Counts

360300240180120600


FLR3110316 : 20 - 40 keV

χν2 ( ) = 3.55polar

χν2 ( ) = 3.82const

6000

4000

2000

0

Counts

360300240180120600


FLR3110316 : 20 - 40 keV

χν2 ( ) = 3.55polar

χν2 ( ) = 3.82const

1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 40 - 60 keV

χν2 ( ) = 1.73polar

χν2 ( ) = 2.12const

1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 40 - 60 keV

χν2 ( ) = 1.73polar

χν2 ( ) = 2.12const

1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 60 -80 keV

χν2 ( ) = 0.82polar

χν2 ( ) = 1.21const

1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 60 -80 keV

χν2 ( ) = 0.82polar

χν2 ( ) = 1.21const

1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 80 - 100 keV

χν2 ( ) = 0.97polar

χν2 ( ) = 1.58const

1500

1000

500

0

-500

-1000

Counts

360300240180120600


FLR3110316 : 80 - 100 keV

χν2 ( ) = 0.97polar

χν2 ( ) = 1.58const



25000

20000

15000

10000

5000

0

Counts per 5 Sec Time Bin

02:00 02:05 02:10 02:15 02:20 02:25 02:30

Time (UT)

FLR411100220 -40 keV

FLR BGD2 (24 hrs after)

25000

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15000

10000

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0


02:00 02:05 02:10 02:15 02:20 02:25 02:30

Time (UT)

FLR411100240 - 60 keV

FLR BGD2 (24hrs after)

25000

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15000

10000

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0


02:00 02:05 02:10 02:15 02:20 02:25 02:30

Time (UT)

FLR411100260 - 80 keV


25000

20000

15000

10000

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0


02:00 02:05 02:10 02:15 02:20 02:25 02:30

Time (UT)

FLR411100280 - 100 keV




800

400

0

-400

Counts

360300240180120600


FLR4111002 : 20 - 40 keV

800

400

0

-400

Counts

360300240180120600


FLR4111002 : 40 - 60 keV

800

400

0

-400

Counts

360300240180120600


FLR4111002 : 60 -80 keV

800

400

0

-400

Counts

360300240180120600


FLR4111002 : 80 - 100 keV



800

400

0

-400

Counts

360300240180120600


FLR4111002 : 20 - 40 keV

χν2 ( ) = 1.52polar

χν2 ( ) = 1.89const

800

400

0

-400

Counts

360300240180120600


FLR4111002 : 20 - 40 keV

χν2 ( ) = 1.52polar

χν2 ( ) = 1.89const

800

400

0

-400

Counts

360300240180120600


FLR4111002 : 40 - 60 keV

χν2 ( ) = 1.37polar

χν2 ( ) = 1.36const

800

400

0

-400

Counts

360300240180120600


FLR4111002 : 40 - 60 keV

χν2 ( ) = 1.37polar

χν2 ( ) = 1.36const

800

400

0

-400

Counts

360300240180120600


FLR4111002 : 60 -80 keV

χν2 ( ) = 1.54polar

χν2 ( ) = 1.98const

800

400

0

-400

Counts

360300240180120600


FLR4111002 : 60 -80 keV

χν2 ( ) = 1.54polar

χν2 ( ) = 1.98const

800

400

0

-400

Counts

360300240180120600


FLR4111002 : 80 - 100 keV

χν2 ( ) = 1.03polar

χν2 ( ) = 1.18const

800

400

0

-400

Counts

360300240180120600


FLR4111002 : 80 - 100 keV

χν2 ( ) = 1.03polar

χν2 ( ) = 1.18const


Selected FlaresSelected Flares

11-Nov-2004N8W62

23-Jul-2002 S13E72

03-Nov-2003 N08W77

21-Apr-2002S14W84


20 - 40 keV Polarization

Flare location : S13E72

8000

6000

4000

2000

Counts

360°300°240°180°120°60°0°

Scatter Angle (η)

2072301FLR20-40 keV

µp = 0.10 ± 0.04

Π ≈ 18%Φ = 79° ± 3°


8000

6000

4000

2000

Counts

360°300°240°180°120°60°0°

Scatter Angle (η)

2072301FLR20-40 keV

µp = 0.10 ± 0.04

Π ≈ 18%Φ = 79° ± 3°

8000

6000

4000

2000

0

Counts

360°300°240°180°120°60°0°

Scatter Angle (η)

µp = 0.15 ± 0.06

Π ≈ 27%Φ = 86° ± 2°

FLR207230120-40 keV

(Ge8-Ge3)+(Ge9-Ge5)

8000

6000

4000

2000

0

Counts

360°300°240°180°120°60°0°

Scatter Angle (η)

µp = 0.07 ± 0.05

Π ≈ 13%Φ = 66° ± 4°

FLR207230120-40 keV

(Ge8-Ge6)+(Ge9-Ge4)


8000

6000

4000

2000

Counts

360300240180120600

Scatter Angle (η)

2072301FLR20-30 keV

µp = 0.07 ± 0.04

Π ≈ 12%Φ = 74° ± 3°

8000

6000

4000

2000

Counts

360°300°240°180°120°60°0°

Scatter Angle (η)

2072301FLR20-40 keV

µp = 0.10 ± 0.04

Π ≈ 18%Φ = 79° ± 3°

1400

1200

1000

800

600

400

200

Counts

360300240180120600

Scatter Angle (η)

2072301FLR30-40 keV

µp = 0.33 ± 0.16

Π ≈ 60%Φ = 92° ± 4°

SummarySummary

Addition of a Be scattering block provides HESSI with significant polarimetric capability.

Polarization sensitivity predicted to be less than a few percent for some X-class flares.

First analysis includes four events :

1) 23-July-2002

2) 21-April-2002

3) 03-November-2003

4) 10-November-2004

Only the July 23rd event shows evidence of polarization (at the ~18% level in the 20-40 keV energy range).

In ProgressIn Progress

Draft paper should be ready soon :Draft paper should be ready soon :

description of methoddescription of method

positive results for 23-July-2002positive results for 23-July-2002

null results for 21-Apr-2002, 3-Nov-2003, 10-Nov-2004 null results for 21-Apr-2002, 3-Nov-2003, 10-Nov-2004

Simulations with proper input spectra.Simulations with proper input spectra.

Quantify resultsQuantify results

Time-dependence of July 23rd event.Time-dependence of July 23rd event.

Polarization Measurements with Coronas-FPolarization Measurements with Coronas-F

Uses similar concept for polarization measurements (Be scattering into CsI).

Looked at data from three events:

1) 28-Oct-2003

2) 29-Oct-2003

3) 04-Nov-2003

Polarization detected only for 29-Oct-2003

40-60 keV polarization >75%

RHESSI Studies of Solar Flare Hard X-Ray Polarization Mark L. McConnell 1, David M. Smith 2, A. Gordon Emslie 4, Martin Fivian 3, Gordon J. Hurford 3,

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