MWA-LFDFaraday Rotation

SubsystemJustin C Kasper

MIT Kavli Institute for Astrophysics and Space ResearchMWA-LFD New England Meeting1 November 2006 MIT

Space WeatherOctober 28, 2003 CME

A sequence of large solar flares in late October 2003Brightest x-ray flares on recordFirst eruption reaches Earth in 18 hours

SOHO

Space WeatherOctober 28, 2003 CME

Solar wind speed ~ 2,000 km/s – high dynamic pressureEvents could have been much more geoeffectiveLack of southward field led to poor couplingHow can we predict this? Wind SWE & MFI

Methods

In-situ measurements (V,T,n,B)IMP-8, Wind, ACEUlyssesVoyager

Remote observationsThompson scattered white light coronagraphsX-ray and uv imagingInterplanetary scintillations of radio sourcesFaraday rotation

Faraday rotationPolarized radiation in magnetized plasma

rad 2λ⋅=Ω RM

2-13 m rad ˆ1063.2

where

∫ ⋅⋅= − dssBNRM e

A rotation measure of RM = 1 rad m-2 yields:Ω= 0.97° at 2.3 GHz (λ=0.13 m)Ω = 57.3° at 300 MHz (λ=1.0 m)Ω = 1432° at 60 MHz (λ=5.0 m)

MWA Faraday Rotation SystemGoals

Determine RM along lines of sightExtragalactic sourcesGalactic: pulsars, diffuse emission

Global structure of quiet inner heliosphere

Model validationCoronal heatingField topologyRadiation risk Earth, Mars

Global structure of transients (CMEs)Earth directedOrientation of B

Power spectrum of turbulenceRadialLatitudinal

Heliospheric boundariesTermination shockHeliosheath

Simulation courtesy C. Manchester UMICH

( ) ( )eRM n s B s ds∝ ⋅∫

MWA Faraday Rotation SystemGoals

Determine RM along lines of sightExtragalactic sourcesGalactic: pulsars, diffuse emission

Global structure of quiet inner heliosphere

Model validationCoronal heatingField topologyRadiation risk Earth, Mars

Global structure of transients (CMEs)Earth directedOrientation of B

Power spectrum of turbulenceRadialLatitudinal

Heliospheric boundariesTermination shockHeliosheath

Simulation courtesy C. Manchester UMICH

( ) ( )eRM n s B s ds∝ ⋅∫

Faraday Rotation with HeliosSpacecraft passes “behind” Sun

Faraday Rotation with HeliosTrack polarization angle with DSN

Faraday Rotation with HeliosFollow Helios during solar passage

|Ωmax| ∝ R-4.15

Faraday Rotation with HeliosProperties of the quiet inner heliosphere

Patzold et al., 1986

Faraday Rotation with HeliosThe effects of a Coronal Mass Ejection

Bird et al., 1985

Faraday Rotation with HeliosFluctuations and dissipation

Efimov et al., 1996

Improved FR Will be a Powerful Tool for Studying Heliosphere

More pointsExtra-galactic sourcesDiffuse emission from Galaxy

Out further from SunSensitive to smaller values of RMOperate at longer wavelengths

Robust against large values of RMOperate at many frequenciesNarrow bandwidth

FR SourcesMonitor galaxies instead of spacecraft

Mancuso and Spangler, 2000

Diffuse galactic

FR SourcesHow many sources at our frequencies?

Polarization tends to decrease with frequencyWesterbork Northern Sky Survey at 327 MHzOne extragalactic source ~ 2 square degreesRM of several hundred sources detectable in five minute integrationPotential to use diffuse galactic emission as well

Haverkorn, 2003

Extra-galactic

Near Auriga constellation

Variable IonosphereSources and spatial scales

Daily variation driven by SunSmall-scale fluctuations due to instabilitiesSolar flaresSolar wind

P. Spencer NOAA/CIRES

Ionospheric calibration Electron column depth with GPS

Erickson et al., 2001

Tracks of GPS spacecraft in sky

Determine the electron column density along line of sight to GPS spacecraft

Combine model ionosphere + geomagnetic field to predict RM ~ 0.01 rad/m2

MWA Ionospheric CalibrationCombine GPS and differential screen

MWA performs calibration equivalent to adaptive optics 10 sigma detection of 200 sources at 16 kHz in 10 secondsApparent displacement of sources inverted to obtain gradient in number densityHigh resolution map of dNecombined with Ne from GPS

MWA CapabilitiesPredicted range of observable RM

Bandwidth depolarizationAngular broadeningDetectible rotationSource brightnessIonosphere

Mileura Wide-Field ArrayObservations over Carrington rotation

Simulated heliosphere based on CR 1971Global coronal and heliospheric MHD simulations from SAIC (P. Riley)

5 min integrations x 200 sources x 8 hours x 30 days = 500,000 constraints/CR

Mileura Wide-Field ArraySimulation of October 2003 CME

Background over Carrington rotationBest-fit rope parameters at 1 AUScale properties of rope back to SunAssume constant expansion speed

Faraday Rotation SubsystemDescription of the design

Database of strong sources

Targeting Accumulateon sources

Correct forionosphere

Innersourcebinner

Outer sourcebinner

Archive?

Solvefor RM

Archive

GPS

Distribute

GSM

GSM

IonosphericCalibration

Monitor and control

Solar stateX-raysRadio

IPS

Solarimaging

Faraday Rotation SubsystemCurrent and future work

Determine how close to the Sun we can monitor

Interference from SunDepolarization of sources

How do we optimize observing frequency?

High frequency for large RMLow frequency for low RM

Targeting patternCenter on SunCirculateHow does this relate to IPS and solar imaging?

Faraday Rotation SubsystemSummary

FR system design proceedingInterfaces with ionosphere, calibration systems20 TB online data archive

More work needed on:Developing ionospheric calibrationTechniques for extracting parameters from FR observations (See presentation by Ying Liu)FC calculations from MHD simulations (SAIC, U Michigan)Combining with other observations (IPS, coronagraphs)