Observation of Solar Wind Charge Exchange Observation of Solar Wind Charge Exchange Emission from Exospheric Material in Emission from Exospheric Material in

Earth's MagnetosheathEarth's Magnetosheath

S. L. Snowden, M. R. Collier, T. Cravens, K. D. Kuntz, I. Robertson

Specifically planned XMM-Newton proposal to observe magnetosheath SWCX emission

Long (100 ks) observation at a dim part of the sky

Designed to test Robertson & Cravens magnetosheath emission model

SWCX emission observed in spite of lower solar wind flux

Local Bubble and Beyond II – Philadelphia, PA – 21-24 April

XMM_Newton Observation GeometryXMM_Newton Observation Geometry Maximum elongation of orbit towards SunMaximum elongation of orbit towards Sun Look direction north through the magnetosheath close to the subsolar point.Look direction north through the magnetosheath close to the subsolar point. Tricky to combine low cosmic background and best scan through the magnetosheathTricky to combine low cosmic background and best scan through the magnetosheath

X-ray ObservationX-ray Observation

The observation was The observation was relatively free from relatively free from soft-proton soft-proton contaminationcontamination

Extract Light CurvesExtract Light Curves

OVII and Hard Band (2.5-12.0 keV)OVII and Hard Band (2.5-12.0 keV) Scatter plot of OVII count rate versus Scatter plot of OVII count rate versus

hard count rate to identify soft proton hard count rate to identify soft proton contaminationcontamination

Correlation indicates contamination => Correlation indicates contamination => exclude outliersexclude outliers

Add MOS1, MOS2 and PN count rates, Add MOS1, MOS2 and PN count rates, uncertainties added in quadratureuncertainties added in quadrature

Include only data where all three Include only data where all three instruments are acceptedinstruments are accepted

Extract the Solar Wind FluxesExtract the Solar Wind Fluxes

Solar wind proton Solar wind proton speedspeed

Solar wind OVII fluxSolar wind OVII flux Solar wind proton fluxSolar wind proton fluxOVII Flux – 103 cm2 s-1

H+ Flux – 103 cm2 s-1

H+ Speed km s-1

Observation

Data and ModelData and Model

Fit constant plus scaled Fit constant plus scaled magnetosheath modelmagnetosheath model

Insufficient heliospheric Insufficient heliospheric model variation to get a model variation to get a significant fitsignificant fit

Best fit has a terrible Best fit has a terrible 2 2

value, ~2.6value, ~2.6 Dominated by scatter, Dominated by scatter,

undersampling of OVII undersampling of OVII variation?variation?

Magnetosheath Model

HeliosphereModel

OVII Flux

Examine CorrelationExamine Correlation

The correlation coefficient is The correlation coefficient is 0.43 for 77 samples, for a 0.43 for 77 samples, for a probablility >99%probablility >99%

While the While the 22 value is bad (~190 value is bad (~190 for 75 dof), the for 75 dof), the 22 minimum is minimum is deepdeep

If the model is shifted in time, If the model is shifted in time, the the 22 minimum at zero shift is minimum at zero shift is relatively narrow and deeprelatively narrow and deep

These are qualitative arguments These are qualitative arguments but support a significant but support a significant correlation between the model correlation between the model and the dataand the data

Spectral FitSpectral Fit Fit for OVII and OVIII – Fit for OVII and OVIII –

the strongest SWCX the strongest SWCX lines in the XMM bandlines in the XMM band

Use XMM-ESAS to Use XMM-ESAS to model the particle model the particle backgroundbackground

Use RASS spectrum to Use RASS spectrum to constrain the fitconstrain the fit

Add a power law for any Add a power law for any soft-proton soft-proton contaminationcontamination

OVIII – 0.39(0.17) LU OVIII – 0.39(0.17) LU totaltotal

OVII – 4.3(0.3) LU totalOVII – 4.3(0.3) LU total 1.6 LU mag.1.6 LU mag.

OVII measurements OVII measurements agree well with other agree well with other local values (Smith et al., local values (Smith et al., Kuntz & Snowden)Kuntz & Snowden)

22 Contours for OVII and OVIII Contours for OVII and OVIII

The spectral fit is The spectral fit is reasonably good so the reasonably good so the contours are significantcontours are significant

OVIII detection marginalOVIII detection marginal OVII significantOVII significant

ConclusionsConclusions Strong correlation found between SWCX Strong correlation found between SWCX

magnetosheath emission modelmagnetosheath emission model=> First clear verification of SWCX model => First clear verification of SWCX model using X-ray datausing X-ray dataModel agrees to 36% on first cutModel agrees to 36% on first cut

Observing SWCX in X-rays can lead to remote Observing SWCX in X-rays can lead to remote sensing of the magnetosheath.sensing of the magnetosheath.

Results will form the basis for modeling the Results will form the basis for modeling the contribution of magnetosheath SWCX emission to contribution of magnetosheath SWCX emission to astrophysical observationsastrophysical observationso Subtraction at this point might be unfeasible but Subtraction at this point might be unfeasible but

marking observations at risk will be easy.marking observations at risk will be easy.