LSSO-10/2007

SWCX in the

XMM era

K.D.KuntzThe Henry A. Rowland Department of Physics

and AstronomyThe Johns Hopkins University

ROSAT• The Long-Term Enhancement (LTE) Problem

– Long observations of the cosmic background showed long-term (~days) variation

• ROSAT All-Sky Survey– Each point observed multiple times– Deconvolved temporal and spatial variation– Removed LTE to some base/threshold/bias level– Formed fiducial for correcting pointed

observations• Difference between obs. And RASS = “LTE Level”

ROSATLSSO-10/2007

ROSAT• Observed LTE rate correlated with solar wind

– But mechanism not clear (Freyberg 1994)

• X-ray count rate towards the dark side of moon consistent with the calculated LTE rate– Implied cis-lunar origin

• “Flaming” comets (Lisse 1996)– Mechanism elucidated by Cravens (1997): SWCX

• Mechanism quickly applied to LTEs and LHB

ROSATLSSO-10/2007

SWCXionSW

+n + H → ionSW+n-1 + H+ + ν

ionSW+n + He → ionSW

+n-1 + He+ + ν

Neutral H&He from:

geocoronal/exospheric neutrals

ISM flowing through heliosphere

Emitted spectrum has no continuum

Since solar wind highly variable in ρ,v, & z,

over both t & (r,θ,φ)

so to is the X-ray emission

SWCXLSSO-10/2007

ROSATSWCX Spectrum is temporally variable:

¼ keV and ¾ keV only partially correlated

SWCX Flux = proton flux × ion abundance

ROSATLSSO-10/2007

Correlation Non-Correlation

SWCX stronger below 0.25 keV than above, but strong in important lines at 0.56 and 0.65 keV

x6x15

SWCX:Time VariabilitySWCXtotal = SWCXnon-local heliospheric

+ SWCXlocal heliospheric

+ SWCXexospheric

SWCXLSSO-10/2007

Highly time variable

Component remaining in RASS

R>5 AUNot variable:Integrated over 5-100 AUAnd many different SW conditions

XMM measurable component

Discovery of SWCX in XMM

HDFLSSO-10/2007

Four successive observations of the same part of the sky First 3 observations statistically the sameLast observation substantially different (1st ½)Difference exactly the type of spectrum expected from SWCX

Discovery of SWCX in XMM

HDFLSSO-10/2007

Four successive observations of the same part of the sky First 3 observations statistically the sameLast observation substantially different (1st ½)Difference exactly the type of spectrum expected from SWCX

The HDF Event• Light-curve made little sense

– XMM high then low– Solar wind (ACE) spikes at XMM drop

HDFLSSO-10/2007

The HDF Event• Solution: X-ray observations integrate LOS

– If solar wind wave-front tilted it can enter the X-ray FOV before hitting ACE

– Collier, Snowden, & Kuntz

HDFLSSO-10/2007

• Solution makes no assumption about neutral distribution other than it must be local

The HDF Event• Koutroumpa et al (2007) propose similar solution, but

attribute tilted wavefront to Parker Spiral structure

HDFLSSO-10/2007

• Solution assumes neutral material to be heliospheric

The HDF Event• Special geometry confuses the issue

HDFLSSO-10/2007

Earth

Magnetopause

BowshockOrbit

Magnetopause ion density 4X free solar wind

HDF4

The HDF Event• But how is HDF4 different from others?

HDFLSSO-10/2007

HDF1 HDF2 HDF4

All observations have similar observation geometry through “nose” of magnetosheathDifference is in the solar wind flux

The Question• In order to see SWCX enhancement

– Need solar wind enhancement– Is the special geometry also required?

• Exospheric or Heliospheric?

HDFLSSO-10/2007

The ProjectCorrelate SWCX enhancements with observation geom.

in sets of observations with exactly the same FOV

10-11 sets of observations at high galactic latitude

Analysis without accurate ∫magnetospheric density

(for now!)

HDFLSSO-10/2007

Program• Compare spectra from different observations

– Top: (raw-inst.back)M1/responseM1 + (raw-inst.back)M2/responseM2

– Bottom: spectrum – min(spectra) = difference spectrum

– Middle: uncertainties in difference spectra

HDFLSSO-10/2007

Program• The other discrepant observation is actually through the flank

of the magnetosheath! (solar wind at 85th percentile)– Special observation geometry is not required

• HDF6 & HDF7 have similar geometry but no excess– Observation through nose does not produce SWCX excess

HDFLSSO-10/2007

HDF5

Program• Two observations through the flanks of the magnetosheath

– Solar wind flux extremely high (99th percentile).

HDFLSSO-10/2007

Program• Four observations with long LOS through the flanks

– One observation has extremely high solar wind flux – but no SWCX!

– (Ignore purple spectrum – due to soft proton contamination)

HDFLSSO-10/2007

Program• Three sets of observations with no problems

– Typically low values of solar wind flux

– Observation SEP2 has ~high solar wind flux but no sig. SWCX

HDFLSSO-10/2007

Program• Three sets of observations where SWCX correlates with S.W.

– Within each set, observation geometries similar

HDFLSSO-10/2007

Summary• Bulk of strongly contaminated spectra from LOS through nose

of magnetosheath

• Some notable counter-examples!

• SWCX contamination often correlated with s.w. strength

ProgramLSSO-10/2007

Sure SWCXPossible SWCXFlank LOS

Summary• A LOS through nose of magnetosheath seems to be more

sensitive to solar wind enhancements (80th percentile) than an LOS through flanks of the magnetosheath.

• LOS through flanks of magnetosheath with strong SWCX but not so strong solar wind enhancement may be due to localized nature of our measure of the solar wind flux– May also be due to special geometries

• A LOS through the nose may have no more SWCX than a LOS through the flank.

• Of 46 observations, 9-12 have SWCX – From a larger sample (15%-25%)

• Need much more detailed modeling of the magnetosheath and the rest of the heliosphere to understand the relative contributions to the total SWCX.

SummaryLSSO-10/2007