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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