# Presentation: 093150

## Solar Wind Charge Exchange Contributions to the Diffuse X-ray Background

*T. E. Cravens (with I. P. Robertson, S. L. Snowden, M. R. Collier, K. Kuntz, and M. Medvedev)*
*At the Local Bubble Bubble and Beyond II*
*Philadelphia, April 2008*

## Yohkoh X-Ray Image of the Solar Corona

*Other solar system x-ray sources*: Earth (aurora and geocorona),
- Venus and Mars (disk and halo), comets, Jupiter (aurora and
- disk), Saturn (disk), heliosphere,......

## The Solar Wind

- Extension of the solar corona
- Frozen-in solar corona composition (mostly protons and alpha particles; 0.1% heavy ions - C, N, O, Si, S, Fe,....)
- At 1 AU, average solar wind properties:
- n ≈ 7 cm-3, u ≈ 400 km/s, T ≈ 10 eV, Mach number M ≈10, B ≈ 10 nT.
- Slow and fast speed solar wind streams.

- THE SOLAR WIND CHARGE EXCHANGE MECHANISM
- FOR X-RAY PRODUCTION

## Slide 4

## Solar Wind Charge Exchange (SWCX) Mechanism for X-Ray Emission

- Solar wind ion  Mq +  (O, N, C, Fe, Si, Ne..)
- Cometary or interstellar neutrals H, He, or H2O, .....
- Charge transfer collisions:
- Mq + + H --->  H+    +   M (q-1) +*
- M (q-1) +*  -----> M (q-1) +   +   h

## Cravens, 2002

## Experimental

- Experimental Charge Transfer Cross Section
- Measurements at Solar Wind Energies

- Charge-Exchange
- Cross Sections
- Comparison
- with simple
- Over Barrier Model
- and Classical
- Trajectory
- Monte Carlo
- calculations
- -- large cross
- sections!

## Nucleus of comet Halley -- Giotto TV image

- Dust and gas (water, CO, ...)

## Cometary X-Ray Emission (Power ≈ 1 GW)

- Soft x-rays

- EUV

- Optical

- MHD model

## Dennerl et al (2003)

- Cometary
- X-Ray Spectrum
- XMM Newton

## X-Ray Emission From the Magnetosheath / Geocorona due to SWCX

- Geocoronal atomic hydrogen extends tens of Earth radii above the surface.
- The shocked solar wind is diverted around the magnetopause.
- The SWCX mechanism operates in the magnetosheath due to collisions with the H.
- Apparently, this has been seen as emission from the dark side of the Moon (ROSAT - Schmidt et al., 1991, and recently CXO -- Wargelin et al. 2004)

## Size of

- each image
- is 60 Earth
- radii.

- X-Ray emission
- from the
- terrestrial
- magnetosheath
- and geocorona due
- to the SWCX
- mechanism.
- Robertson and
- Cravens (2003)

## ROSAT 1/4 keV x-ray background LTE compared with measured IMP-8

- solar wind proton fluxes -- Cravens, Robertson, and Snowden, 2001.

## Lunar X-Ray Emission from CXO (Wargelin et al., 2004)

## Fujimoto et al.

- (2007)
- Suzaku
- observations
- of magnetosheath
- X-rays during
- a solar event/
- LTE.

*CVI*

*CVI*

*OVII*

*OVII*
*OVIII*

*FeXVII*
*OVIII*

*NeIX*
*Fe, O*

*NeX*

*MgXI*

## Martian X-Rays observed by XMM-Newton and organized

- by Spectral Region (Dennerl et al., 2006)

- Red -- carbon K-shell (solar fluor.)
- Blue -- ionized oxygen (SWCX)
- Information
- provided on solar
- wind interaction
- with exosphere of
- Mars:
- Solar wind flow
- around planet
- and exospheric
- neutral density
- distributions.

## Heliospheric X-Ray Emission

- From SWCX mechanism applied to solar wind interaction with interstellar neutral H and He streaming into the heliosphere (Cox, 1998; Cravens, 2000).
- Spectrum is consistent with observed soft x-ray background emission (rockets, ROSAT...)

## Pauls and Zank (1997)   2-fluid model of heliosphere and ISM

## Modeled X-ray map for O7+ ---> O6+.  Units are photons/cm2/s.

- Modeled X-ray map for O7+ ---> O6+.  Units are photons/cm2/s.

- Medvedev et al. (2006)

## Robertson, Cravens, Snowden (2003)

- Robertson, Cravens, Snowden (2003)

- Predicted heliospheric
- (interstellar neutrals)
- and geocoronal x-ray
- emission versus look
- direction.

- (Earth-centered
- Heliolatitude and
- longitude.)
- Note the
- helium “cone”.

## From Henbest

- and Cooper (1994).
- 120 pc by 120 pc
- View in the galactic
- plane of the nearby
- interstellar medium
- (***the local bubble***).

## Line of sight 

- Galaxy

- Local
- Bubble

- Line of sight
- from Earth

- Outer
- heliosphere

- geocorona

- Inner
- Heliosphere

- REGIONS EMITTING SOFT X-RAYS (contributions to
- the observed soft x-ray background (SXRB))

## Possible Ways to Purge the SXRB of SWCX Contributions

- Spatial/directional morphology.
- Temporal variability (already partially successful - LTE removal).
- Spectral differences (such as line ratios) - potentially powerful but high resolution needed.
- Modeling combined with above.

## Slide 24

## Slide 25

## Slide 26

## From Mewe et al. (1990).   Hot plasma - lines and more lines

- Collisional due to electrons.  Similar to SWCX spectrum.

- Use the spectrum to distinguish standard collisional from SWCX?

## Bodewits

- Ph. D.
- Thesis
- (2007)
*Helium-*
*Like ion*
*spectrum*
- OVII line
- complex
- near
- 560 eV.

## Laboratory Simulation of 

- Laboratory Simulation of
- Charge Exchange
- produced X-Ray Emission
-  from Comets using the
- Spare *ASTRO-E*
- Microcalorimeter
- P. Beiersdorfer et al.
- (2003)

## Orion Extended Nebula X-Ray Emission

- Güdel et al. (2007) Science

- The blue designates a soft x-ray emission region (XMM Newton)
- The scale is a few parsecs.

## Güdel et al. (2007) - XMM spectrum of the soft x-rays from the

- Extended Orion Nebula showing OVII lines near 560 eV.

## A SWCX

*trapezium*

- Orion
-  Molecular
- Cloud

*neutrals*

- EON

*X-rays*

- Schematic of plasma outflow in the extended Orion
- nebula and an area of possible charge exchange
- X-ray emission.

*A SWCX*
*Contribution?*
- Probably *not*,
- but it cannot
- be dismissed
- out of hand.

## Summary

- Traditionally x-ray emission has been a diagnostic tool for hot plasmas (e.g., solar corona, supernova remnants, intragalactic medium...).
- Some types of X-ray emission in the solar system can be a diagnostic tool for plasma interactions with neutrals (solar wind - comet/Earth/heliosphere, auroral x-rays,...)
- The *charge exchange mechanism* has been shown to be particularly important for solar system x-ray emission and might also have applications to *astrophysical plasmas*.

## Wargelin et al. (2004)

- CXO X-Ray Spectrum of Dark Side of Moon
- (geocoronal x-rays) -- looks like SWCX x-rays.

## X-Ray Transitions

- O5+ (1s25d --> 1s22p)  106.5 eV
- O6+ (1s2p --> 1s2)  568.4 eV
- O6+ (1s2s --> 1s2)  560.9 eV
- O7+ (2p --> 1s)  654 eV
- C5+ (2p --> 1s)  367.3 eV
- C5+ (4p --> 1s)  459.2 eV

## Janev, 86

- review

- Fully stripped
- carbon ion
- projectiles
- Large
- cross sections
- Initial n ≈ 4

## Slide 37

## Robertson and Cravens

## Wargelin et al. (2004)

- CXO X-Ray Spectrum of Dark Side of Moon
- (geocoronal x-rays) -- looks like SWCX x-rays.

## Interaction of Interstellar Medium with Heliosphere

- Using the velocity vectors in the data (see image), we numerically calculated the solar wind streamlines. We then followed the evolution of solar wind ion ionization states along the stream lines and simultaneously determined the charge exchange production rates as a function of position.
- Using these 3D production rates, we produced 2D X-ray maps (photons/cm2/s).

- Zank and Florinski heliosphere model

## Interstellar Medium

- From Henbest
- and Cooper (1994).
- 500 pc by 500 pc
- view of galactic
- plane near the Sun.

## The Tail Beam Spectrum

- X-axis: photon energy in units of eV

## The Evolution of Ne8+

- The Evolution of Ne8+

- Ne7+

- Ne6+

- Ne8+

- Ne5+

- Ne4+

- The shown figures are modeled X-ray maps as observed from outside the heliosphere starting with Ne8+.  The maps show the transition of the original species to the emitting species. For instance, “Ne8+” represents a map of the transition of Ne8+ → Ne7+,where Ne7+ emits the photon. The large orange contour represents the position of the termination shock, and the small one encircles the position of the Sun. Units are (photons/cm2/s).

## Fisk (2005) -- Heliosphere Schematic

## Slide 45

## Astronomy and Astrophysics, 2006:

- Charge-TransferinducedEUVandSoftX-ray emissions inthe
- Heliosphere
- D.Koutroumpa1, R.Lallement1, V.Kharchenko2,A.Dalgarno2,R.Pepino2,V.Izmodenov3,andE.Qu ́
- emerais1
**X-RAY AND EXTREME ULTRAVIOLET EMISSIONS FROM COMETS** VLADIMIR A. KRASNOPOLSKY1 , JASON B. GREENWOOD2 and PHILLIP C. STANCIL3
- Space Science Reviews (2005)
- Laboratory Simulation of Charge Exchange produced X-Ray Emission from Comets using the Spare *ASTRO-E* Microcalorimeter P. Beiersdorfer∗, K. R. Boyce, G. V. Brown, H. Chen, S. M. Kahn , R. L. Kelley, M. May, R. E. Olson, F. S. Porter, C. K. Stahle , W. A. Tillotson

## Predicted Heliospheric

- X-Ray Emission as seen
- From Earth.
- -- in galactic coordinates.
- Robertson, Cravens,
- and Snowden (2003).
- ROSAT SXRB
- Map is also shown and
- a *preliminary*
- “subtraction” map.