CXC AAS/Chandra12

Covering Solar-Wind Charge-Exchange from Every Angle with Chandra

Brad Wargelin

Chandra X-Ray Center

Smithsonian Astrophysical Observatory

CXC AAS/Chandra12

Heliospheric Solar Wind Charge Exchange

CXC AAS/Chandra12

Charge Exchange: The Forgotten Atomic Physics

CXC AAS/Chandra12

Outline

Astrophysical charge exchange• Solar wind charge exchange

Charge exchange X-ray emission

Solar Wind Charge Exchange (SWCX) X-rays• ROSAT• Geocoronal CX• Heliospheric CX• Soft X-Ray Background and SWCX

SWCX in the Chandra Deep Field-South

Future observations

CXC AAS/Chandra12

Charge Exchange

Charge exchange (CX) is the radiationless transfer of one (or more) electrons from a neutral atom or molecule to an ion.

• Molecular cloud chemistry: O+ + H O + H+ (13.618,13.599 eV)

• Solar wind proton-H CX: H+ + H H + H+

Some SW protons (tied to B field) CX with neutral H from the ISM, particularly between the heliopause and bowshock, creating hot H atoms, or Energetic Neutral Atoms (ENAs).

CXC AAS/Chandra12

Local Interstellar Cloud (partially neutral, 26 km/s)

Hydrogen Wall

CXC AAS/Chandra12

IBEX and ENA Imaging

Energetic Neutral Atoms (ENAs) no longer tied to B field. These can be “seen” by the Interstellar Boundary Explorer (IBEX) to image the CX interaction region.

CXC AAS/Chandra12

Astrospheres and Mass Loss Rates

Excess blue-shifted/broadened Lyman-α absorption due to the hot atoms in the Hydrogen wall can be used to determine mass loss rates of other stars surrounded by partially neutral ISM (Wood, et al. 2001-2005).

Cen B LyLinsky & Wood (1996)

Top line = intrinsic stellar profile (modeled)Dashed = after ISM absorptionHashed = excess absorption vs other lines

CXC AAS/Chandra12

Ionization balance of metals in photoionized nebulae—CX cross sections are large and a tiny fraction of neutral H is all it takes to make CX more important than RR and DR (e.g., Dalgarno 1985, Ferland et al. 1997).

Emission of 511-keV annihilation line in the GC via positronium formation (nearly 100%). Roughly half of the positronium is formed via CX with the rest from RR. (2 emission with opposite spins, 3 with same spin.)

Churazov et al. (2005, 2011)

CXC AAS/Chandra12

Charge Exchange X-Rays

O8+ + H *O7+ + H+ O7+ + H + h Highly charged ions capture electrons into high-n levels (nmax ~ q 3/4) that emit X-rays.

CX is a semi-resonant process. During a collision, energy levels distort and overlap at “curve crossings.”

Cross sections are large (few × 10-15 cm2).

(13.6 eV) (35 eV)

CXC AAS/Chandra12

CX X-Rays in Olden Times

Idea dates back to 1970s:• Galactic Ridge X-rays from

cosmic rays? (Silk & Steigman 1969)

ASCA; Tanaka (2002)

ASCA spectra of GC, Sgr, Sct with identical model curves (other than norm, NH, 6.4-keV line).

S

Fe

CaAr

CXC AAS/Chandra12

CX X-Rays in Olden Times

Idea dates back to 1970s:• Galactic Ridge X-rays from

cosmic rays?

No. Watson (1976), Bussard et al. (1978)…Revnivtsev et al. (2006,

2007)

CXC AAS/Chandra12

CX X-Rays in Olden Times

Idea dates back to 1970s:• Galactic Ridge X-rays from

cosmic rays?• X-ray lasers: population

inversion in “hollow ions”

CXC AAS/Chandra12

CX X-Rays in Olden Times

Idea dates back to 1970s:• Galactic Ridge X-rays from

cosmic rays?• X-ray lasers: population

inversion in “hollow ions”• Tokamaks: plasma edges

and neutral beam heating (e.g., Rice et al. 1986)

Wargelin et al. (1998)

Na10+ n=7-1

CXC AAS/Chandra12

CX X-Rays in Olden Times

Idea dates back to 1970s:• Galactic Ridge X-rays from

cosmic rays?• X-ray lasers: population

inversion in “hollow ions”• Tokamaks: plasma edges

and neutral beam heating• Supernova remnants (Wise

& Sarazin 1989)

CXC AAS/Chandra12

CX X-Rays in Olden Times

Idea dates back to 1970s:• Galactic Ridge X-rays from

cosmic rays?• X-ray lasers: population

inversion in “hollow ions”• Tokamaks: plasma edges

and neutral beam heating• Supernova remnants?

Cygnus Loop; Katsuda et al. (2011)

CXC AAS/Chandra12

CX X-Rays in Olden Times

Idea dates back to 1970s:• Galactic Ridge X-rays from

cosmic rays?• X-ray lasers: population

inversion in “hollow ions”• Tokamaks: plasma edges

and neutral beam heating• Supernova remnants?

CX X-ray emission was known

CXC AAS/Chandra12

Discovery of Solar Wind CX X-Rays

Key events:• Comet Hyakutake, ROSAT

(Lisse et al. 1996)• SWCX explanation (Cravens

1997):Highly charged ions in SW + neutral H2O, CO, CO2

CXC AAS/Chandra12

SWCX X-ray Spectrum (for Slow Wind)

Wargelin et al. (2004)Model CX spectrum (C,N,O) with 6 eV resolution

CXC AAS/Chandra12

Discovery of Solar Wind CX X-Rays

Key events:• Comet Hyakutake, ROSAT

(Lisse et al. 1996)• SWCX explanation (Cravens

1997)• First CCD spectrum of comet,

by Chandra (Lisse et al. 2000)C/1999 S4 (LINEAR)Chandra/Lisse 2000

Beiersdorfer et al. (2003)

LINEAR S4

CXC AAS/Chandra12

Discovery of Solar Wind CX X-Rays

Key events:• Comet Hyakutake, ROSAT

(Lisse et al. 1996)• SWCX explanation (Cravens

1997)• First CCD spectrum of comet,

by Chandra (Lisse et al. 2000)C/1999 S4 (LINEAR)Chandra/Lisse 2000

Beiersdorfer et al. (2003)

LINEAR S4

Two dozen comets and several planets to date by ROSAT, EUVE, BeppoSAX, Chandra, XMM, Swift, Suzaku.

Meanwhile……

CXC AAS/Chandra12

LTEs & Discovery of Geocoronal and Heliospheric Emission

ROSAT All Sky Survey (RASS; 1990) revealed multi-orbit (“Long Term”) enhancements in the SXRB.

Cravens, Robertson, & Snowden (2001): temporal correlations between counting rate and SW flux

LTEs are from geo/helio SWCX fluctuations.

¼-keV band, Galactic coords;Snowden et al. (2009)

CXC AAS/Chandra12

Geocoronal emission = SWCX in Earth’s exosphere, outside the magnetosphere (R > 10RE).

Geocoronal Emission

CXC AAS/Chandra12Robertson et al. (2006)

X-ray missions generally look out through the flanks.

Geocoronal Emission

Geocoronal emission = SWCX in Earth’s exosphere, outside the magnetosphere (R > 10RE).

CXC AAS/Chandra12

Lunar X-Rays (on the Dark Side) are Geocoronal

ROSAT, Schmitt 1990 Chandra, Wargelin et al. 2004

CXC AAS/Chandra12HDF-N, XMM; Snowden et al. (2004)Moon, Chandra; Wargelin et al. (2004)

CXC AAS/Chandra12

Heliospheric Charge Exchange

Solar wind + H/He from ISM 100-AU halo

Heliospheric CX ~ 10x geocoronal CX

Model heliospheric emission from CX with H. Axis units in AU. LIC is moving to the right. Robertson et al. AIP Proc. 719 (2004).

CXC AAS/Chandra12

Heliospheric Emission--looking down on ecliptic plane

More neutral H upwind

He focussing cone downwind

(AU)

(AU

)

Pepino et al. (2004)

CXC AAS/Chandra12

Slow vs Fast Solar Wind

At solar max, wind is a mix of slow and fast at ~all latitudes.

At solar min, wind is stratified, with slow wind near the ecliptic.

The fast wind is much less ionized and produces less CX X-ray emission.

CXC AAS/Chandra12

CX Emission at Solar Min--view from Ecliptic Plane

Pepino et al. (2004)

AU

AU

Stratified wind: slow and highly ionized near ecliptic higher CX emissivity.

Little emission in fast wind.

CXC AAS/Chandra12

The Soft X-Ray Background (SXRB)

SXRB emission components:• Absorbed extragalactic (~power law)• Absorbed thermal Galactic Halo emission• Unabsorbed thermal from Local Bubble• Heliospheric and geocoronal SWCX

How much emission is from CX vs the Local Bubble? The answer strongly affects our models of the LB.

CXC AAS/Chandra12

Modeling CX Emission

Need to know

• H and He distributions

• SW composition and density all along line of sight (LOS)

• State-specific CX cross sections for all ions (and neutrals) as f(v)

• Radiative decay paths and line yields

Local SW measured by ACE

CXC AAS/Chandra12

Living in a Fog

We can try to observationally separate SWCX emission from cosmic components with differential measurements: Spatially (using dark clouds to block distant emission) Spectrally (some day, with high-resolution nondispersive detectors) Temporal changes (periods of hours to Solar Cycle) Observation geometry

CXC AAS/Chandra12

The Chandra Deep Field-South

4 Msec of observations:• 3 in Oct, Nov 1999 (-110 C)• 9 in May, Jun, Dec 2000 • 12 in Sep-Nov 2007• 31 in Mar-Aug 2010

RA,Dec 3:32:28, -27:48:30Gal l,b 223.6, -54.4Ecl lat,lon 41.1, -45.2

The CDFS is the only X-ray deep field conducted during Solar Max and Min and it has the greatest orbital coverage.

CXC AAS/Chandra12

2000

J. Slavin

LOS is 45 down, into page.

CXC AAS/Chandra12

In 2000, there is slow wind all along the LOS and most observations are from within the He cone.

From within the He cone, CX intensity is higher and more of the emission is from nearby, where SW conditions are measured.

CXC AAS/Chandra12

In 2007, SW is stratified, LOS through fast wind, observations all outside He cone, looking downwind.

CXC AAS/Chandra12

Expectations for observed SXRB in 2000 vs 2007:

• Higher baseline level

• More variability

• Closer correlation with ACE-measured SW ion flux

CXC AAS/Chandra12

CXC AAS/Chandra12

CXC AAS/Chandra12

Compare O emission vs average ACE/SWICS O7+ flux

Many thanks to the ACE/SWICS team for their public data!

CXC AAS/Chandra12

2000:

Higher SXRB

Variable

Correlated with local SW

2007:

Lower SXRB

Nearly constant

Little correlation with SW

CXC AAS/Chandra12

The goal is to accurately model and remove SWCX emission and obtain the true cosmic background.

?

CXC AAS/Chandra12

High-resolution spectra from microcalorimeters will help immensely. Astro-H launch in 2014 (E ~ 5 eV) .

• CX spectra differ from collisional: enhanced high-n Lyman, He-like f...

• Explore the 1/4-keV band (where ROSAT LTEs are strongest)

• 500 km/sec E=1 eV at 600 eV

The Future

CXC AAS/Chandra12100 s of SXRB from XQC rocket flight vs thermal model (McCammon et al. 2002)

CXC AAS/Chandra12

CX Spectra

High-n levels are preferentially populated.

CXC AAS/Chandra12

CX Spectra

H-like Fe (with N2 in EBIT)

High-n levels are preferentially populated.• H-like: enhanced high-n

CXC AAS/Chandra12

CX Spectra

Wargelin et al. (2008)

High-n levels are preferentially populated.• H-like: enhanced high-n• He-like: enhanced triplet f and i

CX with N2

10 eV/amu

EIE at 15 keV

He-like Fe

CXC AAS/Chandra12

Astrospheric Charge Exchange

CX must also occur around other stars with highly ionized winds (G,K,M) residing inside clouds with neutral gas (LIC, G).

Imaging + spectra yields:• Mass-loss rate• Local nneutral

• Wind velocity and composition• Astrosphere geometry

Coronal emission is ~104x brighter, though.

Need very large collecting area, good spatial and spectra resolution.

CXC AAS/Chandra12

“Charge Transfer Reactions” Dennerl, Space Sci. Rev. (2010) Astrophysical examples and broad historical review

“EBIT charge-exchange measurements and astrophysical applications,” Wargelin et al., Canadian J. Physics (2008) Astrophysical examples and lab spectra/atomic physics

Reviews

CXC AAS/Chandra12

CXC AAS/Chandra12

Geocoronal emission responds to SW much faster than heliospheric.

CXC AAS/Chandra12

Talk amongst yourselves….

Things to think about:• Roughly 10% of RASS SXRB is from unresolved Galactic point sources• RASS was conducted at solar max• R12 (1/4-keV) rate ~4 x R45 (3/4-keV) rate• LTEs most prominent in R12 band• No models or data for CX in 1/4-keV band

CXC AAS/Chandra12

More detailed correlations:

Short-term X-ray variability vs ACE O7+ flux fractional contribution of geocoronal CX emission

Account for Chandra orbital geometry

CXC AAS/Chandra12

More detailed correlations:

Short-term X-ray variability vs ACE O7+ flux fractional contribution of geocoronal CX emission

Account for Chandra orbital geometry

CXC AAS/Chandra12

Diffuse X-Ray Spectrometer (DXS)

SXRB 150-300 eV. Sanders et al. (2001)

CXC AAS/Chandra12

From within the He cone, CX intensity is higher and more of the emission comes from nearby, where SW conditions can be measured.

Where does the observed SWCX emission originate?

CXC AAS/Chandra12

CX X-Rays in Olden Times

Idea dates back to 1970s:• Galactic Ridge X-rays from

cosmic rays?• X-ray lasers: population

inversion in “hollow ions”• Tokamaks: plasma edges

and neutral beam heating• Supernova remnants (Wise

& Sarazin 1989)

Cygnus Loop; Katsuda et al. (2011)

CXC AAS/Chandra12

CXC AAS/Chandra12

CX Spectra

He-like O (with CO2). Beiersdorfer et al. (2003)

High-n levels are preferentially populated.• H-like: enhanced high-n• He-like: enhanced triplet f and i

CXC AAS/Chandra12Ulysses data. E.J. Smith et al., Science 2003

Solar Max vs Solar MinAt solar max, wind is a mix of slow and fast at ~all latitudes.

At solar min, wind is stratified, with slow between latitude -20 and +20.

The fast wind is much less ionized and produces less CX emission.

CXC AAS/Chandra12

Living in a Fog

Observed geo/helio SWCX emission depends on CX emissivity all along the LOS, which means that it depends on: SW flux for each X-ray emitting ion as f(t,x) (only measured locally) Neutral gas density as f(t,x) (modeled) Observation direction Observation location

We can try to separate SWCX emission from cosmic components with differential measurements: Spatially (using dark clouds to block distant emission) Spectrally (some day, with high-resolution nondispersive detectors) Temporal changes Observation geometry

CXC AAS/Chandra12

Expectations for observed SXRB in 2000 vs 2007:

• Higher baseline level

• More variability

• Closer correlation with ACE-measured SW ion flux

CXC AAS/Chandra12

CX X-Rays in Olden Times

Idea dates back to 1970s:• Galactic Ridge X-rays from

cosmic rays?• X-ray lasers: population

inversion in “hollow ions”• Tokamaks: plasma edges

and neutral beam heating• Supernova remnants?

Cygnus Loop; Katsuda et al. (2011)

CXC AAS/Chandra12

CXC AAS/Chandra12

CXC AAS/Chandra12

Compare O emission (500-700 eV) vs…

Model CX spectrum with 6 eV resolution

CXC AAS/Chandra12

Conducted at solar maximum.

CXC AAS/Chandra12

Merge 52 observations for source detection

CXC AAS/Chandra12

Remove 400+ sources

CXC AAS/Chandra12

Trim radius to common FOV with radius 7.7’.

CXC AAS/Chandra12

Prox Cen M5.5 V

EV Lac M3.5 V

Boo G8 V + K4 V

= III,IV

And, DK Uma are marginal detections.

Wood et al. (2005)