# Presentation: 798796

## The X-ray LHB

- K.D.Kuntz
- (Henry A. Rowland Dept. of Physics & Astronomy)
- With a great deal of help from my friends!

## Basics

- Astronomers and Physicists disagree:
- Transitions in O+7 produces lines labeled OVIII
- In charge exchange O+7 is the parent species producing OVII
- Absorption: σ~E-8/3
- 	the lower the photon energy, the more likely to be absorbed

## The X-ray Background (ca. 1960)

- Studied in 2-10 keV band (Giacconi 1962)
- Power law spectrum
- At lower energies should be entirely absorbed by the neutral H in the Galactic plane
- Observations revealed 1⁄4 keV emission everywhere, including the Galactic plane
- Bowyer et al.(1968), Henry et al.(1968), Bunner et al.(1968)

## The fundamental surveys: Wisconsin

- All-sky rocket borne survey
- Executed 1972-1980
- 6.5° resolution
- In C band τ=2 (15% trans.) at nH~5×1020 cm-2
- Expect to see Gal. disk shadow extragalactic emission

## The fundamental surveys: Wisconsin

- No small scale shadows...

## The fundamental surveys: Wisconsin

- ...large-scale anticorrelation in B band!

## An Old Controversy

- Assuming a uniform distribution of nH,
- three ways of producing the anticorrelation:
- Absorption - all emission extragalactic
- Can’t work with reasonable cross-sections
-  Displacement (cavity) - all emission local
- Absorption and emission interleaved

## The Local Cavity

- Local ISM remarkably deficient in neutral gas
- Knapp (1975) from nH(b)

## The Local Cavity

- Local ISM remarkably deficient in neutral gas
- Knapp (1975) from nH(b)
- Frisch & York (1983) & Paresce (1984):absorption line studies

## The Local Cavity

- Local ISM remarkably deficient in neutral gas
- Knapp (1975) from nH(b)
- Frisch & York (1983) & Paresce (1984):absorption line studies
- Sfeir et al (1999)

## An Old Controversy

- Assuming a uniform distribution of nH,
- three ways of producing the anticorrelation:
- Absorption - all emission extragalactic
- Can’t work with reasonable cross-sections
-  Displacement (cavity) - all emission local
- Fit well with local ISM knowledge
- Absorption and emission interleaved

## An Old Controversy

- Assuming a uniform distribution of nH,
- three ways of producing the anticorrelation:
- Absorption - all emission extragalactic
- Can’t work with reasonable cross-sections
-  Displacement (cavity) - all emission local
- Fit well with local ISM knowledge
- Absorption and emission interleaved
- Demonstrated by ROSAT

## The fundamental surveys: ROSAT

- All-sky satellite borne survey
- Executed 1990-1991
- 12’ effective resolution

## The fundamental surveys: ROSAT

- Lots of shadows by small-scale clouds

## The fundamental surveys: ROSAT

- Even the most opaque clouds show foreground emission

## Isolating the Local Component

- L/D Decomposition
- Assume background and foreground flat
- Plot IX vs. nH
- Fit Iobs=IL+IDe(-σn)

- IL

- ID

## Isolating the Local Component

- L/D Decomposition Caveats
- Flatness requires small area
- nH dynamic range requires large area
- Unreliable if multiple interleaved components
- Must know background spectrum to get σeff

## Isolating the Local Component

- L/D Decomposition
- C band – works well
- M band (3/4 keV) – clouds not sufficiently opaque
- Observe at E such that Local Cavity walls are opaque
- Be band and (to some extent) B band

## Isolating the Local Component

- What do we find?
- B/Be~constant →nH<few ×1018 cm-2
- CL:B:Be or R2L:R1L →model→kT~106K→ε
- 		since Rmax set by the Local Cavity size
- 	CL=∫0RεnenidV → ne~0.002
- 			→ P/k~1.5×104 cm-3K & cs~100 km/s
- →crossing time ~few×106 yrs
- 	→emitting region likely in equilibrium
- 	→ε is the same everywhere and
- 	Remit(l,b)=fIL(l,b) → shape of emitting region

- Shape reflects anticorrelation of B or CL and nH!

## Scaling the LHB

- MBM12 shadows the LHB emission
- 	R=60-90 pc IL=347×10-6 counts/s/arcmin2 (R12)
- Other MBM clouds w/o shadows place consistent limits
- Scaling does not significantly violate Sfeir boundary

- Sfeir et al (1999)

## Isolating the Local Component

- What else do we learn?
- There is a gradient in the emission (Snowden et al 1990)
- B/C is higher towards l=168°, lower towards G.C
- Temperature is lower towards l=168° (log T=5.9 vs. 6.0)
- Similar result from shadow analysis
- logT=6.02 vs. 6.13

## Spectroscopy

## Spectroscopy:DXS (Sanders 2001)

- 148-295 eV with a resolution of 4 eV

## Spectroscopy:DXS (Sanders 2001)

- 148-295 eV with a resolution of 4 eV
- 0.26 sr FOV

## Spectroscopy:DXS

- Lines! → thermal or quasi-thermal
- R&S model (CIE) does not work
- R&S model with Mg, Si, Fe adjusted down by 3X
- Non-CIE models worked no better

## Spectroscopy:DXS

- Potential Problems:
- Bad or missing atomic data
- Non-CIE parameter space is large
- Complex line of sight
- Spans a range of different R2/R1
- Background model
- Absorption due to cavity wall

## Spectroscopy:CHIPS (Hurwitz 2005)

- 82.65-61.99 eV at a resolution of 0.6eV

## Spectroscopy:CHIPS (Hurwitz 2005)

- 82.65-61.99 eV at a resolution of 0.6eV

## Spectroscopy:CHIPS (Hurwitz 2005)

- Best fit 105.8K, EM=0.00014 cm-6pc (solar abund)
- 106.0K, EM=0.00042 cm-6pc at 1/3 solar
- EM~0.0039 cm-6pc (ROSAT) values requires 1/16 solar
- Consistent with WFC(?) EUVE (Jelinsky et al. 1995)
- Marginally consistent with Wisc. data (Bellm & Vaillancourt 2005)

- Fe IX is 6 LU
- (photon/cm2/s/sr)

## Spectroscopy:XQC (McCammon 2002)

- 60-1000 eV at a resolution of 9eV
- FOV~1 sr

## Spectroscopy:XQC (McCammon 2002)

- 60-1000 eV at a resolution of 9eV
- FOV~1 sr

## Spectroscopy:XQC (McCammon 2002)

- Spectrum includes both LHB and Galactic Halo (but not at Fe IX)
- FeIX, FeX, FeXI = 100±50 LU, but bright CHIPS region
- Marginally consistent

## Chandra/XMM/Suzaku

- Resolution of 40 eV at 500 eV
- Need higher nH to block non-LHB emission (5×1021)
- 		Or model transmission of background spectrum
- Pessimist: measuring only high-E tail of LHB
- Optimist: measuring OVIII, OVII, & OVI (FUSE)

## Chandra/XMM/Suzaku

| Object | nH | Instr. |  |  | Log(T) | OVII (LU) | OVIII (LU) | Flare/ SWCX |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| MBM12 | 3-8e21 | Chan | Smith et al |  |  | 1.75±0.55 | 2.34±0.36 | f/major |
| MBM12 | 3-8e21 | XMM | Freyberg&Breits. |  | 6.17 |  |  | f/major |
| MBM12 | 3-8e21 | Suz | Smith et al | on/off | <6.22 | 3.5 | 0.25±0.1 | -/minor |
| Mag | 2.9e21 | XMM | Snowden |  |  | 2.7±0.4 | 0.39±0.17 | -/minor |
| MBM20 | 2e21 | XMM | Galleazzi et al | on/off | 6.04-6.08 | 3.89±0.56 | 0.68±0.24 | f/minor |
| MBM20 | 2e21 | Suz | Galleazzi et al |  |  |  |  |  |
| Filament | 9.6e20 | XMM | Henley et al | on/off | 6.06- | 3.4±0.5 | <1.0 | f/minor |
| Filament | 9.6e20 | Suz | Henley&Shelton | on/off | 5.94-6.00 | 1.1±1.1 | 1.0±1.1 | -/some |
| L=111° | 1e20 | XMM | Kuntz&Snowden |  | 6.06-6.12 | 1.75±0.7 |  | -/minor |

- All use ROSAT to normalize
- The lower the nH, the easier to swap flux from foreground to background
- Strongly model dependent
- Sensitive to assumed abundances

## Chandra/XMM/Suzaku

- Suzaku observation of MBM12
- Measure of OVII and limit of OVIII → limit on T (kT=0.146 keV)
- Measure of OVII and T (106K) → emissivity → overpredicts R12 by 3X
- Depleted abundances
- Out of equilibrium (variation in OVII, gradient)
- OVII is just too high (Koutroumpa 2008; SWCX)

- on-cloud

- off-cloud

- Smith et al (2007)

## Solar Wind Charge eXchange

- Explains X-ray emission from comets (Cravens)
- Extended to all neutrals in heliosphere (Cox 1998)
- Detected by ROSAT
- Long Term Enhancements (LTEs) removed from RASS
- LTE rate consistent with dark side of moon → cis-lunar
- Correlated with solar wind (Cravens, Robertson, Snowden)
- 1⁄4 keV and 3⁄4 keV LTEs only partially correlated

## SWCX

- Local – highly time variable, strongly look-direction dependent
- Magnetosheath
- Exosphere
- Local ISM/local heliosphere (~few a.u.)
- Non-local – only slowly variable, but look-direction dependent
- Remainder of heliosphere
- Heliopause

- ○

## SWCX

- Observed=LHB+helio(t)+exo(t)+mag(t)
- Observed=LHB+min(helio)+(helio(t)-min(helio))+exo(t)+mag(t)

- RASS

- LTEs

## SWCX

- Observed=LHB+helio(t)+exo(t)+mag(t)
- Observed=LHB+min(helio)+(helio(t)-min(helio))+exo(t)+mag(t)

- RASS

- LTEs

- RASS and Wisconsin surveys should have very different min(helio) contributions

- McComas et al 2003

## SWCX

- No offset between RASS R12 and Wisconsin C
- Total heliospheric SWCX small, or
- Total heliospheric SWCX very stable

- Snowden et al.

## SWCX & Spectroscopy

- Two XMM spectra of the same region: HDFN

- SWCX particularly strong in the prime diagnostic lines OVII and OVIII
- Collier et al. (2007) and Koutroumpa (2008) agree on non-magnetosheath

## SWCX & Spectroscopy

- Extend the same method to the XMM archive (Kuntz&Snowden)
- Multiple observations of the same blank field
- Correlate changes in OVII and OVIII with SW and geometry

- For most observations Δline ≤σ

## SWCX & Spectroscopy

- Looking near nose with quiescent SW → Δline insig.
- Looking through flanks w/ high SW →Δline large
- Large Δline w/ low SW → SW fronts missed by ACE

## SWCX & LHB

- Flux – reduced I = fI → n = n√f and P = P√f
- Size – no change
- Shape -

## SWCX & LHB

- Flux – reduced I = fI → n = n√f and P = P√f
- Size – no change
- Shape – may match the Local Cavity, may not
- Gradient – dipole orientation is same as ISM wind direction
- Temperature – unknown

## SWCX & LHB

- DXS – effected only by heliospheric SWCX
- CHIPS – parent species most abundant in SW, but...
- Does this make the problem worse?
- XQC – the slow low density SW favors FeIX
- XMM – observation geometry is important!
- SXG!

## The Once and Future LHB

- LHB Studies should return to their roots: B&Be bands
- Maximize the local/minimize the distant emission
- Lower column density clouds to be used as shadowing targets
- But...
- Energy region for which atomic data more poorly known