# Presentation: 569691

## Separating Local and Cosmic Soft X-Ray Emission in the Chandra Deep Field-South:A Preliminary Report

- Brad Wargelin
*Chandra* X-Ray Center
- Smithsonian Astrophysical Observatory

## The Local Origin X-rays (LOX) Collaboration

- Greg Brown (LLNL)
- Tom Cravens (U. Kansas)
- Alex Dalgarno (CfA)
- Dick Edgar (CfA)
- Mike Juda (CfA)
- Vasili Kharchenko (CfA)
- Paul Plucinsky (CfA)
- John Raymond (CfA)
- Ina Robertson (U. Kansas)
- Jon Slavin (CfA)
- Randall Smith (CfA)
- Brad Wargelin (CfA)

## 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 solar-wind charge exchange (CX)*

- How much emission is from the Local Bubble vs CX?
- What can the Chandra Deep Field-South data tell us about this in the 3/4-keV band?

## RASS conducted at solar maximum.

## M. Juda

- R1                           R2                          R4

- LTE contam?

## The CDFS

- The CDFS observations:
- 3 in Oct, Nov 1999 (-110 C)
- 9 in May, Jun, Dec 2000
- 12 in Sep-Nov 2007 (VF mode)
- RA,Dec 	3:32:28, -27:48:30
- Gal l,b 		223.6, -54.4
- Ecl lat,lon 	41.1, -45.2
- 836 ks in 2000 (most from within He focusing cone, near solar max)
- 981 ks in 2007 (outside He cone, at solar min)

## 2007

**2007**

**2000**

- Because of solar wind charge exchange, the observed SXRB depends on:
- Where you look
- Where you look *from*
- When you look

- J. Slavin

- LOS is 45 down, into page.

## CX Emission--looking down on ecliptic plane

- More neutral H upwind
- He focussing cone downwind

- (AU)

- (AU)

- Pepino et al., ApJ 2004

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

- 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?

## Solar Max vs Solar Min

- Ulysses data --E.J. Smith et al., Science 2003

- At 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.

## CX Emission at Solar Min--view from Ecliptic Plane

- Pepino et al., ApJ 2004

- AU

- AU

- Stratified wind--slow and highly ionized near ecliptic   higher CX emissivity.
- Little emission in fast wind.

## In 2000, there is slow wind all along the LOS and most obs’s are from within the bright He cone.

- In 2007, SW is stratified, LOS through fast wind, obs’s outside He cone.
- Expectations for 2000 vs 2007 data:
- Higher baseline SXRB level
- More variability
- Closer correlation of locally measured SW ion flux and SXRB level.

- LOS

## Data Analysis

- Select field of view common to all 21 observations

## Slide 14

## 244 sources within 7.70 arcmin of aimpoint

## Remove 2 more diffuse sources, increase source region size to reduce source contamination to less than 2%.
Trim radius to 7.5’.

- Trim radius to 7.5’.

## Remove periods with background flaring (less than 10 ks).

Quick comparison of summed 2000 data vs summed 2007 data ....

- Quick comparison of summed 2000 data vs summed 2007 data ....

## Detector BG 70% higher in 2007 than in 2000

## 2007 observations in VF mode   filtering

- 2007 observations in VF mode   filtering

## Lower X-ray signal partly due to lower QE --

- down by 40% at ~600 eV from 2000 to 2007.

## Compare O emission (520-710 eV) vs...

- Wargelin et al., ApJ 2004

- Model CX spectrum with 6 eV resolution

## Compare O emission (520-710 eV) vs...

- Wargelin et al., ApJ 2004

- Model CX spectrum with 6 eV resolution

## ... average ACE/SWICS O7+ flux for each ObsID

- ... average ACE/SWICS O7+ flux for each ObsID

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

## Stronger CX and tighter X-ray/O7+ correlation in 2000--most emission from within He cone.
There may be no correlation with local SW flux depending on viewing geometry.

Did spectral fits for 3 lowest-rate obsids in 2000, lowest 8 in 2007.  Convolved with ROSAT RMF.
R45 rates (in 10-6 cts/sec/arcmin2):
	54 in 2000
	32 in 2007
	25 if no SWCX?

*There may be no correlation with local SW flux depending on viewing geometry.*
- Did spectral fits for 3 lowest-rate obsids in 2000, lowest 8 in 2007.  Convolved with ROSAT RMF.
- R45 rates (in 10-6 cts/sec/arcmin2):
- 	54 in 2000
- 	32 in 2007
- 	25 if no SWCX?

- 2000

- 2007

## Talk amongst yourselves....

- These are preliminary results.  We will redo the analysis more carefully and completely, with painstaking spectral fits, comparisons with model predictions of heliospheric and geocoronal CX, etc, etc. etc.
- Other 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

## More detailed correlations:

- Short-term X-ray variability vs ACE O7+ flux  fractional contribution of geocoronal CX emission
- Account for Chandra orbital geometry

**Notes:**
Comets 1996, planets with Chandra
Moon/geocorona with ROSAT and then Chandra with E res to see O lines
Heliospheric with XMM and Chandra--current hot topic
But I was asked to NOT talk about those....

## More detailed correlations:

- Short-term X-ray variability vs ACE O7+ flux  fractional contribution of geocoronal CX emission
- Account for Chandra orbital geometry

**Notes:**
Comets 1996, planets with Chandra
Moon/geocorona with ROSAT and then Chandra with E res to see O lines
Heliospheric with XMM and Chandra--current hot topic
But I was asked to NOT talk about those....

## Geocoronal emission generally weaker than heliospheric but responds to SW ion flux much faster (because more local) and can sometimes be stronger.

## Account for effect of orbital viewing geometry on observed geocoronal emission.

- May 2000

- Fall 2007

- Dec 2000

- LOS relative to Sun

## Robertson et al., JGR (2006)

## Compare simultaneous data from Chandra, XMM, Suzaku during SW “impulses.”

## Modeling and observationally constraining SWCX is hard.

- “The SWCX problem” will be solved when we have high-resolution spectra from microcalorimeters (E=2-10 eV).
-  CX spectra differ from collisional and we (will) know what they look like from lab work, strong LTEs, and He cone observations (coupled with SW velocity measurements).  Use CX-enhanced lines (high-*n* Lyman, He-like *f*, etc.) to scale and remove CX emission templates from SXRB spectra.
-  400 km/sec    E~1 eV at 600 eV
-  Can also operate in much of the 1/4-keV band

## For more details on CX spectra and a primer on astrophysical X-ray CX emission, see Wargelin, Beiersdorfer, & Brown, “EBIT charge-exchange measurements and astrophysical applications,” Canadian J. Physics, 86, 151 (2008).

## Slide 34

## XMM HDF-N.  Snowden et al, ApJ (2004)

*XMM* HDF-N.  Snowden et al, ApJ (2004)

## X-Ray Quantum Calorimeter (XQC)

- 100s of SXRB from rocket flight.  McCammon et al (2004?)

## ROSAT All-Sky Survey Map (R12) and LTEs

- Long Term Enhancements from geo/helio CX fluctuations.
- Strongest in R12 band.
- Current CX models known to be incomplete (no L-shell Mg, Si, S, Fe).
- Some hints in current data.

- S. Snowden

## Diffuse X-Ray Spectrometer (DXS)

- SXRB 150-300 eV.  Sanders et al. (2004?)

## Heliospheric Charge Exchange

- Solar wind + H/He from ISM  100-AU halo.
- Intensity varies with look direction and solar activity.
- Heliospheric CX ~ 10x geocoronal CX

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

*Geo+Helio CX contributes 5-50**+**% of SXRB, with major implications for models of LISM/Local Bubble.*

## 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 *n**neutral*
- Wind velocity and composition
- Astrosphere geometry

- CX emission weak, coronal emission ~104x brighter.
- Need very large collecting area, good spatial and spectra res---not quite doable yet...

## Slide 41