1. Analyzing Models of the Diffuse Soft X-Ray Background
Eric Bellm
REU 2003, University of Wisconsin
Prof. Dan McCammon, advisor

2. Overview Science background Evaluating the Snowden model
Soft X-Rays
Soft X-Ray Detectors
The Interstellar Medium
Evaluating the Snowden model
Conclusions, Future Directions, &c.

3. Soft X-Rays Energies of 50 eV-2 keV (50-300 eV this study)
Produced by thermal plasmas (T~millions of K): Shell transitions -> lines

4. Absorption of Soft X-Rays
Soft X-rays may be absorbed by neutral Hydrogen
Strong energy dependence (E-3): lower energies more likely to be absorbed

5. Detectors Proportional Counters Bands defined with filters
Absorption will change the relative count rates in different bands

6. The ISM (Roughly) (Note: deviation from orthodoxy)
Matrix of warm H I ( K)
Bubbles of hot gas ( K) emit X-Rays
Distribution of hot gas?
Wisconsin observations: Be band  1/4 keV => local source material

7. ISM Schematic #1

8. ISM Schematic #2 But--shadows toward distant clouds in 1/4 keV
Be band?

9. Snowden Model
Snowden et al used 1/4 keV ROSAT maps, assumed picture #2
Fit local and halo components:
Iobs = Iloc + e-(E) NH Ihalo
Does this model predict Be band counts?

10. Results
Better proportionality between Be band and modeled 1/4 keV local rate than Be band and 1/4 keV total

11. Conclusions Simple model seems to obey both constraints
Some subtleties remain
Large amount of scatter when using model to predict count rates
Choice of model, abundances
Redo fit with better models, more constraints?

12. Acknowledgements Dan McCammon Wilt Sanders Bob Benjamin
NSF/University of Wisconsin