Analyzing Models of the Diffuse Soft X-Ray Background Eric Bellm REU 2003, University of Wisconsin Prof. Dan McCammon, advisor
Overview • Science background • Soft X-Rays • Soft X-Ray Detectors • The Interstellar Medium • Evaluating the Snowden model • Conclusions, Future Directions, &c.
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
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
Detectors • Proportional Counters • Bands defined with filters Absorption will change the relative count rates in different bands
The ISM (Roughly) • (Note: deviation from orthodoxy) • Matrix of warm H I (102-104 K) • Bubbles of hot gas (106-107K) emit X-Rays • Distribution of hot gas? • Wisconsin observations: Be band 1/4 keV => local source material
ISM Schematic #2 • But--shadows toward distant clouds in 1/4 keV Be band?
Snowden Model • Snowden et al. 1998 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?
Better proportionality between Be band and modeled 1/4 keV local rate than Be band and 1/4 keV total Results
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?
Acknowledgements • Dan McCammon • Wilt Sanders • Bob Benjamin • NSF/University of Wisconsin