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

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.

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 #1

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?

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

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