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 #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