Analyzing Models of the Diffuse Soft X-Ray Background

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Analyzing Models of the Diffuse Soft X-Ray
Background

• Eric Bellm
• REU 2003, University of Wisconsin
• Prof. Dan McCammon, advisor

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Overview

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

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Soft X-Rays

• Energies of 50 eV-2 keV (50-300 eV this study)
• Produced by thermal plasmas (Tmillions of K)
  Shell transitions -gt lines

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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

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Detectors

• Proportional Counters
• Bands defined with filters

Absorption will change the relative count rates
in different bands
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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 gt
  local source material

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ISM Schematic 1
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ISM Schematic 2

• But--shadows toward distant clouds in 1/4 keV

Be band?
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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?

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Results

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

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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?

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What I Learned This SummerBy Eric Bellm

• Science X-Ray physics, ISM, detector physics
• Skills FORTRAN, IDL, XSPEC
• Wisdom impossible to quantify

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Acknowledgements

• Dan McCammon
• Wilt Sanders
• Bob Benjamin
• NSF/University of Wisconsin