AAS 203rd Meeting, January 2004
Session 111 Interstellar Medium II
Poster, Thursday, January 8, 2004, 9:20am-4:00pm, Grand Hall

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[111.04] Evidence for Halo Contributions to the 1/4 keV Diffuse Soft X-Ray Background

E. C. Bellm (Harvard College)

The 1/4-keV diffuse soft X-ray background (SXRB) apparently originates in a thermal plasma at around 106 K, but the location of this emission has proven to be difficult to determine. The finite flux in the Galactic plane and similarity of the spectrum at all latitudes led to a model where essentially all of the observed flux originated in a local hot bubble (LHB) surrounding the Sun. Snowden et al. (1998) have proposed a three-component model of the SXRB from the ROSAT All-Sky Survey R12 (1/4 keV) map which consists of an unabsorbed local component, an absorbed halo component, and an absorbed power law to represent the known contribution from AGN, which is quite small.

We have investigated whether this model is consistent with the lower-energy data available from sounding rocket flights in the B and Be bands. We find that the Snowden model provides better correspondence with the low-energy Wisconsin bands than the pure LHB model. The differences are subtle because the bulk of the intensity variation in the Snowden model is still due to differences in the extent of the local bubble.

We have also investigated whether the observed band ratios are fit by the emission models used. We find that with current collisional ionization equilibrium models, depleted abundances are necessary to be consistent with the observed band ratios. We also show that the model predictions depend strongly on the model version, which does little to lend confidence to their predictions.

This work was supported by a NSF-REU site grant (AST-0139563) to the University of Wisconsin-Madison.

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© 2003. The American Astronomical Soceity.