We present results from a sample of XMM-Newton and Suzaku observations of interstellar clouds that cast shadows in the soft X-ray background ( SXRB ) —the first uniform analysis of such a sample from these missions .
By fitting to the on- and off-shadow spectra , we separated the foreground and Galactic halo components of the SXRB .
We tested different foreground models—two solar wind charge exchange ( SWCX ) models and a Local Bubble ( LB ) model .
We also examined different abundance tables .
We found that abundances , commonly used in previous SXRB studies , may result in overestimated foreground brightnesses and halo temperatures .
We also found that assuming a single solar wind ionization temperature for a SWCX model can lead to unreliable results .
We compared our measurements of the foreground emission with predictions of the SWCX emission from a smooth solar wind , finding only partial agreement .
Using available observation-specific SWCX predictions and various plausible assumptions , we placed an upper limit on the LB ’ s O vii intensity of \sim 0.8 photons \mbox { cm } ^ { -2 } \mbox { s } ^ { -1 } \mbox { sr } ^ { -1 } ( 90 % confidence ) .
Comparing the halo results obtained with SWCX and LB foreground models implies that , if the foreground is dominated by SWCX and is brighter than \sim 1.5 \times 10 ^ { -12 } ~ { } \mbox { erg } \mbox { cm } ^ { -2 } \mbox { s } ^ { -1 } \mbox { deg } ^ { -2 } ( 0.4–1.0 keV ) , then using an LB foreground model may bias the halo temperature upward and the 0.5–2.0 keV surface brightness downward by \sim ( \mbox { 0.2 - -0.3 } ) \times 10 ^ { 6 } ~ { } \mbox { K } and \sim ( \mbox { 1 - -2 } ) \times 10 ^ { -12 } ~ { } \mbox { erg } \mbox { cm } ^ { -2 } \mbox { s } ^ { -1 } % \mbox { deg } ^ { -2 } , respectively .
Similarly , comparing results from different observatories implies that there may be uncertainties in the halo temperature and surface brightness of up to \sim 0.2 \times 10 ^ { 6 } ~ { } \mbox { K } and \sim 25 % , respectively , in addition to the statistical uncertainties .
These uncertainties or biases may limit the ability of X-ray measurements to discriminate between Galactic halo models .