PhD Thesis (PDF) - Department of Astronomy - University of Virginia

Fig. 5.13.— Top panel: Cumulative X-ray spectra of the resolved sources in the inner
effective elliptical isophote of NGC 4697 overlayed by the solid histograms of the
best-fit model spectra (Table 5.5, row 3). The different observations are shown in
different colors. Bottom panel: Contribution to χ 2 with the sign indicating the sign
of the residual.
5.9.2 Spectra Grouped by Position
In Table 5.5, rows 3, 4–6, 8 and 9, we compare bremsstrahlung models with
Galactic absorption for different collections of sources grouped by position. When we
compare the independent fits of sources within a < aeff (row 3) and in the annulus
aeff < a < 2aeff (row 5) to the fit when their temperatures are tied together (row 8),
we find a ∆χ 2 = 0.5 for 1 dof. There is no evidence for any spectral variation with
galactocentric distance within 2aeff.
On the other hand, there is evidence for a spectral change in sources within
2aeff < a < 3aeff. First, comparing the fit to the spectra when the temperatures
within 3aeff are grouped together (row 9) to the fits when the temperatures can vary
(rows 3, 5, and 6) indicates a slightly significant statistical difference (∆χ 2 = 7.0
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