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Next: 2.6 UV Response Up: 2.5 Spectral Response Previous: 2.5.4 Spectral Response Matrix

2.5.5 Hardness Ratios

While it is difficult to obtain quantitative spectral information from the HRI (i.e., temperatures or power-law indices), it is possible to obtain qualitative information on a scale of a few arcminutes using hardness (or softness) ratios. Wilson et al. (1992, Ap.J. Lett., 391, L75) showed that the extended emission in NGC1068 is harder than the nuclear component using a softness ratio defined by the channels [1:5]/[6:11]. Since the HRI gain varies temporally and spatially, the user may want to define the PHA boundaries on a case by case basis. For example, in the two observations of N132D shown in Figure 21, the fraction of the total counts in PHA channels 6-11 decreased from 40% to 10%.