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Hardness Ratios

While it is very difficult to obtain quantitative spectral information from the HRI (i.e., , temperatures or power-law indices), it is still possible to obtain qualitative information on a scale of a few arc minutes using hardness (or softness) ratios. Wilson et al. Wilson-etal:ApJ:1992 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 Fig. 5.19, the fraction of the total counts in PHA channels 6-11 decreased from 40% to 10%.

 

sequence date off-axis angle

(arcmin) [1:6] [2:6] [3:6]

110196 7/2/90 1.7 373 354 332

110198 7/2/90 3.9 457 - -

110197 7/2/90 7.8 1685 - -

141809 12/11/91 1.3 60 - -

Note: This table lists the results of fitting HRI observations of HZ 43 with a redistribution matrix derived from the ground based flat field tests. The extracted pulse height distributions are fit to an unabsorbed black body model with kT=0.02 keV, which gives an acceptable fit to the PSPC observations of HZ 43. The pulse height channels included in the fit are given in in the brackets.

[Spectral fitting results for 3C 273]  Spectral fitting results for 3C 273  

0% 2634 1547

2% 1198 55

5% 318 13

Note: This table lists the results of fitting an HRI observation of 3C 273 with a redistribution matrix derived from the ground based flat field tests. The second column gives the value of obtained by fitting PHA channels 1 through 6 to the best fit absorbed power-law model from the PSPC observation of 3C 273 (  cm and ). The third column lists the minimum obtained with  cm , and treated as a free parameter. The fourth column gives the best fit value of with the 90% confidence limits for one interesting free parameter.