The HRI, with its CsI-coated MCPs, was found during ground testing to possess a crude spectral sensitivity which has been verified with in-flight data. Funds to investigate this capability were recently provided by the NASA Astrophysics Data Program(ADP). In this section, we summarize the spectral attributes of the HRI detector and then describe the preliminary results of the ADP investigation to date. This project is still on-going, hence efforts to derive quantitative spectral results from HRI data must entail careful analysis on the part of individual investigators.
Figure 18 shows the PHA distribution from ground-based
measurements at 7 energies, and Table 6 lists the
mean PHA channel at each energy. Note that there is a systematic
increase in the mean pulse height channel with increasing photon
energy except for the Si line (the Si measurement may have been
affected by the presence of Si in the glass in the microchannel
plates). Table 6 shows that the mean PHA varies by
approximately 2 channels over the energy range of the ROSAT
mirror.
| X-ray target | mean PHA |
| B (0.18 keV) | 3.30 |
| C (0.28 keV) | 3.96 |
| O (0.53 keV) | 3.99 |
| Fe (0.71 keV) | 4.15 |
| Cu (0.93 keV) | 4.58 |
| Al (1.49 keV) | 5.44 |
| Si (1.74 keV) | 4.82 |