| About ROSAT |
ROSAT Home Page | ROSAT Images |
|---|
The CsI coated MCP is sensitive to ultraviolet radiation as well as soft
X-rays, and must be protected from the background generated by the
geocoronal UV and hot stellar UV continuum. In addition, since the MCP's
are operated at high negative electrical potential with respect to the
spacecraft ground, positive ions in the satellite environment must be
blocked from reaching the detector. These functions are served
by two aluminized plastic windows (the UV/Ion Filter and an
Electrostatic Shield). These materials were selected to insure a safe
level of attenuation of both the UV and ion background sources, while
still providing high transmission of X-rays in the ROSAT band (0.1 to
2.4 keV). The geocoronal background rate is estimated to be less
than 0.1 counts s 
over the total field of view (or less than
counts arcmin 
s ).The star 
Car (AO III,
V=1.7 mag, d=26 pc) yields a count rate of 
counts s .
This detection of Car by the HRI during the on-orbit calibration
phase, is assumed to be due to far UV flux from the star. additional
calibrations are being planned to confirm this result.
The filter transmission in the ROSAT X-ray band and in the UV band are
plotted in Figures 4.11 
and 4.12. The
features around 0.27 keV and 1.7 keV are due to carbon and aluminum
absorption edges.
