| About ROSAT |
ROSAT Home Page | ROSAT Images |
|---|
The process of determining boresight offsets (systematic
zero-point shifts found by comparing measured and known
positions of catalogued objects) for the HRI has led to
the conclusion that there are time-varying errors in
the attitude solutions used to correct event positions.
Although most known objects are detected at positions
within 10'' of their catalog positions, residual
discrepancies can be present even after application of
the boresight corrections.
This can be particularly evident in a comparison of
observations of the same object taken six months apart
(and hence at spacecraft roll angles differing by 180 
).
Compensation for such effects is possible whenever X-rays are detected from previously known objects whose positions have been accurately catalogued.