| About ROSAT |
ROSAT Home Page | ROSAT Images |
|---|
There are a few number of pointed observations with aspect errors less than 1'' but with the aspect solution drifting away from the nominal position by an appreciable amount. This has the consequence that an unfavourable mean aspect is calculated and not all aspect entries are projected into the aspect histogram and thus these times will not be counted in the exposure map. The situation has been remedied by implementing a new screening technique, accepting only aspects that are within limits from the nominal position (SASS5_9, 1992 August 20). Before 1992 April 22 (SASS5_7), the exposure maps have been produced using an instrument map derived from ground calibration data. In the meantime a set of energy-dependent instrument maps exists in the calibration file, derived from survey data with both PSPC-C and PSPC-B. We therefore urge users to reconstruct their own exposure maps from the attitude file.