A Nearby Bright Optical Source

With certain pointing angles, zeroth-order optical light may be reflected off the telescope optics and cast onto the RGS CCD detectors. If this falls on an extraction region, the current energy calibration will require a wavelength-dependent zero-offset. Stray light can be detected on RGS DIAGNOSTIC images taken before, during and after the observation. This test, and the offset correction, are not performed on the data before delivery.

To check for stray light and apply the appropriate offsets with the GUI:

1)

Call rgsproc. Next to ``calculate offsets from diagnostic mode'' check ``yes''. Immediately below, next to ``Store histograms in a dataset'', check ``no''.

2)

Click ``Run''.