XMM-Newton Science Analysis System


rgsfilter (rgsfilter-1.19) [xmmsas_20230412_1735-21.0.0]

Combined Exposure Map

The combined exposure map covers the area defined by rgsangles as the minimum and maximum legal values (TLMIN and TLMAX) for BETA_CHANNEL or MLAMBDA_CHANNEL and XDSP_CHANNEL. This means that in general the combined map will extend well beyond the exposed surface of the focal plane. Even so it is nevertheless possible for the camera to drift outside these bounds, and in that case the combined exposure map is truncated with respect to the aggregate of node-specific maps (which are aligned to the same grid but not confined by it). The warning emitted in this unlikely circumstance will most likely indicate a serious problem with the aspect correction or GTI filtering. The combined map is output to its own dataset, separate from the event list.

Since rgsangles sets TLMIN=1, event channel coordinates can be located on the combined map without any change of origin. As in the node-specific exposure maps, the transformation from map coordinates to angular coordinates is:

$$\begin{eqnarray*} \beta & = & \index{Attributes!CDELT1}{\tt CDELT1} \cdot ( b -... ...s!CRPIX2}{\tt CRPIX2} ) + \index{Attributes!CRVAL2}{\tt CRVAL2} \end{eqnarray*}$$

The combined map does not define a linear transformation from map coordinates to chip coordinates. Instead, the approximate mapping of the node boundaries is preserved as a linear transform on the dispersion coordinate:

$$\begin{eqnarray*} n & = & \index{Attributes!T\_BETA\_N}{\tt T\_BETA\_N} \cdot b... ...ox{$n$\ is even}\\ 1, & \mbox{$n$\ is odd} \end{array}\right. \end{eqnarray*}$$

The two parameters of the transform are attributes of the output dataset.