XMM Users' Handbook

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OM filter bandpasses

The OM is equipped with a set of filters with bandpasses covering part of the UV and optical range. The filter throughput curves are displayed in Fig. 69. The plotted quantity is the OM effective area with these filters, including the size of the telescope aperture and mirror geometric areas, the reflectivity of the three mirrors and the detector response. In the calculation of the detector response the following effects were taken into account: the open area of the MCP, the RQE of the photocathode and the entrance window transmission.

**Figure 69:** *Throughput curves for the OM filters, folded with the detector sensitivity (the cutoff in the throughput curve of the UVW2 filter is an artifact due to a lack of measured data below 180 nm).*
$\begin{figure} \begin{center} \leavevmode \epsfig{width=0.6\hsize, angle=270, file=figs/omthrough.eps} \end{center} \end{figure}$

As part of the OM default configuration (§ 3.5.3.1), the use of the B, UVW2, U and UVW1 filters is recommended. A specific scientific justification is necessary for the use of a different set of filters. To minimise wear and tear on the OM's moveable parts, users wanting to define a different filter combination must adhere to the order defined above and listed in Tab. 14.

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European Space Agency - XMM Science Operations Centre