XMM-Newton Phase II RPS Users Manual

5.2.4.6 Filling in OM exposure details in ''Science User Defined Mode''

For the OM ''Science User Defined'' mode a number of details has to be specified on a special page by pressing the ''Add Details'' button at the bottom of the exposure page. The appropriate form sheet is displayed in Fig. 18.

Figure 18: Screen shot of an OM exposure details page. Entries for one Image window and one Fast window have already been committed to memory. Below this table, it is possible to add details for further windows, either in Image or Fast mode. Committal of this information will add a third entry in the upper part of the form. Up to 5 windows can be defined.

At the top of the form sheet you see a list of the defined readout windows with their characteristics. At the bottom are the fields used to define the new window to be added, to be exposed simultaneously.

Add new Window / Editing Win No. x

When adding a new readout window (Image or Fast) there are two columns of input fields, only one of which must be filled in. The left column asks for the sky coordinates and the size of the window in angular units. The right column allows inputs in detector coordinates (pixels). The default coordinates for the centre of a new window are the boresight coordinates defined above at the observation level.

Once the window mode is selected, if the box labelled 'Pixel Coords' is ticked, default pixel values are entered that cover the boresight coordinates. The values can be modified but note that the orientation of the CCD chip depends on the position angle of the spacecraft and thus exact time of observation. Readout windows that do not cover the boresight have to be entered in sky units.

Window sizes have to be entered in the same units as the window position. The total number of pixels of all user defined windows must not exceed a certain value due to memory limitations. The default sizes take these limitations into account. The scale for unbinned pixels (BIN=0) is $0.476''$/pix. For example, the maximum size (DX,DY) for a single square window is:

for BIN X=0 BIN Y=0: 5.20 x 5.20 arcmin or 656 x 656 pixels
for BIN X=1 BIN Y=1: 7.75 x 7.62 arcmin or 976 x 960 pixels, i.e. 488 x 480 pixels after binning in the final image.

Upon committal of a set of entries defining a science window, the top part of the form sheet in Fig. 18 is filled in automatically. Up to 5 science windows may be defined in total per exposure, of which up to 2 may be operated in the FAST mode. A single FAST window is not allowed, always define at least one IMAGE window.

The boundary conditions that apply to the definition of the science windows are described in the XMM-Newton Users Handbook. An OM tool that can help when defining the windows was developed at MSSL:

http://www.mssl.ucl.ac.uk/www_astro/xmm/om/om.html

Time Slice Duration (ms)

For each FAST mode window the time slice duration (TSD) must be specified, i.e., the duration of individual readouts within an exposure. The allowed range is 500-20000 ms. The recommended TSD is 500 ms.

DPU binning

In the lower part of the OM exposure settings page the pixel binning in the Digital Processing Unit (DPU) must be specified for each image mode window. The choice is between values from 0 to 1. They stand for the power of 2. Value 0 represents $2^0 = 1$ pixels and $2^1 = 2$. Since only equal binning in both the X and Y directions makes sense, the choice is between binnings of $1\times1$ and $2\times2$ original 0.5'' (DPU) pixels. Default binning is $2\times2$ pixels (i.e. bin=1).

More details on the required input for non-standard OM science windows are provided in the appropriate XMM-Newton Users Handbook chapter. The correct specification of OM science windows, which are constrained by various observation-dependent parameters, is the user's responsibility. Users proposing observations with non-standard OM science windows should ask for SOC enhancement support. However, note that the available SOC support to help users will be limited.