XMM-Newton Users' Handbook

A..3.4 RSim - The RGS Simulator

RSim consists of two major parts, RGASim and RFCSim. The former simulates the physical properties of the RGAs, the latter those of the RFCs.

RGASim represents the continuation of the ray tracing that is performed by MSim. Multiple reflections are allowed, so that every ray that enters RGASim either leaves the module or is absorbed. Those rays leaving the RGAs in the direction of the RFCs are picked up by RFCSim and projected on the 9 CCD surfaces.

The features contained in RGASim are:

• 3D model of grating array

• trapezium shaped grating plates

• ribs on grating back

• the support braces placed in between some of the gratings (including holes).

• missing gratings, allow for partly filled RGA.

• blocking of rays by the walls separating the grating rows.

• scattering off the grating surface.

• grating positioning and alignment errors.

• grating non-flatness (bow, warp).

• variable line density groove spacing and additional random spacing errors.

• tabulated grating efficiency (from the Columbia EM code).

• reflections on grating back, ribs and SiC support structure (specular only).

• multiple reflections in between two grating plates and/or braces.

• misalignment of the RGA relative to telescope and detectors.

Rays can be produced in individual spectral orders in order to speed up the calculations.