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epicbscalgen (ccftools-1.36) [xmmsas_20211130_0941-20.0.0]


The XMM Current Calibration File contains the constituent CCF::Boresight [1] which holds for each instrument a tuple of three angles $(\phi, \theta, \psi)$ describing the misalignment of the respective instrument boresight with respect to the satellite coordinate frame (SACCOORD – see documentation of package cal. The angles are to be interpreted as 3-2-1 Euler rotation angles[2] through which the SACCOORD frame is transformed into the instrument boresight (IBS) frame as depicted in Fig. 1 for the case of EMOS2. Formally, the IBS is defined as follows:


Figure 1: Coordinate frames used in epicbscalgen

The computation of the angles is a purely geometrical problem and, thus, should have a straightforward analytical solution. However, due to the large number of involved independent variables (Ra/Dec of pointing, position angle, position of cameras in satellite frame, uncertainties in focal lengths, position and extent of sources being looked at, etc.) and the fact that math with Euler angles is non-trivial epicbscalgen employs an empirical scheme which is outlined below. The scheme has the following advantages:

XMM-Newton SOC -- 2021-11-30