Calibration Access and Data Handbook

Procedure

The described procedure returns the one-dimensional response distribution in PI channels, based on an input energy. The redistribution function of the MOS cameras comprises a main peak (roughly centred on the input photon energy); a lower-energy secondary peak, whose relative magnitude is inversely correlated with the photon energy, and a noise term which extends down to the detection threshold energy. Details of the current calculation are given in the CCF release note, CAL-SRN-272.

CanonicalRedist retrieves a set of parameters from the appropriate MOS redistribution CCF and passes these to the CALMOSALGO initialisation routine CALMOSALGO_initRmfRow. The routine CALMOSALGO_rmfRow may then be used to calculate the response, in each PI channel bin, for a given input energy and event pattern selection.

The redistribution parameters have been calibrated as a function of:

Observation date

- A gradual decrease in the instrumental resolution with time has been observed, with a discrete jump at the epoch of CCD cooling (Rev. 532). Responses have been divided into steps, with a number of separate, time-dependent, CCF elements, relating to certain ranges of revolutions.

Spatial region

- On the central CCD (1), a patch has developed, centred on the boresight, where the resolution has become degraded. Three spatial regions have been defined, as an on-patch, wings-of-patch and off-patch selection.

Observing mode

Event grade

- The instrumental resolution is most sharp when the electrons generated by an incoming photon are collected in a single pixel. It degrades progressively as events are spread over multiple pixels. A separate calibration is available for single-pixel events (pattern=0) and multi-pattern events (patterns 0-12).