Calibration Access and Data Handbook

Maintenance procedures

EFFAREACORR correction factors are assumed to result from two effects

• wavelength-dependent effective area correction;
• absorption by contamination on the CCD surfaces.

that are analysed with a combination of observations of power-law spectra, particularly of Mkn421, and sources assumed to be constant, namely RXJ1856.6-3754 and the Vela PWN, in which the observed changes are due to changes in absorption by the contamination layer. The power-law reference source, currently Mkn421, and the contamination reference source, RXJ1856.6-3754, are both observed twice per year, the Vela PWN once per year as a contamination control.

EFFAREACORR RGS-pn rectification factors result from more complex mechanisms and therefore need careful consideration before use. The factors are derived from spectral analysis of a number of sources in the XCal archive.