QC PLOTS
	CURRENT	HISTORY
conversion factor
linearity
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To measure the detector parameters a dedicated DETMON calibrations are taken. They consist of sequences of imaging screen flat field pairs in the I_BESS filter taken with the standard readout modes (100Kps/high_gain/2x2 and 200Kps/low_gain/2x2). An appropriate set of bias frames is also included in the template.

QC1 parameters

• conversion factor (gain) (QC1 database table fors2_detmon, column gain)
  For every pair of flat fields with identical exposure times the difference of the average of the bias-corrected frames is compared to the difference in rms between the bias and the flat field difference. This comparison is limited to the illuminated parts of the CCDs. The factor relating the two quantities is the gain in e-/ADU. For method=PTC (Photon Tranfer Curve) a linear relation is fit to these quantities for the various exposure times.
• linearity coefficients (QC1 database table fors2_detmon, columns lin_coefi, lin_coefi_err with i=0,1,2)
  For each exposure time the mean and the median of the bias-corrected flat fields (restricted to the illuminated area of the CCDs) is calculated. Then a second order polynomial is fit to the mean/median vs. the exposure time and the coefficients of that polynomial are stored in the columns mentioned above. In general the constant and the second order terme are 0 within their errors.
• effective non-linearity (QC1 database table fors2_detmon, column non_linear)
  The effective non-linearity is the difference between the polynomial flux and the one predicted by the linear fit at user-defined flux level (column flux_non_linear), normalized with the polynomial flux.

History

• 2011-01-17 checking the flat field data showed that the FlatBlue+3 lamp was unstable. This might explain some of the variations in non-linearity observed since 2009-07.
• 2010-10-01 changed --filter parameter (to exclude saturated data) from 62000 to 60000 ADU
• Since October 2009 the flats rarely reached 60000 ADU, so the ref_level, at which the non-linearity is determined, was reduced to 40000 ADU.
• between April and September 2009 the flats reached only rather low flux levels, so the non-linearity is not well determined.