Changes to the ME CCF
The ME CCF has recently been updated to include the gain change parameters (Express No. 6 p.25) and background difference spectra supplied by Alan Smith. Users can identify the new CCF by a layout number of 4 for the CB (Channel Boundary) data type and by the presence of a new data type DS (Difference Spectra).
The 1st record of the CB data type id unchanged and the 2nd has the following layout:
The layout of data type DS is as follows:
Each of the spectra represent the difference in background counting rate obtained when a detector is fully offset in the +ve direction compared with that obtained when it is co-aligned. See Express No.5 p.48 for a detailed description of background subtraction techniques and difference spectra. These difference spectra should be subtracted from a background spectrum obtained in a fully positive offset configuration and added to a background spectrum obtained in a fully negative configuration prior to subtraction of the background spectrum from an aligned spectrum to obtain the source spectrum.
Note also that an error was introduced into some recently produced CCF's. Two of the configuration (b) Argon detector C resolution coefficients had become transposed. to check if this is the case on a particular CCF compare the configuration values (a) and (b). If they differ, then the configuration (b) values are wrong! Current CCF's (identified by a time of SHF=152634849) are correct and also include a better estimate of the detector D Argon gain drift parameters determined in the recent Crab Nebula calibration.