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Updates to the ME CCF

The recent (1985 February 5) EXOSAT observation of the Crab Nebula has extended the baseline for the measurement of the detector gain drifts reported earlier (EXPRESS No. 6, p.25) allowing a much more accurate measurement of the overall drifts to be made.

Analysis of this data by Alan Smith (ESTEC) in conjunction with the earlier measurements, shows that the average Argon gain drifts are as follows:
DetectorGain Drift/dayDate of Start
of Drift

C0.0001451984 day 240Thin
D0.00033761983 day 309Thin
G0.0000711983 day 168Thin
Three out of the four thin-window detectors show increases in gain whereas all of the thick-window detectors are stable.

The small changes in gains reported earlier for detectors A,B,E,F and H are probably not real and were presumably caused by short term fluctuations in detector gain.

A revised programme of pre-amplifier gain adjustments, based on the above figures, has been implemented to keep the overall gains aligned at 6.7 keV. The revised gain change coefficients given above will be included on ME FOT's in the near future. FOT's that include this update will have a time of last update (bytes 8-11 of record 1 of the CCF) of 161705105.

A.N. Parmar
A. Smith

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