Therefore there are no associated additional calibration files.
The following example shows the typical time dependency of the relative gain. It also shows a temperature HK parameter available to observers (PMT power supply temperature). There is a clear (anti-)correlation with the overall temperature trend (envelope of the temperature profile), i.e. the increase of environment temperature after the first switch on, and the diurnal modulation. There is (fortunately) no correlation with short-term temperature variations due to on-off orbital cycling.
Fig. 4.10.3-I : Example of gain history
The spectra of the calibration sources (referred to detector centre), corresponding to the first and last point of the above M1 gain history, are reported below.
Fig. 4.10.3-II : Example of calibration source spectra, showing typical gain variation
A more precise correlation exists with a different temperature HK parameter, which however is transmitted in the spacecraft (TCU) telemetry, and is not normally available, the DU box temperature (which is not influenced by short term power cycling). SVP observations allowed to verify the existence of a linear trend of gain with temperature.
Fig. 4.10.3-III : Example of gain-temperature correlation (unit M1), covering almost
all Performance Verification phase.
Left frame is for PMT temperature, right frame for DU box temperature. For the PMT case, good temperature values (when instrument is stably on) are in cyan, while gray indicates unstable temperature during switch on.
These are the typical coefficients of the correlation (derived from a "direct" linear fit of gain vs T, and also from a "reverse" fit of T vs gain, indicated in different colours in figure above).
|unit||gain vs PMT temperature||gain vs DU temperature|