Gain Notes for Revolution 332
A very interesting revolution with a High Voltage pre-switch on three steps below
nominal (first two points in each data set) and a small unscheduled switch off
at the beginning of the revolution. Gain smoothing is fine and one might
assume that all data from this revolution should be useable.
However, there is some very interesting behaviour on source 3
(Fe) that is not reflected on the other sources. We don't know what causes
this yet though a full analysis will be available on this website soon.
The effect however, is undeniable. During the first half of the
revolution gain is suppressed on the one source by upto 20%, leading to
corrected energies that will be upto 5% too large, depending on the science
window. In the 12 SCWs of public data that are available we see a Xe line at
30.15 keV, about 2% too high. This is not a catastrophic degradation of the
gain correction, but it isn't optimal.
We still don't know what caused this problem, but take a look at `Full Analysis'
to see what possibilities we've ruled out.
QUICK FIX: Download the table by clicking on `Corrected Table' under
`Other data and results'. It is the gzipped gain history table in
FITS format, with the unusually low source 3 region corrected.
Unzip the file and put it in the directory from which you are doing your
data analyses. When you run the JEM-X Science Analysis Pipeline
(GUI) you will have to edit the hidden input parameter
`gainHist' so that it points to your private version of the
corrected table. Also in the `Other data and results' column you
can see a figure (`Fixed Source 3') of the original and fixed source
3 positions compared with source 1 (both Fe sources).
If you click on `Fixed Xe' `Fixed Mo' and `Fixed Cu' you'll
see the Xenon, Molybdenum and Copper lines derived with the Quick Fix
table. While the lineshapes are barely changed, the position of the
peaks has dropped to values that are well within the general
scatter of detector line positions throughout the mission.
In the longer term this problem will be corrected by the instrument team
supplying a corrected gain history table to ISDC which can be used automaticall
y
by everyone analysing revolution 358 data. However the protocols, data
structures and procedures for doing this are not finalised and will first be
put in place for OSA 6.0
CAO 1/12/2005