Gain Notes for Revolution 1709

This is one of the later revolutions in the mission where the calibration
sources have become so weak that for the best energy determination and
IC Gain History table is needed.

N.B. This revolution begins with a SCO X-1 observation during which there were
considerable non-linear gain changes due to the high photon flux affecting the
microstrip plates. However, using the IC gain tables generated off line (see below)
it is possible to achieve gain determinations that are almost as good for this
observation as for the rest of the revolution (often this is not the case with very
strong sources). Very strong sources trigger the grey-filter mechanism and cause
both primary calibration spectra to be weak or non-existent as well as weakening
the Xe lines in the instrument background used to verify the gain determination.
In this case however, though both sets of spectra are very weak, it has still been
possible to do a satisfactory job with the gain calibration and energy determinations.
 

To get optimal results with this revolution it is necessary to use the IC gain history.
See notes in revolutions prior to revolution 1433 to find out how to do this
if you don't already know.

All offline gain/energy corrections (including the IC tables) are based on the
two Fe calibration sources in JEM-X1, for both units.

Latest OSA software (version 10 and higher) automatically cuts out the first
Science windows of data from each revolution to ensure that people do not use data
from the instrument-settling period. This process can be overruled, but only by
experienced users.
	
JEM-X1: 

The Xe line analysis performed using the IC table shows excellent gain
correction with all science windows (taken 2 SCWs at a time) having a Xe level 
within 1-2% of the ideal, except for one slight outlier above 2% and the usual
settling points at the beginning of the revolution. 
As usual, it is recommended that users avoid the first few science 
windows for energy-sensitive applications (automatically removed by OSA 10.0).

JEM-X2: 

Results for JEM-X2 are broadly the same as for JEM-X one: all but a handful of
points within 1% of ideal and all but one outlier and the settling points,
within 2% of ideal. However the settling period is somewhat longer here and
early points are only within 3% of ideal. There are also a few complete 
misfits during the SCO X-1 observation for which it is impossible to verify
the accuracy of the gain determination - it is generally assumed that these
are with the same range as for Science Windows either side of these points.

The JEM-X2 corrections are based on the JEM-X1 Fe calibration sources, since
all the Cd sources are now to weak to use.

CAO 25/08/2016