Gain Notes for Revolution 1653

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.

NB: The second half of this revolution is strongly affected by SCO X-1 in the FOV -
which causes substantial gain suppression of the microstrip detector plates of both
units, plus reducing the strength of the calibration spaectra due to strong grey-filtering.
This means that many SCWs to not have useable calibration spectra or even detectable
instrumental background lines. Consequently, the calibration policy is to bring what
Xe lines can be found to the corrected level, or something like it, and assume that the
Science Windows where the Xe line cannot be seen have similarly good energy determination,
but the goodness of the determination cannot be verified without the Xe line. Both the
Cu/Co line and the Mo line are missing for this revolution. Users should be very
warying of over-interpreting energy data and spectral from the SCO X-1 observations.
 

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 for the first half of the revolution, without SCO X-a in the FOV:
All science windows (taken 2 at a time) having a Xe level within 2% of the ideal, except 
for the usual settling points and one outlier. 
As usual, it is recommended that users avoid the first few science 
windows for energy-sensitive applications (automatically removed by OSA 10.0).

During the SCO X-1 observation in the second half of the revolution, the useable Xe
background lines fall within about 6-7% of ideal, and presumably this is the case for
the SCWs where a Xe line could not be found. Given the current energy resolution of 
the instruments, about 20% at 20 keV, these are still useable energy determinations,
but users should not try to over-interprete the energy data or spectra produced 
by JEM-X1 during the SCO X-1 observations. For some SCWs energy determination could
be off by as much as 10%. 

	

JEM-X2: 

The Xe line analysis performed using the IC table shows excellent gain
correction for most of the revolution, including the SCO X-1 observation:
All science windows (taken 2 at a time) having a Xe level within 2% of the ideal, 
except for the settling points, and the last part of the revolution. 
As usual however, it is recommended that users avoid the first few science 
windows for energy-sensitive applications (automatically removed by OSA 10.0).

In the last part of the revolution there are missing Xe lines for some SCWs and the
goodness of the energy determination during these SCWs cannot be determined - it could
be as bad as 10% variation from the ideal, but could just be within 2% of ideal like the
neighbouring SCWs. Users are warned to treat energy determinations with caution in the
last part of this revolution.

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 23/03/2016