Gain Notes for Revolution 1574

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: This revolution is heavily affected by a period of very strong grey-filtering
towards the end of the revolution during which three things happen: 
a) gain of the
microstrip plates is suppressed by a hard-to-determine amount thanks to additional
charging of the plates by the influx of x-ray photons
b) the number of calibration events from the calibration sources drops precipitously
making it hard or impossible to determine the position of calibration lines in the
calibration spectrum - a problem made worse in this late part of the mission
because of the weakness of the calibration sources after 13 years in space
c) the fraction of science events transmitted in the telemetry also drops
precipitously effectively removing other instrumental lines used to qualify the
goodness of gain correction. 
So, we know the gain has dropped, but we can only roughly estimate by how much and
cannot in anyway verify if the energy corrections we estimate are any good. For this
reason there is a BAD_RESPONSE BTI for this revolution between 
IJD= 5701.9 and IJD= 5702.2 . This means that no spectral significance should be
placed on any data within this time period, though position and imaging data
should be fine. Fluxes will be affected because of some loss of real events in the
low level discriminator because of the gain suppression. 
to add to this general uncertainty is the fact that one source of each kind is
heavily affected by gain suppression and the other is not, indicating that only
half of each microstrip plate is affected by the increase countrate due to
partial illumination of the plate - further complicating the correction of
science events from different parts of the plates since some will be gain suppressed
and some won't.
 

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 very good gain
correction (outside the BTI) with all science windows having a Xe level 
within 2-3% of the ideal, except for the usual settling points. 
As usual, it is recommended that users avoid the first few science 
windows for energy-sensitive applications (automatically removed by OSA 10.0), 
and data within the BTI should also be treated with caution during the BTI.


JEM-X2: 

The Xe line analysis performed using the IC table shows excellent gain
correction with all science windows outside the BTI 
(taken 2 at a time) having a Xe level within 1-2% of the ideal, except for
the usual early settling points. 
As usual however, it is recommended that users avoid the first few science 
windows for energy-sensitive applications (automatically removed by OSA 10.0)and
data taken during the BTI should not be used for spectral determination.

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 23/8/2015