Gain Notes for Revolution 2691

During the TOO observation, it is not always possible to see the
	Xe line that is used to verify the energy determination.
	However, where a Xe line can be found, it falls within the
	acceptable bounds of usual energy determination. 
Briefly, the instrument gain dips well below 20 channels/keV
	and so this period has to be declared a BTI for gain determination. 
	BTI = 8671.4 to 8671.8 IJD
This is one of the later revolutions in the mission where the calibration
sources have become so weak that for the best energy determination an
IC Gain History table is needed. These gain history tables are found
automatically by OSA, or can be downloaded from the DTU FTP site.
 
All offline gain/energy corrections (including the IC tables) are based on the
two Fe calibration sources in JEM-X1, for both units, then corrected iteratively
using the instrument background lines (Xe, backed up by Cu and Mo).

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 rating: Good  (Xe line positions within 4\%\ of ideal, 
	except for settling zone and TOO observation period where Xe line
	cannot be measured.)
JEM-X2: Good  (Xe line positions within 4\%\ of ideal, 
	except for settling zone and TOO observation period where Xe line
	cannot be measured.

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

CAO 07/10/2023