Gain Notes for Revolution 2671

N.B. This is another revolution with a sudden apparent reset (probably due to
solar activity) wherein  the gain drops rapidly and strongly, and
recovers very slowly as though just switched on. During the period of
low gain, events are lost in the low-level discriminator, which will
cause bad disruption to low-energy spectra. For this reason there is
a BTI declared for poor instrument gain parameter determination during
this period. BTI = 8617.4 to 8618.2 IJD. For JEM-X1 the entire revolution
is very noisy so that it is not always possible to find the Xe line to
determine the goodness of the gain determination. However, where this is
possible the gain determination is a good as usual, outside the BTI.

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  (within  4% of ideal, except for settling zone
	numerous misfitted points with unrealistic widths. Where Xe line can be
	determined unambiguously, the gain determination is as good as usual. 
	However, the noisiness of the revolution means that this isn't possible
	for many science windows.) 


JEM-X2 rating: Very good  (within  2--3% of ideal, except for settling zone)

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 09/08/2023