Gain Calibration Notes for Rev. 365
	
JEM-X1:
Relatively little noise and no large glitches. This is the Crab Calibration
revolution and the sudden drop in gain is due to a 3-step drop in the High
Voltage value that was done as a test of the effect of HV on gain and event
flux. The smoothing program (j_cor_gain 6.4) has however, mananged to smooth
all 3 parts of the gain history table correctly, so there is no problem in
using data from this revolution. Note the gain increase (`rapid aging') that
occurs after the initial switch on due to ion motion in the microstrip plate,
and the gain decay that occurs after switching the HV back up to its nominal
value. This mirrors the decay we see after short unscheduled switch-offs and
is caused by charge distribution settling on the plate. The smoothing model
doesn't quite manage to fit this decay, so maybe best to avoid data taken in
the first minutes after the increase in HV. The time period with the lowered 
HV value is now officially labelled a BTI, and the ISDC system will disregard
science data from this period. The BTI is IJD= 2110.22 to 2110.33.

Xe line analysis shows that the gain correction has worked very well for this
revolution, though the first few Science Windows (as usual) deviate most from
the ideal gain determination, and these should be used with due caution. All
data outside the BTI can be used for science analysis.


JEM-X2: 
This unit was turned on only for the Crab calibration exercises. This
data should not be used since it involves several changes in the HV setting
performed to study the instrument's electronic efficiency. This data is not
suitable for scientific purposes and all JEM-X2 data from this revolution is
covered by a Bad Time Interval, IJD=2110.00 to 2111.00.
For Instrument Team users: there is a bug/loophole in j_cor_gain 7.3 (OSA 6.0
version) which means that it cannot correctly smooth the automatically produced
ISDC Gain History table for JEM-X2 because data is missing for the first row of
the first source. This was not a problem for j_cor_gain 6.4 (OSA 5.1) which would not
take in incomplete rows, but could not handle whole anode segments being 
switched off. This means that an IC gain history delivered to ISDC must be used
instead of the standard gain history table. If you have the newest IC tables
installed and OSA 6.0 this is not a problem - the software will find the IC
table for you. Otherwise, download the corrected table from the Gain History
Archive (the page that linked you to these notes) and use the table by setting
the hidden parameter in the OSA GUI:
gainHist = <path to myDir/<myDir>/JMX2_gainHistoryIC_rev0365_001.fits[JMX2-GAIN-OCL,1]


CAO 16/1/2006