Subject: JEM-X Monday Meeting 2006-08-15

Present: CAO, SB, NL, AH, CBJ, NJW.

JEM-X status (SB): HV reduction for JEM-X1 happened in revol 459 (old news).
JEM-C switched off due to high count rates (Sco X-1). Software trigger
rate limit had been increased to 40,000/8s which turns out to be insufficient
so it has been set to 55,000. We have a hardware limit of 65,000. The software
trigger limit will be reset to 40,000 when Sco X-1 no longer will come into
the JEM-X FOV. Can we disable an anode segment?
No hotspot activity. Some gain changes between orbits due to temperature
changes of about 5 degrees. Due to aging the gain dependence on temperature
has increased.
In orbit 462 and following orbits the switch-on after radiation belt exit
as well as switch-off at radiation belt entry have been delayed by half an
hour.

New Crab calibration in revolution 484 (29/9 - 2/10 2006).
We have to think about what we want to do. Perhaps we could try to
command the anode segments 'off' to see the influence on the general
count rate level.

Source detection sensitivity of j_ima_iros (NL): The fluxes read off the
images decrease systematically with the off-axis angle. The cause is that
the finite detector position resolution is not properly reflected in the
backprojection algorithm. There is a conceptual difference between the
'forward' calculation by raytracing from the sky through the instrument
including all instrumental effects such as collimator and finite resolution
in the detector, and the 'backward' calculation applied in the backprojection.
The collimator plays a different role because an event registrered in a
pixel at a distance from where 'it should have been' will probably be
lost for the source in the geometrical backprojection.
The image reconstruction by correlation (disregarding the collimator)
followed by a vignetting estimate for the found sources could give a better
estimate of the flux.

OSA6 status (NJW): j_cor_gain, j_gain_fitting will be delivered by
CAO within 3 weeks. There is a number of SPRs and SCREWs for j_ima_iros
that will be implemented by NJW. j_src_properties has now the low energy
efficiency handling but spectra (that can be fitted by XSPEC) are not
correct yet.

/NJW