Subject: Jem-X light curve

Dear Colleague,

Here is the Crab light curve in the 2-25 keV band obtained with Jem-X 1.
The fluxes comes from j_ima_iros. The fits file is in
~paltani/CRAB/jemx1.fits. Feal free to peruse it. The selection
criterion is DETSIG>18. The error I used has been calculated with the
formula: ERROR=FLUX/DETSIG. Here are some remarks:

- The FLUX_ERROR column is set to 20% of the FLUX, and is not calculated
on the basis of DETSIG.
- On the other hand FLUX/DETSIG clearly undestimates the uncertainty.
- Fluxes can be completely wrong for DETSIG<18. They are often found at
very low fluxes (10 cps or below). (see jemx_1_all.jpg)
- Position can be off by ~2 deg in these cases.
- There is a clear trend for the flux to increase with time.
- At least during three revolutions, the Crab light curves shows a bump.
- OFFANGLE is 90 degrees for all observations.
- There is a funny correlation between flux and coordinates!

What do you think?

Stephane