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Scientific Performance Summary

The Joint European Monitor for X-rays (JEM-X) on-board INTEGRAL fulfills three roles:

JEM-X operates simultaneously with the main gamma-ray instruments IBIS and SPI. It is based on the same principle as the two gamma-ray instruments on INTEGRAL : sky imaging using a coded aperture mask. The performance of JEM-X is summarized in Table 1.


Table 1: JEM-X parameters and performance.
Energy range 3 - 35 keV
Energy resolution
Field of view (diameter) 4.8 Fully illuminated
  7.5 Half response
  13.2 Zero response
Angular resolution (FWHM) 3
Relative point source location error 1 (90% confidence radius for a 5 isolated source)
Continuum sensitivity ph cm s keV @ 6 keV
for a single JEM-X unit ph cm s keV @ 30 keV
(isolated source on-axis) for a 3 cont. detection in 10 s, E = 0.5E
Narrow-line sensitivity ph cm s @ 6 keV
(isolated source on-axis) ph cm s @ 20 keV
  for a 3 line detection in 10 s
Timing resolution 122 s (relative timing)
  ms (absolute timing)
The energy resolution is slowly changing (degrading) over time.
At the half response angle the sensitivity is reduced by a factor 2 relative to the on-axis sensitivity.

Figure 1: JEM-X effective area with the mask taken into account. The dashed line shows the effective area before the high voltage reduction and the full curve shows efficiency when taking into account the effect of the electronic low-signal cutoff (approximately).
Image effarea_NW


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