Sensitivity

The sensitivity achieved for source detection and flux determination also depends on the performance of the deconvolution software. Figure 8 shows the 3 detection limit as a function of observation time.

The changes in gas gain and corresponding changes in signal patterns led to a large fraction of events being classified as background and rejected on-board until new selection criteria could be determined and uploaded (2003-03-25, revolution 45). Even with the new optimized selection criteria the detector sensitivity below 5 keV is reduced.

Figure 8: Source detection capabilities in the 3 to 10 keV (resp. 10 to 25 keV) band as function of effective accumulated observation (exposure) time in JEM-X mosaic images corrected for dead time, grey filter and vignetting effects. The thick solid curve is obtained from simulations where an isolated source must be detected at in the deconvolved image. The dashed line represents the case where there are additional sources in the field of view giving a background corresponding to a total of 1 Crab. Examples of actual observations are given: the source 3C 273 and the other empty circles are instances of isolated sources, while the crossed circles represent sources observed in the crowded Galactic Centre region. The -values given in parentheses are obtained from a measure of the highest source pixel in significance mosaic maps with default pixel size (1.5 arcmin).