Spatial Analysis

Pixel size

In the SAXDAS linearized event files the pixel size of both LECS and MECS DETX DETY, and X Y coordinates is 8 arcsec. The pixel size of the LECS RAWX RAWY coordinates is 14 arcsec, the pixel size of the MECS RAWX RAWY coordinates is 20 arcsec.

Raster Scan

An in-flight raster scan of the central area of the LECS and MECS detectors has been carried out to a) study the PSF evolution b) to cross-calibrate the instruments and c) to measure the position reconstruction in this area. Preliminary results show that the absolute position reconstruction is around 20-30 arcseconds.

Absolute position determination

The LECS and MECS absolute position determination is limited by statistical and systematic uncertainties.

The analysis of two bright sources (MECS count rate, three units, higher than 10 counts s-1), two medium bright sources (MECS count rate between 1 and 5 counts s-1) and two faint sources (MECS count rate between 0.1 and 1 counts s-1), and of 14 short observations of LMC X-3 (a raster scan performed in the Science Verification Phase) revealed that:

  • the scatter in the reconstructed sky position in the three MECS units is of the order of 10-20 arcsec, depending on the source brightness;
  • the scatter between the LECS and the MECS units is the order of 30 arcsec;
  • the absolute position reconstruction is for both instruments is within 30 arcsec.

    Additional systematic uncertainties add to the above statistical uncertainty and make the 95 % error box of about 1 arcmin when the z startracker is in use. When this startracker is not in use the uncertainty can be as large as 2 arcmin.

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