<title>X-ray calibration of the SODART flight telescopes</title>

Abstract

The on- and off-axis imaging properties and effective area of the two SODART flight telescopes have been measured using the expanded beam x-ray facility at the Daresbury synchrotron. From on-axis measurements the encircled power distribution and the point spread function at three energies 6.627 keV, 8.837 keV and 11.046 keV have been measured using a one-dimensional position sensitive detector. We found that the point spread function can be presented well by a function which is a sum of a Gaussian divided by the radius and two exponential terms where the first has a 1/e value close to 2 arcmin and the other a 1/e value of ca. 15 arcmin. The data have been used to calculate the half power diameter (HPD) for three different SODART focal plane detectors, the high energy proportional counter (HEPC) with a field of view (FOV) of 65 arcmin, the low energy proportional counter (LEPC) with a FOV of 33 arcmin and the 19 element solid state detector array (SIXA) with a FOV of 18 arcmin. We found that the HPD decreases with increasing energy due to poorer figure of the outermost mirrors. The HPD falls in the range from 2.4 to 3.8 arcmin depending on energy and FOV. Data have also been obtained on the on- and off-axis effective area at all three energies and compared to that obtained from a raytracing of an ideal telescope configuration. We found that the measured on-axis effective area integrated over a FOV of 105 arcmin is ca. 65% of the area predicted from an ideal geometry. Finally the one- dimensional detector data has been used to obtain the radial dependence of the on-axis HPD and the on-axis effective area and the data from the two-dimensional position sensitive detector has been used to obtain the azimuthal dependence of the on-axis HPD and the on-axis effective area.