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Session 52 - AXAF, X-ray, Gamma Ray Instruments.
Display session, Thursday, January 08
Exhibit Hall,

[52.02] AXAF Telescope On-axis Effective Area as a Function of Energy

R. J. Edgar (SAO), A. Tennant (NASA-MSFC), B. Wargelin, W. McDermott, K. Michaud, D. Jerius, T. J. Gaetz, P. Zhao (SAO)

During the winter and spring of 1996/1997, the AXAF telescope and science instruments were calibrated at the NASA/Marshall Space Flight Center's X-Ray Calibration Facility (XRCF). We present the analysis of those data that bear on the effective area of the High Resolution Mirror Assembly (HRMA) as a function of energy.

The measurements were made with an assortment of calibration detectors, including seven flow proportional counters (FPC), and two germanium solid state detectors (SSD). Some of these detectors were in front of the mirror assembly, to monitor the telescope's input flux. Others were used at the telescope's focal point. The ratio of the counting rate at a given energy in the focal point detector to the input flux gives, as a function of energy, an efficiency in units of cm^2, which is known as the effective area. Multiplying this quantity by the flux incident on the mirror will allow one to predict the counting rate in flight detectors.

The goal is to derive an effective area to an accuracy of 1-2% over the entire AXAF energy band (roughly 0.1 to 10 keV). Two classes of experiments were performed: [1] using a Bremsstrahlung continuum source, observed with two SSDs (one at the focal plane and one in front of the telescope entrance); and [2] using fluorescent line sources observed by a set of FPCs. The FPC detectors have larger areas and better response at low energies, but poorer energy resolution. We present a comparison between the effective areas derived from these two types of experiments and those obtained from a detailed raytrace model which will be used for on-orbit performance predictions.

Program listing for Thursday