4 Calibration/Maintenance

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The ultimate goal of the AXAF system calibration is to allow absolute fluxes, positions, energies, and times at the earth to be determined from the raw data telemetry from the observatory. It is impractical to calibrate all desired quantities at every detector location and every desired energy. The calibration process measures the quantities for a wide enough range of parameters to characterize and verifies the system response through detailed analytic and numerical models.

Calibration is done in three major stages: laboratory calibration of the individual components, system ground calibration at the NASA MSFC X-ray Calibration Facility (XRCF), and orbital calibration using celestial and spacecraft sources.

All stages of calibration are treated in the ACIS Science Instrument Calibration Report. This report, jointly prepared by the MIT and PSU teams, covers the description of lab and XRCF testing of the ACIS experiment and the current results and conclusions of the analysis of the testing. The following chapter is a summation of those studies. The full Calibration Report will be released in preliminary form in October, 1997. The initial formal release is planned for June, 1998. It will be available electronically from http://acisweb.mit.edu and via ftp from ftp.astro.psu.edu in /pub/axaf/cal_report.ps.gz.