Calibration of the Rossi X-Ray Timing Explorer proportional counter array

We present the calibration and background model for the Proportional Counter Array on board the Rossi X-Ray Timing Explorer. The energy calibration is systematics-limited below 10 keV, with deviations from a power-law fit to the Crab Nebula plus pulsar of less than 1%. Unmodeled variations in the instrumental background amount to less than 2% of the observed background below 10 keV and less than 1% between 10 and 20 keV. Individual photon arrival times are accurate to 4.4 mu s at all times during the mission and to 2.5 mu s after 1997 April 29. The peak pointing direction of the five collimators is known to a precision of a few arcseconds.