In Orbit Performance of the Einstein Observatory/HEAO-2 Imaging Proportional Counter

After two years of orbital operation, the IPC--a soft X-ray (0.2 - 4 keV) position sensitive proportional counter--continues to perform well after some initial gain changes, and is the most widely used focal plane instrument of the Einstein Observatory. X-ray images of several thousand cosmic X-ray sources have been obtained with a resolution of ~ 1.5 arcmin (FWHM) with a 1° field. Particle backgrounds are less than expected. The calibration of the instrument with respect to gain variations and spatial linearity is being refined by in-flight measurements.