In-Flight Characterization of the HETE Soft X-Ray CCD Cameras

We have developed a set of software tools that allow to monitor the performance of the flight X‐ray CCD cameras as soon as data arrive at MIT. An emission line at 5.9 keV from the on‐board Fe‐55 radioactive calibration source is clearly visible in the spectra and provides the means to measure the gain and the noise for each observation in each of the 4 CCD chips in operation. Both parameters can change with time, depending on the phase of the moon and the amount of light leaking into the system. Time vs. position scatter plots were found to be an extremely powerful tool in understanding of the device performance. They illustrate the evolution of the light leaks produced by the dark Earth at the beginning and the end of each orbit. With a bright X‐ray source in the field of view the shadow of the mask projected on the surface of the CCD clearly shows the motions of the spacecraft.