CCD data modes

A count rate of 4000 counts per second per two cameras corresponds to 1 Crab. Typically, the charge cloud produced by an X-ray photon is not localized to one pixel but spread out over several pixels. There are two data modes, ``faint" and ``bright", which correspond to two different ways of telemetering this spread to the ground within the available data rate.

• Faint mode: SIS spectra in this mode have 4096 channels. The pixel position of the center of the event is given, along with the pulse height recorded in the nine pixels around it (central pixel plus eight surrounding pixels in a 3 x 3 grid).
• Bright mode: SIS spectra in this mode have 2048 channels. The pixel position of the center of the event is given, together with the ``grade" describing the nature of the spread, and the total pulse height above an adjustable threshold.

Additional, primarily diagnostic modes also exist. Verification of all modes is the responsibility of ISAS, the Astro-D GOF and the Pennsylvania State University.

In 4-CCD mode, at high bit-rate, the maximum count rates are 32 and 128 counts per second per two cameras in faint and bright modes, respectively. In 1-CCD mode, these figures are four times larger.