The BurstMon pixel fraction measures correlation of hot pixels
in the time-wavelet domain (up to 1 kHz or up to 2 kHz).
For Gaussian, stationary noise, the N>2 pixel fraction (fraction of
clusters with 2 or more pixels) should be about 13%.

Experience in E12 and early S4 shows that the pixel fraction is
highly sensitive to certain artifacts, e.g., oscillator phase noise glitches
above 1 kHz or low-frequency seismic influences. It serves as a
"canary" figure of merit that typically starts degrading before
other figures of merit show an appreciable problem. 

Most analysts can probably tolerate a high pixel fraction, and
so it would not be prudent simply to veto flagged periods.
Instead, the flag is probably better used as a way of comparing
especially clean data with degraded data, that is, the
pixel fraction flags should, for now, be used for comparisons,
not for vetoes.

Pixel fraction has been provided for two different bands of
the time-wavelet plane because many analyses will be insensitive
to glitchiness in the 1.5-2.0 kHz range where oscillator phase noise is
often a problem.

K. Riles - March 11, 2005