Should I worry about "false" periodic effects?
The HRI does not suffer from the wire-grid problems that plague the PSPC, so it is the better instrument for any timing studies. There will be a strong signal at the earth-block period (the continuous data streams usually last about 2000 seconds). The wobble of the observations can introduce a very small amplitude period if the wobble takes the sky region of interest over the face of the detector such that it crosses variations in quantum efficiency in the detector. These QE variations are on the few percent level, and the period detected would be on the wobble timescale (~400 sec).
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