When running marx with default parameters the bestfocus tool suggests to include a DetOffsetX.
That's surprising because the Chandra focus has been optimized numerically.
> marx
[...]
melkor:/melkor/d1/guenther/marx/oneoff/focus> bestfocus --dir point
17932 rays read. 17932 of them used (1.00%).
Best focus position [mm]: (0.187785, 1.924678, -0.992159)
At that position, the mean radius of the spot will be 1.151636 mm
(about 47.984826 ACIS Pixels)
Current DetOffsetX value: 0.000000
Suggested DetOffsetX value: 0.188732 (difference of 0.188732)
The exact number differs between runs (Poisson uncertainty, unstable fitting?), but averages to about 0.1 mm.
Verify what SAOTrace rays say. Could this just be an artefact of the simplifications in he MARX HRMA model?
Herman Marshal used the half-energy width when focussing Chandra. What exactly does bestfocus use? ObsIDs are 62549-62558 for the Chandra observations.
Could be that the focal length or pixel scale is not exactly right (In Chandra those are calculated from the plate scale and the known pixel size at cool temperatures.).
When running marx with default parameters the
bestfocustool suggests to include a DetOffsetX. That's surprising because the Chandra focus has been optimized numerically.The exact number differs between runs (Poisson uncertainty, unstable fitting?), but averages to about 0.1 mm.
bestfocususe? ObsIDs are 62549-62558 for the Chandra observations.