Marx 4.3.0
Caveats for MARX 4.3
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Spatial Dependence of the Quantum Efficiency
The current version of marx does not incorporate the QE uniformity maps and bad-pixel files that give rise to spatial variation in the QE. Consequently, exposure maps and ARFs created by default in CIAO will be inconsistent with MARX simulations. For simulated observations on ACIS-S3, this difference should be small since spatial variations in the QE are relatively small on this CCD. However, simulated ACIS-I observations will be effected to a greater degree due to the larger QE variations produced by CTI effects.
For users of CIAO 2.3 and higher, the tools mkarf and mkinstmap
include the ability to turn off the QE uniformity maps through the use
of ardlib qualifiers. For example, a calling sequence like:
unix% mkarf detsubsys="ACIS-7;uniform;bpmask=0" ......will produce an ARF on ACIS-7 (ACIS-S3) but with bad pixel processing disabled (
bpmask=0) and without the effects of the CALDB
non-uniformity files included. The resulting ARF will be consistent
with a marx simulation. A similar call to mkinstmap can
be used in conjunction with mkexpmap to create exposure maps
appropriate for marx simulations. This technique is illustrated on
the examples page.
Users are refered to the
CIAO documentation for more information on mkarf
and mkinstmap options.
ACIS Response Functions
CIAO includes a couple of different tools for creating ACIS response matrices (RMFs): mkacisrmf and mkrmf. The mkacisrmf tool is designed for the analysis of CTI corrected data, whereas mkrmf creates an RMF for non-CTI corrected data. The response algorithm implemented in marx is based upon the calibration data used by mkrmf. Hence the PHAs generated by marx for the ACIS detector represent non-CTI corrected values and as such are consistent with the responses generated by mkrmf but not with mkacisrmf. Consequently, users should continue to use the CIAO's mkrmf to create RMFs that are consistent with their marx simulations. More information about using mkrmf in the context of a marx simulation may be found on the examples page.Alternatively, marxrsp may be used to apply any RMF to a marx simulation with the caveat that the mapping from photon energy to PHA does not vary over the detector.
LETG+HRC Line Widths
In standard Chandra pipeline processing, the motion of the observatory over the course of an observation is computed and stored in the aspect solution (ASOL) file. The tool marxasp replicates this behavior and produces an aspect solution file for a given marx simulation. A number of factors contribute to the accuracy or inaccuracy of Chandra aspect reconstructions. In marxasp, these noise terms are represented empirically using the sigma parameters inmarxasp.par. The
default values for these noise terms have been calibrated to be
consistent with HETG+ACIS observations and will give erroneously
narrow line widths when used with LETG+HRC simulations. Users wishing
to simulate LETG+HRC instrument combinations should adjust these
values before running marxasp. For example, a calling sequence of the
form:
unix% marxasp RA_Sigma=0.34 Dec_Sigma=0.34 Roll_Sigma=0.34 ......will produce an ASOL file consistent with current pipeline processing for LETG+HRC datasets.
