MARX Frequently Asked Questions¶
I have a question about marx that is not addressed here. Where can I get additional help?¶
marx specific questions should be sent to marx-help@space.mit.edu. If your question is related to CIAO, then you should contact the CXC helpdesk.
I’m using marx on Mac OS X and something does not work.¶
Over half of all user queries we receive are related to the broken compiler that ships with XCode on Mac OS X. Please see Known Bugs and Limitations.
Do you distribute marx binaries?¶
No. There are several reasons for this including the lack of resources. Rather, we have tried to make the installation process as simple as possible so that even the most inexperienced user can do it. Step by step instructions for compiling marx are available on the Downloading and Installing Marx. The reward for compiling it yourself is that you can be sure that marx was built explicitly for your system, and as such, no incompatibilities should arise. One cannot make this guarantee for a precompiled binary version.
How do I create an ARF and RMF that match my marx simulation?¶
The answer to this question may be found Creating CIAO-based ARFs and RMFs for MARX Simulations.
Can I simulate arbitrary combinations of ACIS CCDs in marx?¶
The simple answer is “no”. Out of the box, marx allows users to select either the ACIS-S array (6 CCDs) or the ACIS-I array (4 CCDs). Arbitrary mixtures of chips from the two arrays are not currently supported although we plan to add that option in a future version of marx.
In the meantime, if you do need to simulate other combinations,
one can assemble such composites by creating the desired ACIS-S
and ACIS-I chips separately and them merging the resulting event
lists with the dmmerge tool in CIAO. For such mergers, both pieces
of the simulation must have the same aimpoint position.
This configuration can be accomplished by a SIM translation in marx
using the DetOffsetX and DetOffsetZ parameters.
For example, to create a marx simulation where the default
ACIS-S aimpoint was used, but ACIS-I chips were also active
during the observation, one would do two separate simulations.
The ACIS-S portion of the simulation would utilize the marx defaults.
The simulation of the ACIS-I chips however would require moving
the SIM to position the ACIS-I detector correctly relative to the
default ACIS-S aimpoint. The appropriate values in the marx.par file
would be:
DetOffsetX=0.0990000
DetOffsetZ=43.4590
Note that the DetOffsetY parameter is not modified since SIM motion
along the Y axis is not permitted. For simulations using the default
ACIS-I aimpoint, the ACIS-S simulation would need to be offset
using the values:
DetOffsetX=-0.0990000
DetOffsetZ=-43.4590
The dmmerge tool will produce some warning messages during the combination of the two event lists, but should produce a valid FITS event file. Unwanted CCDs can be removed using dmcopy.
Can I simulate CTI-corrected observations in marx?¶
No. marx does not currently recognize the new format
of the CTI-corrected FEF file available in the CALDB (versions 2.18
and higher). So simulations cannot be created directly
which feature the improved spectral response of the front-illuminated
CCDs after CTI correction. Users wishing to simulate CTI–corrected
spectra can however use the marxrsp tool to fold a given marx
simulation through an existing RMF created from the CTI–corrected FEF.
Is it possible to run marx with a constant effective area?¶
If by “constant” you mean an effective area that does not not depend upon energy, then the answer is yes. To do so, use the following configuration:
DetIdeal=yes
HRMA_Ideal=yes HRMAVig=1.0
Use_Unit_Efficiencies=yes
mode=h
The DetIdeal=yes setting tells marx to assume that the detectors
have 100 percent quantum efficiency. The line involving the
HRMA* parameters indicates that perfect reflectivity from the
mirrors is to be assumed and that no rays will suffer vignetting from
the various baffles. The Use_Unit_Efficiencies=yes parameter
setting comes into play only in when the gratings (LETG or HETG)
are used. It causes the diffraction efficiencies for all orders to
be equal, i.e., all diffraction orders will be equally probable.
Finally, the mode=h line will cause marx to not save these
values in the marx.par file.
Keep in mind that some photons will still be lost if they scatter from the mirror and not hit the detector, fall in detector gaps, etc.
