# Highlights for each version of marx¶

## Marx 5.4 (Dec 2018)¶

Update CalDB files that are shipped with marx to CalDB version 4.8.2.

### HRC PSF¶

The HRC detector PSF has some blur in it. See https://cxc.cfa.harvard.edu/twiki/bin/view/HrcCal/DetectorPSF for how the parameters used in previous versions of marx are determined. However, we recently found that the PSFs are wider than observed. Thus, in this version we change the values of the default marx.par file to use a single Gaussian instead. This change is most important for the profile of the wings in very bright HRC sources. We continue to investigate this and expect another change in the next marx release.

## Marx 5.3.3 (Dec 2017)¶

Small bug fix to the source code to allow compilation with clang (which is the default compiler on Macs).

## Marx 5.3.2 (Dec 2016)¶

Update CalDB files that are shipped with marx. No changes to the source code.

## Marx 5.3.1 (Aug 2016)¶

This fixes two bugs for users of SIMPUT sources; all other runs are unaffected.

## Marx 5.3 (Apr 2016)¶

MARX 5.0, 5.1, and 5.2 contain a bug that affects the PSF for simulations of off-axis sources; this is fixed in 5.3. The root cause for this bug was that the entrance aperture of the Chandra mirrors was chosen to match the size of the mirror opening as seen an on-axis source exactly. For an off-axis source that means that the generated photons hit only part of the mirror, leading to gaps in the simulated PSF. Now, the entrance aperture has been increased to allow sources anywhere in the field-of-view to fill the detector. This necessarily increases the run time of all marx simulations, because more photons need to be generated. See https://github.com/Chandra-MARX/marx/issues/21 for a detailed description of the issue.

### New source type: SIMPUT¶

marx now supports the new SIMPUT standard, which is a fits based description of sources, which allows a large number of source with different spectra, light curves, and shapes on the sky. This file format is supported by a number of other simulators (e.g. for ATHENA), so integrating it in marx allows users to use the same source specification for different X-ray missions. The support in marx is through the SIMPUT code which needs to be installed separately and is linked dynamically at runtime if SourceType="SIMPUT".

## Marx 5.2 (Dec 2015)¶

There are only minor enhancements, calibration updates, and bug fixes in this version.

### Change in default parameters¶

Set the PointingOffsetY and PointingOffsetZ to 0 to match the values in current Chandra observations (was -21 and 12 before). This defines the difference between RA/DEC_NOM and RA/DEC_PNT in the fits headers of event files; it is not used in the code except to output the RA/DEC_PNT values by marx2fits.

### Bug Fixes¶

• Match use of long and double types in fits output to standard CIAO products.
• Previously an ASOL file name > 63 characters would crash marx2fits. Now, it cuts the pathname to shorten the string.

## Marx 5.1 (Apr 2015)¶

marx version 5.1 is a maintenance release. Since more than two years have gone by since release 5.0, there are major changes in the Chandra calibration data that marx uses, particularly in the soft energy response of ACIS. In addition there are several minor changes, some of which are listed below (see the commit log of the git repository for complete details):

• marx now compiles with clang, the compiler that is shipped with Max OS X-code. (Apple sets an alias called gcc, but this really points to clang.)
• Enhanced support for dithered SAOTrace rays on input. In particular, that means that the parameter SAOSAC_Color_Rays is no longer needed. Setting it currently has no effect and this parameter will be removed in the next version.
• marx2fits writes more header keywords in the output fits files, which enables more CIAO tools to work with those files.
• The HRC blur model has been improved. Simulations with HRC-I and HRC-S will give slightly different PSF shapes. In order to describe the HRC blur properly, new parameters have been added to marx.par. These parameters should not be changed by the user; instead we strongly recommend to just copy and modify the version of marx.par that comes with the installation which includes those new parameters.
• marx now includes the LEG misalignment compared to the ACIS chips. Handling this required changes to the default values of the hegTheta, megTheta, and legTheta. These parameters should not be changed by the user; instead we strongly recommend to just copy and modify the version of marx.par that comes with the installation which includes those updated values.

## Marx 5.0¶

marx 5.0 is a major new release. This page is devoted to the new features.

### Subpixel Randomization¶

The EDSER subpixel algorithm was incorporated into CIAO 4.3. When computing Sky coordinates, acis_process_events first converts the integer-valued chip coordinate to a floating point value. There are several ways in which this may be done. One way is to simply cast the integer to a float, e.g,, the integer 2 becomes 2.0. The problem with this approach is that it can cause aliasing artifacts in the resulting Sky image. For this reason, the default up until CIAO 4.3 was to simply add a uniform random deviate from -0.5 to 0.5 to the integer value so that 2 would become a random real number in the semi-open interval [1.5, 2.5). The default was changed in CIAO 4.3 to use a discrete probability distribution based upon flight grade and energy, known as the EDSER method.

The marx 5 version of marx2fits introduces a --pixadj command line parameter that allows the user to select one of several pixel randomization methods. Simply running marx2fits without any command line arguments will display its usage message:

marx2fits v5.0.0:
Usage: marx2fits [options] marxdir outfile
Options:
--pileup             Process a marxpileup simulation
--pixadj=EDSER       Use a subpixel algorithm (default)
--pixadj=RANDOMIZE   Randomize within a detector pixel
--pixadj=NONE        Do not randomize within a detector pixel


The effect of these randomization methods may be seen in the following plot, which shows that the EDSER distribution approaches the exact limit.

Image of PSF with different pixadj values

If using SAOTrace rays with marx, see Current caveats for MARX regarding the use of the EDSER method with such rays. Note: Caveat removed in 2015. SAOTrace now supports dither.

### New dither model¶

The EDSER subpixel algorithm necessitated numerous changes to the marx aspect code. In particular, aspect reconstruction blur had to be cleanly separated into its independently contributing pieces, namely the telescope pointing uncertainty, the blur introduced by pixel quantization/truncation, and the blur associated with pixel randomization. Previous versions of marx incorporated these blurs under the guise of a single parameter, DitherBlur, whose value was the RSS sum of the contributing blurs. This was the source of a lot of confusion among users resulting in numerous help desk inquiries about how this value was obtained and why it was so large. For these reasons, the DitherBlur parameter was removed from marx and replaced by one called AspectBlur whose value represents just the telescope pointing uncertainty, 0.07 arc-seconds. One consequence of this change is that marx 4.x parameter files cannot be used with marx 5.0.

It was also necessary to remove the blur parameters from marxasp, which computes an aspect solution file for use in reprocessing a marx2fits generated event file. Hence any scripts that pass blur parameter values to marxasp will need to be modified.

As mentioned above, the DitherBlur parameter’s value reflected more that just that associated with the aspect uncertainty. It was also tweaked to get the marx PSF to better match Chandra grating line profiles. With this parameter gone, the marx HRMA blur parameters had to be re-calibrated to get the widths of the marx simulated grating line profiles to match those in the Chandra CALDB.

There was a long standing issue of a relative rotation between the LETG and the ACIS detector. The root of this problem was tracked down (with the help of marx) to a rotation offset between the aspect coordinate system and the focal plane detector system. This offset was masked by compensating rotations of the detectors from astrometric analysis, and manifested itself as a small rotation of the LEG dispersion arm on the ACIS detector. Changes were added to CIAO 4.3 that effectively adds an additional rotation to the LETG when used with ACIS. The corresponding change in marx 5.0 is implemented via a new parameter called LETG_ACIS_dTheta.

The marx calibration data have been brought up to date with the Chandra CALDB 4.4.7.

The parameter files for earlier versions of marx (e.g., the marx.par file for version 4.5) cannot be used with marx 5.0. The recalibrations that were necessary for subpixel support resulted in changes to all of the HRMA blur parameters, as well as the introduction of the new AspectBlur parameter discussed above.

The following marx.par parameter values have changed since marx 4.5:

P1Blur: 0.18129215 --> 0.303427
H1Blur: 0.13995037 --> 0.0051428
P3Blur: 0.11527828 --> 0.0951899
H3Blur: 0.16360829 --> 0.0713614
P4Blur: 0.1289134 --> 0.178899
H4Blur: 0.098093014 --> 0.0101367
P6Blur: 0.076202759 --> 0.151085
H6Blur: 0.079767401 --> 0.0239287
MEGRowlandDiameter: 8632.65 --> 8632.48
HEGRowlandDiameter: 8632.65 --> 8632.48
HETG_Shell1_Period: 0.400141 --> 0.400195
HETG_Shell3_Period: 0.400141 --> 0.400195
LETG_Shell1_Theta: -0.07 --> 0.07
LETG_Shell3_Theta: -0.07 --> 0.07
LETG_Shell4_Theta: -0.07 --> 0.07
LETG_Shell6_Theta: -0.07 --> 0.07
legCoarseNumOrders: 11 --> 121


The following parameters have been removed:

DitherBlur


The following parameters have been added:

AspectBlur: 0.07
LETG_ACIS_dTheta: -0.0867
Use_This_Order: 0
DetExtendFlag: no


The latter two parameters were added for the purposes of calibration.

## MARX 4.0¶

MARX 4.0 represents a major upgrade since the previous release. Where possible, MARX now uses CIAO CALDB data files directly for detector responses and quantum efficiencies thus providing the ability to transparently analyze simulations using standard CIAO tools. In addition to calibration changes, a number of improvements and enhancements to MARX’s functionality have been made. These include:

• Simplified source position specification
• Direct CALDB interface for calibration information
• Direct use of FEF files for ACIS spectral response
• New ACIS photon pileup tool
• Enhancements to support processing CHART rayfiles
• Improved compatibility with CIAO data analysis tools
• Miscellaneous bug fixes

As with previous updates, most of these changes should be completely transparent to the returning user.