XRCF Simulations

We have generated a number of simulations of the XRCF measurements. Typically these simulate the XSS (to some degree), the HRMA, and the HRMA Shutters. They do not include gratings or detectors.

Available Simulations

Except for the DCM measurements, the energies are determined from the Line Designation (i.e. Al Ka). Values are taken from the Bearden Catalogue at MSFC.

The latest simulations

The latest simulations use the xrcf_xss_01 configuration, with trace-shellz1 and trace-xrcf1. We've used the DRAFT_as_run.cmdb as of 3 April 1998. Some of the distinguishing features about these simulations are:

the inclusion of ghost rays
additional as-measured HRMA tilts at XRCF
XSS source maps are used, instead of being modelled as point sources
the HRMA surface is modeled as a multi-layer

We have not yet incorporated the following characteristics of the XRCF configuration:

polychromatic source

Presently these are rather sparsely populated; only measurements with the PIGS have been completed.

The ray files are available at ftp://pelf.harvard.edu/pub/dj/rays/XRCF/xrcf_xss_01a/100k/

Previous Simulations

We have not yet incorporated the following characteristics of the XRCF configuration:

finite sized source
polychromatic source
XRCF measured inter-shell tilts

Ghost rays (singly reflected rays) are not included due to inadequacies of our software (this is being fixed). Since ghost rays are by design not supposed to be found within 14 minutes of arc of the optical axis, for most measurements this doesn't affect the validity of the simulations. One should be careful with far off-axis measurements. There are several batches of these rays:

ftp://pelf.harvard.edu/pub/dj/rays/XRCF/xrcf_SAO1G+HDOS_HDOS-scat-970220_03/10k/: These rays represent all of the measurements found in the final req_run.cmdb list as of August 1997. There are 10000 rays per file.
ftp://pelf.harvard.edu/pub/dj/rays/XRCF/xrcf_SAO1G+HDOS_HDOS-scat-970220_03/100k/: These rays represent a select group of measurements which have 100000 rays per file.

Details about the rays

Energy Scans

For DCM and HIREF scans, raytraces were run for each of the energies in the requested energy range (i.e, starting at X_Ray_mono_initial, and incrementing by X_Ray_mono_step_size until the range in X_Ray_mono_range was covered).

HRMA Shutters

The rays have been passed through the appropriate shutter configuration for each test.

Sampling the rays

Rays from the shells have been mixed in the ray files. You can thus take as many as you'd like from the file without worrying about correctly sampling the HRMA.

File Naming Conventions

The ray files have been placed in subdirectories according to their XRCF test Phase (C-H), and are named after their TRW ID's. In the case of energy scans, the names have the energy (in keV) appended to the TRW ID, separated by an underscore. Tests which included a shutter scan will have the open shutter id (t, b, n, or s) appended to the name with an underscore.

Ray file format

The rays are in the XRCF coordinate system, with X = 0 being the fore end of the CAP. The rays have been projected to the HRMA best focus for Al Ka (1.4967KeV), which is at -10274.86670111mm (determined from raytraces). You will undoubtedly need to project them to the appropriate focal plane for your instrument. For projection to a plane perpendicular to the optical axis (X), the formula is:

      t = ( X_final - X_current ) / DC_X
      Y_final = Y_current + t * DC_Y
      Z_final = Z_current + t * DC_Z

where:

	X_final is where you want the rays to end up
	X_current, Y_current, and Z_current 
	     indicate the current position of the ray
	DC_X, DC_Y, and DC_Z are the ray's direction cosines

The rays are in FITS files, as per the

	"AXAF FITS Standard for Ray Trace Interchange"

To get your copy, email Kathy Daigle and ask for document SAO-AXAF-DR-93-039. That document is under revision. The FITS files follow that revision; the sole difference that's noticeable is that ray weights are defined to be the probability of the ray reaching the focal plane. We have pre-filtered the rays so that each has a weight of unity. If you're too anxious to see/use the rays, and can't wait for the document, here's the layout. The files are FITS binary tables, the fields are:

Name Type Units Description

RT_X double mm X Position

RT_Y double mm Y Position

RT_Z double mm Z Position

RT_COSX double X Direction Cosine

RT_COSY double Y Direction Cosine

RT_COSZ double Z Direction Cosine

RT_KEV double keV Photon Energy

RT_WGHT double Ray Weight

RT_ID 32-bit Photon ID

Name	Type	Units	Description
RT_X	double	mm	X Position
RT_Y	double	mm	Y Position
RT_Z	double	mm	Z Position
RT_COSX	double		X Direction Cosine
RT_COSY	double		Y Direction Cosine
RT_COSZ	double		Z Direction Cosine
RT_KEV	double	keV	Photon Energy
RT_WGHT	double		Ray Weight
RT_ID	32-bit		Photon ID

Note that in these files RT_WGHT will always be 1.0.

Utilities

For those without FITS readers, we provide a Perl5 program which will convert the rays into an "rdb" table, which is a simple column delimited ascii table. The program will actually parse any simple binary table. Help is available by passing it the '-help' option on the command line. See ftp://pelf.harvard.edu/pub/dj/rays/XRCF/utils/photfits2rdb

Diab Jerius

Last modified: Wed Sep 9 15:12:55 EDT 1998