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He, X. H., Wise, M., & Glotfelty, K. J. 2001, in ASP Conf. Ser., Vol. 238, Astronomical Data Analysis Software and Systems X, eds. F. R. Harnden, Jr., F. A. Primini, & H. E. Payne (San Francisco: ASP), 518
Enhancements of MKRMF
X. Helen He
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MA 02138
Michael Wise
MIT Center for Space Research, Cambridge, MA 02139
Kenny J. Glotfelty
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MA 02138
Abstract:
MKRMF, a data analysis tool of the Chandra X-ray Science Center
(CXC), has evolved to more effectively create response matrix files
(RMF). It provides new and enhanced features: uniform binning syntax,
all-inclusive FITS embedded function (FEF) file extraction, and non-linear
EBOUNDS calculation. This paper describes the algorithm, application
interfaces and highlights of the future development.
MKRMF generates a response matrix for an arbitrary
redistribution function over a 2-dimensional grid plane. Since last reported by
He (1999) it has evolved to include:
- uniform binning syntax and rebinned RMF output,
- application of generic FEF file, and
- non-linear EBOUNDS calculations to closer reflect real gains.
The tool's parameter file (mkrmf.par) has been
accordingly updated, as listed in Table 1. The table
highlights the most important parameters.
In conjunction with CXC Data Model (DM) filtering,
MKRMF adopts the DM grid binning syntax for the ``axis1'' and
``axis2'' parameters. The binning syntax is consistent
with other CIAO 1 tools.
As previously defined, the binning syntax is grouped into two
categories: command
line and ASCII/FITS table file. The command line input allows the user to
specify discrete grids in lower bound,
upper bound, and binning type, separated by ":". The grid
type can be specified as linear or logarithmic binning
for either the binning step or the total number of bins. The
file input allows the user to tabulate an arbitrary grid. The
ASCII file format contains two columns: lower and upper bounds.
Two columns extracted from the FITS file define
the bounds by following DM filtering syntax.
Table 2 summarizes the binning syntax.
MKRMF always computes the matrix (and EBOUNDS) at full resolution at the specified
<min>:<max>
range. The matrix can be binned by specifying
bin type and step size. MKRMF will use this information to scale down the output
to the requested bin size.
A FEF FITS binary table is a CXC format
convention to allow specification of an n-dimensional image in
the form of an analytic function of n variables in a FITS binary
table HDU. This file format has been developed to be extremely generic
and to allow very cost effective reuse (Rots 2001).
MKRMF takes the analytic redistribution functions which are conventionally
expressed by columns of independent function variables.
These function variable columns are stored in the
FEF format and used by MKRMF to create standard response matrices.
Prior to the release of CIAO 2.0, a FEF file existed for each
individual spatial
region for which (different) redistribution functions were defined.
Because of this, those who wished to perform analyses over large spatial
regions or over multiple chips potentially had to keep track of a large
number of files. In CIAO 2.0, these files have been merged into a single
file, an all-inclusive and spatial varying FEF file.
In addition to columns containing redistribution function parameter
values, the new FEF file contains new columns CCD_
ID, CHIPX, and CHIPY, which provide the location and bounds for each spatial region.
Another new column, REGNUM, contains an integer value that identifies
each spatial region uniquely. The new FEF format also encapsulates
the gain relationship of the CCD for energy in a specific
region. This relationship is defined by a new column, CHANNEL
(or PHA), mapped to ENERGY in that region.
By introducing the ( ENERGY, CHANNEL) pair columns,
the generic FEF extractor can effectively result
in data block consisting of one region for each energy when a
DM filter is applied to the FEF file. Therefore, the generic FEF
file is effectively reusable and backward compatible.
The MKRMF user must now use DM syntax to retrieve information
for one spatial region, as shown in this example:
mkrmf infile=fef.fits[ccd_id=7, chipx=(1:100),chipy=(1:32)]
When mkrmf executes the program with an input FEF file named
"fef.fits"
, it extracts the data containing ( ENERGY,
CHANNEL) gain and redistribution function variables internally sorted
for CCD_
ID of 7 with chip pixel range of 1 to 100
and 1 to 32 along X- and Y-Axis, respectively.
Figure 1 illustrates two MATRIX components generated on
a FEF file with the filter above for a combination of ten embedded
Gaussian functions on linear binned PHA-energy grids.
Figure 1:
RMF MATRIX Output.
|
In previous releases, the EBOUNDS array was calculated through a linear analytic
expression of two constant parameters (keywords): SCALE and
OFFSETS.
MKRMF now employs a new algorithm for the gain calculation from data
tabulated in the new FEF file. The original linear interpolation
still exists for backwards compatibility.
The CHANNEL and ENERGY pairs in the new FEF file encapsulate
the piecewise linear gain information within a given ( CHIPX, CHIPY) region for each
specific energy value. Our
new scheme to calculate the EBOUNDS array is to linearly interpolate the
energy for a given PHA value from the pairs of channel and corresponding
energies that bound the PHA value.
The EBOUNDS energy derived in
this way represents the variation of the CCD gain in that region, or
an effectively non-linear and spatial varying relationship.
Future focus will be on multi-region RMF calculations. The current
tool provides RMF output limited to one region characterized by the same
response function within the given ( ENERGY, CHANNEL) range. However,
those parameters are also functions of spatial variables. This limitation will
be removed by taking a weighting factor into consideration for each region, so
a multi-region RMF output can be achieved by applying the weighting
to redistribution functions of the interesting regions.
As such, MKRMF data I/O is expected also to be updated in the future.
The user interface to MKRMF will also be evaluated to make it easier
for users.
Acknowledgments
We are grateful for many fruitful discussions with various CXC
members. This project is supported by the Chandra X-ray Science
Center as part of NASA contract NAS8-39073.
References
He, H. Wise, M., & Ljungberg, M. 1999, in ASP Conf. Ser., Vol. 216, Astronomical Data
Analysis Software and Systems IX, ed. N. Manset, C. Veillet, &
D. Crabtree (San Francisco: ASP), 636
Rots, A. H. 2001, this volume, 479
Footnotes
- ... CIAO1
- http://asc.harvard.edu/ciao/
© Copyright 2001 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
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