XRCF HRMA On-axis Effective Area
XRCF HRMA On-axis Effective Area
Ping Zhao
Smithsonian Astrophysical Observatory
zhao@cfa.harvard.edu, 617-496-7582
August 9, 2000
NASA's Chandra X-ray Observatory (CXO) was successfully launched on
July 23, 1999 by the space shuttle Columbia. It has returned fruitful
scientific results in the past year. CXO has unprecedented
capabilities of high resolution imaging and spectroscopy over the
X-ray energy band of 0.1 keV - 10 keV. The effective area of its
X-ray mirror - High-Resolution Mirror Assembly (HRMA) - was measured
using the X-Ray Calibration Facility (XRCF) at the Marshall Space
Flight Center (MSFC) in Huntsville, AL from late 1996 to early 1997.
Immediately after the XRCF HRMA calibration, it was found that there
were substantial discrepancies between the experimental results and
the predicted effective area based on the raytrace simulations
according to the HRMA model at that time. The calibration data show
that, for energies higher than 2 keV, the measured effective area was
less than the predicted effective area by 10%, which is beyond the
experimental errors.
During the period from late 1998 to early 1999, improvements were made
in the SAOSAC raytrace model and the discrepancies were reduced to
about 5%.
In early 2000, more improvements were made in the optical constant
used to calculate the mirror reflectivity. This has made the measured
effective area agree reasonably well with the raytrace simulation for
shells 3, 4 and 6. Although there is still a large discrepancy for
shell 1. However, the agreement is very good for the assembly - HRMA.
Using the XRCF measurements to calibrate the raytrace simulations,
here are the predictions of the HRMA on-axis effective area for both
at XRCF and
on-orbit.
The SAOSAC raytrace simulations were generated from the HRMA model
which is based on measurements of HDOS metrology, Kodak assembly and
the XRCF X-ray test. Its trace-shell configuration file can be found
here.
The key raytrace configurations are:
- Optical Constant:
- E < 0.940 keV: Gullikson '95 optical constant table.
- E > 0.940 keV: AXAF mirror witness GO flat 065 reflectivity data
measured at the BNL synchrotron by Dale Graessle et al.
- Reflectivity:
- Fresnel equation of multilayer reflection with Iridium (328 A),
Chromium (97 A), and semi-infinite Zerodur.
- Interface reflection reduction with the Nevot-Croce factor.
- Mirror Surface Roughness Scattering:
- Based on PSD produced from the HDOS metrology measurements and
calculated by Leon Van Speybroeck's program "foldw1", which is based
on the scattering theory by Beckmann and Spizzichino.
- Scattering table was generated on 6/23/98.
- Mirror rigid body specs.
- Mirror surface deformations (including gravity).
- Mirror cap, pre- and post-collimators, p6 ghost baffle.
- XRCF source distance.
There are three kinds of XRCF calibration measurement of the HRMA
on-axis effective area:
X-ray spectral line measurements with the Flow Proportional Counter (FPC).
X-ray spectral line measurements with the Solid State Detector (SSD).
X-ray carbon continuum measurements with the Solid State Detector
(SSD).
Here are the comparisons of the XRCF HRMA on-axis effective area
between the measurements and the raytrace simulations with a 2mm
diameter aperture, which was the largest aperture used with the SSD
measurements:
The top panels show the raytrace simulations (generated by Diab
Jerius), spectral line FPC and SSD data (analyzed by Richard Edgar)
and C-continuum SSD data (analyzed by Ping Zhao). The bottom panels
show the ratio of measurement/simulation. A polynomial was fit to
each of the ratio curve.
The XRCF HRMA On-axis Effective Area, as well as the
On-orbit HRMA On-axis Effective Area, were generated by
multiplying the raytrace simulations with the XRCF calibration data
scaling factors.
The XRCF calibration data scaling factors are:
- E < 2 keV: the average ratio between the raytrace and FPC rerun
data analyzed by Dick Edgar.
Errors include: FPC data errors; standard deviation of the FPC data;
beam nonuniformity errors; aperture size errors; raytrace statistical
error (this is very small).
- E > 2 keV: a fourth order polynomial fit of the ratio between
the raytrace and the SSD C-K continuum data analyzed by Ping Zhao.
(The SSD data analysis has included pileup, pulser deadtime, relative
QE and beam uniformity corrections.)
Errors include: standard deviation of SSD continuum data within each
energy bin; errors from the polynomial fit; beam nonuniformity errors;
aperture size errors; raytrace statistical error (this is very small).
Here are the results of XRCF HRMA On-axis Effective Area:
- XRCF HRMA on-axis effective area within 2 mm diameter aperture:
rdb table and
figure.
- XRCF HRMA on-axis effective area within 35 mm diameter aperture:
rdb table and
figure.
- XRCF HRMA on-axis effective area within 2 pi steradian:
rdb table and
figure.
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