Version "N0003"
HETG (and LETG) efficiency products
have been produced based on subassembly measurements, improved optical constant
values, and corrections to the effective subassembly reference
gratings efficiencies. The general steps are described in
Subassembly Efficiency Analysis
; and some specifics are highlighted here.
Based on
XRCF measurements made in Phase 1
(non-flight detectors) and Phase 2 (with ACIS-S), see below,
we have confidence that the tabulated first and zeroth order
efficiencies are accurate at the 10% level in an absolute sense.
The
relative effective area tests
(a.k.a. "continuum" or "molecular contamination" tests) confirm
the detailed structure in the HETGS effective area at the
few percent(TBR) level.
Note that MARX version 2.22 uses 'N0002 versions of both HETG
and LETG gratings. See the n0003_effic_corr.pro procedure
below for changes from 'N0002 to 'N0003 for HETG; for
LETG the first order efficiency changes were less than 4% over
the energy range.
There are two changes which have lead to the 'N0003
efficiencies: i) the effective efficiency of the reference
gratings in the HETG X-GEF setup have been revised and ii) new
optical constants for gold, optical-constants.990510.tbl,
have been produced.
For the LETG, new efficiencies were directly calculated
with the new optical constants.
- LETG N0003/N0002 first-order ratio in gold M region:
.gif ,
.ps
For the HETG, it is not possible to simply recalculate the
efficiencies with new optical constants because the bar-shape models
fitting the X-GEF data are based on the 96116 optical constants.
A proper recalculation requires that the X-GEF measured efficiencies
be fit with the 990510 optical constants to generate the grating
model parameters; this will take some time to carry out.
However, the effects and validity of these two changes on HETG efficiency
values have been assessed by reprocessing some X-GEF measurements
with the new values. The general changes seen in the 1st and 0th
order efficiencies were encoded in an IDL routine,
n0003_effic_corr.pro,
and applied as corrections to the N0002 "membrane" efficiencies.
The HETG N0003 efficiencies thus have the same edge structures
as the N0002.
Error values were created as part of the 'N0003 products
by the procedures
cip_weights_and_errors.pro and, for LETG,
letg_cip_etc.pro. For the HETG the errors are:
- Zero-order: 10% error, all energies.
- First-order: 10% error, all energies.
- Second-order: 20% error, all energies.
- Third-order: 30% error, all energies.
- higher-order: 90% error, all energies (basically unmeasured and
untested.)
In addition, "pruned" efficiency
files were created by the procedures
cip_hetg_prune.pro and, for LETG,
cip_letg_prune.pro; the actual pruning is
accomplished with the pruning routines
interp_pruned_x.pro and
interp_prune_err.pro.
See also the terse record in the
hetg/docs/cip_config.txt and
letg/docs/cip_config.txt files.
