The widths enclosing different fractions of counts, as
determined from MARX simulations of HRC-S/LETG, for the
+ve (top) and -ve (bottom) orders. The 84% (green), 90% (red),
and 95% (blue) enclosed fractions are shown. Also shown is
an outline (black line) of the bow-tie spectral extraction region.
As above, but for HRC-S/LETG flight data with coadded
data from Capella (ObsIDs 1420, 1248), HZ 43 (59), Algol (2),
PKS 2155-304 (331, 1013, 1704, 3166). Systematic errors due
to modeling the background dominate; work is in progress to
minimize these errors. The results from the flight data
agree qualitatively with the simulations at all wavelengths
except below 10 Angstrom.
Comparison of measured and reference wavelengths. The
plot shows that there is no single value of the Rowland diameter
that can explain the wavelength registration errors on all three
plates. This has long been suspected to be due to a software bug.
The true wavelengths (from MARX simulations) are compared
with the wavelengths derived after processing the simulated
events with CIAO tools. The deviations as a function of
wavelength (top panels) and dispersion angle (bottom panels)
are shown, with the best-fit measured locations (green line)
and 1-sigma errors (vertical red bars). Plots for the +ve (1st
page) and -ve (2nd page) orders are shown.
NOTE: The bug was identified by J.Davis on Nov 15 and a
fix has been implemented in the CIAO tool tg_resolve_events
(still undergoing testing, but see
preliminary result of the fix).
Comparison of +ve and -ve orders via a moving window
cross-correlation. The figure shows the deviation of the
-ve order w.r.t. the +ve order that results in a best match
(darker shades) as a function of wavelength; the vertical width
of the shaded regions indicate the errors. This is based on
coadded flight data from HRC-S/LETG Capella observations. Note
that the pattern is irregular and deviations much larger than a
line width are seen at long wavelengths.
A moving-window cross-correlation as above, but for two
sets of -ve order spectra extracted from counts falling in
the extreme ends of the dither pattern,
similar irregular deviations.
Lab v/s Flight:
Because it is possible that errors in degapping may
account for much of the observed wavelength deviations, we
compare the results of the HRC-S degapping as derived from
lab data and coadded flight data for various taps:
We compare the change in the locations of detected source
photons as determined by fits to lab data (blue curves in top-left
[all counts], top-right [H-filtered and status-bit filtered], and
bottom-left [status-bit filtered, PI-filtered to remove PI=255,
and fineU=0 and fineV=0 removed] plots) and an exact solution
as derived for this particular set of source photons (black and
green curves); these position changes are plotted as a function
of the final fine position as determined by lab data. The green
curve forces the origin to be at a fine position of 0, while the
black curve does not. The expectation is that the blue curves
should be good fits to the green curves. As can be seen from
the plots, this is not generally true.
The plot on the lower right shows the histogram of counts,
with the uncorrected (black), lab-corrected (blue), and exact
Particles v/s Photons: Photons and particle background
shows different degapping characteristics, as can be seen by
comparing similar plots as above, but excluding source photons:
The plots are similar to those shown for source photons,
except that (i) the x-axis is for the fine position as determined
by the exact solution, (ii) different filterings are applied (see
labels at top of each figure), and (iii) the histograms in the
lower-right plot are color-coded differently (red for all events,
progressing to purple for all filters applied).