HSI Analyses

HSI Analyses

http://space.mit.edu/HETG/hsi/hsi.html go to HETG Calibration


  • HSI QE

  • HSI QE Depression

  • HSI QE ( Energy, shell, phi )

    HSI QE
    Revised 6/2/99 The 'N19990530 HSI QE curve has updated QE values and
    improved agreement with the HSI UVIS edge structure.

    The current best estimate of the "normal incidence" QE of the HSI detector as a function of energy is given by the CALDB file $CALDBaxafcal/xrcf/cip/hsi_qe_N19990530.rdb. This represents an update from the 'N19961106 preliminary values based on Nov.97 XRCF flat-field data and post-XRCF SAO lab flat-field data, combined with Brad Wargelin's assessment. Finally, the QE at Carbon was adjusted down somewhat because of the low QE implied by HSI-FPC grating dispersed-order analysis ( .gif, .ps, created by heae_do_it_all.pro ). The edge structure indicated in the HSI UV-ion shield transmission, hsi_uvis_N19980529.rdb, has been incorporated at a coarse level.

    Plots of the 'N1996 QE and 'N1999 QE values are given below. The plots also show the HSI's QE divided by the UVIS transmission to give the underlying MCP QE. These are somewhat different for the 'N1996 and 'N1999 QE files.

    These plots were made by hsi_brad_qe.pro

    HSI QE Depression

    HSI flat-field data:
    central tile w/ color-coded PHA
    Revised 5/22/99 The HSI "QE Depression" near the center of the HSI
    is seen here as an artificial "dip" in the broad B-K line.

    Introduction and Summary

    Ever-diligent Chandra Project Scientist Martin Weisskopf has called attention to Figures 7.7 and 7.8 of the October '98 MST Calibration Report. These figures show a "QE depression" near the center of the central HSI tile. Quantitatively the QE in the depression's center is ~ 0.7 times the nominal QE; this value was measured in the lab after XRCF using an ensemble of flat field tests. It is expected that the actual QE depression factor varied from 1.0 at the beginning of XRCF to the ~0.7 value at end of Phase 1.

    The cause of the depressed QE is thought to be due to local gain depression - this is seen clearly in the post-XRCF data and not so well in the XRCF data (due to its vagaries no doubt.)

    This QE depression will has two effects on HETG data analysis:

    The HSI behavior in this depressed region was studied using the post-XRCF flat field exposures and the XRCF data sets. A few clear measurements of the depressed value were combined with HSI cummulative counts in depressed region to create an estimate of the depression for each run id.

    The effects of the depression can be mitagated by software that uses a statistical technique to create proxies for the events which may have been lost due to the depression. The depression is modeled by a 2D Gaussian QE depression characterized by location, sigma, and the QE depression factor which varies through Phase 1. These QE depression values are provided by a function which returns the value based on a simple runid lookup, (hsi_qe_depress.pro) . The statistical correction is applied when the HSI raw data are read in by the procedure xrcf_hsi_read.pro. By using this interface to the data the correction is then routinely included in HSI data analysis, e.g., the source spectral analysis.


    Post-XRCF Flat Fields

    Nine flat-field exposures of the HSI taken post-XRCF were taken and provided by Ian Evans. These were processed with hsi_flats.pro and output .gif files are available. Note that plots with "_ZY_" in the name have had the HSI Y and Z axes interchanged and thus the "Y-axis Projection" is really a Z axis projection...

    These data show that the central tile QE depression is roughly energy independent (at the 20%-of-effect level), the depression is centered at {Y,Z} = {2046.7,2045.5}, it has an end of life depression value of order 0.685, the depression is well fit with a Gaussian(r) with sigma of 17.5 pixels. There is evidence for some non-symmetry in the depression (e.g., sigma-Y is ~18.6, sigma-Z ~16.4) but the statistical correction technique will probably not need to model this...

    XRCF Data Sets

    In the XRCF data, there is clear evidence for the depression in the analysis of the B-K line dispersed image, giving a QE depression value of 0.83, centered at {Y_HSI, Z_HSI} = {2043.0 (+/-1.0), 2045.5} (the Z value is from post-XRCF data) and with a 2D Gaussian shape with a sigma of 13.4 HSI pixels (+/-0.7). Other XRCF data sets also hint at the depression's existence and its evolution; see comments in the Table below.

    A simple selection on the DRAFT-as-rum CMDB for tests which use the HSI at the CA5 aim point and which are in-focus yields a list of 163 measurements. Again using the DRAFT-as-run CMDB it is possible to construct the requested HSI CA5 exposure vs time, as plotted here. Of course these plots are for guidance only.

    To examine specific HSI exposures, the procedure hsi_tile_plots.pro was used, as on the flat-field data, to make plots from the events in the central tile of an HSI image, available in the Table below. The output .gif file shows three panels:

    These plots were made using "raw" HSI data uncorrected for the QE depression and also "corrected" versions where extra events were added based on the local QE depression value; QE depression correction effects are summarized in the X-axis label of the top panel.

    XRCF Data Sets: Plots from the HSI central tile

    line #
    TRW IDHSI filehsi_tile_plots: Comments
    10 C-IXH-SF-2.001:
    follow up image in focus
    not listed in trm.rdb!
    QE depress ~ 1.00
    Y,Z peak = 2044.5, 2046.5
    Al-K, Alx4 filter
    First image in-focus at
    depressed location !
    20 C-IXH-HF-7.001:
    bright image in focus
    961220/hsi106738i0.fits raw
    QE depress ~ 1.00
    Y,Z peak = 2045.0, 2036.0
    Al-K, Alx4 filter
    Z center is low?!?
    313 D-IXH-PI-3.002 970104/hsi107545i0.fits raw , corrected
    QE depress ~ 0.988
    Y,Z peak = 2046.0, 2047.5
    Al-K, Alx4 filter
    This test gives -1.2%
    +/- 1.7% the QE from
    earlier measurement,
    so QED ~ 0.988
    536 D-LXH-3D-11.047 970113/hsi108577i0.fits raw , corrected C-K, dispersed
    537 D-HXH-3D-11.048 970113/hsi108578i0.fits raw , corrected
    QE depress used: 0.95
    compatible with:
    QE depress = 0.8 ?
    C-K, dispersed
    QE depress value
    of 0.8 possible?
    586 D-HXH-dF-16.002 970116/hsi109002i2.fits raw , corrected Mg-K, dispersed
    587 D-HXH-dF-16.003 970116/hsi109003i2.fits raw , corrected Mg-K, dispersed
    694 D-HXH-3D-11.038 970119/hsi109313i0.fits raw , corrected Si-K, dispersed
    748 D-LXH-dF-7.002 970120/hsi109635i0.fits raw , corrected Penning, Bex2
    891 D-LXH-3D-12.004 970125/hsi110192i0.fits raw , corrected Be-K, dispersed
    simliar to B-K
    897 D-LXH-3D-22.045 970126/hsi110212i0.fits raw , corrected
    QE depress = 0.83
    B-K, dispersed
    927 E-IXH-PI-13.001 970128/hsi110299i0.fits raw , corrected
    Y,Z peak = 2056.5, 2052.0
    C-K, filtered
    987 E-IXH-SF-13.001 970129/hsi110391i0.fits raw , corrected C-K, filtered
    1208 E-LXH-EA-36.001 970207/hsi111402i0.fits raw , corrected HIREFS, 0.2 keV
    QE_DEPRESS ~ 0.7
    clear dip
    1279 E-HXH-FC-28.005 970208/hsi111492i0.fits raw , corrected Al-K, dispersed

    QE Depression
    vs Time
    Revised 5/22/99 The (few) measured values of the HSI QE depression
    are well fit with a quadratic function of the
    cummulative counts in the depressed region.
    A procedure was written to go through all the recorded HSI exposures and record the number of counts in three regions: the full image, the central tile, and in the depressed region, for specifics see the following: Using the few measured QE depression points available, the QE depression was plotted vs cummulative counts in the depressed region and, with admitadly scanty data, appears to follow a quadratic variation, as shown in the plot above. Using this QED-of-cummulative-counts relation, a QED value was assigned to each of the HSI exposures, the last column in the rdb table above. To simplify the lookup of QED value from run_id, the routine hsi_qe_depress.pro uses a simple pruned version of the full data file - and returns QED vaules of reasonable accuracy (1%).
    HSI QE: Azimuthal Varaitions
    Revised 9/27/00 The HSI QE varies as a function of
    mirror shell, phi, and energy.
    Data files with smoothed relative QE vs angle are available for two energies (taken from ring focus tests hsi108944 and hsi106856, analyzed with hsi_az_play.pro and hsi_qe_corr.pro).

    Variation at C-K (0.277 keV):

    Variation at Al-K (1.49 keV):

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