• Introduction and Summary
• Post-XRCF Flat Fields
• XRCF Data Sets
• QE Depression vs Time

• Summary and Data files

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.

• 0.1 - 10 keV Plots .gif , .ps , Looking at the bottom panel, MCP QE, the two curves differ most in the low-energy behavior...
• 0.05 - 0.60 keV Plots .gif , .ps , Coarse approximations to the C-K and O-K edge structure are included in the 'N1999 file.

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:

• i) The measured HSI source spectra will be inaccurate especially if one line (e.g., the main one) lands in the depression and other(s) (contamination) lie outside the depressed area.
• ii) HSI-measured PSFs/LRFs will be distorted by the depression.

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.

To-do

• [enough!]

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

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:

• top panel: HSI-Y HSI-Z event scatter plot in the central tile.
• mid panel: HSI-Y projection of all events between the dashed lines of the top panel.
• bot panel: PHA distributions of events. The colored solid histogram is from events in the rectangle of the top panel - including most QE depressed events. The white +'s are from events (in the tile) outside of the rectangle - generally un-depressed events.

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.

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.

• CODE: hsi_snooper.pro
• PLOT: Cummulative counts in the regions
• DATA: rdb file of counts vs run id, also includes modeled QE deporession value in last column.

• CODE: hsi_snoop_anal.pro
• PLOT: QED vs Counts modeling plots
• CODE: hsi_qe_depress.pro

HSI QE: Azimuthal Varaitions
Revised 9/27/00	The HSI QE varies as a function of mirror shell, phi, and energy.

Variation at C-K (0.277 keV):

• hsi_qecorr_0.28mp1.rdb
• hsi_qecorr_0.28mp3.rdb
• hsi_qecorr_0.28mp4.rdb
• hsi_qecorr_0.28mp6.rdb

Variation at Al-K (1.49 keV):

• hsi_qecorr_1.49mp1.rdb
• hsi_qecorr_1.49mp3.rdb
• hsi_qecorr_1.49mp4.rdb
• hsi_qecorr_1.49mp6.rdb

This web page is: http://space.mit.edu/HETG/hsi.hsi.html
Please send any comments and updates: send e-mail to dd@space.mit.edu.