HETG Calibration Status (SWG 4/28/97)

This page is http://space.mit.edu/HETG/swg497.html

Return to http://space.mit.edu/HETG/xrcf.html

Predictions pre-XRCF

Effective Area

Each of the gratings on the flight HETG has been X-ray tested in the MIT X-ray Grating Evaluation Facility, X-GEF. These sub-assembly data are used to generate the predicted Effective Efficiency and, along with HRMA predictions, the predicted HRMA-MEG and HRMA-HEG Effective Areas.

Resolving Power, LSF

The Resolving Power of the HETGS is the result of several major terms, detailed in a Resolving Power Error Budget.

At the subassembly level the period and period variations of each facet are measured by a Laser Reflection setup. These period variations, "dp/p", are the main HETG contribution to the LSF in the dispersion direction. Regarding the cross-dispersion blur, the polarization-alignment of the facets to the HETG support structure is the main fabrication contributor.

Summary of XRCF HETG Measurements

Types and Phases of Measurements

The measurements broadly divide into LSF related and Effective Area related. Depending on the calibration phase, focal plane detector, different types of measurements were carried out.

Measurement Examples

These examples give a feel for the range of data taken at XRCF.

Table of HETG XRCF Measurement Purpose by Type & Detector

Meas.Type:-- ---
Focus Check-verify focusverify focus verify focus-
dFocus--find focus--
Alignment-gross vignetting, mis-aligned gratings ---
PSF/Inner--core, wings; offaxis images -core, wings; offaxis images
PSF/1DLSF core, wings----
PSF/Outer-wings, scatter---
Scattering--wings, scatter--
dFocus-defocus images- --
3D: Offaxis -offaxis images-- -
--- ---
EEOrder locations, Effective area----
3D: EAEffective area, high ordersSource spectra ---
EAEffective area-Effective area Effective areaEffective area
3D: Molec. Contam.-edges, etc. ---
Molec. Contam.--edges, etc. -edges, etc.
dF: Molec. Contam.--edges, etc.--

Measurement Results

Scalar Parameters

Some key "scalar" calibration values deduced/confirmed from XRCF measurements are tabulated below. The measured periods are based on a Rowland distance of 8782.8 mm, Al-K line E = 1.4867 keV, and an assumed accuracy of the HXDS prime Y stage encoders.

Descriptionvalueerrorunits sub-assembly expectation
MEG period4000.77~ 0.10 ALR/NIST gives: 4001.13 +/- 2.00
HEG period2000.95~ 0.10 ALR/NIST gives: 2000.81 +/- 0.05
MEG Angle4.740.05 deg.sCEI spec 5.0 +/- 0.5
HEG Angle-5.190.05 deg.sCEI spec 5.0 +/- 0.5
MEG-HEG Angle9.930.01 deg.sCEI spec 10.0 +/- 0.7
LEG period9903.90~ 0.30 Aexpect 9912.5
LEG Angle0.0060.05 deg.sCEI spec 0.0 +/- 0.5

Source Spectra

The gratings at XRCF are able to give detailed spectra of the XRCF sources. This information is particularly needed for Grating Effective Area measurements to know what fraction of BND or focal plane detected counts are in the desired line.

Effective Area

Data analysis is still in process for effective area / efficiency measurements.

Resolving Power, LSF

There is much data to analyze, however some conclusions are possible at this time.