HETG Calibration Status (SWG 4/28/97)

• Predictions pre-XRCF
  • Effective Area
  • Resolving Power, LSF
• Summary of XRCF HETG Measurements
  • Types and Phases of Measurements
  • Examples
• Measurement Results
  • Scalar Parameters
  • Source Spectra
  • Effective Area
  • Resolving Power, LSF

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.

• Predicted Effective Efficiency, 1st order
• Comparison to simple rectangular grating model
• Predicted Effective Efficiency, 0th order
• Predicted Effective Area, 1st order
• Predicted Effective Area, 0th order
• Details and data: http://space.mit.edu/HETG/xrcf_cal/xrcf_calibration.html#HETGsub

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.

• Flight grating measured period variations
  • HEG period variation plot
  • MEG period variation plot
• Flight facets alignment distribution
• Conservative (for CEI spec) Resolving Power predictions
  • HEG : plot and data.
  • MEG : plot and data.

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.

• Table of Measurement Purpose by Type and Detector

Measurement Examples

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

• LSF
  • Mg-K/HEG/HSI : 2nd order spectral histogram, E/dE ~1100 is achieved
  • DCM/HETG/'2C Scattering Image (MEG and HEG first orders). The similarity of the pulse-height distributions in the "field" region and the scattered region shows that the scattered events are truly scattered.
  
  
• Effective Area / Efficiency
  • HXDS PHA data from Al-K/MEG/FPC_X2 effective area measurement. Note that focal plane detector FPC_X2 (upper left) does not see continuum due to spectrometer operation.
  • Automated FPC EA results with ROI fitting; need to deal with systematics and validate data
  • Al-K/HETG/2C effective area / efficiency measurement image and pha distribution
  • DCM/HETG/HRC-I measurements: 1st to 0 order ratio (.ps), (.gif)

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.

Description	value	error	units	sub-assembly expectation
MEG period	4000.77	~ 0.10	A	LR/NIST gives: 4001.13 +/- 2.00
HEG period	2000.95	~ 0.10	A	LR/NIST gives: 2000.81 +/- 0.05
MEG Angle	4.74	0.05	deg.s	CEI spec 5.0 +/- 0.5
HEG Angle	-5.19	0.05	deg.s	CEI spec 5.0 +/- 0.5
MEG-HEG Angle	9.93	0.01	deg.s	CEI spec 10.0 +/- 0.7
LEG period	9903.90	~ 0.30	A	expect 9912.5
LEG Angle	0.006	0.05	deg.s	CEI 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.

• Fe-La,Fex2 LETG HSI image and spectrum
• Source details are available at http://space.mit.edu/HETG/xrcf_sources/sources.html

Effective Area

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

• Sub-assembly effective efficiency combined with XRCF-measured HRMA effective areas is best calibration now.

Resolving Power, LSF

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

• The grating dp/p values are confirmed to be < 400 ppm rms (E/dE > 1000 achieved), further analysis should lower this limit
• New: HEG grating shows low level (~0.5 % of line total) scattering over large energy range (>0.1E).
• New: Outlying spots on MEG quadrant images are the result of a handful of "mis-aligned" gratings. This leads to "shoulders" on the cross-dispersion line profile. More detective details at http://space.mit.edu/HETG/misalign_image.html .
• New: At a lower level the mis-alignment mechanism may result in an alignment blur value larger than the 0.42 arc minute rms expected from sub-assembly - perhaps ~ 1 arc minte rms.