Energy Scale and Spectral  CCD Performance  De-coupling Detection Efficiency and

Overview of Detector Calibration Measurements

As has been indicated in the introduction to this report, the calibration of the ACIS instrument has been performed at several levels. Figure  4.4 provides summary of the various calibration stages.   

Figure 4.4: ACIS ground calibration flow. 

  

In nearly every stage of this process, data were obtained that constrain the response of the CCDs themselves. Moreover, a number of ancillary measurements, not shown in figure  4.4, were made to address particular calibration issues. These include measurement of X-ray Absorption Fine Structure near the relevant edges in the detector response, measurement of structure within a single CCD pixel, and measurement of pileup effects for a variety of source spectral and spatial distributions. At this writing, not all of these data have been analyzed.

Here we summarize the objectives and some salient characteristics of each type of measurement that bears directly on CCD performance calibration. It is intended that this summary serve as a guide to the analysis presented in the remainder of this chapter, as well as an indication of what additional data remain to be analyzed.

Specifically, spectral response function measurements are discussed in section  4.3, and pileup effects and sub-pixel structure are considered in sections  4.4 and  4.5, respectively. Absolute quantum efficiency measurements are described in section  4.6, while comparision of the flight detectors to absolutely calibrated standards is discussed in section  4.7.

It should be noted that the confidence we may ultimately place in the ACIS calibration will depend critically on the extent to which the elements of this large, overlapping measurement set can be compared, one to another. The power of this intercomparison is illustrated, for example, in section  4.7.3, which compares relative detection efficiency measurements made at MIT subassembly calibration with those made using the integrated instrument at XRCF. It is clear at present, that much work remains to be done if we are to achieve a calibration that is as accurate as this vast data set allows.

ACIS Detector Response Function Measurements are summarized by objective in Table  4.3.
 
 

 

$$^{\dagger}$$ Measurement Objective Site Spatial Distribution Energies (keV) Flight Devices? Analysis Status Remarks

Spectral Response MIT Mon. QM. Diffuse 0.2-1.5(cont) yes TBD HIREFS,IFM

Diffuse 0.5 - 9.9 (15 energies) yes Done

PTB/BESSY Mono. Diffuse 0.2-1.5 no Done SX-700 grating mon.

 Mono.  Diffuse  1.5-6  no  Done KMC 2-crys. mono.

XRCF(I) Mon.,QM. Diffuse 0.3 - 8.1 (7 energies) yes In prog.  4.3

Detection Efficiency (Primary Std.) PTB/BESSY Continuum Diffuse 0.2 -4 no Done sec.  4.6.1

Undisp. S. R. 0.2-12 no Done WLS; 4.6.1

Mono. Diffuse 0.2-1.5 no Done SX-700; FI and BI

$$2 \times 10^{6}$$ Detection Efficiency (Secondary. Std.) MIT QM Diffuse 0.2-8.0 (8 energies) yes Done

XRCF(F,G) QM,Mon. HRMA 0.3 - 10 no In Prog. ACIS 2C

XRCF(H) QM,Mon. HRMA 0.3 - 8 yes In Prog. Flight Instr.

XRCF(I) QM,Mon. Diffuse 0.3 - 8.0 yes In Prog. Flight Instr. sec.  4.7.3

XAFS ALS,UW/SRC
PTB/BESSY Mon. Diffuse N-K,O-K,Si-L,K no Done Thin Films
sec.  4.6.3

$$4\mu$$ Sub-pixel Structure/Spatial Lin. MIT QM 0.5 -2 no In Prog. sec.  4.5

XRCF(F) QM,Mon. HRMA 0.3 - 8 no In Prog. ACIS 2C

XRCF(H) QM,Mon. HRMA 0.3 - 8 yes In Prog. Flight Instr.

Pileup/Count Rate  Linearity MIT QM Diffuse 0.2-8.0 no In Prog. sec.  4.4

PTB/BY Cont. S.R. Diffuse 0.2 -4 no In Prog. sec.  4.4

XRCF(F,G) QM,Mon. HRMA 0.3 - 10 no In Prog. ACIS 2C

XRCF(H) QM,Mon. HRMA 0.3 - 8 yes In Prog. Flight Instr.

8l$\dagger$:
8l Mon.: monochromatic;$\frac{E}{\Delta E} \gt 100$;.
8l QM: quasi-monochromatic (electron-impact or photon-fluor.;
8l S.R: Synchrotron Radiation

   
 Energy Scale and Spectral  CCD Performance  De-coupling Detection Efficiency and

11/20/1997