Background Rates of the HRC

HRC-I Quantum Efficiencey Verification

Cross-Cal HRC-I with ACIS-S3 using SN Remnant G21.5-0.9

K. Tabetha Hole, Deron Pease, Hank Donnelly

For this study we employed the supernova remnant G21.5-0.9 to perform cross-calibration of HRC-I (ObsID 1242) with ACIS-S3 (ObsIDs 159,1230), for energies greater than 1.0 keV.

Predicted Counts

Norbert Schulz provided a power-law source model which he derived from the ACIS-S3 observations (see model below). Using the current state of the HRC-I QE model (version 1.1), Dick Edgar built/formatted the HRC response function with which we were able to generate predicted HRC-I counts using the "fakeit" command in XSPEC (version 10).

The predicted counts with total model uncertainties are: 7799 ± 11.3%

Observed Counts

The HRC-I observed counts were extracted from a box around the source [tdetx(7332:8041),tdety(7311:7967); 1 HRC-I pixel = 6.429um], corresponding to the size of Norbert's ACIS box [tdetx(4080:4270),tdety(2136:2312); 1 ACIS-S pixel = 24.0um]. A very large HRC-I background region was defined as the active detector minus the source region.

The background-subtracted observed counts are: 7928 ± 1.3%

Comparison with Error Analysis

The source model derived from ACIS-S3 has an uncertainty of 5.3%. The HRC-I QE over this range has an additional uncertainty of ~10%. Thus, the total model uncertainty resulting from convolving the source model with the model of the HRC-I response becomes ~11.3%.

So even though HRC-I actually sees 1.6% more (absolute difference) than predicted by our model, the observed matches the predicted within the 11.3% total model uncertainty.

1) NORBERT's MODEL for G21.5-0.9  derived from ACIS-S3

  mo = wabs[1]( powerlaw[2] )
  Model Fit Model Component  Parameter  Unit     Value
  par   par comp
    1    1    1   wabs       nH       10^22      2.119     +/-  0.3929E-01
    2    2    2   powerlaw   PhoIndex            1.919     +/-  0.3259E-01
    3    3    2   powerlaw   norm               1.7820E-02 +/-  0.8404E-03

source model uncertainity of 5.3%

Contact CXC Calibration (cxccal@cfa.harvard.edu) for further information

Last modified: 09/25/12

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