Background Rates of the HRC

HRC-I Quantum Efficiency Verification

Cross-Cal HRC-I with ACIS-S3 using SN Remnant Cas A

K. Tabetha Hole, Deron Pease, Hank Donnelly

For this study we employed the supernova remnant Cas A to perform cross-calibration of HRC-I (ObsID 171) with ACIS-S3 (ObsID 214), over the energy range of 0.7 - 2.5 keV.

Predicted Counts

Dick Edgar provided a line flux source model which we fit to the ACIS-S3 observations (see model below). Using the current state of the HRC-I QE model (version 1.1), Dick 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: 754561 ± 16.0%

Observed Counts

The HRC-I observed counts were extracted from a circle around the source [in sky coords: cir(xcen,ycen,r)=cir(940,950,230); 1 HRC-I pixel = 6.429um], corresponding to the size of the ACIS circle [in tdet coords: cir(4380,4045,450); 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: 810925 ± 0.1%

Comparison with Error Analysis

The source model derived from ACIS-S3 has an uncertainty of ~5%. The HRC-I QE over this range has an additional uncertainty of ~10-15%. Thus, the total model uncertainty resulting from convolving the source model with the model of the HRC-I response becomes ~16.0%.

So even though HRC-I actually sees 7.0% more (absolute difference) than predicted by our model, the observed matches the predicted within the 16.0% total model uncertainty.

1) MODEL for Cas A  derived from ACIS-S3 (casa.xcm)


  mo = ( gaussian[1] + ( gaussian[2] + gaussian[3] + gaussian[4] + gaussian[5] 
        + gaussian[6] + gaussian[7] + gaussian[8] + gaussian[9] + gaussian[10] 
        + gaussian[11] + gaussian[12] + gaussian[13] + gaussian[14] 
        + gaussian[15] + gaussian[16] + gaussian[17] + gaussian[18] 
        + gaussian[19] + powerlaw[20] )wabs[21] ) + powerlaw/b[22]
  Model Fit Model Component  Parameter  Unit     Value
  par   par comp
    1    1    1   gaussian   LineE    keV       0.3323     frozen
    2    2    1   gaussian   Sigma    keV       2.8582E-02 frozen
    3    3    1   gaussian   norm               6.1720E-03 +/-  0.1572E-03
    4    4    2   gaussian   LineE    keV        1.060     frozen
    5    5    2   gaussian   Sigma    keV           0.     frozen
    6    6    2   gaussian   norm               8.5412E-02 +/-  0.1580E-02
    7    7    3   gaussian   LineE    keV       0.9457     +/-  0.2475E-02
    8    8    3   gaussian   Sigma    keV           0.     frozen
    9    9    3   gaussian   norm               6.3098E-02 +/-  0.2119E-02
   10   10    4   gaussian   LineE    keV        1.129     frozen
   11   11    4   gaussian   Sigma    keV           0.     frozen
   12   12    4   gaussian   norm               1.3506E-02 +/-  0.9180E-03
   13   13    5   gaussian   LineE    keV        1.385     frozen
   14   14    5   gaussian   Sigma    keV           0.     frozen
   15   15    5   gaussian   norm               2.3193E-02 +/-  0.4451E-03
   16   16    6   gaussian   LineE    keV        1.515     frozen
   17   17    6   gaussian   Sigma    keV           0.     frozen
   18   18    6   gaussian   norm               7.0877E-03 +/-  0.3877E-03
   19   19    7   gaussian   LineE    keV        1.893     frozen
   20   20    7   gaussian   Sigma    keV           0.     frozen
   21   21    7   gaussian   norm               0.1170     +/-  0.4270E-03
   22   22    8   gaussian   LineE    keV        2.047     frozen
   23   23    8   gaussian   Sigma    keV           0.     frozen
   24   24    8   gaussian   norm               2.1968E-02 +/-  0.2537E-03
   25   25    9   gaussian   LineE    keV        2.370     frozen
   26   26    9   gaussian   Sigma    keV           0.     frozen
   27   27    9   gaussian   norm               8.9934E-03 +/-  0.2790E-03
   28   28   10   gaussian   LineE    keV        2.218     +/-  0.2619E-02
   29   29   10   gaussian   Sigma    keV           0.     frozen
   30   30   10   gaussian   norm               9.9173E-03 +/-  0.2589E-03
   31   31   11   gaussian   LineE    keV        2.487     frozen
   32   32   11   gaussian   Sigma    keV           0.     frozen
   33   33   11   gaussian   norm               4.3544E-02 +/-  0.3162E-03
   34   34   12   gaussian   LineE    keV        2.618     frozen
   35   35   12   gaussian   Sigma    keV           0.     frozen
   36   36   12   gaussian   norm               6.8336E-03 +/-  0.2343E-03
   37   37   13   gaussian   LineE    keV        2.954     frozen
   38   38   13   gaussian   Sigma    keV           0.     frozen
   39   39   13   gaussian   norm               3.5371E-03 +/-  0.2055E-03
   40   40   14   gaussian   LineE    keV        3.164     frozen
   41   41   14   gaussian   Sigma    keV           0.     frozen
   42   42   14   gaussian   norm               6.9491E-03 +/-  0.1668E-03
   43   43   15   gaussian   LineE    keV        3.925     frozen
   44   44   15   gaussian   Sigma    keV           0.     frozen
   45   45   15   gaussian   norm               1.8196E-03 +/-  0.1489E-03
   46   46   16   gaussian   LineE    keV        6.658     frozen
   47   47   16   gaussian   Sigma    keV           0.     frozen
   48   48   16   gaussian   norm               2.7364E-03 +/-  0.1772E-03
   49   49   17   gaussian   LineE    keV        6.839     frozen
   50   50   17   gaussian   Sigma    keV           0.     frozen
   51   51   17   gaussian   norm               1.3231E-03 +/-  0.1892E-03
   52   52   18   gaussian   LineE    keV        7.030     +/-  0.2732E-01
   53   53   18   gaussian   Sigma    keV           0.     frozen
   54   54   18   gaussian   norm               3.7170E-04 +/-  0.1686E-03
   55   55   19   gaussian   LineE    keV        7.971     frozen
   56   56   19   gaussian   Sigma    keV           0.     frozen
   57   57   19   gaussian   norm               1.8948E-04 +/-  0.2383E-03
   58   58   20   powerlaw   PhoIndex            2.935     +/-  0.6447E-02
   59   59   20   powerlaw   norm                1.560     +/-  0.1094E-01
   60   60   21   wabs       nH       10^22     0.9214     +/-  0.2898E-02
   61   61   22   powerlaw/b PhoIndex               0.     frozen
   62   62   22   powerlaw/b norm               7.2173E-02 frozen
  ---------------------------------------------------------------------------
  ---------------------------------------------------------------------------
 Chi-Squared =      10842.07     using  2048 PHA bins.
 Reduced chi-squared =      5.359403     for   2023 degrees of freedom
 Null hypothesis probability =    0.


source model uncertainty of ~ 5%

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

Last modified: 09/25/12

Chandra Science | Chandra Home | Astronomy links | iCXC (CXC only) | Search

The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory.
60 Garden Street, Cambridge, MA 02138 USA. Email: cxcweb@head.cfa.harvard.edu
Smithsonian Institution, Copyright © 1998-2004. All rights reserved.