In-Flight ACIS Charge Transfer Inefficiency and Gain Corrections

Valid for -110 C data
Last updated December 14, 1999
Previous releases:
Ftools script (by L. Van Speybroeck) and coefficients for correcting CTI and converting PHA to PI
(16896 byte tar file)
Plots of peak centroids vs row number for corrected data:

I0 I1
I2 I3
S0 S1 S2 S3 S4 S5
CTI correction for centroids of peaks: [Explanation]

 cti = a1 + (b1*pha0) + (c1*(pha0^2.))

 eps = a2 + (b2*pha0) + (c2*(pha0^2.))

 pha = (1. + (cti*rows) + (eps*(rows^2)) ) * pha0
Energy scale correction for spectrum: 
 E = (x0 + pha) / x

IDL CTI correction routine
ASCII table of coefficients (read in by correction routine)

List of OBSIDs used for determining CTI and gain corrections
ASCII version of this table
Coefficients:
Chip Node a1 b1c1 a2 b2c2 x0 x
0 0 +0.0003445 -2.590e-07 +7.634e-11 -6.540e-08 +4.439e-11 -6.289e-15 +0.0 +260.8
1 +0.0004050 -2.956e-07 +8.288e-11 -7.314e-08 +1.560e-11 +1.509e-14 +0.0 +252.1
2 +0.0004173 -3.396e-07 +1.067e-10 -8.445e-08 +7.563e-11 -1.931e-14 +0.0 +260.4
3 +0.0003482 -2.648e-07 +7.952e-11 -5.068e-08 +2.812e-11 +1.047e-15 -0.9 +253.9
1 0 +0.0003811 -2.949e-07 +8.843e-11 -7.660e-08 +4.998e-11 -4.465e-15 -0.3 +253.5
1 +0.0004209 -3.535e-07 +1.162e-10 -8.864e-08 +7.932e-11 -2.158e-14 +0.5 +248.9
2 +0.0004266 -3.547e-07 +1.134e-10 -9.859e-08 +8.545e-11 -2.037e-14 +0.3 +250.7
3 +0.0003656 -2.762e-07 +8.209e-11 -7.691e-08 +4.253e-11 -2.140e-15 +0.1 +253.9
2 0 +0.0004356 -3.241e-07 +9.324e-11 -7.329e-08 +3.768e-11 +2.553e-15 +1.7 +260.3
1 +0.0005178 -4.182e-07 +1.260e-10 -1.237e-07 +1.126e-10 -2.554e-14 +0.9 +263.8
2 +0.0005052 -4.063e-07 +1.229e-10 -1.146e-07 +1.062e-10 -2.457e-14 -0.4 +265.1
3 +0.0004361 -3.426e-07 +1.031e-10 -9.551e-08 +7.714e-11 -1.426e-14 -0.6 +260.2
3 0 +0.0004770 -4.117e-07 +1.349e-10 -1.207e-07 +1.245e-10 -3.760e-14 -0.6 +255.0
1 +0.0005191 -4.361e-07 +1.390e-10 -1.266e-07 +1.175e-10 -2.967e-14 +0.1 +253.6
2 +0.0005390 -4.803e-07 +1.597e-10 -1.377e-07 +1.498e-10 -4.546e-14 +0.0 +249.9
3 +0.0004565 -3.641e-07 +1.105e-10 -9.559e-08 +8.089e-11 -1.577e-14 +0.1 +255.4
4 0 +0.0006309 -5.003e-07 +1.507e-10 -1.624e-07 +1.574e-10 -4.096e-14 +0.5 +270.7
1 +0.0006890 -5.413e-07 +1.625e-10 -1.677e-07 +1.585e-10 -3.931e-14 +0.3 +266.4
2 +0.0007323 -6.219e-07 +2.007e-10 -1.940e-07 +2.154e-10 -6.582e-14 -0.4 +257.0
3 +0.0007425 -6.491e-07 +2.159e-10 -2.223e-07 +2.656e-10 -8.970e-14 +0.6 +256.3
5 0 +5.122e-05 -7.589e-08 +2.773e-11 -2.036e-09 +1.524e-11 -5.364e-15 +19.4 +235.0
1 +5.629e-05 -9.608e-08 +4.069e-11 +6.288e-10 +1.625e-11 -8.991e-15 +27.9 +217.8
2 +5.891e-05 -1.000e-07 +4.098e-11 -8.522e-09 +3.177e-11 -1.392e-14 +24.8 +222.8
3 +4.816e-05 -9.149e-08 +4.138e-11 -4.714e-09 +3.664e-11 -1.961e-14 +25.1 +229.0
6 0 +0.0005516 -4.553e-07 +1.435e-10 -1.500e-07 +1.440e-10 -3.535e-14 -1.0 +252.1
1 +0.0005954 -4.868e-07 +1.552e-10 -1.640e-07 +1.645e-10 -4.741e-14 +0.0 +261.4
2 +0.0006005 -4.869e-07 +1.542e-10 -1.583e-07 +1.437e-10 -3.670e-14 -0.3 +254.6
3 +0.0005632 -4.600e-07 +1.467e-10 -1.624e-07 +1.646e-10 -4.825e-14 -0.2 +261.2
7 0 +1.590e-05 -1.294e-08 +4.096e-12 +2.335e-08 -3.338e-11 +1.238e-14 +13.4 +223.1
1 +1.122e-05 -1.651e-08 +9.285e-12 +2.738e-08 -3.052e-11 +8.668e-15 +16.6 +212.7
2 +1.058e-05 -8.717e-09 +2.891e-12 +3.151e-08 -4.130e-11 +1.485e-14 +15.9 +215.2
3 +2.376e-05 -2.196e-08 +6.505e-12 +2.056e-08 -2.742e-11 +9.882e-15 +18.4 +223.6
8 0 +0.0004510 -3.871e-07 +1.332e-10 -1.080e-07 +8.466e-11 -1.861e-14 +1.1 +231.9
1 +0.0005019 -4.332e-07 +1.472e-10 -1.291e-07 +9.925e-11 -1.979e-14 +0.7 +226.8
2 +0.0005142 -4.425e-07 +1.492e-10 -1.416e-07 +1.060e-10 -2.012e-14 +0.4 +228.5
3 +0.0004456 -3.662e-07 +1.192e-10 -1.096e-07 +7.567e-11 -1.077e-14 +0.4 +237.9
9 0 +0.0005439 -4.562e-07 +1.459e-10 -1.586e-07 +1.501e-10 -4.040e-14 -0.6 +253.8
1 +0.0005893 -4.841e-07 +1.535e-10 -1.831e-07 +1.676e-10 -4.610e-14 -0.5 +255.5
2 +0.0005542 -4.581e-07 +1.451e-10 -1.679e-07 +1.583e-10 -4.405e-14 +1.5 +257.9
3 +0.0004403 -3.887e-07 +1.371e-10 -9.241e-08 +6.603e-11 -9.836e-15 +0.1 +222.8

This entire procedure should be done separately for each node of each chip.

  1. Sum up several different data sets to get good signal-to noise. [Sample spectrum]

  2. Calculate the CTI for this summed data. We did this for blocks of 100 rows, across the chip. [Sample plots]

  3. Plot the coefficients for each line vs. the line centroids for the 100-row section closest to the node. Fit 3rd-degree polynomials to this data. These polynomials are the corrections given above in "CTI correction for centroids of peaks". [Sample plots]

  4. Plot line centroids vs. true line energies for the 100-row section closest to the node and fit a line. The coefficients of this fit are the energy scale correction coefficients. [Sample plots]

  5. Apply these corrections to each individual data set. [Sample plots]

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