HETGS Line Profiles  

Comparison of new and old grating RMFs

 

Comparison of new and old grating RMFs

We compare a set of new RMFs based on the new LSFPARM products with the canned grating RMF (version N0004) in CALDB. In this example we also use a 43 ksec Calibration/GTO observation of Capella (ObsID 1103) taken with Chandra HETG/ACIS-S.

Once again we use isis to perform a simple line profile fitting, though at this time using a Gaussian function with a fixed narrow width (1e-10 Angstrom). Likewise we also add a 1st order polynomial function to adjust the baseline.

Once again, the plots themselves speak a thousand word. Please look at fitting results shown in the following figures.

Line Profile Fitting

HETG/ACIS-S HEG +1st order spectra:

Fe XVII \bf{\lambda{15.015}}

HEG: Fe XVII: New LSFPARMS
HEG: Fe XVII: Old Canned RMF (N0004)
Figure 11: Results of line profile fitting at Fe XVII with different RMF/fitting kernels. The red line shows the best-fit model. The difference \delta\chi is also displayed for your entertainment: (top) New RMF based on the new LSFPARMS (goodness of fit: {\chi}^{2} =0.24); (bottom) Old RMF N0004 (+1st order HEG) in CALDB (goodness of fit: {\chi}^{2} =0.39).

Mg XII \bf{\lambda{8.421}}

HEG: Mg XII: New LSFPARMS
HEG: Mg XII: Old Canned RMF (N0004)
Figure 12: The same as for Figure 11. (Top) New (goodness of fit: {\chi}^{2} =0.298); (bottom) Old (goodness of fit: {\chi}^{2} =0.292).

Si XIII Triplet \bf{\lambda\lambda{6.647, 6.685, 6.740}}

HEG: Si XIII: New LSFPARMS
HEG: Si XIII: Old Canned RMF (N0004)
Figure 13: The same as for Figure 11. (Top) New (goodness of fit: {\chi}^{2} =0.484); (bottom) Old (goodness of fit: {\chi}^{2} =0.382). (NB: For some technical binning reason we could not center one of Si XIII lines (6.647AA) accurately with the new RMF. Upon changing the rebinning scale, it results in a better fit than the given goodness value here.)

Fe XVII + Ne X Blend \bf{\lambda\lambda{12.125, 12.136}}

HEG: Fe XVII + Ne X: New LSFPARMS
HEG: Fe XVII + Ne X: Old Canned RMF (N0004)
Figure 14: The same as for Figure 11. (Top) New (goodness of fit: {\chi}^{2} =0.211); (bottom) Old (goodness of fit: {\chi}^{2} =0.274).

HETG/ACIS-S HEG -1st order spectra:

Fe XVII \bf{\lambda{15.015}}

HEG: Fe XVII: New LSFPARMS
HEG: Fe XVII: Old Canned RMF (N0004)
Figure 15: Results of line profile fitting at Fe XVII with different RMF/fitting kernels. The red line shows the best-fit model. The difference \delta\chi is also displayed for your entertainment: (top) RMF based on the new LSFPARMS (goodness of fit: {\chi}^{2} =0.400); (bottom) RMF N0004 (+1st order HEG) in CALDB (goodness of fit: {\chi}^{2} =0.405).

Mg XII \bf{\lambda{8.421}}

HEG: Mg XII: New LSFPARMS
HEG: Mg XII: Old Canned RMF (N0004)
Figure 16: The same as for Figure 15. (Top) New (goodness of fit: {\chi}^{2} =0.318); (bottom) Old (goodness of fit: {\chi}^{2} =0.315).

Si XIII Triplet \bf{\lambda\lambda{6.647, 6.685, 6.740}}

HEG: Si XIII: New LSFPARMS
HEG: Si XIII: Old Canned RMF (N0004)
Figure 17: The same as for Figure 15. (Top) New (goodness of fit: {\chi}^{2} =0.256); (bottom) Old (goodness of fit: {\chi}^{2} =0.244).

Fe XVII + Ne X Blend \bf{\lambda\lambda{12.125, 12.136}}

HEG: Fe XVII + Ne X: New LSFPARMS
MEG: Fe XVII + Ne X: Old Canned RMF (N0004)
Figure 18: The same as for Figure 15. (Top) New (goodness of fit: {\chi}^{2} =0.365); (bottom) Old (goodness of fit: {\chi}^{2} =0.407).

HETG/ACIS-S MEG +1st order spectra:

Fe XVII \bf{\lambda{15.015}}

MEG: Fe XVII: New LSFPARMS
MEG: Fe XVII: Old Canned RMF (N0004)
Figure 19: Results of line profile fitting at Fe XVII with different RMF/fitting kernels. The red line shows the best-fit model. The difference \delta\chi is also displayed for your entertainment: (top) RMF based on the new LSFPARMS (goodness of fit: {\chi}^{2} =1.70); (bottom) RMF N0004 (+1st order MEG) in CALDB (goodness of fit: {\chi}^{2} =1.73).

Mg XII \bf{\lambda{8.421}}

MEG: Mg XII: New LSFPARMS
MEG: Mg XII: Old Canned RMF (N0004)
Figure 20: The same as for Figure 19. (Top) New (goodness of fit: {\chi}^{2} =0.436); (bottom) Old (goodness of fit: {\chi}^{2} =0.494).

Si XIII Triplet \bf{\lambda\lambda{6.647, 6.685, 6.740}}

MEG: Si XIII: New LSFPARMS
MEG: Si XIII: Old Canned RMF (N0004)
Figure 21: The same as for Figure 19. (Top) New (goodness of fit: {\chi}^{2} =0.843); (bottom) Old (goodness of fit: {\chi}^{2} =0.876).

Fe XVII + Ne X Blend \bf{\lambda\lambda{12.125, 12.136}}

MEG: Fe XVII + Ne X: New LSFPARMS
MEG: Fe XVII + Ne X: Old Canned RMF (N0004)
Figure 22: The same as for Figure 19. (Top) New (goodness of fit: {\chi}^{2} =0.665); (bottom) Old (goodness of fit: {\chi}^{2} =0.743).

HETG/ACIS-S MEG -1st order spectra:

Fe XVII \bf{\lambda{15.015}}

MEG: Fe XVII: New LSFPARMS
MEG: Fe XVII: Old Canned RMF (N0004)
Figure 23: Results of line profile fitting at Fe XVII with different RMF/fitting kernels. The red line shows the best-fit model. The difference \delta\chi is also displayed for your entertainment: (top) RMF based on the new LSFPARMS (goodness of fit: {\chi}^{2} =4.914); (bottom) RMF N0004 (+1st order MEG since there is no minus 1st order MEG) in CALDB (goodness of fit: {\chi}^{2} =4.324). (N.B: Large {\chi}^{2} values because of its neighboring line not being modeled in the fitting properly.)

Mg XII \bf{\lambda{8.421}}

MEG: Mg XII: New LSFPARMS
MEG: Mg XII: Old Canned RMF (N0004)
Figure 24: The same as for Figure 23. (Top) New (goodness of fit: {\chi}^{2} =0.724); (bottom) Old (goodness of fit: {\chi}^{2} =0.941).

Si XIII Triplet \bf{\lambda\lambda{6.647, 6.685, 6.740}}

MEG: Si XIII: New LSFPARMS
MEG: Si XIII: Old Canned RMF (N0004)
Figure 25: The same as for Figure 23. (Top) New (goodness of fit: {\chi}^{2} =1.06); (bottom) Old (goodness of fit: {\chi}^{2} =0.643). (N.B: see caption in Figure 13.)

Fe XVII + Ne X Blend \bf{\lambda\lambda{12.125, 12.136}}

MEG: Fe XVII + Ne X: New LSFPARMS
MEG: Fe XVII + Ne X: Old Canned RMF (N0004)
Figure 26: The same as for Figure 23. (Top) New (goodness of fit: {\chi}^{2} =0.908); (bottom) Old (goodness of fit: {\chi}^{2} =1.10).

Note that the derived goodness of fit for each case is more or less the same, i.e., the old RMFs are still O.K. for line profile analysis of a low signal-to-noise dataset. However, note that the old RMF assumes intrumental line profile to be symmetric, whearas the \it{true} instrumental line profile is very slightly skewed (esp. in HEG +/- orders).

Line Centroid and Flux Estimates

We have estimated line centroid and flux for each line (per order per grating) and the results are tabulated in Table 3.

Table 3: Validation of HEG +1st Order Centroid and Flux Estimates with different RMF kernels


HEG +1st
Atomic Wavelength(AA) Flux (photon/cm2/s) Flux Ratio
Elements New Old New Old (Old/New)
Fe XVII 15.0125 15.0125 3.91e-3 3.47e-3 89%
Mg XII 8.420 8.420 2.23e-4 2.20e-4 99%
Si XIII 6.6475 6.6475 2.02e-4 2.09e-4 103%
Si XIII 6.6851 6.6851 3.90e-5 3.83e-5 98%
Si XIII 6.7375 6.7381 1.87e-4 1.83e-4 98%
Ne X 12.135 12.1339 8.89e-4 8.68e-4 98%
Fe XVII 12.1225 12.1228 5.00e-4 4.70e-4 94%
HEG -1st
Atomic Wavelength(AA) Flux (photon/cm2/s) Flux Ratio
Elements New Old New Old (Old/New)
Fe XVII 15.015 15.015 3.64e-3 3.42e-3 94%
Mg XII 8.4225 8.4225 2.34e-4 2.29e-4 98%
Si XIII 6.6497 6.6500 2.04e-4 2.00e-4 98%
Si XIII 6.6899 6.6899 5.39e-5 5.22e-5 97%
Si XIII 6.7400 6.7425 1.79e-4 1.68e-4 94%
Ne X 12.1375 12.1375 8.16e-4 8.92e-4 109%
Fe XVII 12.1250 12.1250 5.99e-4 6.25e-4 104%
MEG +1st
Atomic Wavelength(AA) Flux (photon/cm2/s) Flux Ratio
Elements New Old New Old (Old/New)
Fe XVII 15.0061 15.0050 3.48e-3 3.29e-3 95%
Mg XII 8.415 8.415 2.41e-4 2.29e-4 95%
Si XIII 6.645 6.645 2.33e-4 2.23e-4 96%
Si XIII 6.685 6.685 6.52e-5 5.96e-5 91%
Si XIII 6.735 6.735 1.43e-4 1.42e-4 99%
Ne X 12.130 12.130 4.26e-4 5.02e-4 118%
Fe XVII 12.120 12.125 6.49e-4 6.71e-4 103%
MEG -1st
Atomic Wavelength(AA) Flux (photon/cm2/s) Flux Ratio
Elements New Old New Old (Old/New)
Fe XVII 15.015 15.015 3.88e-3 3.67e-3 95%
Mg XII 8.4200 8.4202 2.02e-4 1.89e-4 94%
Si XIII 6.6500 6.6500 2.07e-4 2.02e-4 98%
Si XIII 6.6850 6.6850 5.05e-5 4.68e-5 93%
Si XIII 6.7400 6.7400 1.52e-4 1.50e-4 99%
Ne X 12.1355 12.1400 7.99e-4 8.52e-4 107%
Fe XVII 12.1250 12.1273 4.06e-4 3.08e-4 76%

The results show that the derived centroid wavelengths are nearly identical at any given wavelength, while the new fluxes are generally higher than the old ones. The systematic difference in flux is due to the corrected normalization factors (or a.k.a. encircled energy fraction) provided with the new LSFPARM. Note, however, that counting statistics in this case dominates over the systemic error as the derived fluxes vary in a quite large scale between orders and gratings.

Validity of the old RMF N0004 (CALDB)

In brief, we have demonstrated that the old RMF N0004 products in CALDB is likely suitable for simple spectral analysis. However, if users wish to perform much more careful analysis on line emission/absorption profile of Chandra X-ray spectra, then we strongly recommend users to make their own RMFs based on the new LSFPARM.

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This page was last updated Apr 11, 2003 by Bish K. Ishibashi. To comment on it or the material presented here, send email to bish@space.mit.edu.
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