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This version of the LETG+HRC-S effective area reflects an improved calibration over the full range employing observations of Sirius B and PKS 2155-304, along with the improved calibration of the higher order efficiencies (in particular, m=2,4,5,6,7), and an updated extraction region efficiency. For details on the higher order efficiencies see the LETG Higher Order Efficiency Calibration webpage.
Prior to in-flight calibration, the on-axis HRC-S QE was calibrated in the laboratory over the energy range 0.28-10.0 keV. QE calibration below 0.28 keV was incomplete, as was the HRC-S QE uniformity, required for computing the LETGS dispersed effective area which physically covers three michrochannel plates (MCPs) and spectrally covers more than two orders of magnitude. Since there is no single source available to cover this broad energy range, the calibration of the LETGS effective area has been achieved in multiple phases.
For the low energy calibration (E < 0.277 keV; wavelengths > 44 AA) we compared observations of Sirius B and HZ 43 with pure hydrogen non-LTE white dwarf emission models. For the mid-range calibration (2.0 > E > 0.277 keV; 6 < wavelengths < 44 AA) we compared observations of the active galactic nuclei PKS 2155-304 and 3C 273 with simple power-law models of their seemingly featureless continua. The residuals of the model comparisons were taken to be true residuals in the HRC-S quantum efficiency (QE) model. Additional in-flight observations of celestial sources with well-understood X-ray spectra have served to verify and fine-tune the calibration. Thus, from these studies we have derived corrections to the HRC-S QE to match the predicted and observed spectra over the full practical energy range of the LETGS.
Furthermore, from pre-flight laboratory flatfield data we have constructed an HRC-S quantum efficiency uniformity (QEU) model. Application of the QEU to our semi-empirical in-flight HRC-S QE has resulted in an improved HRC-S on-axis QE. Implementation of the HRC-S QEU with the on-axis QE now allows for the computation of effective area for any reasonable Chandra/LETGS pointing.
For a detailed account of the LETGS effective area calibration see the contribution from Pease et al. at the 2004 Chandra Calibration Workshop
Positive and Negative 1st Order Dispersed Effective Area; nominal aimpoint; Based on in-flight mid-energy QE calibration with PKS 2155-304 and 3C 273, and low-energy QE calibration with Sirius B and HZ43; WITHOUT microchannel plate gaps.Note: The above effective area files include a correction for the efficiency of the LETG bow-tie spectral extraction region. If you wish to use these GARFs, and do your own spectral extraction outside of CIAO, you will need to remove (divide out) the bow-tie region extraction efficiency with the following EEARF files. Also, If you want to use GARFs created by the CIAO tool MKGARF using the default bow-tie region (these GARFs will not include the extraction efficiencies), then you will need to supply the EEARF files in Sherpa manually.
Positive & Negative dispersion (ASCII)
Positive dispersion (FITS)
Negative dispersion (FITS)
| (ASCII) | Positive dispersion (FITS) | Negative dispersion (FITS) |
This 0th Order Effective Area is a low estimate, derived from the above dispersed EA; the HRC-S QE non-uniformities in the above dispersed EA are NOT corrected for. The true LETG+HRC-S 0th Order Effective Area is being tested and will be higher (better).
0th Order (ASCII) (FITS)
Positive and Negative N Order Dispersed Effective Areas for nominal aimpoint Current best estimate of higher orders; in the process of being tested.
NOTE: for these files, wavelength scale is already transposed (ie. order m * wave).
NOTE: These higher order effective area files are same as above, but wavelengths are not transposed.
Before using the LETGS grating response matrices please READ THIS. The following files are the combined response matrices for orders 1 through 6, obtained by multiplying the above effective areas with the RMFs currently in the CALDB.
1st Order only Positive dispersion (FITS) Negative dispersion (FITS) 1st thru 2nd Order Positive dispersion (FITS) Negative dispersion (FITS) 1st thru 3rd Order Positive dispersion (FITS) Negative dispersion (FITS) 1st thru 4th Order Positive dispersion (FITS) Negative dispersion (FITS) 1st thru 5th Order Positive dispersion (FITS) Negative dispersion (FITS) 1st thru 6th Order Positive dispersion (FITS) Negative dispersion (FITS)
The following 2 files are the LETGS response, in channel space, for a flat spectrum with intensity 1 ph/keV, for combined orders 1-6, derived from the gRSPs above. These files are similar to, but are not gARFs.
Positive dispersion (FITS) Negative dispersion (FITS)
Previously Posted Data Files:
Follow this link to the files which were available from August 2004 to November 2004. This previous suite of files was derived from the calibration dated August 2004 ("0408" in the file names).
Follow this link to the files which were available from July 2002 to August 2004. This previous suite of files was derived from the calibration dated July 2002 ("0207" in the file names).
Follow this link to the files which were available from December 2001 to July 2002. This previous suite of files was derived from the calibration dated December 2001 ("0112" in the file names).
Follow this link to the files which were available from October 2000 to December 2001. This previous suite of files was derived from the calibration dated 31 October 2000 ("001031" in the file names).
Positive and Negative 1st Order Dispersed Effective Area;
Preliminary version based on in-flight low-energy QE calibration
same as above but WITHOUT microchannel plate gaps
Based on pre-flight calibration
Using PKS 2155-304 and 3C 273, implementing HRC-S QEU (August 2002)
Warning: Large postscript files (PaperPS/3.5MB PaperPDF/2.2MB Poster/12.4MB)
Using PKS 2155-304 and 3C 273 (November 2000)
Warning: Large postscript file (9.2 MB)
Using white dwarfs Sirius B and HZ 43 (March 2000)
Warning: Large postscript files (Paper/5.2MB, Poster/8.3 MB)
Last modified: 04/15/11
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