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LETG Observer Information: LETG+HRC-S EA

LETG Observer Information: LETG+HRC-S EA

last update: November 2004

This page is has been superseded by a newer calibration.

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

Data files (version date: November 2004):

jump to:
1st Order Effective Area
0th Order Effective Area
Orders 2-10 Effective Areas
Orders 1-6 Grating Response Matrices

Previously Posted Data Files:

Analysis & Documentation:

Last modified: 04/15/11

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