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D. Pease, J.J. Drake (SAO), H.L. Marshall (MIT), C.O. Johnson, V. Kashyap, R.P. Kraft, P.W. Ratzlaff, B.J. Wargelin (SAO), A.C. Brinkman, J.S. Kaastra, R.L.J. van der Meer (SRON), P. Predehl, V. Burwitz (MPE)
We present the in-flight mid-energy (10-80~Å;~~ 0.16-1.2~keV) effective area calibration of the High Resolution Camera Spectroscopic readout (HRC-S) combined with the Low Energy Transmission Grating (LETG) aboard the Chandra X-ray Observatory. These instruments comprise the Low Energy Transmission Grating Spectrometer (LETGS).
For this study, we employ LETGS data from the quasar 3C~273 and the blazar PKS~2155-304, which both appear to be essentially featureless continua sources. The flux as a function of energy for these sources can be described by power-law models (N ~E-\Gamma). For 3C~273 we use a broken power-law with \Gamma1 = 1.64, \Gamma2 = 2.23 and a break at ~15~Å. For PKS~2155-304 we find that a single power-law with \Gamma = 2.45 can be used to describe the LETGS spectrum from ~~5~Å~to the long wavelength ISM cut-off of ~~80~Å. The residuals of the model fits are taken to be errors in the HRC-S quantum efficiency (QE) model. Thus, from the residuals we derive a correction to the HRC-S QE to match the predicted and observed spectra over the mid-energy range.
A similar calibration procedure for the low energy regime of the LETGS has already been reported (Pease, et al., 2000, Proc. SPIE, 4012, 700). The present study enables us to present for the first time an empirically calibrated in-flight HRC-S QE model encompassing the entire LETGS active energy range of 2-200~Å~(~0.06-6~keV).
This research was supported by Chandra X-ray Center~ NASA contract NAS8-39073.
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