In-flight effective area calibration of the Chandra low-energy transmission grating spectrometer

Deron O. Pease; Jeremy J. Drake; Vinay L. Kashyap; Herman L. Marshall; Erica L. Raffauf; Peter W. Ratzlaff; Bradford J. Wargelin

doi:10.1117/12.461275

11 March 2003 In-flight effective area calibration of the Chandra low-energy transmission grating spectrometer

Deron O. Pease, Jeremy J. Drake, Vinay L. Kashyap, Herman L. Marshall, Erica L. Raffauf, Peter W. Ratzlaff, Bradford J. Wargelin

Author Affiliations +

Proceedings Volume 4851, X-Ray and Gamma-Ray Telescopes and Instruments for Astronomy; (2003) https://doi.org/10.1117/12.461275
Event: Astronomical Telescopes and Instrumentation, 2002, Waikoloa, Hawai'i, United States

Abstract

We present the in-flight effective area calibration of the Low Energy Transmission Grating Spectrometer (LETGS), which comprises the High Resolution Camera Spectroscopic readout (HRC-S) and the Low Energy Transmission Grating (LETG) aboard the Chandra X-ray Observatory. Previous studies of the LETGS effective area calibration have focused on specific energy regimes: 1) the low-energy calibration for which we compared observations of Sirius B and HZ 43 with pure hydrogen non-LTE white dwarf emission models; and 2) the mid-energy calibration for which 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.

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Deron O. Pease, Jeremy J. Drake, Vinay L. Kashyap, Herman L. Marshall, Erica L. Raffauf, Peter W. Ratzlaff, and Bradford J. Wargelin "In-flight effective area calibration of the Chandra low-energy transmission grating spectrometer", Proc. SPIE 4851, X-Ray and Gamma-Ray Telescopes and Instruments for Astronomy, (11 March 2003); https://doi.org/10.1117/12.461275

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