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arXiv · 1102.4610

Accounting for Calibration Uncertainties in X-ray Analysis: Effective Areas in Spectral Fitting

Hyunsook Lee·Vinay L. Kashyap·David A. van Dyk·Alanna Connors·Jeremy J. Drake·Rima Izem·Xiao-Li Meng·Shandong Min·Taeyoung Park·Pete Ratzlaff·Aneta Siemiginowska·Andreas Zezas
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Abstract

While considerable advance has been made to account for statistical uncertainties in astronomical analyses, systematic instrumental uncertainties have been generally ignored. This can be crucial to a proper interpretation of analysis results because instrumental calibration uncertainty is a form of systematic uncertainty. Ignoring it can underestimate error bars and introduce bias into the fitted values of model parameters. Accounting for such uncertainties currently requires extensive case-specific simulations if using existing analysis packages. Here we present general statistical methods that incorporate calibration uncertainties into spectral analysis of high-energy data. We first present a method based on multiple imputation that can be applied with any fitting method, but is necessarily approximate. We then describe a more exact Bayesian approach that works in conjunction with a Markov chain Monte Carlo based fitting. We explore methods for improving computational efficiency, and in particular detail a method of summarizing calibration uncertainties with a principal component analysis of samples of plausible calibration files. This method is implemented using recently codified Chandra effective area uncertainties for low-resolution spectral analysis and is verified using both simulated and actual Chandra data. Our procedure for incorporating effective area uncertainty is easily generalized to other types of calibration uncertainties.

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Hyunsook Lee, Vinay L. Kashyap, David A. van Dyk, Alanna Connors, Jeremy J. Drake, Rima Izem, Xiao-Li Meng, Shandong Min, Taeyoung Park, Pete Ratzlaff, Aneta Siemiginowska, Andreas Zezas. 2011-02-22. Accounting for Calibration Uncertainties in X-ray Analysis: Effective Areas in Spectral Fitting. https://doi.org/10.1088/0004-637x%2F731%2F2%2F126

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