On the use of Cstat in testing models for Xray spectra
Abstract
Context. It has been shown that for the analysis of Xray spectra the Cstatistic, contrary to the χ^{2}statistic, provides unbiased estimates of the model parameters and their uncertainty ranges.
Aims: However, it is often stated that the Cstatistic cannot be used to carry out statistical tests on the goodness of fit of the model, and therefore several investigations are still based on χ^{2}statistics.
Methods: Here we show that it is straightforward to calculate the expected value and variance of the Cstatistic so that it can be used in tests.
Results: We provide formulae and simple numerical approximations to evaluate these expected values and variances. We also give examples indicating that tests based on only the expected value and variance of the Cstatistic are reliable for spectra even with only 30 counts.
Conclusions: The Cstatistic can be used for statistical tests such as assessing the goodness of fit of a spectral model.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 September 2017
 DOI:
 10.1051/00046361/201629319
 arXiv:
 arXiv:1707.09202
 Bibcode:
 2017A&A...605A..51K
 Keywords:

 instrumentation: spectrographs;
 methods: data analysis;
 methods: statistical;
 Xrays: general;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 4 pages, 3 figures, accepted for publication in Astronomy and Astrophysics