Astronomy and Astrophysics – Astrophysics – High Energy Astrophysical Phenomena
Scientific paper
2012-02-16
Astronomy and Astrophysics
Astrophysics
High Energy Astrophysical Phenomena
Submitted to ApJ
Scientific paper
We discuss some practical aspects of measuring the variability amplitude of faint and distant active galactic nuclei (AGN), characterized by sparsely sampled lightcurves and low statistic. In such cases the excess variance, commonly used to estimate the intrinsic lightcurve variance, is affected by strong biases and uncertainties since it represents a maximum likelihood variability estimator only for identical/normal distributed measurements errors and uniform sampling. We performed realistic Monte Carlo simulations of AGN lightcurves, reproducing both the sampling pattern and measurement errors typical of multi-epoch deep surveys, such as the XMM-Newton observations of the Chandra Deep Field South (CDFS), or assuming different sampling patterns that may characterize long surveys with sub-optimal observing conditions. We used the results to estimate our ability to measure the intrinsic source variability as well as to constrain the observing strategy of future X-ray missions studying distant and/or faint AGN populations.
Allevato Viola
Paolillo Maruizio
Papadakis Iosif
Pinto Cecilia
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