Allevato Viola, Paolillo Maurizio, Iossif Papadakis, Pinto Ciro
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.
View original:
http://arxiv.org/abs/1202.3786
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