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Keywords:

  • quasars: general;
  • cosmology: observations

ABSTRACT

In this paper we set out to measure time dilation in quasar light curves. In order to detect the effects of time dilation, sets of light curves from two monitoring programmes are used to construct Fourier power spectra covering time-scales from 50 d to 28 yr. Data from high- and low-redshift samples are compared to look for the changes expected from time dilation. The main result of the paper is that quasar light curves do not show the effects of time dilation. Several explanations are discussed, including the possibility that time dilation effects are exactly offset by an increase in time-scale of variation associated with black hole growth, or that the variations are caused by microlensing in which case time dilation would not be expected.