منابع مشابه
Time Dilation and Quasar Variability
The timescale of quasar variability is widely expected to show the effects of time dilation. In this paper we analyse the Fourier power spectra of a large sample of quasar light curves to look for such an effect. We find that the timescale of quasar variation does not increase with redshift as required by time dilation. Possible explanations of this result all conflict with widely held consensu...
متن کاملQuasar Variability in the Framework of Poissonian Models
Quasar optical monitoring campaigns are reaching a new standard of quality as a result of long term, accurate CCD observations. In this paper we review the basic Poissonian formulation of quasar variability, using it as a mathematical tool to extract relevant parameters such as the energy, rate and lifetimes of the flares through the analysis of observed light curves. It is shown that in this v...
متن کاملCorrelated X-ray/Optical Variability in the Quasar MR2251-178
Emission from Active Galactic Nuclei is known to vary strongly over time over a wide energy band, but the origin of the variability and especially of the inter-band correlations is still not well established. Here we present the results of our X-ray and optical monitoring campaign of the quasar MR 2251-178, covering a period of 2.5 years. The X-ray 2–10 keV flux is remarkably well correlated wi...
متن کاملQuasar Optical Variability in the Palomar-QUEST Survey
The ensemble variability properties of nearly 23,000 quasars are studied using the PalomarQUEST Survey. The survey has covered 15,000 square degrees multiple times over 3.5 years using 7 optical filters, and has been calibrated specifically for variability work. Palomar-QUEST allows for the study of rare objects using multiple epochs of consistently calibrated, homogeneous data, obviating the c...
متن کاملExtreme X - ray variability in the luminous quasar PDS 456
We present evidence from BeppoSAX and XMM-Newton of extreme X-ray variability in the high luminosity radio-quiet quasar PDS 456, the most luminous known AGN at z < 0.3. Repeated X-ray flaring is found in PDS 456, over the duration of the 340 ksec long BeppoSAX observation. The X-ray flux doubles in just 30 ksec, whilst the total energy output of the flaring events is as high as 10 51 erg. Under...
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ژورنال
عنوان ژورنال: Nature
سال: 1994
ISSN: 0028-0836,1476-4687
DOI: 10.1038/371210a0