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Statistical analysis of variability

Statistical analysis of variability. In a sample of intensively observed blazars. Massimo Fiorucci, Gino Tosti Sezione INFN Perugia, Università di Perugia Nicola Marchili Università di Perugia. Statistical analysis of variability.

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Statistical analysis of variability

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  1. Statistical analysis of variability In a sample of intensively observed blazars Massimo Fiorucci, Gino Tosti Sezione INFN Perugia, Università di Perugia Nicola Marchili Università di Perugia

  2. Statistical analysis of variability • Blazars are characterised by rapid and large variability at all frequencies • In the last years, many efforts have been spent to understand the physical mechanisms responsible for the variable emission • However, blazars emit signals that appear to vary chaotically with time.

  3. Radio Variability

  4. Optical Variability

  5. X Variability

  6. This behaviour is expected in two qualitatively different situations: • In a system consisting of a large number of weakly correlated elements which appear at random and live only a short time. • The global evolution of a system described by non-linear differential equations which shows deterministic chaos.

  7. Optical and gamma-ray variability seem to be strongly correlated

  8. Optical variability: chaotic behaviour or correlated signal? • The Perugia monitoring program started in 1992. • We have collected more than 20000 BVRI observations and our sample forms one of the larger set of optical data available. • We are cooperating with other international teems to improve the sampling for many blazars. • We can use this large database to study variability with statistical techniques.

  9. Discrete Fourier Transform

  10. Discrete Auto-correlation

  11. Structure Function

  12. The Grassberger-Procaccia Correlation Integral

  13. Optical variability: chaotic behaviour or correlated signal? • Preliminary results show that the observed variability is truly stochastic and is not caused by deterministic chaos • Blazar variability seems to be characterised by shot or flicker noise • The system probably consist of a large number of weakly correlated elements which appear at random, live only a short time and decay

  14. Simulation of optical variability

  15. and GLAST ? • The simulation of variability can be extended towards high energy with the theoretical models. • Our statistical analysis can be used to discriminate faint variable sources against the background noise

  16. Simulated light curve

  17. Variable source + background noise

  18. Final light curve

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