1. Multi-Wavelength Time Variability of Active Galactic Nuclei Ritaban Chatterjee Advisor: Prof. Alan P. Marscher Collaborators: Svetlana Jorstad (B.U.), Phil Uttley (U. Southampton, UK).

2. “An active galactic nucleus (AGN) is a compact region at the centre of a galaxy which has a much higher than normal luminosity over some or all of the electromagnetic spectrum. The radiation from AGN is believed to be a result of accretion on to a super-massive black hole at the centre of the host galaxy.” -Wikipedia

3. Image courtesy of NRAO/AUI Jets of AGN: kpc and pc scale

4. AGN : Schematic Model Cartoon courtesy: Prof. Alan Marscher

5. Why Time Variability?

6. 3C 279 Z=0.536 1 mas = 6.3 pc 3C 279

7. Steps of Time Variability Studies Long-term monitoring in multiple wavelengths and VLBA Power spectral density (PSD) Comparison of flux at different wavelengths : Correlation and light curve decomposition Simulation of time variable non-thermal radiation

8. X-RAY OPTICAL RADIO

9. Steps of Time Variability Studies Long-term monitoring in multiple wavelengths and VLBA Power spectral density (PSD) Comparison of flux at different wavelengths : Correlation and light curve decomposition Simulation of time variable non-thermal radiation

10. Variability in Different Timescales 2000 Days : Years Maximum/Average ~ 2.5 70 Days : Months Maximum/Average ~ 1.5 10 Days : Weeks Maximum/Average ~ 1.3

11. First PSD of nonthermal radiation from AGN jets

13. PSD Analysis There is higher amplitude variability at longer timescales than at shorter timescales Simulation of artificial light curves for comparison X-ray PSDs of accretion disk systems show characteristic time scale

14. Simulation of Light Curves Using PSD

15. Long-term monitoring in multiple wavelengths and VLBA Power spectral density (PSD) Comparison of flux at different wavelengths : Correlation analysis and light curve decomposition Simulation of time variable non-thermal radiation Steps of Time Variability Studies

16. 3C 279 : X-ray-optical Cross-Correlation Optical leads X-ray by ~ 19 Days Chatterjee et al. 2008 (ApJ, 489, 79)

17. Correlation Time Window

18. X-RAY OPTICAL RADIO

19. Long-term monitoring in multiple wavelengths and VLBA Power spectral density (PSD) Comparison of flux at different wavelengths : Correlation analysis and light curve decomposition Simulation of time variable non-thermal radiation Steps of Time Variability Studies

20. Decomposition into flares X-ray light curve : 10-day Gaussian smoothing applied

21. X-ray light curve : Sum of model flares & real data Chatterjee et al. 2008 (ApJ, in press)

22. Optical light curve : Sum of model flares & real data Chatterjee et al. 2008 (ApJ, in press)

23. X-ray and Optical : Superposed 1.Time lag between peaks 2.Power of flares : Area under the curve

24. Time Delay (Days) X/Op Ratio 1.270.4 2.240.62 3.490.67 4.150.44 5.221.4 6.160.18 7.250.38 8.270.3 9.30.95 10.80.98 11.30.87 12.60.88 Larger time delay, Smaller ratio Smaller time delay, Ratio ~1

25. 6 out of 12 optical flares have more power than the related X-ray flare. Optical => Synchrotron X-ray=> Synchrotron self-Compton (SSC) => SSC/Synch Puzzling! When x/op ~1, time delay is very small. Summary of correlation and flare decomposition

26. Long-term monitoring in multiple wavelengths and VLBA Power spectral density (PSD) Comparison of flux at different wavelengths : Correlation analysis and light curve decomposition Simulation of time variable non-thermal radiation Modeling of synchrotron (optical) and synchrotron self- Compton (X-ray) flares B ~r -b, N 0 ~r -n, R ~r Steps of Time Variability Studies

27. Real and Simulated Light Curves Red: Optical (Synchrotron), Green: X-ray (SSC)

28. Real and Simulated Light Curves SIMULATEDREAL Red: Optical (Synchrotron), Green: X-ray (SSC)

29. Downstream SSC (Green) maybe smaller than Synchrotron (Red) UPSTREAMDOWNSTREAM

30. Sketch of emission region upstream and downstream x/op~1 x/op<1 UpstreamDownstream

31. Sketch of emission region upstream and downstream ∆ t smaller x/op~1 ∆ t larger x/op<1 UpstreamDownstream

32. Time Delay (Days) X/Op Ratio 1.270.4 2.240.62 3.490.67 4.150.44 5.221.4 6.160.18 7.250.38 8.270.3 9.30.95 10.80.98 11.30.87 12.60.88 Larger time delay, Smaller ratio Smaller time delay, Ratio ~1

33. CONCLUSIONS: LOCATION AND MECHANISM OF EMISSION There is higher amplitude variability at longer timescales than at shorter timescales X-ray and optical variations are highly correlated. X-ray/optical correlation changes over time. Contemporaneous X-ray and optical flares: X/OP ≈ 1 => closer to the base of the jet X/OP farther from the base of the jet

34. THE END

38. Multi-wavelength Light Curves of 3C 120 between 2002 and 2007

39. PSD of Cygnus X-1 : Break Frequency Credit : Uttley et al. (2004)

40. 3C 120 PSD with break

41. AGN : Unified Picture