COLOR STUDY OF BLAZARS Robert Filgas Supervisor: RNDr. Ren é Hudec, CSc., A Ú AV ČR

1. COLOR STUDY OF BLAZARSRobert FilgasSupervisor: RNDr. René Hudec, CSc., AÚ AV ČR

2. Goals of the thesis • To summarize and discuss known facts about blazar spectra, luminosity in optical band and its time evolution. • To build and analyze my own database of optical photometry of blazars. • To interpret and discuss acquired results; conclusions, comparison with theoretical models, physics of the environment.

3. Active galaxies 1943 Carl Seyfert – fundamentals of AGN class (Seyfert galaxies) Great luminosity (1042 to 1047 erg s-1) in a very compact region => supermassive black hole (107 to 109 MS) in the center of the galaxy with accretion disk, dust torus and sometimes a jet.

4. Rarities of AGN • Strong emission lines emission lines much broader than absorption lines broadness caused by Doppler effect, gravity, velocity, temperatures • Variability of the luminosity variability of such giant objects unexpected brightness can increase 1000x on scale of days gives us the upper limit for size of the radiating area • Differences in spectra dominates non-thermal emission due to presence of active nuclei

5. Types of AGN • Blazars • name given by Ed Spiegel, 1978 • these days blazar rather a phenomenon then a category of objects • common is a relativistic jet pointed almost at us • radiation of the jet is non-thermal, relativistically boosted and polarized

6. Physical processes in jets of AGN • Superluminal motion • Relativistic beaming • increasing or decreasing of the radiation intensity from the source moving with relativistic speed where for homogenous sphere P = 3 + α Lorentz factor ~ 10 => boosting 100x – 1000x !can explain why we see only one jet!

7. Spectra of blazars

8. Spectra of blazars • Synchrotron emission • radiation of relativistic electron accelerated in a magnetic field gyrofrequency Larmor radius energy radiated by the electron increases as • spectrum broad and centered on the critical frequency

9. Spectra of blazars • Synchrotron emission • nature of spectrum depends on the speed of electrons • electron energy distribution has a power-law nature => power-law synchrotron spectrum • some of radio sources so compact => under certain frequency electrons optically thick for their own radiation • synchrotron self-absorption

10. Spectra of blazars • Synchrotron emission

11. Variability of blazars • Long-term variation • variations on time scales of months to years • many models: binary BH, precession of the jet, perturbations to the disk,.. • periodicity found

12. Variability of blazars • Short-term variation • days to months • orbital motion of jet from less massive BH? • Intraday variation • night to night variations • can give upper limit to the mass of central BH and the size of emitting region

13. Variability of blazars • Microvariation • minutes to hours

14. Causes of the variability • Extrinsic causes • microlensing • interstellar scintillation • Intrinsic causes • accretion disk models • geometrical effects • shocks in jet

15. Causes of the variability • Interstellar scintillation • result of wavefronts from a distant radio source being perturbed by refractive index fluctuations in the turbulent, ionized interstellar medium of our Galaxy • observed only in the most compact radio sources • principal cause of the rapid radio IDV in BL Lac objects • !affects only radio band of the spectrum!

16. Causes of the variability • Microlensing • one of Einstein’s general relativity predictions • light from distant source bent around massive object • microlensing: no distortion in shape amount of light received increases • brightness variations: • Symmetric outburst • Frequency independence across spectrum • Duration related to the lens speed

17. Causes of the variability • Accretion disk models • bright spots on disks • modulation of variability by radiating flare • vortices forming within a disk • plasma dominated events just above disk • spiral shocks produced in disk by passing massive stars, molecular clouds or companion BH

18. Causes of the variability • Geometrical effects • based on changing of Doppler factor • binary BH • precession of system • gravitational lensing from the secondary BH • helical jet models • knots or blobs of plasma spiraling in the jet

19. Causes of the variability • Shock-in-jet model • major increase in bulk velocity or internal energy of the jet flow will cause shock waves to form and propagate down the jet • decelerates supersonic flows to subsonic speeds • compression of plasma and enhancement of parallel component of magnetic field • flares results from increased density behind the shock front and increased magnetic field • frequency dependent effect

20. Causes of the variability • Shock-in-jet model

21. Data analysis • Dataset • 33 blazars – 11 LBLs, 19 HBLs and 2 FSRQs

22. Data analysis • Finding power-law spectra

23. Data analysis • Bluer-when-brighter tendency

24. Data analysis

25. Data analysis

26. Data analysis • not corresponding, SED deformation (thermal contribution from host galaxy or non-thermal contribution from different regions ?)

27. Data analysis

28. Data analysis • Inconsistent models: • Interstellar scintillation – affects radio and only • Gravitational lenses – frequency independent • Acceptable models: • Accretion disk models – thermal contribution from disk during quiescent state of HBLs and FSRQs • Geometrical effects – extreme dependency on slight changes of Doppler factor, binary holes commonly accepted • Shock-in-jet model – consistent with spectral hardening, need for data in all spectral bands

29. Data analysis • Color analysis • color-color diagrams project dispersion of light on its way to the Earth

30. Data analysis

31. Data analysis

32. Data analysis • Color analysis • color-color diagrams project dispersion of light on its way to the Earth • compared with OA of GRBs we see similarities

33. Data analysis

34. Data analysis

35. Data analysis • Color analysis • color-color diagrams project dispersion of light on its way to the Earth • compared with OA of GRBs we see similarities • comparison with AGN shows large differences

36. Data analysis

37. Data analysis

38. Data analysis • Color analysis • color-color diagrams project dispersion of light on its way to the Earth • compared with OA of GRBs we see similarities • comparison with AGN shows large differences • GRB and blazars have either similar or no environment • possibility that dust and other environment is destructed along the line of sight by high-energy photons • for blazars the origin for destruction might be in the jet

39. Data analysis • Color-color diagram positions • possibility to distinguish between various types of objects like it is with stars

40. Data analysis

41. Data analysis

42. Data analysis • Conclusions • synchrotron emission confirmed due to power-law spectra • spectral index ~1.5 for LBLs well corresponding with theory • bluer-when-brighter tendency observed – models • small scatter in color-color diagrams – dust destruction • mean values:

43. THE END