COLOR STUDY OF BLAZARS Robert Filgas Supervisor: RNDr. Ren

1
COLOR STUDY OF BLAZARSRobert FilgasSupervisor
RNDr. René Hudec, CSc., AÚ AV CR
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 gt 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 a
• Lorentz factor 10 gt 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 gt
• power-law synchrotron spectrum
• some of radio sources so compact gt 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 Einsteins 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