COLOR STUDY OF BLAZARS Robert Filgas Supervisor: RNDr. René Hudec, CSc., AÚ AV ČR

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.

Active galaxies 1943 Carl Seyfert – fundamentals of AGN class (Seyfert galaxies) Great luminosity (10 42 to erg s -1 ) in a very compact region => supermassive black hole (10 7 to 10 9 M S ) in the center of the galaxy with accretion disk, dust torus and sometimes a jet.

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

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

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!

Spectra of blazars

Synchrotron emission –radiation of relativistic electron accelerated in a magnetic field gyrofrequencyLarmor radius energy radiated by the electron increases as –spectrum broad and centered on the critical frequency

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

Spectra of blazars Synchrotron emission

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

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

Variability of blazars Microvariation –minutes to hours

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

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!

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

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

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

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

Causes of the variability Shock-in-jet model

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

Data analysis Finding power-law spectra

Data analysis Bluer-when-brighter tendency

Data analysis

not corresponding, SED deformation (thermal contribution from host galaxy or non-thermal contribution from different regions ?)

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

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

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

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

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

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

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:

THE END