Modeling the SED and variability of 3C66A in 2003/2004 Presented By Manasvita Joshi Ohio University, Athens, OH ISCRA, Erice, Italy 2006

Outline Introduction Motivation Model Sketch Observational Constraints Parameter Estimates Motivation of Parameters Summary

Blazar Modeling Relativistic jet outflow with  ≈ 10 Injection, acceleration of ultrarelativistic electrons Q e ( ,t)  Synchrotron emission F Compton emission F    -q Seed photons: Synchrotron (SSC), Accr. Disk + BLR (EC) Injection over finite length near the base of the jet. Additional contribution from absorption along the jet

Motivation 3C66A - promising candidate for detection by new generation of atmospheric Cherenkov telescopes (STACEE, VERITAS). Has been studied in radio, IR, optical, X-ray and -ray. Multiwavelength SED and correlated broadband spectral variability not been completely understood. Few attempts towards simultaneous observations, making it difficult to constrain physical emission models. Led to the organization of an intensive multiwavelength campaign from July 2003-April 2004.

One-zone homogenous, time-dependent leptonic model considered. Particle distribution and spectrum of emitted radiation calculated self-consistently. Instantaneous and time-integrated spectra calculated for various sets of parameters. Model Sketch

1. Emitting region as a sphere of constant co- moving radius R B. 2. Homogenous and tangled magnetic field B. 3. Ultra-relativistic non-thermal e - s injected at a time-dependent rate into the blob. Basic assumptions :

Solve simultaneously for evolution of electron distribution, and co-moving photon distribution, Rad. + Adiab. lossesel./pair inj. escape Sy., comp. emission SSA, γγ absorption escape e - density Photon density

Synchrotron Self Absorption (SSA) calculated self-consistently. Pair production negligible for present choice of parameters. For Synchrotron Self Compton (SSC), isotropic (co-moving frame) radiation field assumed. External Inverse Compton (EIC) component not considered yet.

Modelling Strategy Code of Boettcher & Chiang (2002) used. 1. Reproduce broadband spectrum of 3C66A for equilibrium situation (quiescent state). 2. Adjust parameters to fit both (time-averaged) Spectral Energy Distribution (SED) and optical spectral variability patterns.

Spectral Energy Distribution

Observational Constraints SL motion up to, = Bulk Lorentz Factor Optical variability, hr, cm Doppler Factor, Peak synchrotron flux ergs cm -2 s -1

Analytical Parameter Estimates and, = Equipartition Parameter Magnetic field, G Electron Lorentz Factor, synchrotron peak, synchrotron high-energy cutoff,

Synchrotron cooling time scale in observer’s frame s For optical frequencies, hr Particle spectral index, p ~ 4 Particle injection spectral index, q ~ 3 Disk injection luminosity, ergs/sec Boettcher et al., 2005

Motivation of Parameters VLBA observations indicate bending of jet in the line of sight Viewing angle, assuming Jet components don’t exhibit superluminal motion except one, hence Doppler Factor not well constrained. gives good fit. X-rays being dominated by outbursts.

Boettcher et al., 2005

Optical spectral variability Hardness Brightness Low brightness High brightness Slight positive correlation No correlation

0.72 Brighter in B, Harder in B-R

Spectral Energy Distribution

absorption

Summary & used to reproduce the SED. Magnetic field allowed to evolve in time by setting e B = 1. Flaring state of 3C66A simulated using Gaussian flaring profile. Optical and soft X-ray photons of flaring state produced by synchrotron emission. Hard X-ray and VHE photons from SSC emission.

Object exhibits a positive correlation of brighter when harder for a 10 day period –May not apply for long term variability of over a month. Synchrotron cooling, minimum variability & dynamical timescale all of the same order –Size of emission region absorption due to IIRB not significant till 100 GeV. Summary contd…..