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 ModelingRelativistic jet outflow with ≈ 10

Injection, acceleration of ultrarelativistic

electrons

Qe (,

t)

Synchrotronemission

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 RB.

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,

eesc

eee

e

t

tntQn

t

tn

,

,,

,

phesc

phabsphemph

ph

t

tntntn

t

tn

,,,

,,,

,

Rad. + Adiab. losses

el./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 DistributionHzsyn

15100.1

Hzcutoffsyn18

_ 10

Observational Constraints • SL motion up to , = Bulk Lorentz

Factor

• Optical variability, hr, cm

• Doppler Factor,

• Peak synchrotron flux ergs cm -2 s-1

99~ app

115102.2 DRB

15~10 1DD

11105~ syf

2~mint

Analytical Parameter Estimates

• and , = Equipartition Parameter

• Magnetic field, G

• Electron Lorentz Factor,

synchrotron peak,

synchrotron high-energy cutoff ,

7/2114.4 Be eDB

B

2/12/12/1

153

9.215101.3

G

BD

31 101.3

52 105.1

5.11 D 1Be Be

• 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

2/115

2/32/13

, 9.215108.2

G

BDobssycool

2, obssycool

41108.6 injL

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.

4.2~obs

1

24D

hrscoolsyn 3.1,

Hzsyn141028.4

Hzssc211069.1

Hzsyn151013.1

HzSSC22109.2

.min46, coolsyn

HzcutoffSSC26

, 1042.2

Hzcutoffsyn18

_ 1004.1

HzcutoffSSC25

_ 1053.5

Boettcher et al., 2005

dayst 10

magR 53.0

• 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

ee

HzcutoffSSC25

, 1089.2

Summary

• & used to reproduce the SED.• Magnetic field allowed to evolve in time by

setting eB = 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.

24 4.2obs

• 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…..

cmRB15104

JyHzF keV 96.01,