P Mimica talk at Ringberg Caste, 9th of December 2008

8/14/2019 P Mimica talk at Ringberg Caste, 9th of December 2008

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Introduction Hydrodynamic model Non-thermal particles and emission Summary

Spectral evolution of superluminalcomponents in parsec scale jets

Petar Mimica1

in collaboration with

M.-A. Aloy1 I. Agudo2

J. M. Mart1 J. L. Gmez2 J. A. Miralles3

1Departament dAstronomia i Astrofsica, Universitat de Valncia

2Instituto de Astrofsica de Andaluca (CSIC), Granada

3Departament de Fsica Aplicada, Universitat dAlacant

Ringberg Castle, December 9th, 2008


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Emission from parsec scale jets

intensive VLBI monitoring of innermost regions of relativistic jetsreveals rich emission structure and variability, e.g.:

stationary features: standing knots of increased radio emission associatedwith the internal oblique shockssuperluminal components: radio emitting plasma moving at apparent

superluminal velocities, associated with injection of material into the jettrailing components: slow or quasi-stationary features trailing superluminalcomponents

observed emission influenced by a number of effects (timedelays, Doppler boost, light abberation, opacity, Faraday rotation,...) and not a direct map of jet physical state

comparisons with relativistic (magneto)hydrodynamics andemission simulations needed to understand the inner jet

dynamics


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Modeling jet emission (1)

Analytical models

basis for the interpretation of observations: radiation coming from

relativistic compact source (Blandford & Knigl 1979), observed spectrum

due to non-thermal (synchrotron and inverse-Compton) emission (e.g.,

Marscher 1980; Knigl 1981)

apparent superluminal motions associated to travelling shock waves

(Blandford & McKee 1976; Marscher & Gear 1985; Hughes, Aller & Aller 1985;

Marsher & Travis 1992)

Numerical kinematic models

tests of jet hypothesis through detailed comparison with observations

assume idealized jet models and integrate radiative transfer equations

(e.g., Daly & Marscher 1988; Hugher, Aller & Aller 1989, 1991; Gmez, Alberdi &Marcaide 1993, 1994; Gmez et al. 1994)


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Modeling jet emission (2)

Numerical hydrodynamic models

modern high resolution R(M)HD schemes study jet properties underrealistic conditions (strong shocks, relativistic internal energy, relativistic

bulk velocities, presence of magnetic field, ...)

calculation of emission from hydrodynamic simulations (e.g. Gomez et al.

1995, 1997; Duncan, Hughes & Opperman, Komissarov & Falle 1997), assumerelation between the thermal fluid and the loclal magnetic field,

synchrotron emission and absorption, no transport or synchrotron losses

Non-thermal particle transport

spectral evolution and transport of non-thermal particles innon-relativistic plasmas (Jones, Ryu & Engel 1999; Micono et al. 1999;

Tregillis, Jones & Ryu 2001; Casse & Marcowith 2003)

relevant for multiband observations (e.g., optical to X-ray), where

radiative losses may be important


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Motivation for our work

goal: as consistenly as possible couple R(M)HD simulations toNTP transport, evolution and radiation

ingredient 1: RMHD simulations


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Hydrodynamic model

Introduction Hydrodynamic model Non thermal particles and emission Summary


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Building blocks

based on models of Gomez et al. (1997) and Agudo et al. (2001)

atmosphere (fills the whole domain)

quiescent jet (radius Rb at the nozzle, underdense)

velocity perturbation injected at the nozzle (generation ofhydrodynamic perturbations)



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Atmosphere

the pressure in the atmosphere follows the law (Gomez et al. 1997)

P(z) = Pa[1 + (z/zc)n]m/n

atmosphere adiabatic, profile kept frozen via the extra forceadded to it

this profile induces paraboloid shape of the jet



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Jet parameters

Pressure-matched jet (PM)

b/a = 103

Pb(z = 0) = Pb

b = 4

ideal gas EOS withad = 4/3

Overpressured jet (OP)

b/a = 103

Pb(z = 0) = 1.5Pb

b = 4

ideal gas EOS withad = 4/3



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Numerical hydrodynamics scheme

RGENESIS (Mimica et al. 2004) was used for RHD simulations(conservative, Eulerian, Godunov-type, high-resolution shockcapturing scheme)

cyllindrical symmetry with (10Rb 200Rb) domain in the (r z)plane

8 numerical cells per Rb



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y y p y

Jets

PM jet density



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y y p y

Jets

PM jet Lorentz factor



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Jets

OP jet density



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Jets

OP jet Lorentz factor



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Perturbation parameters

duration: 0.75Rb/c

p = 10

p = b

Pp = Pb



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Evolution of the perturbation



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Non-thermal particles and emission



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Method overview

Modules

NTP transport and spectral evolution (SPEV)

synchrotron emission and absorption

radiative transfer



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SPEV

a large number of Lagrangian particles injected through the jet nozzle

their energy losses are of the form

dp

dt= p

3 + B(p,t)

adiabatic and synhcrotron terms

= D ln Dt

; B(p,t) = 4Tp2UB

3m2ec2

within a hydro time step we assume

p dpdt

= kap ksp2

non-thermal particle evolution in momentum space is governed by theensemble-averaged Boltzmann equation (e.g.,Webb 1985; Miralles et al.

1993; Kirk 1995)



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SPEV

discretization in momentum space ( p/mec) in Nb bins with interfaces

i(t = 0) = min

maxmin

(i1)/Nb; i = 1, ..., Nb + 1

evolution of interfaces

i(t) = i(t0) eka(tt0)

h1 + it0(e

ka(tt0) 1)ks/kai1

evolution of the differential number density at the interfaces

n(t, i(t)) = n(t0, i(t0)) e2ka(tt0) h1 + it0(eka(tt0)

1)ks/kai2

evolution of the number density in each bin

N(t, i(t), i+1(t)) =N(t0, i(t0), i+1(t0)) e3ka(tt0)

in each bin n(t, ) = n(t, i(t)) [/i(t)]qi(t)



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Synchrotron emission and radiative transfer

j(t, ) and (t, ) computed numerically for each Lagrangianparticle, assuming randomly oriented magnetic field

b =

8P/B

we compute images at several observational frequencies for anumber of instants in the observer time

radiative transfer equation is solved for each element of eachimage



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Parameters

following Gomez et al. (1997), Agudo et al. (2001)

NTP particle number N = cN/mp and energy density U= cUPchosen such that min 300 at the nozzle

power-law index at injection p = 2.2

fiducial model b = 0.02 G at the nozzle

high-B model: b = 0.2 G at the nozzle

viewing angle = 10

thin emission at observing frequencies (15, 22 and 43 GHz)



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Radio emission (fiducial)

OP fiducial at 43 GHz

SPEV

adiabatic

bright knots associated to cross (recollimation) shocks

intensity decreasing with distance (jet opens)

source optically thin at the core (actually first recollimation shock)



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Radio emission (high-B)

OP highB at 43 GHz

SPEV

adiabatic

models with losses produce shorter jet

relative variation in intensity larger in models with losses

same hydro as previous slide, magnetic field still dynamicallyunimportant, but much shorter jet!



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Particle evolution



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Particle evolution



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Particle evolution



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Spectral properties

0

1

2

13

15 GHz22 GHz43 GHz

PM OP

0 5 10 15 20 25

zobs

[Rb]

0

1

2

0 5 10 15 20 25

zobs

[Rb]

PM

-0,6

-0,4

-0,2

0

0,2

13

OP

0 5 10 15 20 25

zobs

[Rb]

0 5 10 15 20 25

zobs

[Rb]

-2,5

-2

-1,5

-1

-0,5

0

13

ave

rage

specific

intensity



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Quiescent emission

losses-dominated and adiabatic regions (e.g. Marscher & Gear 1985)

for the same background hydro, increase in the magnetic field,shortens the jet

observed intensity constrast between shocked and unshocked jetregions increases with magnetic field

flat optically thin spectrum at the nozzle



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Fiducial model



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High-B models



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High-B models



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Evolution of the component



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Spectral evolution (1)



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PM highB

-1

-0,5

0

0,5

1

-1

-0,5

0

0,5

1

0 10 20

zobs

[Rb]

-1

-0,5

0

0,5

1

0 10 20

zobs

[Rb]

0.02 y

0.39 y

0.75 y 4.58 y

1.94 y

1.12 y

RGB:

(IP(z) IQ(z))/max|Ip(z) IQ(z)|for 15, 22, and 43 GHz

black:

5(P13(z) Q13(z))/max|Q13(z)|main component clearly seen in all

three frequencies

spectral steepening behind intensity

maximum, because NTPs cool faster

than emiting volume light crossing

time (e.g. Chiaberge & Ghisellini 1999)

at 43 GHz features behing the localspectral index minimum (1.94 and 4.58years) identifiable with the trailing

components (e.g. Agudo et al. 2001)

observational imprint strongly

frequency dependent



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PM fiducial

-1

-0,5

0

0,5

1

-1

-0,5

0

0,5

1

0 10 20

zobs

[Rb]

-1

-0,5

00,5

1

0 10 20

zobs

[Rb]

0.02 y

0.39 y

0.75 y 4.58 y

1.94 y

1.12 y

OP fiducial

-1

-0,5

0

0,5

1

-1

-0,5

0

0,5

1

0 10 20

zobs

[Rb]

-1

-0,5

00,5

1

0 10 20

zobs

[Rb]

0.02 y

0.39 y

0.75 y 4.58 y

1.94 y

1.12 y



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Spacetime anaysis

main component is superluminal,

intermittent for OP model

PM: trailing components with

increasing apparent velocities(Agudo et al. 2001), associated to

KH modes in the beam

OP: trailing components due to

non-linear interaction with

standing shocks

clear identification of trailings

close to the nozzle only at 43 GHz



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Summary

numerical method

SPEV, a new method for consistent calculation of transport, evolution andsynchrotron emission from non-thermal particles developed and validatedto do: injection at shocks, polarization, inverse Compton

emission from pc scale jetquiescent jet emission: losses-dominated and adiabatic regimes, with knotsclose to nozzle brighter than if losses are ignoredeven dynamically negligible mag. field play a major role when going fromhydro to observationscomponent emission: with respect to the adiabatic models, superluminalcomponent appears brighter (dimmer) in the losses-dominated (adiabatic)

regimeMimica et al. 2008, ApJ submitted, arXiv:0811.1143



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Spectral properties (2)

102

103

104

105

106

10-5

10-4

10-3

10-2

10-1

100

n()

R15

(x)

R43

(x)

n() R15

(x)

n() R43

(x)

jsyn() =

3e3B

4mec2 Zmax

min

d n0p R

02

(1p)/2



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Spectral properties (2)

102

103

104

105

106

10-5

10-4

10-3

10-2

10-1

100

n()

R15

(x)

R43

(x)

n() R15

(x)

n() R43

(x)

jsyn() =

3e3B

4mec2

Zmaxmin

d n0p R

02

not (1p)/2

P Mimica talk at Ringberg Caste, 9th of December 2008

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