Emissions from Shells Associated with Dying

Radio Sources

＠Workshop on East-Asian Collaboration for the SKA　 2011 12/2

Hirotaka Ito 　 YITP, Kyoto University 　　　Collabolators

Nozomu Kawakatu 　 Tsukuba University 　　Motoki Kino 　 NAOJ 　

Shocked Shell

Forward shock

Radio lobe

Jet

Lobe 　　　　　　　

Shell 　　　　　　　　　

Energy dissipation

shell

Shell = shocked ambient gas

Comparable energy is deposited in the lobe and shell

Non-thermal synchrotron emission (S ν∝ -α )

Centausus A

Shell γe ~ 108 　 (B/10μ Ｇ ) -1/2

Chandra

e.g., 　 Fujita+(2007, 2011), Berezhko (2008), Ito+(2011)

X-ray observation of shell

Shocked shells offer sites for particle accelerations

Croston + (2009)

- comparable energy is deposited in the lobe and shell

e.g., Carilli et al. 1998

- prominent radio emission from lobe is confirmed in large number of sources

- no radio emission is detected in shell 　　（ few nearby sources are detected X-ray ）

Lobe emission dominated over the shell emissions

- lobe and shell are site of particle acceleration

　 Shells in dying radio sourcesThe fraction （ ~15-30% ） of young compact radio sources （ R<few kpc ） in the flux-limited catalogues is much larger than that expected from their age (~0.01%)

e.g., Gugliucci + 2005, Kunert-Bajaszewska+2005, 2006, Orienti+2008,2010

Lobe emission fades rapidly (fader)

Emission from sources after the jet injection has ceased

e.g, Reynolds+ 1997, Mocz+2010, Nath 2010

fresh electrons are no longer supplied

electrons are continuously supplied from the bow shock

Shell emission becomes dominant

Shell emissions only show gradual decrease

significant fraction of young sources may be short-lived

Present StudyEvolution of emissions from lobe and shell of dying radio sources 　　　　　　　

jet

Lobe-dominated

shell-dominated

Fading phase

Jet active phase

・ spherical symmetry Assumptions

Dynamicsthin shell approximation (e. g., Ostriker & McKee 1988)

tj ： duration of jet injection

(I) blast wave with continuous energy injection

(II)

blast wave of instant energy (Sedov-Taylor expansion)

・ ambient density profile

Lj ： jet power

Non-thermal electrons (shell)

Adiabatic cooling

Synchrotron

Inverse Compton （ IC ）

・ cooling

・ injection

Maximum energy

Normalization factor- UV emission (accretion disc)

- CMB

- IR emission (dusty torus)

- NIR emission (host galaxy)

Seed photons

- Radio emission (Lobe) compression of ISM magnetic field

・ cooling

・ injection

Maximum energy

Normalization factor

No emission from core

compression of ISM magnetic field

Adiabatic cooling

Synchrotron

Inverse Compton （ IC ）

- CMB

- NIR emission (host galaxy)

Seed photons

- Radio emission (Lobe)

Non-thermal electrons (shell)

・ cooling

・ injection

Maximum energy

Normalization factor

10% of the equipartition value

Non-thermal electrons (lobe)

Adiabatic cooling

Synchrotron

Inverse Compton （ IC ）

- UV emission (accretion disc)

- CMB

- IR emission (dusty torus)

- NIR emission (host galaxy)

Seed photons

- Radio emission (Lobe)

・ cooling

・ injection

No injection

Non-thermal electrons (lobe)

No emission from core

Adiabatic cooling

Synchrotron

Inverse Compton （ IC ）

- CMB

- NIR emission (host galaxy)

Seed photons

- Radio emission (Lobe)

Evolution of energy distribution of non-thermal electrons

High energy electrons within the lobe depletes due to the absence of injection

t=10^5 yr (R~1.5kpc)

t=5×10^5 yr (R~5kpc)

t=10^6 yr (R~8kpc)

t=10^7 yr (R~30kpc)

Radiative cooling

SHELL LOBE

after the jet injection has ceased emission is dominted by the shell

Evolution of emission spectrum

candidates for unID radio sources

good target for SKA

D=1Gpc

Detectection prospects

Using simple dynamical model, we evaluated the emissions from dying young radio sources

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Target for SKA

Shell emissions becomes dominant after the jet injection has ceased due to the rapid decrease of lobe emissions

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Summary

- Emissions from the shell is essential for studying the properties of dying radio sources

- Some of the unidentified radio sources may be attributed by the shell emissions