Emissions from Shells Associated with Dying Radio Sources ＠ Workshop on East-Asian Collaboration for the SKA /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 γ e ~ 10 8 (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 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 sources The 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 , 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 Study Evolution of emissions from lobe and shell of dying radio sources jet Lobe-dominated shell-dominated Fading phase Jet active phase

・ spherical symmetry Assumptions Dynamics thin shell approximation (e. g., Ostriker & McKee 1988) t j ： duration of jet injection (I) blast wave with continuous energy injection (II) blast wave of instant energy (Sedov-Taylor expansion) ・ ambient density profile L j ： 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 - Target for SKA Shell emissions becomes dominant after the jet injection has ceased due to the rapid decrease of lobe emissions - 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