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KEY SCIENCE OBSERVATIONS OF AGNs WITH THE KaVA ARRAY
KINO, MOTOKI,NIINUMA, KOTARO,ZHAO, GUANG-YAO,SOHN, BONG WON The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
KaVA (KVN and VERA Array) is a new combined VLBI array composed of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). Here, we report the following two issues. (1) We review the initial results of imaging observations of M87 at 23 GHz following Niinuma et al. (2014). The KaVA images reveal extended outflows including complex substructures such as knots and limb-brightening, in agreement with previous VLBI observations. KaVA achieves a high dynamic range of ~1000, more than three times better than that achieved by VERA alone. (2) Based on subsequent observations and discussions led by the KaVA AGN SubWorking Group, we set monitoring observations of Sgr $A^{\ast}$ and M87 as our Key Science Project (hereafter KSP) because of the closeness and largeness of their central super-massive black holes. The main science goals of the KSP are (i) testing the magnetically-driven-jet paradigm by mapping velocity fields of the M87 jet, and (ii) obtaining tight constraints on physical properties of the radio emitting region in Sgr $A^{\ast}$. Towards KSP, we show the first preliminary images of M87 at 23 GHz and Sgr $A^{\ast}$ at 43 GHz with the bandwidth of 256 MHz.
Probing the precise location of the radio core in the TeV blazar Mrk 501 with VERA at 43 GHz
Koyama, Shoko,Kino, Motoki,Doi, Akihiro,Niinuma, Kotaro,Hada, Kazuhiro,Nagai, Hiroshi,Honma, Mareki,Akiyama, Kazunori,Giroletti, Marcello,Giovannini, Gabriele,Orienti, Monica,Isobe, Naoki,Kataoka, Jun Astronomical Society of Japan 2015 Publications of the Astronomical Society of Japan Vol.67 No.4
THE FATE OF DEAD RADIO-LOUD ACTIVE GALACTIC NUCLEI: A NEW PREDICTION OF LONG-LIVED SHELL EMISSION
Ito, Hirotaka,Kino, Motoki,Kawakatu, Nozomu,Orienti, Monica IOP Publishing 2015 The Astrophysical journal Vol.806 No.2
<P>We examine the fate of a dead radio source in which jet injection from the central engine has stopped at an early stage of its evolution (t = t(j) less than or similar to 10(5) years). To this aim, we theoretically evaluate the evolution of the emission from both the lobe and the shell, which are composed of shocked jet matter and a shocked ambient medium (i.e., shell), respectively. Based on a simple dynamical model of expanding lobe and shell, we clarify how the broadband spectrum of each component evolves before and after the cessation of the jet activity. It is shown that the spectrum is strongly dominated by the lobe emission while the jet is active (t <= t(j)). On the other hand, once the jet activity has ceased (t> t(j)), the lobe emission fades out rapidly, since fresh electrons are no longer supplied from the jet. Meanwhile, shell emission only shows a gradual decrease, since fresh electrons are continuously supplied from the bow shock that is propagating into the ambient medium. As a result, overall emission from the shell overwhelms that from the lobe at a wide range of frequencies from radio up to gamma-ray soon after the jet activity has ceased. Our result predicts a new class of dead radio sources that are dominated by shell emission. We suggest that the emission from the shell can be probed in particular at radio wavelengths with the Square Kilometer Array phase 1.</P>