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RADIO RELICS IN CLUSTERS OF GALAXIES
GIOVANNINI GABRIELE,FERETTI LUIGINA The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.5
In this paper we review the observational results on Relic radio sources in clusters of galaxies. We discuss their observational properties, structures and radio spectra. We will show that Relics can be divided according to their size, morphology, and location in the galaxy cluster. These differences could be related to physical properties of Relic sources. The comparison with cluster conditions suggests that Relics could be related to shock waves originated by cluster mergers.
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
Hada, Kazuhiro,Doi, Akihiro,Wajima, Kiyoaki,D’Ammando, Filippo,Orienti, Monica,Giroletti, Marcello,Giovannini, Gabriele,Nakamura, Masanori,Asada, Keiichi American Astronomical Society 2018 The Astrophysical journal Vol.860 No.2
<P>We investigated the detailed radio structure of the jet of 1H 0323+342 using high-resolution multifrequency Very Long Baseline Array observations. This source is known as the nearest gamma-ray emitting radio-loud narrow-line Seyfert 1 (NLS1) galaxy. We discovered that the morphology of the inner jet is well characterized by a parabolic shape, indicating that the jet is continuously collimated near the jet base. On the other hand, we found that the jet expands more rapidly at larger scales, resulting in a conical shape. The location of the 'collimation break' is coincident with a bright quasi-stationary feature at mas from core (corresponding to a deprojected distance on the order of similar to 100 pc), where the jet width locally contracts together with highly polarized signals, suggesting a recollimation shock. We found that the collimation region is coincident with the region where the jet speed gradually accelerates, suggesting a coexistence of the jet acceleration and collimation zone, ending up with the recollimation shock, which could be a potential site of high-energy 7-ray flares detected by the Fermi-LAT. Remarkably, these observational features of the 1H 0323+342 jet are overall very similar to those of the nearby radio galaxy M87 and HST-1 as well as some blazars, suggesting that a common jet formation mechanism might be at work. Based on the similarity of the jet profile of the two sources, we also briefly discuss the mass of the central black hole of 1H 0323+342, which is also still highly controversial in this source and NLS in general.</P>