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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>
SAWADA-SATOH, S.,AKIYAMA, K.,NIINUMA, K.,NAGAI, H.,KINO, M.,D'AMMANDO, F.,KOYAMA, S.,HADA, K.,ORIENTI, M.,HONMA, M.,SHIBATA, K.M. The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
We present a kinematic study of the parsec-scale radio jet in OJ 287, one of the most studied BL Lac objects, during ${\gamma}$-ray flares, to explore the relation between parsec-scale radio jet activity and ${\gamma}$-ray emission. The 22-GHz light curve of OJ 287 show three obvious flare events around 2011 May, 2011 October, and 2012 March. The second radio flare occurred during the ${\gamma}$-ray flaring period, and the third radio flare seemed to precede the ${\gamma}$-ray flare by one month. One jet component moved outward with respect to the core component with an apparent superluminal speed (~ 11c) from 2010 November to 2011 November. Then it changed direction, moving apparently inward in 2011 November, when the ${\gamma}$-ray flare occurred. The observed apparent inward motion of the jet at 22 GHz could be caused by a new jet component, unresolved at 22 GHz, in the innermost region.