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The East-Asian VLBI Network: Recent Progress and Results of the First Imaging Test Observation
Kiyoaki Wajima,Duk-Gyoo Roh,Se-Jin Oh,Taehyun Jung,Jongsoo Kim,Yoshiaki Hagiwara,Kazuhiro Hada,Noriyuki Kawaguchi,Hideyuki Kobayashi,Yuanwei Wu,Kenta Fujisawa,Tao An,Willem A. Baan,Wu Jiang,Zhi-Qiang 한국천문학회 2016 天文學會報 Vol.41 No.1
Intraday Variability Feature and Milliarcsecond-Scale Structure in PKS 1622-297
Kiyoaki Wajima,Hayley E. Bignall,Hideyuki Kobayashi,Hisashi Hirabayashi,Kenta Fujisawa,Masato Tsuboi,Philip G. Edwards,Yasuhiro Murata 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.4
PKS 1622.297 is the most luminous gamma-ray emitting active galactic nucleus (AGN) ever detected and shows a gamma-ray intraday variability (IDV). We made a high-resolution space very long baseline interferometry (VLBI) observation of the source almost three years after the gammaray IDV. The source shows a compact core-jet structure, and all jet components have an apparent superluminal motion up to 12 h.1c. As an alternative probe of the sub-parsec scale structure, we also present the results from multi-epoch Australia Telescope Compact Array (ATCA) total flux monitoring, which indicate the presence of IDV. We examine the inner structure of the gamma-ray emitting AGN in light of these observations.
A FANAROFF-RILEY TYPE I CANDIDATE IN NARROW-LINE SEYFERT 1 GALAXY Mrk 1239
Doi, Akihiro,Wajima, Kiyoaki,Hagiwara, Yoshiaki,Inoue, Makoto IOP Publishing 2015 ASTROPHYSICAL JOURNAL LETTERS - Vol.798 No.2
<P>We report finding kiloparsec-scale radio emissions aligned with parsec-scale jet structures in the narrow-line Seyfert 1 (NLS1) galaxy Mrk 1239 using the Very Large Array and the Very Long Baseline Array. Thus, this radio-quiet NLS1 has a jet-producing central engine driven by essentially the same mechanism as that of other radio-loud active galactic nuclei (AGNs). Most of the radio luminosity is concentrated within 100 parsecs and overall radio morphology looks edge-darkened; the estimated jet kinetic power is comparable to Fanaroff-Riley Type I radio galaxies. The conversion from accretion to jet power appears to be highly inefficient in this highly accreting low-mass black hole system compared with that in a low-luminosity AGN with similar radio power driven by a sub-Eddington, high-mass black hole. Thus, Mrk 1239 is a crucial probe to the unexplored parameter spaces of central engines for a jet formation.</P>
Lee, Sang-Sung,Wajima, Kiyoaki,Algaba, Juan-Carlos,Zhao, Guang-Yao,Hodgson, Jeffrey A.,Kim, Dae-Won,Park, Jongho,Kim, Jae-Young,Miyazaki, Atsushi,Byun, Do-Young,Kang, Sincheol,Kim, Jeong-Sook,Kim, Soo American Astronomical Society 2016 The Astrophysical journal Supplement series Vol.227 No.1
<P>We present results of single-epoch very long baseline interferometry (VLBI) observations of gamma-ray bright active galactic nuclei (AGNs) using the Korean VLBI Network (KVN) at the 22, 43, 86, and 129 GHz bands, which are part of a KVN key science program, Interferometric Monitoring of Gamma-Ray Bright AGNs. We selected a total of 34 radio-loud AGNs of which 30 sources are gamma-ray bright AGNs with flux densities of >6 x 10(-10) ph cm(-2) s(-1). Single-epoch multifrequency VLBI observations of the target sources were conducted during a 24 hr session on 2013 November 19 and 20. All observed sources were detected and imaged at all frequency bands, with or without a frequency phase transfer technique, which enabled the imaging of 12 faint sources at 129 GHz, except for one source. Many of the target sources are resolved on milliarcsecond scales, yielding a core-jet structure, with the VLBI core dominating the synchrotron emission on a milliarcsecond scale. CLEAN flux densities of the target sources are 0.43-28 Jy, 0.32-21 Jy, 0.18-11 Jy, and 0.35-8.0 Jy in the 22, 43, 86, and 129 GHz bands, respectively. Spectra of the target sources become steeper at higher frequency, with spectral index means of -0.40, -0.62, and -1.00 in the 22-43 GHz, 43-86 GHz and 86-129 GHz bands, respectively, implying that the target sources become optically thin at higher frequencies (e.g., 86-129 GHz).</P>
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>