Korean VLBI Network (KVN)

KVN Science Highlights


B-field environments of a blazar S5 0716+714

A KVN Key Science Program, the iMOGABA, has monitored a very compact, variable blazar S5 0716+714 simultaneously at four cm-mm bands (13mm-2.5mm) on sptial resolutions of milli-arcseconds. Observations were conducted in 29 sessions from 2013 January 16 to 2016 March 1, with the source being detected and imaged at all available frequencies. In all epochs, the source was compact on the milliarcsecond scale, yielding a compact VLBI core dominating the synchrotron emission on these scales. The turnover frequency was found to vary between 21 and 69 GHz during the observations. By assuming a synchrotron self-absorption model for the relativistic jet emission in S5 0716+714, the authors found the magnetic field strength in the mas emission region to be ≤5 mG during the observing period, yielding a weighted mean of 1.0 ± 0.6 mG for higher turnover frequencies (e.g., >45 GHz).

Variation in peak flux densitie s (1), turnover frequencies (2), magnetic fields (3), KVN flux densities (4), and deconvolved core sizes (5) in the time domain.
Variation in peak flux densities (1), turnover frequencies (2), magnetic fields (3), KVN flux densities (4), and deconvolved core sizes (5) in the time domain.
Publication: Interferometric Monitoring of Gamma-Ray Bright AGNs: S5 0716+714, 2017, ApJ 841, 119
Authors: Jee Won Lee, Sang-Sung Lee, Jeffrey A. Hodgson, Dae-Won Kim, Juan-Carlos Algaba,Sincheol Kang, Jiman Kang, Sungsoo S. Kim

Single-epoch results of a KVN KSP: iMOGABA

The iMOGABA program continues to aim at revealing the origins of the gamma-ray flares that are often detected in AGNs. One of the observing sessions in the program was conducted in 2013 on November 19 and 20, yielding 32 sources that were detected and imaged at all frequency bands with or without the use of the FPT technique. The first 129 GHz VLBI images were made from most of the sources, establishing a 129 GHz VLBI image database with a size of 32 sources. Thanks to simultaneous multifrequency VLBI observations, the authors are able to investigate the spectral properties, free from any source variability. We find that the sources become fainter at higher frequencies, yielding optically thin spectra at mm wavelengths.

 Spectra of the CLEAN flux density (black dot) and core flux density (red circle) for sources imaged at 22 129 GHz. The black solid lines are the best fitting power law.
Spectra of the CLEAN flux density (black dot) and core flux density (red circle) for sources imaged at 22 129 GHz. The black solid lines are the best fitting power law.
Publication: Interferometric Monitoring of Gamma-Ray Bright AGNs. I. The Results of Single-epoch Multifrequency Observations, 2016, ApJS 227, 8
Authors: Sang-Sung Lee, Kiyoaki Wajima, Juan-Carlos Algaba, Guang-Yao Zhao, Jeffrey A. Hodgson, Dae-Won Kim, Jongho Park, Jae-Young Kim, Atsushi Miyazaki, Do-Young Byun, Sincheol Kang, Jeong-Sook Kim, Soon-Wook Kim, Motoki Kino, Sascha Trippe

Spatially Resolved HCN Absorption Features in NGC 1052

The first VLBI detection of HCN molecular absorption in the nearby active galactic nucleus NGC 1052 was achieved by the KVN, spatially resolving the HCN absorption against a double-sided nuclear jet structure. Two velocity features of HCN absorption are detected significantly at the radial velocity of 1656 and 1719 km/s, redshifted by 149 and 212 km/s with respect to the systemic velocity of the galaxy. The absorption features show high optical depth localized on the receding jet side, where the free– free absorption occurred due to the circumnuclear torus. The redshifted velocities of the HCN absorption features imply that HCN absorbing gas traces ongoing infall motion inside the circumnuclear torus onto the central engine.

Possible model of the oriented double-sided jet and the circumnuclear torus. (A) A circumnuclear torus. (B) Eastern approaching jet. (C) HCN clouds. (D) Warm molecular region. (E) Plasma region. (F) Western receding jet.
Possible model of the oriented double-sided jet and the circumnuclear torus. (A) A circumnuclear torus. (B) Eastern approaching jet. (C) HCN clouds. (D) Warm molecular region. (E) Plasma region. (F) Western receding jet.
Publication: Spatially Resolved HCN Absorption Features in the Circumnuclear Region of NGC 1052, 2016, ApJL 830, 3
Authors: Satoko Sawada-Satoh, Duk-Gyoo Roh, Se-Jin Oh, Sang-Sung Lee, Do-Young Byun, Seiji Kameno, Jae-Hwan Yeom, Dong-Kyu Jung, Hyo-Ryoung Kim, and Ju-Yeon Hwang

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Korean VLBI Network (KVN)