• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.59.3-59.3
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• 2017

We will present the activities of East Asian VLBI Network, EAVN, which consists of around 20 radio telescopes in Japan, Korea, and China with 6,500 km extend. It is a most sensitive and highest VLBI array in the world. We have conducted science verification observations at mainly 8 and 22 GHz. And Japanese VLBI array, VERA, and Korean VLBI array, KVN have combined as KaVA, Korean and VERA Array, and started science observations with open use at 22 and 43 GHz. We will presents some commissioning and science results based on it. Moreover Taiwan is constructing the Greenland telescope to be a millimeter and submillimeter VLBI station, which will be a very powerful station in Global millimeter and submillimeter VLBI array. These activities will be introduced as well.

• The Bulletin of The Korean Astronomical Society
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• v.34 no.1
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• pp.185.2-185.2
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• 2009

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.77-79
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• 2005

We had the first committee meeting of the East Asia VLBI Consortium during the EAMA6 meeting held in Seoul. A VLBI network composed of telescopes in the East Asia region could provide extreme properties, and the coordination of them has been expected. The Committee of the East Asia VLBI Consortium is a standing committee to promote activities of the consortium, in which participating countries at present are China, Japan, and Korea over eight institutes/observatories. Here we introduce the Consortium and Committee.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.240.2-240.2
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• 2012

AGN(Active Galactic Nucleus) consists of a supermassive black hole located at its center, an accretion disk around the black hole, and bipolar jets. Since May 2011, we have performed the MOGABA(Monitoring Of GAmma-ray Bright AGN) project for observing gamma-ray bright AGN once a week at multifrequencies using KVN(Korean VLBI Network) 21m radio telescopes. The MOGABA project is the observations for measuring the degree of polarization, polarization angle, and total flux of about 20 AGN at 22, 43 and 86GHz. By this project, we are able to investigate polarization characteristics, spectral index, and variation of rotation measure at radio wavelengths of gamma-ray bright AGN and to study possible relation between gamma-ray flares and magnetic field structure change in AGN. According to previous research, gamma-ray flares of some AGN are coincident with large changes in angle of linear polarization. In this paper we report the preliminary results of linear polarization and total flux at 22, 43, 86GHz of gamma-ray bright quasars 3C279 and 1510-089 showing noticeable variation of total flux at 22GHz in late 2011, and discuss possible correlation with gamma ray light curves.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.54.2-54.2
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• 2015

Phase referencing is an important tool to study weak radio sources, especially in mm-VLBI (Very Long Baseline Interferometry) which are usually too faint to be observed using conventional VLBI. VLBI astrometry is a unique method to measure the position and to identify radio emitting regions of a radio source with unprecedented angular resolution. In order to evaluate the phase referencing and astrometric capabilities of KVN and KaVA, several observations have been conducted and analyzed. I will present the observational results and discuss constraints and requirements for high precision VLBI astrometry.

• Publications of The Korean Astronomical Society
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• v.23 no.2
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• pp.37-45
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• 2008

We present the results of image simulations of 43.1 GHz SiO maser emission toward a Mira variable using the KVN (Korean VLBI Network) and other facilities which can make joint VLBI experiments with the KVN. To test the imaging capability of the KVN we used the image of SiO masers in the simulation obtained by the VLBA, which is considered to be the optimum VLBI facility at present to study SiO masers toward evolved stars. The simulated images of SiO maser emission confirm that coordinate VLBI expriments of KVN with several more stations in Japan or in the neighborhood of Korean Peninsula are necessary to exert the functional benefit of the KVN as the first mm VLBI facility which can perform simultaneous observations at four different frequency bands.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.104.1-104.1
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• 2014

한국우주전파관측망(KVN, Korea VLBI Network)의 우주전파수신시스템(22GHz, 43GHz, 86GHz, 129GHz의 4파수 동시관측 시스템)으로부터 수신된 전파신호를 디지털 신호로 바꾸어 주는 장치인 초고속 샘플러의 국산화와 성능 향상을 위하여, 우리는 1GHz 샘플링을 할 수 있는 전파관측 자료의 샘플링 장치를 설계, 제작하였다. GHz 샘플링 기본 기술 확보와 독자 개발을 위하여 제작된 1GHz 샘플러를 KVN울산전파천문대에 설치하여 관측 시험한 결과, 연구 관측에 적용할 수 있음을 보여 주었다. 한편, 광대역 관측과 e-VLBI 구현을 위하여 샘플러에서 직접 첨단망으로 VDIF(VLBI Data Interchange Format, VLBI 자료전송 규격)의 자료를 보낼 수 있는 차세대 4GHz 샘플러를 개발 중에 있다. 이번 발표에서는 1GHz 샘플러에 대한 개발 내용과 관측 결과 및 향후 계획을 소개한다.

• Journal of the Institute of Convergence Signal Processing
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• v.17 no.2
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• pp.83-92
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• 2016

In this paper, we introduce the results of the testing and observation systems for performance wideband expansion in the Korean VLBI Network(KVN). The KVN performs VLBI observations to 1024 Mbps data rate, and 8192 Mbps observing for four simultaneous observation is now evaluating for normal operation. The VLBI stations in several world countries developed their own wideband observing systems to observe the celestial objects with high precision and high resolution or are working with several countries. The KVN is planning to introduce a high-speed sampler, OCTAD, for sampling directly up to 2048 MHz bandwidth for RF signal of K/Q/W/D band in the frequency band without conversion. Therefore, as a preliminary study for the performance scalability of the KVN then through the close cooperation with National Astronomical Observatory of Japan (NAOJ), the OCTAD high-speed sampler and OCTADISK2 high-speed recorder were installed in the KVN Yonsei station, and verify the performance through a wideband.

• Publications of The Korean Astronomical Society
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• v.27 no.1
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• pp.1-16
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• 2012

In this paper, we describe the installation of VLBI Correlation Subsystem (VCS) main product and its performance at the Korea-Japan Correlation Center (KJCC). The VCS main product was installed at KJCC in August 2009. For the overall performance evaluation of VCS, playbacks, Raw VLBI Data Buffer (RVDB) system, and Data Archive (DA) system were installed together. The VCS main product was connected between RVDB and DA, and the correlation results were put into the DA to confirm the normal operation of VCS 16 station mode configuration. The evaluation test was first performed with 4 station mode, same as the factory test of VCS main product. Based on the results of 4 station mode, the same evaluation test was conducted for 16 station mode of VCS. We found that the correlation results of VCS were almost similarly compared to those of the Mitaka FX Correlator. Through the test results, we confirmed that the problems such as spectrum errors, delay parameter processing module and field programmable gate array errors in antenna unit, which were generated at the factory test of VCS main product, were clearly solved. And we verified the performance and connectivity of VCS by obtaining the expected correlation results and we also confirmed that the performance of VCS was sufficient for real VLBI observation data in both 4 and 16 station modes.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.51.1-51.1
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• 2018

동아시아 VLBI 관측망(East-Asian VLBI Network; EAVN)은 한 중 일 각국의 전파망원경을 통합해서 구성되는 동아시아 지역의 새로운 VLBI 네트워크이다. EAVN은 2013년부터 공동이용관측을 실시하고 있는 한일 VLBI 관측망(KaVA)을 중심으로 총 20개 전파망원경을 포함한다. 4개 주파수(6.7/8/22/43 GHz)로 관측할 수 있으며, 최대로 0.6 mas (22 GHz)의 해상도로 관측할 수 있는 기능을 가지고 있다. 우리는 2017년 3월부터 5월까지 EAVN을 이용한 총 17번의 AGN 관측 캠페인을 실시하였다. 이것은 ALMA를 이용한 Event Horizon Telescope (EHT) 관측과 같은 시기에 실시되며, 총 15개의 전파망원경이 참가하였다. 이 관측을 통해서 EAVN으로 얻은 영상이 KaVA의 영상에 대해 80% 정도 성능이 개선되는 것을 확인하였다. 또한, 주된 관측천체인 M87과 Sgr A*의 영상은 과거의 결과를 재현해서 AGN 중심 주변의 sub-pc 스케일의 제트 구조를 보다 자세히 볼 수가 있었다. 이 결과에 의거해서 우리는 KaVA의 관측시간의 일부를 이용해서 2018년 하반기부터 EAVN의 공동이용관측을 시작한다. 공개될 범위는 KaVA, 일본 Nobeyama 45 m, 중국 Tianma 65 m의 총 9개 망원경이며, 중국 Nanshan 26 m 망원경도 Large Program 관측에 한해서 참가한다. 관측주파수는 22 GHz (KaVA + Tianma) 및 43 GHz (KaVA + Tianma + Nobeyama) 이며, 오는 관측시즌(2018년 8월부터 2019년 1월까지)에 제공될 총 관측시간은 100 시간이다. 관측제안서 제출 마감날은 6월 1일이며, 많은 관측제안서가 제출될 것을 기대한다. 이 발표에서는 EAVN AGN 캠페인의 결과 및 EAVN 공동이용 관측의 자세한 내용을 보고한다.