• 천문학회보
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• 제34권1호
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• pp.185.1-185.1
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• 2009

• 천문학회보
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• 제39권2호
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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.

• 천문학회보
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• 제42권2호
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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.

• 천문학회지
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• 제48권5호
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• pp.229-236
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• 2015

We report results of investigation of amplitude calibration for very long baseline interferometry (VLBI) observations with Korean VLBI Network (KVN). Amplitude correction factors are estimated based on comparison of KVN observations at 22 GHz correlated by Daejeon hardware correlator and DiFX software correlator in Korea Astronomy and Space Science Institute (KASI) with Very Long Baseline Array (VLBA) observations at 22 GHz by DiFX software correlator in National Radio Astronomy Observatory (NRAO). We used the observations for compact radio sources, 3C 454.3, NRAO 512, OJ 287, BL Lac, 3C 279, 1633+382, and 1510–089, which are almost unresolved for baselines in a range of 350-477 km. Visibility data of the sources obtained with similar baselines at KVN and VLBA are selected, fringe-fitted, calibrated, and compared for their amplitudes. We find that visibility amplitudes of KVN observations should be corrected by factors of 1.10 and 1.35 when correlated by DiFX and Daejeon correlators, respectively. These correction factors are attributed to the combination of two steps of 2-bit quantization in KVN observing systems and characteristics of Daejeon correlator.

• 천문학회보
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• 제44권1호
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• pp.73.3-73.3
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• 2019

A Korean VLBI Network $1^{st}$ generation key science program, the Interferometric Monitoring of Gamma-ray Bright AGNs (iMOGABA) program has revealed various natures of gamma-ray flares in active galactic nuclei (AGNs). Here in this presentation, we would like to introduce a new candidate of KVN $2^{nd}$ generation key science program, so called, the AiMOGABA (Astrometric iMOGABA), aiming at studying a wondering radio core effect of relativistic jets from AGNs with high resolution VLBI astrometric monitoring of high-energy bursting AGNs with KVN as well as a Australian millimeter radio telescope MOPRA. The introduction will include the current scientific highlights of the iMOGABA, and the overview of the AiMOGABA.

• Journal of Astronomy and Space Sciences
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• 제27권2호
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• pp.107-116
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• 2010

We developed the playback control software for a high-speed playback system which is a component of the Korea-Japan Joint VLBI Correlator (KJJVC). The Mark5B system, which is a recorder and playback system used in the Korean VLBI Network (KVN), has two kinds of operation mode. That is to say, the station unit (SU) mode, which is for the present Mark4 system, and the VSI mode, which is for the new VLBI standard interface (VSI) system. The software for SU is already developed and widely used in the Mark4 type VLBI system, but the software for VSI has only been developed for recording. The new VLBI system is designed with a VSI interface for compatibility between different systems. Therefore, the playback control software development of the VSI mode is needed for KVN. In this work, we developed the playback control software of the Mark5B VSI mode. The developed playback control software consists of an application part for data playing back, a data input/output part for the VSI board, a module for the StreamStor RAID board, and a user interface part, including an observation time control part. To verify the performance of developed playback control software, the playback and correlation experiments were performed using the real observation data in Mark5B system and KJJVC. To check the observation time control, the data playback experiment was performed between the Mark5B and Raw VLBI Data Buffer (RVDB) systems. Through the experimental results, we confirmed the performance of developed playback control software in the Mark5B VSI mode.

• 천문학회보
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• 제36권2호
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• pp.60.2-60.2
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• 2011

We introduce the preliminary results of flux monitoring of BL Lac object 0716+714 with the KVN Ulsan 21m radio telescope. This radio source is well known as the intraday variable (IDV) source which is characterized by the rapid flux variation on the time scale of a day or less. In general, the IDV phenomenon is interpreted as the effect of refractive scintillation in the interstellar medium or the evidence of intrinsic flux variation. In previous observations that took a few days, however, it had not been detected the flux variation of short time scale but the monotonic increase and decrease. Therefore, to investigate the longer time scale of 0716+714, we had the flux variation monitoring at 22GHz and 43GHz simultaneously for 9 months from October 2010 to June 2011. We present here the structure functions and the cross correlation functions between different frequencies as well as the light curves.

• Journal of Astronomy and Space Sciences
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• 제22권1호
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• pp.1-12
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• 2005

한국우주전파관측망(Korean VLBI Network: KVN)은 우리나라 최초의 초장기선 전파간섭계로 새로운 천문우주 연구 분야 및 측지, 지구물리 등의 연구를 위하여 3기의 21m 최첨단 밀리미터파 전파 안테나를 이용하여 우주를 바라보는 새로운 영역을 개척할 예정이다. 전파간섭계의 성능은 안테나 배열 및 관측 대상 천체의 적위, 그리고 천체와 크기 및 형태에 따른 의존성이 매우 크다. 본 연구는 현재 설정되어있는 KVN관측소 및 시스템 자료를 근거로 단일 점광원, 다중 점광원, 원형광원 2개, Cygnus A의 5개 모델 영상에 대하여 가상관측을 수행하였다. 적위에 따른 KVN의 UV 궤적 분포로부터 가장 이상적이라고 여겨지는 적위 60도인 천체에 대하여 22GHz의 관측 파장으로 12시간 동안 가상관측을 수행하여 얻어진 UV데이터를 가지고 간섭계 표준 영상처리를 하였다. 그 결과 22GHz에서 예상되는 KVN의 빔 크기에 의해 분해가 되지 않는 모델들의 RMS 대비 최대밝기 강도(Jy/Beam)가 대략 점광원의 징우 l0000:1, 지름 6mas(milli arcsecond) 원형 광원의 경우 5000:1 정도로 매우 높은 반면, 빔 크기보다 큰 모델에서는 115:1 및 34:1정도로 현저하게 감소하였으며 영상의 복원 정도도 이와 같은 결과를 보였다. 이것은 KVN이 상대적으로 적은 기선의 개수로 인하여 UV평면을 충분히 채우지 못하며, 동시에 짧은 기선이 부족하여 넓은 분포를 가지는 천체들에 대한 영상화능력이 떨어지기 때문이다. 그러나 각 모델과 CLEAN 영상과의 픽셀 좌표비교에서는 12mas 원형광원을 제외하고는 정확하게 일치함을 보였다. 그러므로 KVN의 주요한 관측 대상은 콤팩트한 천체들이 적당할 것이며, 이러한 천체들에 대하여 KVN은 위치측정에 우수한 성능을 보였다.

• 천문학회보
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• 제41권1호
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• pp.74.2-74.2
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• 2016

It is important to know how well observation errors are removed in the calibration process prior to ensuing scientific research. In mm-VLBI observations, a radio wave suffers from an atmospheric propagation delay due to the rapid change of atmospheric refraction. It makes phases of VLBI correlation output fluctuate rapidly, which essentially decreases the coherence of phases and reduces the integration time. Consequently, it is challenging to achieve a high signal-to-noise ratio and enhance the quality of scientific output. Among the causes of the atmospheric propagation delay, water vapor in the troposphere is the most decisive factor to affect phase errors in the high frequency range (> 10GHz). It is expected to have the non-dispersive characteristic that enables to introduce new calibration strategy, Frequency Phase Transfer (FPT). This new method utilizes low frequency phases to compensate phase errors in high frequency bands. In addition, Korean VLBI Network (KVN) which benefits from the simultaneous 4-channels (22/43/86/129 GHz) observations is ideal to probe FPT performance. In order to evaluate FPT performance of KVN, we present the results of FPT phase analysis and discuss its performance.

• Journal of Astronomy and Space Sciences
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• 제38권4호
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• pp.193-202
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• 2021

We present analysis results of Korean VLBI Network (KVN) four-band data for the highly variable blazar 3C 279. We measured the 22, 43, 86, and 129 GHz flux densities and spectral indices of the source using contemporaneous data taken over 5.6 years. We used the discrete correlation function to investigate correlations between the radio emission properties and those measured in the optical (2 × 10¹⁴ - 1.5 × 10¹⁵ Hz), X-ray (0.3-10 keV), and gamma-ray (0.1-300 GeV) bands. We found a significant correlation between the radio spectral index and gamma-ray flux without a time delay and interpreted the correlation using an extended jet scenario for blazar emission.