• Journal of The Korean Astronomical Society
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• v.52 no.2
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• pp.31-40
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• 2019

A long standing problem in the study of Active Galactic Nuclei (AGNs) is that the observed VLBI core is in fact a blending of the actual AGN core (classically defined by the ${\tau}=1$ surface) and the upstream regions of the jet or optically thin flows. This blending may cause some biases in the observables of the core, such as its flux density, size or brightness temperature, which may lead to misleading interpretation of the derived quantities and physics. We study the effects of such blending under the view of the Korean VLBI Network (KVN) for a sample of AGNs at 43 GHz by comparing their observed properties with observations obtained using the Very Large Baseline Array (VLBA). Our results suggest that the observed core sizes are a factor ~ 11 larger than these of VLBA, which is similar to the factor expected by considering the different resolutions of the two facilities. We suggest the use of this factor to consider blending effects in KVN measurements. Other parameters, such as flux density or brightness temperature, seem to possess a more complicated dependence.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.35.3-35.3
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• 2019

Blazars are a subclass of active galactic nuclei (AGNs) with relativistic jets aligned with our line of sight. The jet physics is yet to be understood, but can be studied with blazar variability (e.g., flares). The highly variable blazar 3C 279 has shown a general decline of its radio flux density since 2013, but the flux density has been increasing since 2017. To better understand physical properties of 3C 279 related with the flux variations, we analyze multi-frequency new radio data obtained with Korean VLBI Network (KVN), as well as archival data from Owens Valley Radio Observatory (OVRO) and Submillimeter Array (SMA). We measure the radio spectral variability and infer the relativistic jet properties of 3C 279. The high-cadence OVRO and SMA observations are used to construct detailed light curves of the source, and KVN data supplement the spectral coverage and allow us to locate the spectral break frequencies precisely. In this talk, we present our analysis results and interpret them using a blazar jet model.

• Journal of The Korean Astronomical Society
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• v.55 no.6
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• pp.207-213
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• 2022

The Seoul Radio Astronomy Observatory (SRAO) operates a 6.1-meter radio telescope on the Gwanak campus of Seoul National University. We present the efforts to reform SRAO to a Very Long Baseline Interferometry (VLBI) station, motivated by recent achievements by millimeter interferometer networks such as Event Horizon Telescope, East Asia VLBI Network, and Korean VLBI Network (KVN). For this goal, we installed a receiver that had been used in the Combined Array for Research in Millimeter-wave Astronomy and a digital backend, including an H-maser clock. The existing hardware and software were also revised, which had been dedicated only to single-dish operations. After several years of preparations and test observations in 1 and 3-millimeter bands, a fringe was successfully detected toward 3C 84 in 86 GHz in June 2022 for a baseline between SRAO and KVN Ulsan station separated by 300 km. Thanks to the dual frequency operation of the receiver, the VLBI observations will soon be extended to the 1 mm band and verify the frequency phase referencing technique between 1 and 3-millimeter bands.

• Journal of the Institute of Convergence Signal Processing
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• v.16 no.4
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• pp.175-181
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• 2015

In this paper, we propose a design method for a digital filter using software in order to analyze the radio astronomy observation data. Recently the analysis method for radio astronomy observing system is transferring from hardware to software by developing of state-of-the-art of computer system. The existing hardware system is not able to easily change the specification because it is implemented to meet special requirements and it takes a high cost and time. In case of software, however, it has an advantage to implement with small cost if open software is used, and flexibly changes to satisfy the desired specification. But, in order to analyze the massive data like radio astronomy with software, the good performance system is needed for computer. Therefore, this paper proposes a digital filter design method using software with the same performance as that of digital filter implemented with hardware in observation system which is operated by the KVN(Korean VLBI Network). To design a digital filter, the proposed method is performed with standard C language and the simulation is conducted with GNU(GNU's Not Unix) Octave and investigated to show its effectiveness. In addition, for the high speed operation of the designed digital filter, the SSE(Streaming SIMD Extensions) library is adopted for available parallel operation. By the proposed digital filter, the digital filtering is performed for the wide band observation data in the KVN observation mode, the filtering result of narrow band observation has no ripple inside of stop band, and confirmed the effectiveness of the proposed method.

• The Bulletin of The Korean Astronomical Society
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• v.32 no.1
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• pp.104.1-104.1
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• 2007

• The Bulletin of The Korean Astronomical Society
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• v.32 no.1
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• pp.66.1-66.1
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• 2007

• The Bulletin of The Korean Astronomical Society
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• v.32 no.1
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• pp.63.2-63.2
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• 2007

• The Bulletin of The Korean Astronomical Society
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• v.32 no.1
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• pp.65.2-65.2
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• 2007

• KASI NEWSLETTER
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• s.41
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• pp.1-4
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• 2003

원자외선 분광기(FIMS) 발사 성공/창립 29주년 기념행사 실시/국회 정무위원회 소속 의원 소백산천문대 시찰/ 2003년 직원연찬회 실시/서귀포 별의 축제와 서울 화성축제 개최/ 대덕연구단지 30주년 기념 연구성과 전시회 참가/ 연구기관 개방행사 실시/ 여성신직업페스티벌 참가/ 2003 KVN 과학 워크샵 개최/ 2003년도 한국천문학회 추계 학술발표대회 개최/ 천문 계산용 리눅스 클러스터 구축 기념식 개최/ 대형망원경을 이용한 천체관측연구 워크샵 개최/ 경북대와 학 연 협동 석박사 학위과정 설치/ 학회동정/ 신규임용/ 직원동정/ 창립29주년 기념 우수직원 포상자 및 10년 장기근속자/ 콜로키움/ 원자외선 분광기 개발을 돌아보며

• Bulletin of the Korean Space Science Society
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• 2007.10a
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• pp.56.1-56.1
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• 2007