Early Science With the Korean Vlbi Network: Evaluation of System Performance

Lee, Sang-Sung; Petrov, Leonid; Byun, Doyoung; Kim, Jong-Soo; Jung, Taehyun; Song, Mingyu; Oh, Chung Sik; Roh, Duk-Gyoo; Je, Do‐Heung; Wi, Seog-Oh; Sohn, Bong Won; Oh, Se-Jin; Kim, Kee‐Tae; Yeom, Jae-Hwan; Chung, Moon Hyun; Kang, Jin Wook; Han, Seog-Tae; Lee, Jung Won; Kim, Bong Gyu; Chung, Hyunsoo; Kim, Hyun‐Goo; Kang, Yong-Woo; Cho, Se-Hyung

doi:10.1088/0004-6256/147/4/77

Cited by 75 publications

(74 citation statements)

References 20 publications

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“…The KVN is a telescope that consists of three antennas within South Korea in Seoul (Yonsei; KY), Ulsan (KU) and Jeju Island (Tamna; KT) (Lee et al 2014). In order to describe the pipeline and analyse its performance, we selected a recent dataset observed as part of the interferometric MOnitoring of GAmma-ray Bright AGN (iMO-GABA) program.…”

Section: Observationsmentioning

confidence: 99%

The Automatic Calibration of Korean Vlbi Network Data

Hodgson¹,

Lee²,

Zhao³

et al. 2016

Journal of The Korean Astronomical Society

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The calibration of Very Long Baseline Interferometry (VLBI) data has long been a time consuming process. The Korean VLBI Network (KVN) is a simple array consisting of three identical antennas. Because four frequencies are observed simultaneously, phase solutions can be transferred from lower frequencies to higher frequencies in order to improve phase coherence and hence sensitivity at higher frequencies. Due to the homogeneous nature of the array, the KVN is also well suited for automatic calibration. In this paper we describe the automatic calibration of single-polarisation KVN data using the KVN Pipeline and comparing the results against VLBI data that has been manually reduced. We find that the pipelined data using phase transfer produces better results than a manually reduced dataset not using the phase transfer. Additionally we compared the pipeline results with a manually reduced phase-transferred dataset and found the results to be identical.

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Section: Observationsmentioning

confidence: 99%

The Automatic Calibration of Korean Vlbi Network Data

Hodgson¹,

Lee²,

Zhao³

et al. 2016

Journal of The Korean Astronomical Society

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“…Here we generated the VERA images by clipping the visibilities of VERA out of the AIPScalibrated visibilities. As the imaging capability of KVN was recently evaluated by Lee et al (2014), we focus on evaluating and comparing the imaging capabilities of KaVA and VERA in this paper.…”

Section: Test Observations and Vlbi Imagesmentioning

confidence: 99%

IMAGING CAPABILITY OF THE KVN AND VERA ARRAYS (KaVA)

Niinuma

Lee²,

Kino³

et al. 2015

Publications of The Korean Astronomical Society

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The Korean very-long-baseline interferometry (VLBI) network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA) is the first international VLBI array dedicated to high-frequency (23 GHz (K-band) and 43 GHz (Q-band)) observations in East Asia. To evaluate the imagine capability of KaVA, we performed imaging observations of three bright active galactic nuclei (AGNs) known for their complex morphologies: 4C 39.25, 3C 273, and M87 by KaVA at K-/Q-band. Our KaVA images reveal extended outflows with complex substructure such as knots and limb brightening, in agreement with previous observations by other VLBI facilities. Angular resolutions are better than 1.4 and 0.8 milliarcsecond (max) at K-/Q-band, respectively. KaVA achieves a high dynamic range of ∼1000, more than three times the value achieved by VERA. We conclude that KaVA is a powerful array with a great potential for the study of AGN outflows, at least comparable to the best existing radio interferometric arrays.

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“…In this paper we will focus on two aspects that limit the potential of mm-VLBI observations: (1) achieving improved sensitivity through increased coherence times, to increase the number of targets; (2) achieving astrometry, and in particular for "bona fide" registration of images at multiple frequency bands, to reveal the physical processes in a number of fields of astronomy. The first case study presented in this paper uses observations with the Korean VLBI Network (KVN) [2,3]. The KVN is the first dedicated mm-VLBI array and addresses one of the fundamental limitations of the field, the atmospheric stability.…”

Section: Introductionmentioning

confidence: 99%

The Power of (Near) Simultaneous Multi-Frequency Observations for mm-VLBI and Astrometry

et al. 2017

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Simultaneous or near-simultaneous observations at multiple frequency bands have the potential to overcome the fundamental limitation imposed by the atmospheric propagation in mm-VLBI observations. The propagation effects place a severe limit in the sensitivity achievable in mm-VLBI, reducing the time over which the signals can be coherently combined, and preventing the use of phase referencing and astrometric measurements. We present two demonstrations of the power of (near) simultaneous multi-frequency observations with the KVN and VLBA, and our recently developed analysis strategies to enable new measurements at mm-VLBI. The first case comprises simultaneous observations at 22, 43, 87 and 130 GHz of a group of five AGNs, the weakest of which is ∼200 mJy at 130 GHz, with angular separations ranging from 3.6 to 11 degrees, using the KVN. We analysed this data using the Frequency Phase Transfer (FPT) and the Source Frequency Phase Referencing (SFPR) techniques, which use the observations at a lower frequency to correct those at a higher frequency. The results of the analysis provide an empirical demonstration of the increase in the coherence times at 130 GHz from a few tens of seconds to about twenty minutes, with FPT, and up to many hours with SFPR. Moreover the astrometric analysis provides high precision relative position measurements between two frequencies, including, for the first time, astrometry at 130 GHz. The second case is a variation of the above, whereby adding dedicated wide-band cm-wavelength observations to measure the ionosphere eliminates the need for a second, calibrator, source. This addresses the scarcity of calibrators at mm-VLBI. We dubbed this technique Multi Frequency Phase Referencing (MFPR). We present bona fide astrometrically aligned VLBA images of BL Lacertae at 22 and 43 GHz using MFPR, which, combined with results from conventional phase referencing at cm-wavelengths, suggests the VLBI core has a recollimation shock that is revealed at mm-wavelengths. These shocks could be responsible for the γ-ray emission in blazar jets.

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Early Science With the Korean Vlbi Network: Evaluation of System Performance

Cited by 75 publications

References 20 publications

The Automatic Calibration of Korean Vlbi Network Data

The Automatic Calibration of Korean Vlbi Network Data

IMAGING CAPABILITY OF THE KVN AND VERA ARRAYS (KaVA)

The Power of (Near) Simultaneous Multi-Frequency Observations for mm-VLBI and Astrometry

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