EARLY SCIENCE WITH THE KOREAN VLBI NETWORK: THE QCAL-1 43 GHz CALIBRATOR SURVEY

Petrov, Leonid; Lee, Sang-Sung; Kim, Jong-Soo; Oh, Junghwan; Sohn, Bong Won; Byun, Doyoung; Chung, Moon Hyun; Je, Do‐Heung; Wi, Seog-Oh; Song, Mingyu; Kang, Jin Wook; Han, Seog-Tae; Lee, Jung Won; Kim, Bong Gyu; Chung, Hyunsoo; Kim, Hyun‐Goo

doi:10.1088/0004-6256/144/5/150

Cited by 15 publications

(8 citation statements)

References 22 publications

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“…The double-layer patterns are clearer for the observations of stronger sources like 3C 454.3 with a correlated flux density of ∼20 Jy (Figure 4), whereas they are less clear for relatively weaker sources like 3C 345 and NRAO 512 with flux densities of 1-4 Jy (Figures 5 and 6). This is because the amplitude of the double-layer pattern is about 15% and it is similar to the amplitude calibration uncertainty of KVN observations at 22 GHz (see Petrov et. al 2012;Lee et.…”

Section: Visibility Comparison With Difxsupporting

confidence: 77%

A New Hardware Correlator in Korea: Performance Evaluation Using KVN Observations

Lee¹,

Oh²,

Roh³

et al. 2015

Journal of The Korean Astronomical Society

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Abstract:We report results of the performance evaluation of a new hardware correlator in Korea, the Daejeon correlator, developed by the Korea Astronomy and Space Science Institute (KASI) and the National Astronomical Observatory of Japan (NAOJ). We conduct Very Long Baseline Interferometry (VLBI) observations at 22 GHz with the Korean VLBI Network (KVN) in Korea and the VLBI Exploration of Radio Astrometry (VERA) in Japan, and correlated the aquired data with the Daejeon correlator. For evaluating the performance of the new hardware correlator, we compare the correlation outputs from the Daejeon correlator for KVN observations with those from a software correlator, the Distributed FX (DiFX). We investigate the correlated flux densities and brightness distributions of extragalactic compact radio sources. The comparison of the two correlator outputs shows that they are consistent with each other within < 8%, which is comparable with the amplitude calibration uncertainties of KVN observations at 22 GHz. We also find that the 8% difference in flux density is caused mainly by (a) the difference in the way of fringe phase tracking between the DiFX software correlator and the Daejeon hardware correlator, and (b) an unusual pattern (a double-layer pattern) of the amplitude correlation output from the Daejeon correlator. The visibility amplitude loss by the double-layer pattern is as small as 3%. We conclude that the new hardware correlator produces reasonable correlation outputs for continuum observations, which are consistent with the outputs from the DiFX software correlator.

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Section: Visibility Comparison With Difxsupporting

confidence: 77%

A New Hardware Correlator in Korea: Performance Evaluation Using KVN Observations

Lee¹,

Oh²,

Roh³

et al. 2015

Journal of The Korean Astronomical Society

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“…The 43-GHz observations made by the KVN in 2011 December in the QCAL-1 observing campaign inferred a flux density of 108 ± 13 mJy (Petrov et al 2012), which is 2.5 times higher than the values in 2004 and 2005 (Table 5). We mention that, at least at 15 GHz, the radio flux density of the source was at its maximum at the end of 2011 (Fig.…”

Section: Variabilitymentioning

confidence: 64%

J0906+6930: a radio-loud quasar in the early Universe

Zhang

Frey

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Radio-loud high-redshift quasars (HRQs), although only a few of them are known to date, are crucial for the studies of the growth of supermassive black holes (SMBHs) and the evolution of active galactic nuclei (AGN) at early cosmological epochs. Radio jets offer direct evidence of SMBHs, and their radio structures can be studied with the highest angular resolution using Very Long Baseline Interferometry (VLBI). Here we report on the observations of three HRQs (J0131−0321, J0906+6930, J1026+2542) at z > 5 using the Korean VLBI Network and VLBI Exploration of Radio Astrometry Arrays (together known as KaVA) with the purpose of studying their pc-scale jet properties. The observations were carried out at 22 and 43 GHz in 2016 January among the first-batch open-use experiments of KaVA. The quasar J0906+6930 was detected at 22 GHz but not at 43 GHz. The other two sources were not detected and upper limits to their compact radio emission are given. Archival VLBI imaging data and single-dish 15-GHz monitoring light curve of J0906+6930 were also acquired as complementary information. J0906+6930 shows a moderate-level variability at 15 GHz. The radio image is characterized by a core-jet structure with a total detectable size of ∼5 pc in projection. The brightness temperature, 1.9 × 10 11 K, indicates relativistic beaming of the jet. The radio properties of J0906+6930 are consistent with a blazar. Follow-up VLBI observations will be helpful for determining its structural variation.

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“…The fluxes of HR 5907 reported by the AT20G survey are respectively: 46 ± 3 mJy at 5 GHz (λ ≈ 6 cm), 95 ± 5 mJy at 8 GHz (λ ≈ 4 cm), and 104 ± 6 mJy at 20 GHz (λ ≈ 1.5 cm). HR 5907 was further detected by the Korean VLBI Network (KVN) at 43 GHz (λ ≈ 7 mm) (Petrov et al 2012). The reported 43 GHz fluxes measured by the KVN are 140 ± 21 mJy and 123 ± 20 mJy, as a function of the projected baseline length.…”

Section: The Magnetic Early B-type Star Hr 5907mentioning

confidence: 99%

A combined multiwavelength VLA/ALMA/Chandra study unveils the complex magnetosphere of the B-type star HR5907

Leto

Trigilio

Oskinova

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We present new radio/millimeter measurements of the hot magnetic star HR 5907 obtained with the VLA and ALMA interferometers. We find that HR 5907 is the most radio luminous early type star in the cm-mm band among those presently known. Its multi-wavelength radio light curves are strongly variable with an amplitude that increases with radio frequency. The radio emission can be explained by the populations of the non-thermal electrons accelerated in the current sheets on the outer border of the magnetosphere of this fast rotating magnetic star. We classify HR 5907 as another member of the growing class of strongly magnetic fast rotating hot stars where the gyro-synchrotron emission mechanism efficiently operates in their magnetospheres. The new radio observations of HR 5907 are combined with archival X-ray data to study the physical condition of its magnetosphere. The X-ray spectra of HR 5907 show tentative evidence for the presence of non-thermal spectral component. We suggest that non-thermal X-rays originate a stellar X-ray aurora due to streams of non-thermal electrons impacting on the stellar surface. Taking advantage of the relation between the spectral indices of the X-ray power-law spectrum and the non-thermal electron energy distributions, we perform 3-D modeling of the radio emission for HR 5907. The wavelength-dependent radio light-curves probe magnetospheric layers at different heights above the stellar surface. A detailed comparison between simulated and observed radio light-curves leads us to conclude that the stellar magnetic field of HR 5907 is likely non-dipolar, providing further indirect evidence of the complex magnetic field topology of HR 5907.

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EARLY SCIENCE WITH THE KOREAN VLBI NETWORK: THE QCAL-1 43 GHz CALIBRATOR SURVEY

Cited by 15 publications

References 22 publications

A New Hardware Correlator in Korea: Performance Evaluation Using KVN Observations

A New Hardware Correlator in Korea: Performance Evaluation Using KVN Observations

J0906+6930: a radio-loud quasar in the early Universe

A combined multiwavelength VLA/ALMA/Chandra study unveils the complex magnetosphere of the B-type star HR5907

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