Jeewon Lee

THE FIRST VERY LONG BASELINE INTERFEROMETRY IMAGE OF A 44 GHz METHANOL MASER WITH THE KVN AND VERA ARRAY (KaVA)

We have carried out the first very long baseline interferometry (VLBI) imaging of a 44 GHz classI methanol maser (70‐61A + ) associated with a millimeter core MM2 in a massive star-forming region IRAS 18151−1208 with KaVA (KVN and VERA Array), which is a newly combined array of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We have succeeded in imaging compact maser features with a synthesized beam sizeof2.7milliarcseconds ×1.5milliarcseconds(mas).Thesefeaturesaredetectedatalimitednumber ofbaselines within the length of shorter than ≈ 650 km corresponding to 100 Mλ in the uv-coverage. The central velocity and the velocity width of the 44 GHz methanol maser are consistent with those of the quiescent gas rather than the outflow traced by the SiO thermal line. The minimum component size among the maser features is ∼5mas×2mas, which corresponds to the linear size of ∼15 AU × 6 AU assuming a distance of 3 kpc. The brightness temperatures of these features range from ∼3.5 × 10 8 to 1.0 × 10 10 K, which are higher than the estimated lower limit from a previous Very Large Array observation with the highest spatial resolution of ∼50 mas. The 44 GHz classI methanol maser in IRAS 18151−1208 is found to be associated with the MM2 core, which is thought to be less evolved than another millimeter core MM1 associated with the 6.7 GHz classII methanol maser.

Detection of millimeter-wavelength intraday variability in polarized emission from S5 0716+714

We report the detection of millimeter-wavelength intraday variability in polarized emission from S5 0716+714 based on multifrequency polarization observations using the Korean VLBI Network (KVN) radio telescopes. The observations were conducted on November 7, 2013 at 22, 43, and 86 GHz in dual polarization using two 21 m radio telescopes belonging to KVN Yonsei and Ulsan. We found significant variations in the degree of linear polarization at 86 GHz and in polarization angle at 43 and 86 GHz during ~10 h. We measured mean flux densities of 2.8 Jy, 2.8 Jy, and 2.7 Jy at 22, 43, and 86 GHz, respectively, with a flux modulation index ranging from 1.5% to 7.2% at the frequencies. The spectrum of the source is quite flat with spectral indices of −0.07 to 0.07 at 22−43 GHz and −0.23 to 0.04 at 43−86 GHz. The measured degree of the linear polarization ranges from 2.3% to 3.3% at 22 GHz from 0.9% to 2.2% at 43 GHz and from 0.4% to 4.0% at 86 GHz, yielding prominent variations at 86 GHz over 4−5 h. The linear polarization angle is in the range of 4° to 12° at 22 GHz, −39° to 81° at 43 GHz, and 66° to 119° at 86 GHz with a maximum rotation of 110° at 43 GHz over ~4 h. We estimated the Faraday rotation measures (RM) ranging from −9200 to 6300 rad m -2 between 22 and 43 GHz, and from −71 000 to 7300 rad m -2 between 43 and 86 GHz, respectively. The frequency dependency of RM was investigated, yielding a mean power-law index, a , of 2.0. This implies that the polarized emission from S5 0716+714 at 22−86 GHz moves through a Faraday screen in or near the jet of the source.

Interferometric Monitoring of Gamma-Ray Bright AGNs: S5 0716+714

We present the results of very long baseline interferometry (VLBI) observations of gamma-ray bright blazar S5 0716+714 using the Korean VLBI Network (KVN) at the 22, 43, 86, and 129 GHz bands, as part of the Interferometric Monitoring of Gamma-ray Bright AGNs (iMOGABA) KVN key science program. Observations were conducted in 29 sessions from January 16, 2013 to March 1, 2016, with the source being detected and imaged at all available frequencies. In all epochs, the source was compact on the milliarcsecond (mas) scale, yielding a compact VLBI core dominating the synchrotron emission on these scales. Based on the multi-wavelength data between 15 GHz (Owens Valley Radio Observatory) and 230 GHz (Submillimeter Array), we found that the source shows multiple prominent enhancements of the flux density at the centimeter (cm) and millimeter (mm) wavelengths, with mm enhancements leading cm enhancements by -16

Korean VLBI Network Calibrator Survey (KVNCS). 1. Source Catalog of KVN Single-dish Flux Density Measurement in the K and Q Bands

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Simultaneous dual-frequency radio observations of S5 0716+714: A search for intraday variability with the Korean VLBI Network

8 days. The turnover frequency was found to vary between 21 to 69GHz during our observations. By assuming a synchrotron self-absorption model for the relativistic jet emission in S5 0716+714, we found the magnetic field strength in the mas emission region to be

Single-Dish Performance of KVN 21 m Radio Telescopes: Simultaneous Observations at 22 and 43 GHz

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VLBI observations of bright AGN jets with the KVN and VERA Array (KaVA): Evaluation of imaging capability

5 mG during the observing period, yielding a weighted mean of 1.0

SiO MASERS AROUND WX PSC MAPPED with the KVN and VERA ARRAY (KaVA)

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Detection of short-term flux variability and intraday variability in polarized emission at millimeter-wavelength from S5 0716+714

0.6 mG for higher turnover frequencies (e.g., >45 GHz).

KOREAN VLBI NETWORK CALIBRATOR SURVEY (KVNCS): 1. SINGLE DISH FLUX MEASUREMENT IN THE K AND Q BANDS

We present the catalog of the KVN Calibrator Survey (KVNCS). This first part of the KVNCS is a single dish radio survey conducted at 22 (K band) and 43 GHz (Q band) simultaneously using the Korean VLBI Network (KVN) from 2009 to 2011. A total 2045 sources selected from the VLBA Calibrator Survey (VCS) with an extrapolated flux density limit of 100 mJy at K band. The KVNCS contains 1533 sources in the K band with a flux density limit of 70 mJy and 553 sources in the Q band with a flux density limit of 120 mJy; it covers the whole sky down to