Korean VLBI Network (KVN)

B-field environments of a blazar S5 0716+714

A KVN Key Science Program, the iMOGABA, has monitored a very compact, variable blazar S5 0716+714 simultaneously at four cm-mm bands (13mm-2.5mm) on sptial resolutions of milli-arcseconds. Observations were conducted in 29 sessions from 2013 January 16 to 2016 March 1, with the source being detected and imaged at all available frequencies. In all epochs, the source was compact on the milliarcsecond scale, yielding a compact VLBI core dominating the synchrotron emission on these scales. The turnover frequency was found to vary between 21 and 69 GHz during the observations. By assuming a synchrotron self-absorption model for the relativistic jet emission in S5 0716+714, the authors found the magnetic field strength in the mas emission region to be ≤5 mG during the observing period, yielding a weighted mean of 1.0 ± 0.6 mG for higher turnover frequencies (e.g., >45 GHz).

Variation in peak flux densitie s (1), turnover frequencies (2), magnetic fields (3), KVN flux densities (4), and deconvolved core sizes (5) in the time domain.
Variation in peak flux densities (1), turnover frequencies (2), magnetic fields (3), KVN flux densities (4), and deconvolved core sizes (5) in the time domain.

KVN joined scientific observations of EAVN

Scientific operation of the EAVN (East Asia VLBI Network) has started in 2017. After the commissioning in 2016, the EAVN conducted a series of 17 scientific observatinos at 22/43GHz of M87 and SgrA* between 2017 March and May, some of which were in synchronized with EHT-ALMA 230 GHz VLBI campaign. KVN joined these EAVN observations together with Sejong (Korea), VERA (Japan), Tianma and Urumqi (China), and other EVAN telescopes.

Commissioning of 130 GHz VLBI polarization observation

A KVN KSP (PAGaN) team, led by Prof. Trippe, S. (Seoul National University), has successfully obtained high resolution linear polarization images of AGNs using KVN at 130 GHz by correcting for the instrumental polarization effect from KVN polarization observations. The instrumental leakage term (D-term) is measured to be about 10% at 130 GHz.

Multi frequency polarization images of CTA 102
Linear polarization images of CTA 102 obtained with KVN in 22.682, 43.332, 86.632, and 129.334 GHz bands, respectively from the left. Contour map shows the distribution of total intensity and colored map indicates the linear polarization distribution with red vector for polarization direction.

KASI logo image

Korean VLBI Network (KVN)