• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.88.2-88.2
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• 2012

We present kinematic properties of the narrow-line region in three type-2 QSOs at z~0.35, using 2-D spectra obtained with the VIMOS integral field unit spectrograph at the Very Large Telescope. One of the objects shows a line-of-sight velocity shift of the [OIII] and $H{\beta}$ lines up to 40km/s on a 15 kpc scale, which can be interpreted as either outflow or rotation. The outflow scenario is supported by the presence of blue wings and a radio structure showing lobes in the same direction. Another object features double-peaked emission lines which can be decomposed into two velocity components. Its Hubble Space Telescope image shows two nuclei separated by ~0.2"(~1kpc), implying this may be a binary AGN.

• Journal of The Korean Astronomical Society
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• v.51 no.6
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• pp.171-183
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• 2018

To celebrate the tenth anniversary since the launch of Fermi Gamma-ray Space Telescope, we take a retrospect to a series of breakthroughs Fermi has contributed to pulsar astronomy in the last decade. Apart from significantly enlarging the population of ${\gamma}$-ray pulsars, observations with the Large Area Telescope onboard Fermi also show the population is not homogeneous. Instead, many classes and sub-classes have been revealed. In this paper, we will review the properties of different types of ${\gamma}$-ray pulsars, including radio-quiet ${\gamma}$-ray pulsars, millisecond pulsars, ${\gamma}$-ray binaries. Also, we will discuss the prospects of pulsar astronomy in the high energy regime.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.77-78
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• 1996

We perfom a large project for complex study of Blue Compact Galaxies (BCGs) with strong star formation, which includes optical spectroscopy, BVR CCD photometry and HI 21 cm radio survey. The most interesting galaxies are studied also with HST and VLA. In the frame of this project we began the study of H$\alpha$ morphology of BCGs with 6-m telescope. We present and discuss here the results for the first 6 galaxies. We found the noticeable variety of forms for H$\alpha$ morphology comparing to broad band images: from very compact HII region in very center of stellar body (Mark 996, possible dwarf post-merger, old galaxy experiencing strong star formation burst), to very extended gas emission encompassing the whole area traced by stars (SBS 0335-052, the most probable young galaxy in formation).

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.63.1-63.1
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• 2021

We present status of solar astronomy in North Korea through analysis of research papers written by North Korea scientists. For the study, we collected 42 papers published in North Korea and international journals. We have analyzed the papers statistically according to three criteria such as research subject, research field, and research members. The main research subjects are the sunspot (28%), observation system (21%), and space environments (19%). The research fields are distributed with data analysis (50%), numerical method (29%), and instrument development (21%). There have been 25 and 9 researchers in the solar astronomy and space environment, respectively since 1995. North Korea's solar research activities were also investigated in three area: instrument, solar physics, and international research linkage. PAO(Pyongyang Astronomical Observatory) has operated two of sunspot telescope and solar horizontal telescope for spectroscopy and polarimetry, but there is no specific information on solar radio telescopes. North Korea has cooperated in solar research with Europe and China. We expect that the results of this study will be used as useful resource in supporting astronomical cooperation between South and North Korea in the future.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.37.1-37.1
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• 2015

It is suggested that relativistic jets associated with active galactic nuclei (AGNs) can have great impacts on the evolution of the host galaxy. However, the physical properties of AGN jets including the formation mechanism are not well known to date, and hence the AGN feedback on the host galaxy is yet poorly understood. OVV 1633+382 as a highly variable AGN source (a.k.a. blazer) with a compact core and very well developed jet components is an excellent laboratory to study the jet formation mechanism of radio-loud AGN. Near 2002, a major flare was reported at mm wavelength with a dramatic increase of the flux, which is likely to be followed by a dense and bright outflow. In order to probe the evolution of the innermost region of this radio-loud AGN, we have monitored using the Very Large Baseline Array (VLBA) and the Effelsberg 100m single-dish radio telescope in 12 epochs from 2002 and 2005. The observations were conducted at 22, 43 and 86 GHz in full polarization mode. In this work, we present the intensity and spectral index maps at 22 and 43 GHz from our monitoring observations. We probe the kinematics and geometry of individual jet components to discuss the evolution of the jet.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.737-743
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• 2004

A fixed-tuned SIS(Superconductor-Insulator-Superconductor) mixer across 120∼180 GHz band has been developed. This mixer employs an SIS chip fabricated by Nobeyama radio observatory which consists of a series array of 6 Nb/Al-Al$_2$O$_3$/Nb junctions in a microstrip line on a fused quartz substrate. The SIS chip is placed at the center of the half-height waveguide mixer mount to have a good incoming signal coupling over the whole frequency band. No mechanical tuner was used in the SIS mixer and the RF signal and local oscillator power are injected to the mixer via a cooled cross-guide coupler. In order to prevent the IF signal loss, the If output impedance of the SIS mixer was matched to the 50 $\Omega$ input impedance of the IF chain. Measured double sideband noise temperatures of a receiver using the SIS mixer are 32∼131 K over 120∼180 GHz band. The developed SIS mixer is now in use for radio astronomical observations on the TRAO 14 m radio telescope.

• Journal of The Korean Astronomical Society
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• v.50 no.5
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• pp.151-155
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• 2017

We investigate the radio properties of the dwarf galaxy SDSS J133245.62+263449.3 which shows optical signatures of black hole activity. Dwarf galaxies are known to host intermediate mass black holes (IMBHs) with masses $M_{BH}{\sim}10^{4-6}M_{\odot}$, some of them being radio loud. Recently, Reines et al. (2013) found dwarf galaxy candidates which show signatures of being black hole hosts based on optical spectral lines. SDSS J133245.62+263449.3 is one of them; it shows a flux density of ~ 20 mJy at 1.4 GHz, which corresponds to $L_{1.4GHz}{\sim}10^{23}W\;Hz^{-1}$. This is much brighter than other black hole host dwarf galaxies. However, star formation activity can contribute to radio continuum emission as well. To understand the nature of the radio emission from SDSS J133245.62+263449.3, we imaged this radio loud dwarf galaxy at low frequencies (325 MHz and 610 MHz) using the Giant Metrewave Radio Telescope (GMRT). We present here the high resolution images from our GMRT observations. While we detect no obvious extended emission from radio jets from the central AGN, we do find the emission to be moderately extended and unlikely to be dominated by disk star formation. VLBI observations using the Korean VLBI Network (KVN) are now being planned to understand the emission morphology and radiation mechanism.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.3 s.106
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• pp.239-248
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• 2006

In this paper, the cryogenically cooled low noise amplifier module for radio telescope receiver front-end using pHE-MT MMIC is designed and fabricated. In the selection of MMIC, the MMIC fabricated with the pHEMTS providing successful cryogenic operation are chosen. They are mounted in the housing using the thin film substrate. In the design of the housing, the absorber and the elimination of the gap between the carrier and the housing as well removed the unnecessary oscillations by its structure. The mismatch is improved by ribbon-tuning to provide the best performance at room temperature. The fabricated module shows the gain of $35dB{\pm}1dB$ and the noise figure of $2.37{\sim}2.57dB$ at room temperature over $21.5{\sim}23.5GHz$. In the cryogenic temperature of $15^{\circ}K$ cooled by He gas, the measured gain was above 35 dB and flatness ${\pm}2dB$ and the noise temperatures of $28{\sim}37^{\circ}K$.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.61.1-61.1
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• 2011

We have performed simultaneous observations at 22GHz and 43GHz on AGNs hosted by elliptical galaxies using KVN radio telescope. We have constructed the sample, based on two major surveys in radio and optical band, i.e. Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) and Sloan Digital Sky Survey (SDSS) DR7, respectively. We restricted the redshift range 0.01 < z < 0.06 and the absolute magnitude Mr < -19.4 in order to satisfy volume limited sample. We also checked clear detection of four distinctive emission lines ([NII], [OIII], $H{\alpha}$, $H{\beta}$) so as to utilize on BPT diagram, distinguishing AGNs from star-forming galaxies. Elliptical galaxies have been selected by visual inspection making use of SDSS optical images. Then, we cross-matched the elliptical galaxies with FIRST detections. About 35% of the galaxies have been detected throughout KVN observations. We derive spectral index, applying the flux of different radio frequencies from FIRST (1.4GHz) and KVN (22GHz) and classify into steep, flat or inverted spectrum. We have found that most of the detected galaxies have flat spectrum while the rest of them have steep spectrum. This implies that a number of detected galaxies might have compact structure associated with the central region of the galaxies. The relation between black hole mass and radio luminosity has shown relatively tighter correlation in high frequency than in low frequency, which confirms that high frequency in radio band is appropriate to study the center of the galaxies.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.6
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• pp.1175-1182
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• 2021

The receiver of each radio telescope of KVN, has a sampler that converts astronomical radio signal to digital data. The ability of this sampler (the bandwidth, sampling frequency, and sampling bits) is improved by sqrt(n), if the bandwidth is increased by n times, and the number of observable objects increases exponentially in the case of continum spectrum radio sources. As the bandwidth increases, there are the more spectrum lines that can be simultaneously monitored in the radio source. This will greatly expand the research area in astronomical radio observation. For this reason, we are trying to independently develop the technology of the fast digital sampler. Therefore, based on the research experience and technology accumulated so far, An ability of sampling up to 3.5 GHz, that can vary the sampling frequency and can observe in a wider band, was designed and made for proto-type. In this study, we introduce the development details and test results for new sampling system.