Bong Won Sohn
A5031750380- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- GNSS positioning and interference
- Galaxies: Formation, Evolution, Phenomena
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Geophysics and Gravity Measurements
- Superconducting and THz Device Technology
- Particle Accelerators and Free-Electron Lasers
- Astronomy and Astrophysical Research
- Neutrino Physics Research
- Astrophysics and Star Formation Studies
- Solar and Space Plasma Dynamics
- Ionosphere and magnetosphere dynamics
- Stellar, planetary, and galactic studies
- Radio Wave Propagation Studies
- Particle accelerators and beam dynamics
- Advanced X-ray Imaging Techniques
- History and Developments in Astronomy
- Atomic and Subatomic Physics Research
- Dark Matter and Cosmic Phenomena
- Particle Detector Development and Performance
- Wireless Communication Networks Research
Yonsei University
2012-2025
Korea Astronomy and Space Science Institute
2016-2025
Korean Association for the Study of Intestinal Diseases
2016-2025
Korea Institute of Science & Technology Information
2025
Korea University of Science and Technology
2015-2024
East Asian Observatory
2022
Max Planck Institute for Radio Astronomy
2003-2019
International Centre for Radio Astronomy Research
2015
Max Planck Society
2015
Yamaguchi University
2015
Abstract We study the kinematics of M87 jet using first-year data KVN and VERA Array (KaVA) large program, which has densely monitored at 22 43 GHz since 2016. find that apparent speeds generally increase from ≈0.3 c ≈0.5 mas base to ≈2.7 ≈20 mas, indicating is accelerated subluminal superluminal on these scales. perform a complementary kinematic analysis by archival Very Long Baseline monitoring observed in 2005–2009 1.7 moving relativistic up ≈5.8 distances 200–410 mas. combine two results...
We explore the degree of magnetization at jet base M87 by using observational data event horizon telescope (EHT) 230~GHz obtained Doeleman et al. By utilizing method in Kino al., we derive energy densities magnetic fields ($U_{B}$) and electrons positrons ($U_{\pm}$) compact region detected EHT (EHT-region) with its full-width-half-maximum size $40~{\rm \mu as}$. First, assume that an optically-thick for synchrotron self absorption (SSA) exists EHT-region. Then, find SSA-thick should not be...
Aims. The BL Lac object S5 0716+71 was observed in a global multi-frequency campaign to search for rapid and correlated flux density variability signatures of an inverse-Compton (IC) catastrophe during the states extreme apparent brightness temperatures.
We report the very long baseline interferometry (VLBI) observing performance of Korean VLBI Network (KVN). The KVN is first millimeter-dedicated network in East Asia. consists three 21 m radio telescopes with lengths a range 305–476 km. quasi-optical system equipped on antennas allows simultaneous observations at 22, 43, 86, and 129 GHz. fringes were obtained 22 GHz 2010 June 8. Test 43 September 30 2011 April 4 confirmed that full cycle works according to specification: scheduling, antenna...
We report simultaneous multifrequency observing performance at 22 and 43 GHz of the 21 m shaped-Cassegrain radio telescopes Korean VLBI Network (KVN). KVN is first millimeter-dedicated network in Korea having a maximum baseline length 480 km. It currently operates planned to operate four frequency bands: 22, 43, 86, 129 GHz. The unique quasi optics enable observations based on efficient beam filtering accurate antenna-beam alignment found that offset beams within less than 5'' over all...
We report the initial results of our high-cadence monitoring program on radio jet in active galaxy M87, obtained by KVN and VERA Array (KaVA) at 22 GHz. This is a pilot study that preceded larger KaVA-M87 program, which currently ongoing. The was mostly performed every two to three weeks from December 2013 June 2014, recording rate 1 Gbps, obtaining data for total 10 epochs. successfully sequence good quality maps revealed rich structure this <~1 mas 20 mas, corresponding physical scales...
To fully exploit the scientific potential of Fermi mission, we initiated F-GAMMA program. Between 2007 and 2015 it was prime provider complementary multi-frequency monitoring in radio regime. We quantify variability gamma-ray blazars. investigate its dependence on source class examine whether is related to loudness. Finally, assess validity a putative correlation between two bands. The monitored monthly sample about 60 sources at up twelve frequencies 2.64 228.39 GHz. perform time series...
The Event Horizon Telescope (EHT) has successfully revealed the shadow of supermassive black hole, M87*, with an unprecedented angular resolution approximately 20 uas at 230 GHz. However, because limited short baseline lengths, EHT been constrained in its ability to recover larger scale jet structures. extended Korean VLBI Network (eKVN) is committed joining from 2024 that can improve coverage. This study evaluates impact participation eKVN on recovery M87* jet. Synthetic data, derived a...
We report the results of high-resolution 5 GHz Very Long Baseline Array and European VLBI Network observations 36 nearby galaxies, an extension Legacy e-MERLIN Multi-band Imaging Nearby Galaxies (LeMMINGs) survey. Our sample includes 21 low ionization nuclear emission regions (LINERs), 4 Seyferts, 3 absorption line galaxies (ALGs), 8 HII galaxies. achieved unprecedented detection rate, successfully imaging 23 out sources with a threshold $\sim$20 $\mu$Jy beam$^{-1}$. The radio sizes are...
Abstract Frequency phase transfer (FPT) is a technique designed to increase coherence and sensitivity in radio interferometry by making use of the nondispersive nature troposphere calibrate high-frequency data using solutions derived at lower frequency. While Korean very long baseline (VLBI) network has pioneered simultaneous multiband systems for routine FPT up an observing frequency 130 GHz, this remains largely untested (sub)millimeter regime. A recent effort been made outfit dual-band...
The quasar 3C 279 was the target of an extensive multiwavelength monitoring campaign from 2006 January through April. An optical-IR-radio by Whole Earth Blazar Telescope (WEBT) collaboration organized around target-of-opportunity X-ray and soft γ-ray observations with Chandra INTEGRAL in mid-January, additional coverage RXTE Swift XRT. In this paper we focus on results WEBT campaign. source exhibited substantial variability optical flux spectral shape, a characteristic timescale few days....
Abstract The Korean very-long-baseline interferometry (VLBI) network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA) is the first international array dedicated to high-frequency (23–43 GHz bands) observations in East Asia. Here, we report imaging three bright active galactic nuclei (AGNs) known for their complex morphologies: 4C 39.25, 3C 273, M 87. This one initial results KaVA's early operation. Our KaVA images reveal extended outflows with substructures such as knots...
Sagittarius A* (Sgr A*), the Galactic Center supermassive black hole (SMBH), is one of best targets to resolve innermost region SMBH with very long baseline interferometry (VLBI). In this study, we have carried out observations toward Sgr at 1.349 cm (22.223 GHz) and 6.950 mm (43.135 East Asian VLBI Network, as a part multi-wavelength campaign Event Horizon Telescope (EHT) in 2017 April. To mitigate scattering effects, physically motivated kernel model from Psaltis et al. (2018) parameters...
Context. Because of its proximity and the large size black hole, M 87 is one best targets for studying launching mechanism active galactic nucleus jets. Currently, magnetic fields are considered to be an essential factor in accelerating jet. However, current observational estimates field strength jet limited innermost part (≲100 r s ) or HST-1 (∼10 5 ). No attempt has yet been made measure between. Aims. We aim infer out a distance several thousand by tracking distance-dependent changes...
We present results from the first 22 GHz space very-long-baseline interferometric (VLBI) imaging observations of M87 by RadioAstron. As a part Nearby AGN Key Science Program, source was observed in Feb 2014 at with 21 ground stations, reaching projected $(u,v)$-spacings up to $\sim11\,$G$\lambda$. The experiment complemented snapshot RadioAstron data obtained during 2013--2016 Survey Program. Their longest baselines extend $\sim25\,$G$\lambda$. For all these measurements, fringes are...
Simultaneous observations at multiple frequency bands have the potential to overcome fundamental limitation imposed by atmospheric propagation in (sub)millimeter very long baseline interferometry (mm-VLBI) observations. The effects place a severe limit on sensitivity achievable mm-VLBI, reducing time over which signals can be coherently combined, and preventing use of phase referencing astrometric measurements. We carried out simultaneous 22, 43, 87, 130 GHz group five active galactic...
The Korean VLBI Network (KVN) is a new mm-VLBI dedicated array with capability for simultaneous observations at multiple frequencies, up to 129 GHz. innovative multi-channel receivers present significant benefits astrometric measurements in the frequency domain. aim of this work verify performance KVN using comparative study VLBA, well established instrument. For that purpose, we carried out nearly contemporaneous and 14/7 mm, April 2013. consisted dual observations, while VLBA used fast...
Recent VLBI monitoring has found transverse motions of the M87 jet. However, due to limited cadence previous observations, details motion have not been fully revealed yet. We regularly monitored jet at KVN and VERA Array (KaVA) 22 GHz from December 2013 June 2016. The average time interval observation is ∼0.1 year, which suitable for tracking short-term structural changes. From these well represented by double ridge lines in region 2–12 mas core. that exhibit oscillations all observed...
We present RadioAstron space-based very long baseline interferometry (VLBI) observations of the nearby radio galaxy 3C84 (NGC1275) at centre Perseus cluster. The were carried out on September 21-22, 2013 and involved a global array 24 ground telescopes observing 5 GHz 22 GHz, together with Space Radio Telescope (SRT). Furthermore, Very Long Baseline Array (VLBA) phased Large (VLA) observed source quasi-simultaneously 15 43 GHz. Fringes between SRT detected lengths up to 8.1 times Earth's...
Radio-loud high-redshift quasars (HRQs), although only a few of them are known to date, crucial for the studies growth supermassive black holes (SMBHs) and evolution active galactic nuclei (AGN) at early cosmological epochs. Radio jets offer direct evidence SMBHs, their radio structures can be studied with highest angular resolution using Very Long Baseline Interferometry (VLBI). Here we report on observations three HRQs (J0131-0321, J0906+6930, J1026+2542) z>5 Korean VLBI Network...