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Simulation Study of Binary Mergers of Galaxy Clusters I: Properties of Merger Shocks and Radio Emission
Hyesung Kang, Dongsu Ryu, Jeongbhin Seo
We investigate binary mergers of galaxy clusters, the formation of shocks, and the resulting radio relics using three-dimensional simulations. The initial setup consists of two ide…
Energy Spectrum and Mass Composition of Ultra-High-Energy Cosmic Rays Originating from Relativistic Jets of Nearby Radio Galaxies
Jeongbhin Seo, Dongsu Ryu, Hyesung Kang
Relativistic jets of radio galaxies (RGs) are possible sources of ultra-high-energy cosmic rays (UHECRs). Recent studies combining relativistic hydrodynamic simulations with Monte…
Diffusive Shock Acceleration Efficiencies for Weak ICM Shocks in the Test Particle Regime
Hyesung Kang
During the formation of large-scale structures in the universe, weak internal shocks are induced within the hot ICM, while strong accretion shocks arise in the WHIM within filament…
A Simulation Study of Low-Power Relativistic Jets: Flow Dynamics and Radio Morphology of FR-I Jets
Ayan Bhattacharjee, Jeongbhin Seo, Dongsu Ryu +1
Radio galaxies are classified into two primary categories based on their morphology: center-brightened FR-I and edge-brightened FR-II. It is believed that the jet power and interac…
Impact of Postshock Turbulence on the Radio Spectrum of Radio Relic Shocks in Merging Clusters
Hyesung Kang
This study investigates the impact of magnetic turbulence on cosmic ray (CR) electrons through Fermi-II acceleration behind merger-driven shocks in the intracluster medium and exam…
Radio surface fluctuations in radio relics
Paola Domínguez-Fernández, Dongsu Ryu, Hyesung Kang
Recent observations have revealed detailed structures of radio relics in a wide range of frequencies. In this work, we perform three-dimensional magnetohydrodynamical simulations o…
Model Spectrum of Ultra-High-Energy Cosmic Rays Accelerated in FR-I Radio Galaxy Jets
Jeongbhin Seo, Dongsu Ryu, Hyesung Kang
Nearby radio galaxies (RGs) of Fanaroff-Riley Class I (FR-I) are considered possible sites for the production of observed ultra-high-energy cosmic rays (UHECRs). Among those, some…
A Simulation Study of Ultra-relativistic Jets -- III. Particle Acceleration at FR-II Jets
Jeongbhin Seo, Dongsu Ryu, Hyesung Kang
We study the acceleration of ultra-high-energy cosmic rays (UHECRs) at FR-II radio galaxies by performing Monte Carlo simulations for the transport, scattering, and energy change o…
Cosmic Ray Acceleration and Nonthermal Radiation at Accretion Shocks in the Outer Regions of Galaxy Clusters
Ji-Hoon Ha, Dongsu Ryu, Hyesung Kang
Cosmology models predict that external accretion shocks form in the outer region of galaxy clusters due to supersonic gas infall from filaments and voids in the cosmic web. They ar…
Electron Preacceleration at Weak Quasi-perpendicular Intracluster Shocks: Effects of Preexisting Nonthermal Electrons
Ji-Hoon Ha, Dongsu Ryu, Hyesung Kang +1
Radio relics in the outskirts of galaxy clusters imply the diffusive shock acceleration (DSA) of electrons at merger-driven shocks with Mach number in the intrac…
Re-acceleration of Cosmic Ray Electrons by Multiple ICM Shocks
Hyesung Kang
Radio relics could be generated by multiple shocks induced in the turbulent intracluster medium during galaxy mergers. Kang (2021) demonstrated that the re-acceleration of cosmic r…
A Simulation Study of Ultra-relativistic Jets -- II. Structures and Dynamics of FR-II Jets
Jeongbhin Seo, Hyesung Kang, Dongsu Ryu
We study the structures of ultra-relativistic jets injected into the intracluster medium (ICM) and the associated flow dynamics, such as shocks, velocity shear, and turbulence, thr…
A Simulation Study of Ultra-Relativistic Jets -- I. A New Code for Relativistic Hydrodynamics
Jeongbhin Seo, Hyesung Kang, Dongsu Ryu +2
In an attempt to investigate the structures of ultra-relativistic jets injected into the intracluster medium (ICM) and the associated flow dynamics, such as shocks, velocity shear,…
Diffusive Shock Acceleration by Multiple Weak Shocks
Hyesung Kang
The intracluster medium (ICM) is expected to experience on average about three passages of weak shocks with low sonic Mach numbers, , during the formation of galaxy cl…
Microinstabilities in the Transition Region of Weak Quasi-Perpendicular Intracluster Shocks
Sunjung Kim, Ji-Hoon Ha, Dongsu Ryu +1
Microinstabilities play important roles in both entropy generation and particle acceleration in collisionless shocks. Recent studies have suggested that in the transition zone of q…
Effects of Multi-scale Plasma Waves on Electron Preacceleration at Weak Quasi-perpendicular Intracluster Shocks
Ji-Hoon Ha, Sunjung Kim, Dongsu Ryu +1
Radio relics associated with merging galaxy clusters indicate the acceleration of relativistic electrons in merger-driven shocks with low sonic Mach numbers ()…
Reaching thermal noise at ultra-low radio frequencies: the Toothbrush radio relic downstream of the shock front
F. de Gasperin, G. Brunetti, M. Bruggen +14
Ultra-low frequency observations (<100 MHz) are particularly challenging because they are usually performed in a low signal-to-noise ratio regime due to the high sky temperature an…
Modeling of Cosmic-Ray Production and Transport and Estimation of Gamma-Ray and Neutrino Emissions in Starburst Galaxies
Ji-Hoon Ha, Dongsu Ryu, Hyesung Kang
Starburst galaxies (SBGs) with copious massive stars and supernova (SN) explosions are the sites of active cosmic-ray production. Based on the predictions of nonlinear diffusive sh…
Limiting the shock acceleration of cosmic-ray protons in the ICM
Denis Wittor, Franco Vazza, Dongsu Ryu +1
Observations of large-scale radio emissions prove the existence of shock accelerated cosmic-ray electrons in galaxy clusters, while the lack of detected -rays limits the acceler…
Semi-analytic Models for Electron Acceleration in Weak ICM Shocks
Hyesung Kang
We propose semi-analytic models for the electron momentum distribution in weak shocks that accounts for both in situ acceleration and re-acceleration through diffusive shock accele…
Electron Firehose Instabilities in High- ICM shocks
Sunjung Kim, Ji-Hoon Ha, Dongsu Ryu +1
The preacceleration of electrons through reflection and shock drift acceleration (SDA) is essential for the diffusive shock acceleration (DSA) of nonthermal electrons in collisionl…
Chandra Observations of the Spectacular A3411-12 Merger Event
Felipe Andrade-Santos, Reinout J. van Weeren, Gabriella Di Gennaro +17
We present deep Chandra observations of A3411-12, a remarkable merging cluster that hosts the most compelling evidence for electron re-acceleration at cluster shocks to date. Using…
Gamma-ray and Neutrino Emissions due to Cosmic-Ray Protons Accelerated at Intracluster Shocks in Galaxy Clusters
Ji-Hoon Ha, Dongsu Ryu, Hyesung Kang
We examine the cosmic-ray protons (CRp) accelerated at collisionless shocks in galaxy clusters using cosmological structure formation simulations. We find that in the intracluster…
Propagation of ultra-high-energy cosmic rays in the magnetized cosmic web
Jihyun Kim, Dongsu Ryu, Soonyoung Roh +2
A high concentration of ultra-high-energy cosmic ray (UHECR) events, called a hotspot, was reported by the Telescope Array (TA) experiment, but its origin still remains unsolved. O…