• 천문학회지
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• 제56권1호
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• pp.117-124
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• 2023

A Forbush decrease (FD) is a depression of cosmic ray (CR) intensity observed by ground-based neutron monitors (NMs). The CR intensity is thought to be modulated by the heliospheric magnetic structures including the interplanetary coronal mass ejection (ICME) surrounding the Earth. The different magnitude of the decreasing in intensity at each NM was explained only by the geomagnetic cutoff rigidity of the NM station. However, sometimes NMs of almost the same cutoff rigidity in northern and southern hemispheres observe the asymmetric intensity depression magnitudes of FD events. Thus, in this study we intend to see the effects on CR intensity modulation of FD event recorded at different NMs due to different ICME propagation directions as an additional parameter in the model explaining the CR modulation. Fortunately, since 2006 the coronagraphs of twin spacecraft of the STEREO mission allow us to infer the propagation direction of ICME associated with the FD event in 3-dimension with respect to the Earth. We suggest the hypothesis that the asymmetric CR modulations of FD events are determined by the propagation directions of the associated ICMEs.

• 천문학회보
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• 제42권2호
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• pp.66.1-66.1
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• 2017

Nuclear reactions in explosive stars such as novae, X-ray bursts, and supernovae are responsible for producing many of the elements that make up our world. Exotic nuclei not normally found on earth can play an important role in these events due to the extreme conditions that occur in the explosion. A frontier area of research involves utilizing beams of radioactive nuclei to improve our understanding of these explosions and the implications on cosmic element production. At the future radioactive ion beam facility of Korea, RAON, we will measure astrophysically important reactions using exotic beams to probe the details of cosmic events. Details of RAON and possible day-1 experiments at the facility will be presented.

• 천문학회보
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• 제44권2호
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• pp.66.1-66.1
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• 2019

We study cosmological shock waves in and around protoclusters at cosmic noon in the Horizon Run 5 Simulation (HR5), one of the world's largest hydrodynamic cosmological simulations. We select the local peaks of X-ray luminosity at z=2.5-3 in the HR5 lightcone volume as protocluster candidates. We find shock waves with Ms > 1.3 within the virial radii of the HR5 protocluster candidates by applying several shock-finding algorithms based on the Rankine-Hugoniot jump condition. We compare the properties of shock waves from different shock-finding algorithms.

• 천문학회지
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• 제37권5호
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• pp.593-596
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• 2004

We introduce a method of identifying evidence of shocks in the X-ray emitting gas in clusters of galaxies. Using information from synthetic observations of simulated clusters, we do a blind search of the synthetic image plane. The locations of likely shocks found using this method closely match those of shocks identified in the simulation hydrodynamic data. Though this method assumes nothing about the geometry of the shocks, the general distribution of shocks as a function of Mach number in the cluster hydrodynamic data can be extracted via this method. Characterization of the cluster shock distribution is critical to understanding production of cosmic rays in clusters and the use of shocks as dynamical tracers.

• Journal of Astronomy and Space Sciences
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• 제13권2호
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• pp.149-162
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• 1996

1992년 8월에 발사된 한국의 첫번째 위성인 우리별 1호에는 저궤도 고에너지 입자환경를 관측하는 탑재체 cosmic ray experiment(CRE)가 실렸다. CRE는 크게 cosmic particle experiment(CPE)와 total dose esperiment(TDE) 두 시스템으로 구성된다. 이와 더불어 실험 탑재물은 아니지만, 프로그램 메모리와 램디스크(RAM disk)의 비트바뀜현상(SEU) 결과를 통해서 고에너지 입자환경에 대한 간접적인 정보를 얻을 수 있었다. 1993년 9월에 발사된 두 번재 위성 우리별 2호에는 OBCI인 KASCOM에서 프로그램 메모리와 램디스크 메모리에 대한 비트바뀜현상실험을 수행하였다. 우리별 1호와 2호는 그 구조는 비슷하지만 서로의 궤도가 다르기 때문에 두 위성의 실험결과를 분석해본다면 각 궤도에서의 고에너지 입자환경에 대한 비교연구할 수 있는 좋은 기회가 된다.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2005년도 한국우주과학회보 제14권1호
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• pp.67-67
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• 2005

• 천문학회보
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• 제29권2호
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• pp.28.1-28.1
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• 2004

• 천문학회보
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• 제18권
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• pp.7.1-7.1
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• 1993

• 대한방사선방어학회:학술대회논문집
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• 대한방사선방어학회 2010년도 춘계 학술발표회 및 심포지엄
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• pp.228-229
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• 2010

• 천문학회지
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• 제43권2호
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• pp.25-39
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• 2010

We perform kinetic simulations of diffusive shock acceleration (DSA) in Type Ia supernova remnants (SNRs) expanding into a uniform interstellar medium (ISM). Bohm-like diffusion due to self-excited $Alfv\acute{e}n$ waves is assumed, and simple models for $Alfv\acute{e}nic$ drift and dissipation are adopted. Phenomenological models for thermal leakage injection are considered as well. We find that the preshock gas temperature is the primary parameter that governs the cosmic ray (CR) acceleration efficiency and energy spectrum, while the CR injection rate is a secondary parameter. For SNRs in the warm ISM of $T_0\lesssim10^5K$, if the injection fraction is $\xi\gtrsim10^{-4}K$, the DSA is efficient enough to convert more than 20% of the SN explosion energy into CRs and the accelerated CR spectrum exhibits a concave curvature flattening to $E^{-1.6}$, which is characteristic of CR modified shocks. Such a flat source spectrum near the knee energy, however, may not be reconciled with the CR spectrum observed at Earth. On the other hand, SNRs in the hot ISM of$T_{0}\approx10^{6}K$ with a small injection fraction, $\xi$<$10^{-4}$, are inefficient accelerators with less than 10% of the explosion energy getting converted to CRs. Also the shock structure is almost test-particle like and the ensuing CR spectrum can be steeper than $E^{-2}$. With amplified magnetic field strength of order of $30{\mu}G$ $Alfv\acute{e}n$ waves generated by the streaming instability may drift upstream fast enough to make the modified test-particle power-law as steep as $E^{-2.3}$, which is more consistent with the observed CR spectrum.