간행물
Journal of Astronomy and Space Sciences KCI 등재 SCOPUS
- 발행기관 한국우주과학회
- 자료유형 학술지
- 간기 계간
- ISSN 2093-5587 (Print)2093-1409 (Online)
- 수록기간 1984 ~ 2022
- 주제분류 자연과학 > 천문학 자연과학 분류의 다른 간행물
- 십진분류KDC 443DDC 520
권호리스트/논문검색
제30권 2호 (2013년 6월) 8건
1.
2013.06
서비스 종료(열람 제한)
We present the Hilbert-Huang transform (HHT) analysis on the quasi-periodic modulation of SMC X-1. SMC X-1, consistingof a neutron star and a massive companion, exhibits superorbital modulation with a period varying between ~40 d and ~65 d.We applied the HHT on the light curve observed by the All-Sky Monitor onboard Rossi X-ray Timing Explorer (RXTE) to obtainthe instantaneous frequency of the superorbital modulation of SMC X-1. The resultant Hilbert spectrum is consistent with thedynamic power spectrum while it shows more detailed information in both the time and frequency domains. According to theinstantaneous frequency, we found a correlation between the superorbital period and the modulation amplitude. Combiningthe spectral observation made by the Proportional Counter Array onboard RXTE and the superorbital phase derived in theHHT, we performed a superorbital phase-resolved spectral analysis of SMC X-1. An analysis of the spectral parameters versusthe orbital phase for different superorbital states revealed that the diversity of nH has an orbital dependence. Furthermore,we obtained the variation in the eclipse profiles by folding the All Sky Monitor light curve with orbital period for differentsuperorbital states. A dip feature, similar to the pre-eclipse dip of Her X-1, can be observed only in the superorbital ascendingand descending states, while the width is anti-correlated with the X-ray flux.
2.
2013.06
서비스 종료(열람 제한)
Wu, Jason Hung Kit, Hui, Chung Yue, Huang, Regina Hsiu Hui, Kong, Albert Kwok Hing, Cheng, Kwong Sang, Takata, Jumpei, Tam, Pak Hin Thomas, Wu, Eric Man Ho, Liu, Joe
Anomalous X-ray pulsars (AXPs) are thought to be magnetars which are young isolated neutron stars with extremely strongmagnetic fields of >1014 Gauss. Their tremendous magnetic fields inferred from the spin parameters provide a huge energyreservoir to power the observed X-ray emission. High-energy emission above 0.3 MeV has never been detected despiteintensive search. Here, we present the possible Fermi Large Area Telescope (LAT) detection of γ-ray pulsations above 200MeV from the AXP, 1E 2259+586, which puts the current theoretical models of γ-ray emission mechanisms of magnetars intochallenge. We speculate that the high-energy γ-rays originate from the outer magnetosphere of the magnetar.
3.
2013.06
서비스 종료(열람 제한)
We have investigated the X-ray emission from the shock-heated plasma of the Galactic supernova remnant Kesteven 69 withXMM-Newton. Assuming the plasma is at collisional ionization equilibrium, a plasma temperature and a column absorptionare found to be kT ~ 0.62 keV and NH ~ 2.85 ×1022 cm-2 respectively by imaging spectroscopy. Together with the deducedemission measure, we place constraints on its Sedov parameters.
4.
2013.06
서비스 종료(열람 제한)
We use the outer gap model to explain the spectrum and the energy dependent light curves of the X-ray and soft γ-rayradiations of the spin-down powered pulsar PSR B1509-58. In the outer gap model, most pairs inside the gap are createdaround the null charge surface and the gap’s electric field separates the opposite charges to move in opposite directions.Consequently, the region from the null charge surface to the light cylinder is dominated by the outflow current and that fromthe null charge surface to the star is dominated by the inflow current. We suggest that the viewing angle of PSR B1509-58 onlyreceives the inflow radiation. The incoming curvature photons are converted to pairs by the strong magnetic field of the star.The X-rays and soft γ-rays of PSR B1509-58 result from the synchrotron radiation of these pairs. The magnetic pair creationrequires a large pitch angle, which makes the pulse profile of the synchrotron radiation distinct from that of the curvatureradiation. We carefully trace the pulse profiles of the synchrotron radiation with different pitch angles. We find that thedifferences between the light curves of different energy bands are due to the different pitch angles of the secondary pairs, andthe second peak appearing at E > 10 MeV comes from the region near the star, where the stronger magnetic field allows thepair creation to happen with a smaller pitch angle.
5.
2013.06
서비스 종료(열람 제한)
In this paper we examine a total of 16 dipolarization events that were observed by THEMIS spacecraft in space close togeosynchronous orbit, r < ~ 7 RE. For the identified events, we examine the characteristics of the plasma flows and associatedbubbles as defined based on pV5/3, where p is the plasma pressure and V the volume of unit magnetic flux. First, we find thatthe flow speed in the near-geosynchronous region is very low, mostly within a few tens of km/s, except for a very few events forwhich the flow can rise up to ~200 km/s but only very near the dipolarization onset time. Second, the bubble parameter, pV5/3,decreases by a much smaller factor after the dipolarization onset than for the events in the farther out tail region. We suggestthat the magnetic dipolarization in the near-geosynchronous region generates or is associated with only very weak plasmabubbles. Such bubbles in the near-geosynchronous region would penetrate earthward only by a small distance before theystop at an equilibrium position or drift around the Earth.
6.
2013.06
서비스 종료(열람 제한)
The length of solar cycle 23 has been prolonged up to about 13 years. Many studies have speculated that the solar cycle 23/24 minimum will indicate the onset of a grand minimum of solar activity, such as the Maunder Minimum. We check the trends of solar (sunspot number, solar magnetic fields, total solar irradiance, solar radio flux, and frequency of solar X-ray flare), interplanetary (interplanetary magnetic field, solar wind and galactic cosmic ray intensity), and geomagnetic (Ap index) parameters (SIG parameters) during solar cycles 21-24. Most SIG parameters during the period of the solar cycle 23/24 minimum have remarkably low values. Since the 1970s, the space environment has been monitored by ground observatories and satellites. Such prevalently low values of SIG parameters have never been seen. We suggest that these unprecedented conditions of SIG parameters originate from the weakened solar magnetic fields. Meanwhile, the deep 23/24 solar cycle minimum might be the portent of a grand minimum in which the global mean temperature of the lower atmosphere is as low as in the period of Dalton or Maunder minimum.
7.
2013.06
서비스 종료(열람 제한)
Nam, Uk-Won, Lim, Chang Hwy, Lee, Jae Jin, Pyo, Jeonghyun, Moon, Bong-Kon, Lee, Dae-Hee, Park, Youngsik, Kim, Hyun Ok, Moon, Myungkook, Kim, Sunghwan
Tissue equivalent proportional counter (TEPC) can measure the Linear Energy Transfer (LET) spectrum and calculate the equivalent dose for the complicated radiation field in space. In this paper, we developed and characterized a TEPC for radiation monitoring in International Space Station (ISS). The prototype TEPC which can simulate a 2 μm of the site diameter for micro-dosimetry has been tested with a standard alpha source (241Am, 5.5 MeV). Also, the calibration of the TEPC was performed by the 252Cf neutron standard source in Korea Research Institute of Standards and Science (KRISS). The determined calibration factor was kf = 3.59×10-7 mSv/R.
8.
2013.06
서비스 종료(열람 제한)
Heumgyeonggaknu is a water-hammering type automatic water clock which was made by Jang Yeong-Sil in 1438. The water clock that is located in Heumgyeonggaknu consists of Suho which is equipped with 2-stage overflow. Constant water wheel power is generated by supplying a fixed amount of water of Suho to Sususang, and this power is transferred to each floor at the same time. The 1st floor rotation wheel of Gasan consists of the operation structure which has the shape of umbrella ribs. The 2nd floor rotation wheel is made so that the 12 hour signal, Gyeong-Jeom signal, and Jujeon constitute a systematic configuration. The 3rd floor rotation wheel is made so that the signal and rotation of Ongnyeo and four gods can be accomplished. Based on the above conceptual design, this paper analyzed the internal signal generation and power transmission of Heumgyeonggaknu.
