• Journal of Astronomy and Space Sciences
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• v.30 no.3
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• pp.145-152
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• 2013

Rotation-powered pulsars are excellent laboratories for studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. Particle acceleration and high-energy emission from the polar caps is expected to occur in connection with electron-positron pair cascades. I will review acceleration and gamma-ray emission from the pulsar polar cap and associated slot gap. Predictions of these models can be tested with the data set on pulsars collected by the Large Area Telescope on the Fermi Gamma-Ray Telescope over the last four years, using both detailed light curve fitting, population synthesis and phase-resolved spectroscopy.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.99-99
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• 2013

If the magnetic field is extremely strong, as in pulsar/black hole magnetospheres, the Alfven speed approaches to the speed of light and we need relativity to describe interactions of Alfvenic waves. In this poster, we discuss physics of Alfvenic turbulence in this limit. We first discuss interaction of Alfvenic wave packets and scaling relations of resulting turbulence. Then we show results of numerical simulations. Finally we compare relativistic Alfvenic turbulence and its Newtonian counterpart.

• Journal of The Korean Astronomical Society
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• v.3 no.1
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• pp.17-27
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• 1970

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.76.1-76.1
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• 2010

The successful launch of the Fermi Gamma-Ray Space Telescope has led us into an entirely new era of high-energy astrophysics. The sensitivity of the Large Area Telescope (LAT) on the spacecraft is much higher than that of its predecessors. Furthermore, the data policy of LAT is completely open so that everyone can access the data. All these enable a wide variety of investigations. In order to utilize the golden opportunity at the early stage of this mission, we have established the Fermi Asian Network (FAN) in 2010. Since the establishment, we have carried out intensive investigations in both observational and theoretical aspect. In this talk, I will highlight the recent discoveries made by FAN with particular focus on pulsar astrophysics.

• Journal of Astronomy and Space Sciences
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• v.33 no.3
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• pp.167-172
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• 2016

We used the 4 m Discovery Channel Telescope (DCT) at Lowell observatory in 2014 to observe the Guitar Nebula, an Hα bow-shock nebula around the high-velocity radio pulsar B2224+65. Since the nebula's discovery in 1992, the structure of the bow-shock has undergone significant dynamical changes. We have observed the limb structure, targeting the "body" and "neck" of the guitar. Comparing the DCT observations to 1995 observations with the Palomar 200-inch Hale telescope, we found changes in both spatial structure and surface brightness in the tip, head, and body of the nebula.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.56.2-56.2
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• 2013

Compact binaries are important sources of gravitational waves. They are also prime targets for long baseline laser interferometers. In this talk, we present latest progresses made in the Galactic merger rate calculations for compact binaries in the Galactic disk, with an emphasis on NS-NS binaries. For the first time, the non-recycled pulsar found in the Double Pulsar system (PSR J0737-3039B) is included in the rate calculation. We then discuss the prospects of detecting gravitational waves for Earth-based detectors such as advanced LIGO (Laser Interferometer Gravitational-wave Observatory) in US and advanced Virgo in Europe, extrapolating the Galactic rate estimates up to the detection volume of the advanced LIGO-Virgo network, Our results support the expectation that gravitational waves emitted from compact binary mergers will be detected within a decade. However, the detection rate of gravitational waves associated with NS-NS mergers is most likely to be several per year that is much smaller than what has been previously known.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.47.2-47.2
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• 2011

Gravitational waves from the pulsar glitch can be detected by next generation gravitational wave observatories. We investigate characteristics of the modes that can emit the gravitational waves excited by three different types of perturbations satisfying conservation of total rest mass and angular momentum. These perturbations mimic the pulsar glitch theories i.e., change of moment of inertia due to the star quakes or angular momentum transfer by vortex unpinning at crust-core interface. We carry out numerical hydrodynamic simulations using the pseudo-Newtonian method which makes weak field approximation for the dynamics, but taking all forms of energies into account to compute the Newtonian potential. Unlike other works, we found that the first and second strongest modes that give gravitational waves are $^2p_1$ and $H_1$ rather than$^2f$. We also found that vortex unpinning model excites the inertial mode in quadrupole moment quite effectively. The inertial mode may evolve into the non-axisymmetric r-mode.

• Journal of The Korean Astronomical Society
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• v.52 no.5
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• pp.173-180
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• 2019

We present IR flux density measurements, models of the broadband SED, and results of SED modeling for the Pulsar Wind Nebula (PWN) 3C 58. We find that the Herschel flux density seems to be slightly lower than suggested by interpolation of previous measurements in nearby wavebands, implying that there may be multiple electron populations in 3C 58. We model the SED using a simple stationary one-zone and a more realistic time-evolving multi-zone scenario. The latter includes variations of flow properties in the PWN (injected energy, magnetic field, and bulk speed), radiative energy losses, adiabatic expansion, and diffusion, similar to previous PWN models. From the modeling, we find that a PWN age of 2900-5400 yrs is preferred and that there may be excess emission at ${\sim}10^{11}Hz$. The latter may imply multiple populations of electrons in the PWN.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.219-221
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• 1996

The x-ray pulsar GX 1+4 was observed by us in four balloon- borne experiments carried out from Hyderabad, India during 1991-1995 period with a hard x-ray telescope. The x-ray telescope consists of two collimated large area xenon-filled proportional counters with an effective area of $2400 cm^2$, a field of view of $5^{\circ}{\times}5^{\circ}$ and sensitive in the energy band of 20 - 100 keV. The pulsar was detected in bright state in two of the four experiments and x-ray pulsations with 120 second period were detected clearly. Pulsation period, rate of change of period with time, pulse fraction, pulse profile and energy spectra of the source were determined from these studies. During March 1995 observation, the x-ray pulse of GX 1+4 was found to be double-peaked compared to a single-peak pulse profile detected in December 1993. Details of these results are presented and their interpretation discussed in terms of the current accretion models of x-ray binaries.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.55.1-55.1
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• 2019

We investigate broadband emission properties of the pulsar wind nebula (PWN) 3C 58 using a spectral energy distribution (SED) model. We attempt to match simultaneously the broadband SED and spatial variations and emission about 3C 58 in X-ray band. We further the model to explain a possible far-IR feature of which a hint is recently suggested in 3C 58: a small bump at ~10^11 GHz in the PLANCK and Herschel band. While external dust emission may easily explain the observed bump, it may be internal emission of PWNe implying an another additional population of particles. Although significance for the bump in 3C 58 is not higher than other PWNe, here we explore possible origins of the IR bump using the emission model and find that a population of electrons with GeV energies can explain the bump. If it is produced in the PWN, it may provide new insights into particle acceleration and flows in PWNe.