• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.209-211
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• 1996

Recent surveys at Parkes, in particular the 70 cm survey of the southern sky, have discovered many pulsars, including 17 miilisecond pulsars in the Galactic disk. Timing and polarization observations of some of these pulsars are described. The only two pulsars known to be in orbit around massive non-degenerate stellar compamons were also discovered at Parkes, and some recent observational results for these pulsars are also presented.

• Journal of Astronomy and Space Sciences
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• v.33 no.3
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• pp.147-166
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• 2016

A radio-quiet γ-ray pulsar is a neutron star that has significant γ-ray pulsation but without observed radio emission or only limited emission detected by high sensitivity radio surveys. The launch of the Fermi spacecraft in 2008 opened a new epoch to study the population of these pulsars. In the 2^nd Fermi Large Area Telescope catalog of γ-ray pulsars, there are 35 (30 % of the 117 pulsars in the catalog) known samples classified as radio-quiet γ-ray pulsars with radio flux density (S₁₄₀₀) of less than 30 μJy. Accompanying the observations obtained in various wavelengths, astronomers not only have the opportunity to study the emitting nature of radio-quiet γ-ray pulsars but also have proposed different models to explain their radiation mechanism. This article will review the history of the discovery, the emission properties, and the previous efforts to study pulsars in this population. Some particular cases known as Geminga-like pulsars (e.g., PSR J0633+1746, PSR J0007+7303, PSR J2021+4026, and so on) are also specified to discuss their common and specific features.

• Journal of Astronomy and Space Sciences
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• v.30 no.3
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• pp.153-158
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• 2013

In this review paper we explain the following gamma-ray emission features from the millisecond pulsars. (1) Why is the dipolar field of millisecond pulsars so weak but the magnetic pair creation process may still be able to control the size of the outergap? (2) A sub-GeV pulse component could occur in the vicinity of the radio pulse of millisecond pulsars. (3) Orbital modulated gamma-rays should exist in the black widow systems for large viewing angle.

• Journal of Astronomy and Space Sciences
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• v.33 no.2
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• pp.101-104
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• 2016

More than 100 γ−ray pulsars have been discovered by the Fermi Gamma-ray Space Telescope. With a significantly enlarged sample size, it is possible to compare the properties of different classes. Radio-quiet (RQ) γ−ray pulsars form a distinct population, and various studies have shown that the properties of the RQ population can be intrinsically different from those of radio-loud (RL) pulsars. Utilizing these differences, it is possible to further classify the pulsar-like unidentified γ−ray sources into sub-groups. In this study, we suggest the possibility of distinguishing RQ/RL pulsars by their spectral shape. We compute the probabilities of a pulsar to be RQ or RL for a given spectral curvature. This can provide a key to the estimation of the intrinsic fraction of radio-quietness in the γ−ray pulsar population, which can place a tight constraint on the emission geometry.

• Journal of The Korean Astronomical Society
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• v.25 no.1
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• pp.47-64
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• 1992

Cores of globular clusters are an ideal place for close encounters between stars. The outcome of tidal capture can be stellar mergers, close binaries between normal stars (W UMa type), cataclysmic variables composed of white dwarf and normal star pairs, or low-mass X-ray binaries consisting of a neutron star and a normal star pairs. Stellar mergers can be the origin of blue stragglers in dense globular clusters although they are hard to observe. Low mass X-ray binaries would eventually become binary pulsars with short pulse periods after the neutron stars accrete sufficient amount of matter from the companion. However, large number of recently discovered, isolated millisecond pulsars (as opposed to binary pulsars) in globular clusters may imply that they do not have to gain angular speeds during the X-ray binary phase. We propose that these isolated millisecond pulsars may have formed through the disruptive encounters, which lead to the formation of accretion disk without Roche lobe filling companion, between a neutron star and a main-sequence star. Based on recently developed multicomponent models for the dynamical evolution of globular clusters, we compute the expected numbers of various systems formed by tidal capture as a function of time.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.79.2-79.2
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• 2014

Galactic radio pulsar population is diverse. So far about 2300 radio pulsars are known in the Milky Way, in addition to Large and Small Magellanic Clouds. Radio pulsar observations at a few hundreds MHz up to ~10 GHz have been active and they are proved to be fruitful. Low frequencies are preferred mainly because of the steep ratio spectrum of pulsars. However, developments in pulsar backends (e.g. a wide-band spectrometer) and improved system sensitivities make it possible to observe pulsars at higher frequencies using large, single-dish telescopes up to ~18 GHz. Going forward, mm-wavelength observations is expected to open a new window in pulsar astronomy. In particular, frequencies well above ~15 GHz are pre-requisite to detect pulsars in the Galactic Center where radio pulsed signals are severely scattered by interactions with the interstellar medium. Recent discoveries strongly imply that there are subsets of pulsars with an apparently flat spectrum, such as magnetars. In April 2014, the first pulsar (magnetar) was discovered only 3 arcmin from Sgr A*, PSR J1745-2900. We will present a brief overview on pulsar populations focusing on those observable at high frequencies. We will also discuss prospects of pulsar observations in mm-wavelengths and how we can utilize the Korean VLBI network.

• Journal of The Korean Astronomical Society
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• v.51 no.6
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• pp.171-183
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• 2018

To celebrate the tenth anniversary since the launch of Fermi Gamma-ray Space Telescope, we take a retrospect to a series of breakthroughs Fermi has contributed to pulsar astronomy in the last decade. Apart from significantly enlarging the population of ${\gamma}$-ray pulsars, observations with the Large Area Telescope onboard Fermi also show the population is not homogeneous. Instead, many classes and sub-classes have been revealed. In this paper, we will review the properties of different types of ${\gamma}$-ray pulsars, including radio-quiet ${\gamma}$-ray pulsars, millisecond pulsars, ${\gamma}$-ray binaries. Also, we will discuss the prospects of pulsar astronomy in the high energy regime.

• The Bulletin of The Korean Astronomical Society
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• v.31 no.2
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• pp.19-19
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• 2006

• 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.

• Journal of Astronomy and Space Sciences
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• v.33 no.2
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• pp.75-92
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• 2016

It is generally believed that the high energy emissions from isolated pulsars are emitted from relativistic electrons/positrons accelerated in outer magnetospheric accelerators (outergaps) via a curvature radiation mechanism, which has a simple exponential cut-off spectrum. However, many gamma-ray pulsars detected by the Fermi LAT (Large Area Telescope) cannot be fitted by simple exponential cut-off spectrum, and instead a sub-exponential is more appropriate. It is proposed that the realistic outergaps are non-stationary, and that the observed spectrum is a superposition of different stationary states that are controlled by the currents injected from the inner and outer boundaries. The Vela and Geminga pulsars have the largest fluxes among all targets observed, which allows us to carry out very detailed phase-resolved spectral analysis. We have divided the Vela and Geminga pulsars into 19 (the off pulse of Vela was not included) and 33 phase bins, respectively. We find that most phase resolved spectra still cannot be fitted by a simple exponential spectrum: in fact, a sub-exponential spectrum is necessary. We conclude that non-stationary states exist even down to the very fine phase bins.