• Journal of The Korean Astronomical Society
• /
• v.47 no.5
• /
• pp.167-178
• /
• 2014

We search for misclassified type 1 AGNs among type 2 AGNs identified with emission line flux ratios, and investigate the properties of the sample. Using 4 113 local type 2 AGNs at 0.02 < z < 0.05 selected from Sloan Digital Sky Survey Data Release 7, we detected a broad component of the $H{\alpha}$ line with a Full-Width at Half-Maximum (FWHM) ranging from 1 700 to $19090km\;s^{-1}$ for 142 objects, based on the spectral decomposition and visual inspection. The fraction of the misclassified type 1 AGNs among type 2 AGN sample is ~3.5%, implying that a large number of missing type 1 AGN population may exist. The misclassified type 1 AGNs have relatively low luminosity with a mean broad $H{\alpha}$ luminosity, log $L_{H\alpha}=40.50{\pm}0.35\;erg\;s^{-1}$, while black hole mass of the sample is comparable to that of the local black hole population, with a mean black hole mass, log $M_{BH}=6.94{\pm}0.51\;M_{\odot}$. The mean Eddington ratio of the sample is log $L_{bol}/L_{Edd}=-2.00{\pm}0.40$, indicating that black hole activity is relatively weak, hence, AGN continuum is too weak to change the host galaxy color. We find that the O III lines show significant velocity offsets, presumably due to outflows in the narrow-line region, while the velocity offset of the narrow component of the $H{\alpha}$ line is not prominent, consistent with the ionized gas kinematics of general type 1 AGN population.

• Publications of The Korean Astronomical Society
• /
• v.8 no.1
• /
• pp.265-272
• /
• 1993

Recent X-ray observations of the accretion disks in stellar black hole candidates have revealed rather complex behavior, which cannot be fully described by the simple picture of the standard disk model. In this paper, therefore, we discuss the effects of e+e- pair creation on the structure and the stability of hot accretion disks, aiming at the thorough understanding of emission properties of X-ray binaries containing black holes.

• Proceedings of the KSEEG Conference
• /
• 2007.04a
• /
• pp.604-604
• /
• 2007

See Full Text

• Publications of The Korean Astronomical Society
• /
• v.14 no.2
• /
• pp.57-60
• /
• 1999

We derive the Grad-Shafranov equation in the Macdonald-Thorne magnetosphere of the super-massive black hole in an active galactic nucleus. Our major assumption is that the plasma velocity is not only toroidal but also poloidal. As a result, we get the correction terms which are related to the poloidal motion of plasma like electrodynamic jets.

• Bulletin of the Korean Space Science Society
• /
• 1999.09a
• /
• pp.69-69
• /
• 1999

No Abstract, See Full Text

• The Bulletin of The Korean Astronomical Society
• /
• v.29 no.2
• /
• pp.44.1-44.1
• /
• 2004

• Publications of The Korean Astronomical Society
• /
• v.19 no.1
• /
• pp.11-16
• /
• 2004

In this review article the famous 'jet equation' in a Minkowski magnetosphere around the compact objects will be fully derived for the pedagogical purposes.

• Journal of The Korean Astronomical Society
• /
• v.34 no.4
• /
• pp.215-224
• /
• 2001

We present the whole basis of numerical method and useful formulae for general relativistic magnetohydrodynamic simulations in Kerr space-time.

• Journal of The Korean Astronomical Society
• /
• v.34 no.4
• /
• pp.247-249
• /
• 2001

The accretion disks are usually supposed symmetric to reflection on the Z=0 plane. Asymmetries in the flow are be ver-y small in the vicinity of the compact accretor. However their existence can have a important role in the case of subkeplerian accretion flows onto black holes. These flows lead to strong heating and even to the formation of shocks close to the centrifugal barrier. Large asymmetries are due to the development of the KH instability triggered by the small turbulences at the layer separating the incoming flow from the out coming shocked flow. The consequence of this phenomenon is the production of asymmetric outflows of matter and quasi periodic oscillations of the inner disk regions up and down the Z=0 plane.

• The Bulletin of The Korean Astronomical Society
• /
• v.41 no.1
• /
• pp.31.3-31.3
• /
• 2016

Exploring a universe with gravitational waves (GWs) was only theoretical expectation for long time. In September 2015, the Laser Interferometer GW Observatory (LIGO) first detected GWs emitted from the collision of two stellar-mass black holes in cosmological distance (1.3 billion light years) on Earth. This confirms the existence of black-hole binary mergers, and further, opens a new field of GW astronomy. We begin our discussion with a list of important GW sources that can be detectable on Earth by large-scale laser interferometers such as LIGO. Focusing on compact objects such as neutron stars and black holes, we then discuss possible research in the context of GW astronomy. By coordinating with existing observatories, searching for electromagnetic waves or particles from astronomical objects, around the world, multi-messenger astronomy for the universe's most cataclysmic phenomena (e.g. gamma-ray bursts) will be available in the near future.