• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.465-470
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• 2004

I address the issue of nonthermal processes in the large scale structure of the universe. After reviewing the properties of cosmic shocks and their role as particle accelerators, I discuss the main observational results, from radio to $\gamma$-ray and describe the processes that are thought be responsible for the observed nonthermal emissions. Finally, I emphasize the important role of $\gamma$-ray astronomy for the progress in the field. Non detections at these photon energies have already allowed us important conclusions. Future observations will tell us more about the physics of the intracluster medium, shocks dissipation and CR acceleration.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.125-128
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• 2005

In this paper, we argue that the gigahertz peaked spectrum (GPS) quasars are special blazars, blazars in dense and dusty gas enviornment. The ROSAT detection rate of GPS quasars is similar to that of flat spectrum radio quasars (FSRQs), suggesting that the relativistic jets in GPS quasars are oriented at small angle to the line of sight. Due to strong inverse Compton scattering off infrared photons from dense and dusty nuclear interstellar media in GPS quasars, most of them may have significant soft gamma-ray and X-ray emission, which is consistent with ASCA X-ray observations. Because Compton cooling in GPS quasars is stronger than that in FSRQs, synchrotron emission in GPS quasars may less dominate over thermal emission of the accretion disk and hot dust, hence most GPS quasars show low optical polarization and small variability, consistent with observations. We suggest that it is the significant radio emission of electron/positron pairs produced by the interaction of gamma-rays with the dense gas and dust grains in GPS quasars that makes GPS quasars show steep radio spectra, low radio polarization, and relatively faint VLBI/VLBA cores. Whether GPS quasars are special blazars can be tested by gamma-ray observations with GLAST in the near future, with the detection rate of GPS quasars being similar to that of FSRQs.

• Publications of The Korean Astronomical Society
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• v.10 no.1
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• pp.15-30
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• 1995

It has been recognized that the morphologies of the SNRs from the radio observation are "barrel shaped". To interpret the mechanism of the radiation and the physical state of the environments, we have analytically calculated the dynamical structure of the interacting region in the case where the ejectum has a steep power-law density profile($\rho{\sim}r^{-n}$) and the ambient medium has a shallow power-law density profile($\rho{\sim}r^{-s}$), assuming that the cosmic rays are isotropically accelerated in the shock wave and the magnetic fields are very weak. The calculated synchrotron radio maps show that the emission from the equator is intense and the emissions from the central and polar regions are less intense. Also the thicknesses of the shell are strongly dependent on s and weakly on n. The azimuthal intensity ratio $\alpha$ increases as the efficiency of the cosmic ray acceleration increases and s decreases. We compared the results with the morphology of the SNR A. D. 1006(type I SNR). It does agree with the case of s = 0, w = 0.3 - 0.5. This value for w is consistent with the results by Eichler(1979). It provides us the evidence of the cosmic ray acceleration in the shock wave.