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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of Astronomy and Space Sciences
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The Korean Space Science Society
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Volume & Issues
Volume 33, Issue 3 - Sep 2016
Volume 33, Issue 2 - Jun 2016
Volume 33, Issue 1 - Mar 2016
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Theoretical Study of Gamma-ray Pulsars
Song, Yuzhe ; Cheng, Kwong Sang ; Takata, Jumpei ;
Journal of Astronomy and Space Sciences, volume 33, issue 2, 2016, Pages 69~73
DOI : 10.5140/JASS.2016.33.2.69
We use the non-stationary three dimensional two-layer outer gap model to explain gamma-ray emissions from a pulsar magnetosphere. We found out that for some pulsars like the Geminga pulsar, it was hard to explain emissions above a level of around 1 GeV. We then developed the model into a non-stationary model. In this model we assigned a power-law distribution to one or more of the spectral parameters proposed in the previous model and calculated the weighted phase-averaged spectrum. Though this model is suitable for some pulsars, it still cannot explain the high energy emission of the Geminga pulsar. An Inverse-Compton Scattering component between the primary particles and the radio photons in the outer magnetosphere was introduced into the model, and this component produced a sufficient number of GeV photons in the spectrum of the Geminga pulsar.
Probing Gamma-ray Emission of Geminga and Vela with Non-stationary Models
Chai, Yating ; Cheng, Kwong-Sang ; Takata, Jumpei ;
Journal of Astronomy and Space Sciences, volume 33, issue 2, 2016, Pages 75~92
DOI : 10.5140/JASS.2016.33.2.75
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.
Exploring the Extra Component in the Gamma-ray Emission of the New Redback Candidate 3FGL J2039.6-5618
Ng, Cho-Wing ; Cheng, Kwong-Sang ; Takata, Jumpei ;
Journal of Astronomy and Space Sciences, volume 33, issue 2, 2016, Pages 93~99
DOI : 10.5140/JASS.2016.33.2.93
A redback system is a binary system composed of a pulsar and a main sequence star. The inverse Compton (IC) scattering between the stellar soft photons and the relativistic pulsar wind will generate orbital-modulating GeV photons. We look for these IC emissions from redback systems. A multi-wavelength observation of an unassociated gamma-ray source, 3FGL J2039.6-5618, by Salvetti et al. (2015) detected an orbital modulation with a period of 0.2 days in both X-ray and optical cases. They suggested 3FGL J2039.6-5618 to be a new redback candidate. We analyzed the gamma-ray emission of 3FGL J2039.6-5618 using the data from the Fermi large area telescope (Fermi-LAT) and obtained the spectrum in different orbital phases. We propose that the spectrum has orbital dependency and estimate the characteristic energy of the IC emission from the stellar-pulsar wind interaction.
On the Spectral Shape of Non-recycled γ-ray Pulsars
Hui, Chung-Yue ; Lee, Jongsu ;
Journal of Astronomy and Space Sciences, volume 33, issue 2, 2016, Pages 101~104
DOI : 10.5140/JASS.2016.33.2.101
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.
SEDs and Beaming Effect for Fermi Blazars
Fan, Jun-Hui ; Yang, Jiang-He ; Liu, Yi ; Yuan, Yu-Hai ; Lin, Cao ; Xiao, Hu-Bing ;
Journal of Astronomy and Space Sciences, volume 33, issue 2, 2016, Pages 105~108
DOI : 10.5140/JASS.2016.33.2.105
In this work, based on our previous calculations of spectral energy distributions for a sample of Fermi blazars (Fan et al. 2015a), we calculated the radio loudness and performed correlation analyses. Our analysis results show that radio loudness is closely anti-correlated with synchrotron peak frequency and positively correlated with gamma-ray luminosity, suggesting that the gamma-ray emissions are strongly beamed.
The Spectral Sharpness Angle of Gamma-ray Bursts
Yu, Hoi-Fung ; van Eerten, Hendrik J. ; Greiner, Jochen ; Sari, Re'em ; Bhat, P. Narayana ; Kienlin, Andreas von ; Paciesas, William S. ; Preece, Robert D. ;
Journal of Astronomy and Space Sciences, volume 33, issue 2, 2016, Pages 109~117
DOI : 10.5140/JASS.2016.33.2.109
We explain the results of Yu et al. (2015b) of the novel sharpness angle measurement to a large number of spectra obtained from the Fermi gamma-ray burst monitor. The sharpness angle is compared to the values obtained from various representative emission models: blackbody, single-electron synchrotron, synchrotron emission from a Maxwellian or power-law electron distribution. It is found that more than 91% of the high temporally and spectrally resolved spectra are inconsistent with any kind of optically thin synchrotron emission model alone. It is also found that the limiting case, a single temperature Maxwellian synchrotron function, can only contribute up to 58
% of the peak flux. These results show that even the sharpest but non-realistic case, the single-electron synchrotron function, cannot explain a large fraction of the observed spectra. Since any combination of physically possible synchrotron spectra added together will always further broaden the spectrum, emission mechanisms other than optically thin synchrotron radiation are likely required in a full explanation of the spectral peaks or breaks of the GRB prompt emission phase.
Dust Disks Around Young Stellar Objects
Suh, Kyung-Won ;
Journal of Astronomy and Space Sciences, volume 33, issue 2, 2016, Pages 119~126
DOI : 10.5140/JASS.2016.33.2.119
To reproduce the spectral energy distributions (SEDs) of young stellar objects (YSOs), we perform radiative transfer model calculations for the circumstellar dust disks with various shapes and many dust species. For eight sample objects of T Tauri and Herbig Ae/Be stars, we compare the theoretical model SEDs with the observed SEDs described by the infrared space observatory and Spitzer space telescope spectral data. We use the model, CGPLUS, for a passive irradiated circumstellar dust disk with an inner hole and an inner rim for the eight sample YSOs. We present model parameters for the dust disk, which reproduce the observed SEDs. We find that the model requires a higher mass, luminosity, and temperature for the central star for the Herbig Ae/Be stars than those for the T Tauri stars. Generally, the outer radius, total mass, thickness, and rim height of the theoretical dust disk for the Herbig Ae/Be stars are larger than those for the T Tauri stars.
Determining the Rotation Periods of an Inactive LEO Satellite and the First Korean Space Debris on GEO, KOREASAT 1
Choi, Jin ; Jo, Jung Hyun ; Kim, Myung-Jin ; Roh, Dong-Goo ; Park, Sun-Youp ; Lee, Hee-Jae ; Park, Maru ; Choi, Young-Jun ; Yim, Hong-Suh ; Bae, Young-Ho ; Park, Young-Sik ; Cho, Sungki ; Moon, Hong-Kyu ; Choi, Eun-Jung ; Jang, Hyun-Jung ; Park, Jang-Hyun ;
Journal of Astronomy and Space Sciences, volume 33, issue 2, 2016, Pages 127~135
DOI : 10.5140/JASS.2016.33.2.127
Inactive space objects are usually rotating and tumbling as a result of internal or external forces. KOREASAT 1 has been inactive since 2005, and its drift trajectory has been monitored with the optical wide-field patrol network (OWL-Net). However, a quantitative analysis of KOREASAT 1 in regard to the attitude evolution has never been performed. Here, two optical tracking systems were used to acquire raw measurements to analyze the rotation period of two inactive satellites. During the optical campaign in 2013, KOREASAT 1 was observed by a 0.6 m class optical telescope operated by the Korea Astronomy and Space Science Institute (KASI). The rotation period of KOREASAT 1 was analyzed with the light curves from the photometry results. The rotation periods of the low Earth orbit (LEO) satellite ASTRO-H after break-up were detected by OWL-Net on April 7, 2016. We analyzed the magnitude variation of each satellite by differential photometry and made comparisons with the star catalog. The illumination effect caused by the phase angle between the Sun and the target satellite was corrected with the system tool kit (STK) and two line element (TLE) technique. Finally, we determined the rotation period of two inactive satellites on LEO and geostationary Earth orbit (GEO) with light curves from the photometry. The main rotation periods were determined to be 5.2 sec for ASTRO-H and 74 sec for KOREASAT 1.
Correlation Between the “seeing FWHM” of Satellite Optical Observations and Meteorological Data at the OWL-Net Station, Mongolia
Bae, Young-Ho ; Jo, Jung Hyun ; Yim, Hong-Suh ; Park, Young-Sik ; Park, Sun-Youp ; Moon, Hong Kyu ; Choi, Young-Jun ; Jang, Hyun-Jung ; Roh, Dong-Goo ; Choi, Jin ; Park, Maru ; Cho, Sungki ; Kim, Myung-Jin ; Choi, Eun-Jung ; Park, Jang-Hyun ;
Journal of Astronomy and Space Sciences, volume 33, issue 2, 2016, Pages 137~146
DOI : 10.5140/JASS.2016.33.2.137
The correlation between meteorological data collected at the optical wide-field patrol network (OWL-Net) Station No. 1 and the seeing of satellite optical observation data was analyzed. Meteorological data and satellite optical observation data from June 2014 to November 2015 were analyzed. The analyzed meteorological data were the outdoor air temperature, relative humidity, wind speed, and cloud index data, and the analyzed satellite optical observation data were the seeing full-width at half-maximum (FWHM) data. The annual meteorological pattern for Mongolia was analyzed by collecting meteorological data over four seasons, with data collection beginning after the installation and initial set-up of the OWL-Net Station No. 1 in Mongolia. A comparison of the meteorological data and the seeing of the satellite optical observation data showed that the seeing degrades as the wind strength increases and as the cloud cover decreases. This finding is explained by the bias effect, which is caused by the fact that the number of images taken on the less cloudy days was relatively small. The seeing FWHM showed no clear correlation with either temperature or relative humidity.