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On the Spectral Shape of Non-recycled γ-ray Pulsars
허종우,이종수 한국우주과학회 2016 Journal of Astronomy and Space Sciences Vol.33 No.2
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.
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허종우 한국우주과학회 2013 Journal of Astronomy and Space Sciences Vol.30 No.3
Here we review the effort of Fermi Asian Network (FAN) in exploring the supernova remnants (SNRs) with state-of-art high energy observatories, including Fermi Gamma-ray Space Telescope and Chandra X-ray Observatory, in the period of 2011-2012. Utilizing the data from Fermi LAT, we have discovered the GeV emission at the position of the Galactic SNR Kes 17 which provides evidence for the hadronic acceleration. Our study also sheds light on the propagation of cosmic rays from their acceleration site to the intersteller medium. We have also launched an identification campaign of SNR candidates in the Milky Way, in which a new SNR G308.3-1.4 have been uncovered with our Chandra observation. Apart from the remnant, we have also discovered an associated compact object at its center. The multiwavelength properties of this X-ray source suggest it can possibly be the compact binary that survived a supernova explosion.
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Spider Invasion Across the Galaxy
허종우 한국우주과학회 2014 Journal of Astronomy and Space Sciences Vol.31 No.2
The nature of the exotic stellar corpses which reincarnate by consuming their companion is reviewed. Apart from sucking lifefrom their partners, they are actually eating the doomed companions away by their deadly and powerful particle/radiationbeams. Such situation resembles that a female “black widow” spider that eats its mate after mating. These celestial zombiesare called - Millisecond pulsars (MSPs). In this review article, I will focus on the effort of Fermi Asian Network (FAN) inexploring these intricating objects over the last five years. Two special classes of MSPs are particularly striking. Since FermiGamma-ray Space Telescope has started surveying the gamma−ray sky, the population of “black widows” has been boosted. Another dramatic class is so-called “redbacks” (Australian cousin of “black widows”) which has just emerged in the last fewyears. These MSPs provide us with a long-sought missing link in understanding the transition between accretion-poweredand rotation-powered systems. The strategy of hunting MSPs through mulitwavelength observations of the unidentified Fermiobjects is also reviewed.
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Exploring the Diffuse X-ray Emission of Supernova Remnant Kesteven 69 with XMM-Newton
서경애,허종우 한국우주과학회 2013 Journal of Astronomy and Space Sciences Vol.30 No.2
We have investigated the X-ray emission from the shock-heated plasma of the Galactic supernova remnant Kesteven 69 with XMM-Newton. Assuming the plasma is at collisional ionization equilibrium, a plasma temperature and a column absorption are found to be kT ~ 0.62 keV and NH ~ 2.85 ×1022 cm-2 respectively by imaging spectroscopy. Together with the deduced emission measure, we place constraints on its Sedov parameters.
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Gamma-ray Emission from Globular Clusters
Pak-Hin T. Tam,허종우,Albert K. H. Kong 한국우주과학회 2016 Journal of Astronomy and Space Sciences Vol.33 No.1
Over the last few years, the data obtained using the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope has provided new insights on high-energy processes in globular clusters, particularly those involving compact objects such as MilliSecond Pulsars (MSPs). Gamma-ray emission in the 100 MeV to 10 GeV range has been detected from more than a dozen globular clusters in our galaxy, including 47 Tucanae and Terzan 5. Based on a sample of known gammaray globular clusters, the empirical relations between gamma-ray luminosity and properties of globular clusters such as their stellar encounter rate, metallicity, and possible optical and infrared photon energy densities, have been derived. The measured gamma-ray spectra are generally described by a power law with a cut-off at a few gigaelectronvolts. Together with the detection of pulsed γ-rays from two MSPs in two different globular clusters, such spectral signature lends support to the hypothesis that γ-rays from globular clusters represent collective curvature emission from magnetospheres of MSPs in the clusters. Alternative models, involving Inverse-Compton (IC) emission of relativistic electrons that are accelerated close to MSPs or pulsar wind nebula shocks, have also been suggested. Observations at >100 GeV by using Fermi/LAT and atmospheric Cherenkov telescopes such as H.E.S.S.-II, MAGIC-II, VERITAS, and CTA will help to settle some questions unanswered by current data.
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Pulsed γ-ray emission from magnetar 1E 2259+586
Jason Hung Kit Wu,허종우,Regina Hsiu Hui Huang,Albert Kwok Hing Kong,Kwong Sang Cheng,Jumpei Takata,Pak Hin Thomas Tam,Eric Man Ho Wu,Joe Liu 한국우주과학회 2013 Journal of Astronomy and Space Sciences Vol.30 No.2
Anomalous X-ray pulsars (AXPs) are thought to be magnetars which are young isolated neutron stars with extremely strong magnetic fields of >1014 Gauss. Their tremendous magnetic fields inferred from the spin parameters provide a huge energy reservoir to power the observed X-ray emission. High-energy emission above 0.3 MeV has never been detected despite intensive search. Here, we present the possible Fermi Large Area Telescope (LAT) detection of γ-ray pulsations above 200MeV from the AXP, 1E 2259+586, which puts the current theoretical models of γ-ray emission mechanisms of magnetars into challenge. We speculate that the high-energy γ-rays originate from the outer magnetosphere of the magnetar.
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