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Mode Change of a Gamma-Ray Pulsar, PSR J2021+4026
Zhao, J.,Ng, C. W.,Lin, L. C. C.,Takata, J.,Cai, Y.,Hu, C.-P.,Yen, D. C. C.,Tam, P. H. T.,Hui, C. Y.,Kong, A. K. H.,Cheng, K. S. American Astronomical Society 2017 The Astrophysical journal Vol.842 No.1
<P>A glitch of a pulsar is known as a sudden increase in the spin frequency and spin-down rate (frequency time derivative), and it can be caused by a sudden release of the stress built up in the solid crust of the star or pinned vortices in the superfluid interior. PSR J2021+4026 is the first pulsar that shows a significant change in the gamma-ray flux and pulse profile at the glitch that occurred around 2011 October 16. We report the results of timing and spectral analysis of PSR J2021+4026 using similar to 8 yr Fermi. Large Area Telescope data. We find that the pulsar stayed at a high spin-down rate (similar to 4% higher than the pre-glitch value) and a low gamma-ray state (similar to 18% lower) for about 3 yr. after the glitch. Around 2014 December, the spin-down rate and gamma-ray flux gradually returned to pre-glitch values within a timescale of a. few months. The phase-resolved spectra and pulse profiles after the relaxation are also consistent with those before the glitch. The observed long-term evolution of the spin-down rate and the gamma-ray flux indicates that the glitch triggered a mode change in the global magnetosphere. We speculate that the glitch changed. the local magnetic field structure around the polar cap and/or the inclination angle of the. dipole axis, leading to. a change in the electric current circulating in the. magnetosphere.</P>
THE MEGAMASER COSMOLOGY PROJECT. IX. BLACK HOLE MASSES FOR THREE MASER GALAXIES
Gao, F.,Braatz, J. A.,Reid, M. J.,Condon, J. J.,Greene, J. E.,Henkel, C.,Impellizzeri, C. M. V.,Lo, K. Y.,Kuo, C. Y.,Pesce, D. W.,Wagner, J.,Zhao, W. American Astronomical Society 2017 The Astrophysical journal Vol.834 No.1
<P>As part of the Megamaser Cosmology Project, we present VLBI maps of nuclear water masers toward five galaxies. The masers originate in sub-parsec circumnuclear disks. For three of the galaxies, we fit Keplerian rotation curves to estimate their supermassive black hole (SMBH) masses, and determine (2.9 +/- 0.3) x 10(6)M(Theta) for J0437+2456, (1.7 +/- 0.1) x 10(7)M(Theta) for ESO 558-G009, and (1.1 +/- 0.2) x 10(7)M(Theta) for NGC 5495. In the other two galaxies, Mrk 1029 and NGC 1320, the geometry and dynamics are more complicated and preclude robust black hole mass estimates. Including our new results, we compiled a list of 15 VLBI-confirmed disk maser galaxies with robust SMBH mass measurements. With this sample, we confirm the empirical relation of R-out proportional to 0.3M(SMBH) reported in Wardle & Yusef-Zadeh. We also find a tentative correlation between maser disk outer radii and Wide-Field Infrared Survey Explorer luminosity. We find no correlations of maser disk size with X-ray 2-10 keV luminosity or [O III] luminosity.</P>
Zhao, K.J.,Nagashima, Y.,Li, F.M.,Shi, Yuejiang,Diamond, P.H.,Dong, J.Q.,Itoh, K.,Itoh, S.-I.,Zhuang, G.,Liu, H.,Chen, Z.P.,Cheng, J.,Nie, L.,Ding, Y.H.,Hu, Q.M.,Chen, Z.Y.,Rao, B.,Cheng, Z.F.,Gao, L. IOP 2017 Nuclear fusion Vol.57 No.12
<P>The temporal-spatial structures of plasma flows and turbulence around tearing mode islands are presented. The experiments were performed using Langmuir probe arrays in the edge plasmas of J-TEXT tokamak. The correlation analyses clearly show that the flows have similar structures of <I>m</I>/<I>n</I> = 3/1 as the magnetic island does (<I>m</I> and <I>n</I> are the poloidal and toroidal mode numbers, respectively). The sign of the potential fluctuations for the flows inverses and the powers significantly reduce at <I>q</I> = 3 surface. Approaching to the last closed flux surface for the magnetic islands, the radially elongated flow structure forms. The flows are concentrated near separatrix and show quadrupole structures. The turbulence is concentrated near X-point and partly trapped inside the magnetic islands.</P>
X-Ray Study of Variable Gamma-Ray Pulsar PSR J2021+4026
Wang, H. H.,Takata, J.,Hu, C.-P.,Lin, L. C. C.,Zhao, J. American Astronomical Society 2018 The Astrophysical journal Vol.856 No.2
<P>PSR J2021+4026 showed a sudden decrease in the gamma-ray emission at the glitch that occurred around 2011 October 16, and a relaxation of the flux to the pre-glitch state at around 2014 December. We report X-ray analysis results of the data observed by XMM-Newton on 2015 December 20 in the post-relaxation state. To examine any change in the X-ray emission, we compare the properties of the pulse profiles and spectra at the low gamma-ray flux state and at the post-relaxation state. The phase-averaged spectra for both states can be well described by a power-law component plus a blackbody component. The former is dominated by unpulsed emission and probably originated from the pulsar wind nebula as reported by Hui et al. The emission property of the blackbody component is consistent with the emission from the polar cap heated by the back-flow bombardment of the high-energy electrons or positrons that were accelerated in the magnetosphere. We found no significant change in the X-ray emission properties between two states. We suggest that the change of the X-ray luminosity is at an order of similar to 4%, which is difficult to measure with the current observations. We model the observed X-ray light curve with the heated polar cap emission, and we speculate that the observed large pulsed fraction is owing to asymmetric magnetospheric structure.</P>
Ranot, M.,Seong, W.K.,Jung, S.G.,Lee, N.H.,Kang, W.N.,Joo, J.H.,Zhao, Y.,Dou, S.X. North-Holland 2009 Physica. C, Superconductivity Vol.469 No.15
We report on Ag and Cu doping in MgB<SUB>2</SUB> thick films using amorphous Ag- and Cu-impurity layers with various thicknesses, 4, 8, 16, and 32nm. Firstly, Ag- and Cu-impurity layers were deposited on Al<SUB>2</SUB>O<SUB>3</SUB>(0001) substrates at room temperature by using pulsed laser deposition system. Subsequently MgB<SUB>2</SUB> films were grown on the top of Ag or Cu/Al<SUB>2</SUB>O<SUB>3</SUB> substrates at 560 and 600<SUP>o</SUP>C by using hybrid physical-chemical vapor deposition. The effect of Ag and Cu doping as well as growth temperature on the microstructure and critical current density (J<SUB>c</SUB>) of MgB<SUB>2</SUB> films were investigated. It was found that both of Ag/Cu doping and low growth temperature can significantly enhance J<SUB>c</SUB> without suppression of T<SUB>c</SUB>. The increase in J<SUB>c</SUB> results from improved grain connectivity and strong flux pinning by high density of grain boundaries and other types of defects introduced by Ag- or Cu-impurity layers.
Dependence of the properties of hydrothermally grown ZnO on precursor concentration
Zhao, X.,Lee, J.Y.,Kim, C.-R.,Heo, J.,Shin, C.M.,Leem, J.-Y.,Ryu, H.,Chang, J.-H.,Lee, H.C.,Jung, W.-G.,Son, C.-S.,Shin, B.C.,Lee, W.-J.,Tan, S.T.,Zhao, J.,Sun, X. North-Holland 2009 Physica E, Low-dimensional systems & nanostructure Vol.41 No.8
This study evaluated the effects of precursor concentration ranging from 0.06 to 1.5M on the properties of hydrothermally grown ZnO on annealed ZnO buffered Si substrates. At relatively low concentrations (no more than 0.5M), well-aligned ZnO arrays were grown on ZnO/Si(100) due to heterogeneous nucleation. As the concentration was increased to 1.0M, the morphologies changed to randomly accumulated particles as a result of homogeneous nucleation. The crystal and optical properties of the materials were investigated by X-ray diffractometer (XRD) and photoluminescence (PL) measurement, respectively. It was found that the best crystal and optical properties were obtained with concentrations of 0.5 and 0.3M, respectively. These properties were observed to degrade when the concentration was raised to more than 1.0M.
Effects of Buffer Layer Annealing on ZnO Thin Films Grown by using Atomic Layer Deposition
J. Y. Leem,C. R. Kim,J. H. Heo,C. M. Shin,J. H. Park,T. M. Lee,류혁현,J. H. Chang,C. S. Son,B. C. Shin,W. J. Lee,S. T. Tan,J. L. Zhao,X. W. Sun 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.6
In this study, the effects of buffer layer annealing duration on ZnO thin films deposited by using the remote plasma atomic layer deposition (ALD) method are discussed. ZnO thin films were grown on ZnO-buffer/Si (100) and were annealed for various durations between 0.5 and 60 min. The structural and the optical properties of the ZnO thin films were investigated by using atomic force microscopy, X-ray diffraction, and photoluminescence measurements. The ZnO thin films grown on a rough ZnO buffer layer were found to have high optical quality. The results from this study possibly contribute to advances in ZnO-base LED technologies.