http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
DISCOVERY OF X-RAY PULSATIONS FROM THE NEXT GEMINGA, PSR J1836+5925
Lin, L. C. C.,Hui, C. Y.,Li, K. T.,Takata, J.,Hu, C. P.,Kong, A. K. H.,Yen, D. C. C.,Chou, Y. IOP Publishing 2014 ASTROPHYSICAL JOURNAL LETTERS - Vol.793 No.1
<P>We report recent XMM-Newton investigations of PSR J1836+5925, the 'next Geminga,' which determined an X-ray pulsation of similar to 173.3 ms. Its X-ray periodicity is consistent with the gamma-ray ephemeris at the same epoch. The X-ray folded light curve has a sinusoidal structure that is different from the double-peaked gamma-ray pulse profile. We have also analyzed the X-ray phase-averaged spectra which shows that the X-ray emission from PSR J1836+5925 is thermal dominant. This suggests that the X-ray pulsation mainly originates from the modulated hot spot on the stellar surface.</P>
DISCOVERY OF X-RAY PULSATION FROM THE GEMINGA-LIKE PULSAR PSR J2021+4026
Lin, L. C. C.,Hui, C. Y.,Hu, C. P.,Wu, J. H. K.,Huang, R. H. H.,Trepl, L.,Takata, J.,Seo, K. A.,Wang, Y.,Chou, Y.,Cheng, K. S. IOP Publishing 2013 ASTROPHYSICAL JOURNAL LETTERS - Vol.770 No.1
<P>We report the discovery of an X-ray periodicity of similar to 265.3 ms from a deep XMM-Newton observation of the radio-quiet gamma-ray pulsar, PSR J2021+4026, located at the edge of the supernova remnant G78.2+2.1 (gamma-Cygni). The detected frequency is consistent with the gamma-ray pulsation determined by the observation of the Fermi Gamma-ray Space Telescope at the same epoch. The X-ray pulse profile resembles the modulation of a hot spot on the surface of the neutron star. The phase-averaged spectral analysis also suggests that the majority of the observed X-rays have thermal origins. This is the third member in the class of radio-quiet pulsars with significant pulsations detected from both X-ray and gamma-ray regimes.</P>
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>
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>
EXPLORING THE X-RAY AND gamma-RAY PROPERTIES OF THE REDBACK MILLISECOND PULSAR PSR J1723-2837
Hui, C. Y.,Tam, P. H. T.,Takata, J.,Kong, A. K. H.,Cheng, K. S.,Wu, J. H. K.,Lin, L. C. C.,Wu, E. M. H. University of Chicago Press for the American Astro 2014 ASTROPHYSICAL JOURNAL LETTERS - Vol.781 No.1
We have investigated the X-ray and gamma-ray properties of the redback millisecond pulsar PSR J1723-2837 with XMM-Newton, Chandra, and Fermi. We have discovered the X-ray orbital modulation of this binary system with a minimum that coincides with the phases of radio eclipse. The X-ray emission is clearly non-thermal in nature, which can be described well by a simple power law with a photon index of similar to 1.2. The phase-averaged luminosity is similar to 9 x 10(31) erg s(-1) in 0.3-10 keV, which consumes similar to 0.2% of the spin-down power. We have detected the gamma-ray emission in 0.1-300 GeV from this system at a significance of similar to 6 sigma for the first time. The gamma-rays in this energy range consume similar to 2% of the spin-down power and can be modeled by a power law with a photon index of similar to 2.6. We discuss the high energy properties of the new redback in the context of an intrabinary shock model.
SEARCHES FOR MILLISECOND PULSAR CANDIDATES AMONG THE UNIDENTIFIED<i>FERMI</i>OBJECTS
Hui, C. Y.,Park, S. M.,Hu, C. P.,Lin, L. C. C.,Li, K. L.,Kong, A. K. H.,Tam, P. H. T.,Takata, J.,Cheng, K. S.,Jin, Ruolan,Yen, T.-C.,Kim, Chunglee IOP Publishing 2015 The Astrophysical journal Vol.809 No.1
<P>Here we report the results of searching millisecond pulsar (MSP) candidates from the Fermi LAT second source catalog (2FGL). Seven unassociated gamma-ray sources in this catalog are identified as promising MSP candidates based on their gamma-ray properties. Through the X-ray analysis, we have detected possible X-ray counterparts, localized to an arcsecond accuracy. We have systematically estimated their X-ray fluxes and compared them with the corresponding gamma-ray fluxes. The X-ray to gamma-ray flux ratios for 2FGL J1653.6-0159 and 2FGL J1946.4-5402 are comparable with the typical value for pulsars. For 2FGL J1625.2-0020, 2FGL J1653.6-0159, and 2FGL J1946.4-5402, their candidate X-ray counterparts are bright enough to perform a detailed spectral and temporal analysis to discriminate their thermal/non-thermal nature and search for the periodic signal. We have also searched for possible optical/IR counterparts at the X-ray positions. For the optical/IR source coincident with the brightest X-ray object associated with 2FGL J1120.0-2204, its spectral energy distribution is comparable with a late-type star. Evidence for the variability has also been found by examining its optical light curve. All the aforementioned 2FGL sources resemble a pulsar in one or more aspects, making them promising targets for follow-up investigations.</P>
DISCOVERY OF AN ULTRACOMPACT GAMMA-RAY MILLISECOND PULSAR BINARY CANDIDATE
Kong, Albert K. H.,Jin, Ruolan,Yen, T.-C.,Hu, C.-P.,Hui, C. Y.,Tam, P. H. T.,Takata, J.,Lin, L. C. C.,Cheng, K. S.,Park, S. M.,Kim, C. L. IOP Publishing 2014 ASTROPHYSICAL JOURNAL LETTERS - Vol.794 No.2
<P>We report multi-wavelength observations of the unidentified Fermi object 2FGL J1653.6-0159. With the help of high-resolution X-ray observations, we have identified an X-ray and optical counterpart to 2FGL J1653.6-0159. The source exhibits a periodic modulation of 75 minutes in the optical and possibly also in the X-ray. We suggest that 2FGL J1653.6-0159 is a compact binary system with an orbital period of 75 minutes. Combining the gamma-ray and X-ray properties, 2FGL J1653.6-0159 is potentially a black-widow-/redback-type gamma-ray millisecond pulsar (MSP). The optical and X-ray light curve profiles show that the companion is mildly heated by the high-energy emission and that the X-rays are from intrabinary shock. Although no radio pulsation has yet been detected, we estimated that the spin period of the MSP is similar to 2 ms based on a theoretical model. If pulsation can be confirmed in the future, 2FGL J1653.6-0159 will become the first ultracompact rotation-powered MSP.</P>
SPECTROSCOPICALLY SELECTED<i>SPITZER</i>24<i>μm</i>ACTIVE GALACTIC NUCLEI
Choi, P. I.,Yan, Lin,Helou, G.,Storrie-Lombardi, L. J.,Fadda, D.,Im, M.,Shim, H. IOP Publishing 2011 The Astrophysical journal Vol.732 No.1
<P>We investigate the active galactic nucleus (AGN) sub-population of a 24 mu m flux-limited galaxy sample in the Spitzer Extragalactic First Look Survey. Using deep Keck optical spectroscopy and a series of emission-line diagnostics, we identify AGN-dominated systems over broad redshift 0 < z < 3.5 and luminosity 9 < log(L-TIR) < 14 ranges, with sample means of < z > = 0.85 and < log(LTIR)> = 11.5. We find that down to the flux limits of our Spitzer MIPS sample (f(24) > 200 mu Jy), 15%-20% of sources exhibit strong AGN signatures in their optical spectra. At this flux limit, the AGN population accounts for as much as 25%-30% of the integrated 24 mu m flux. This corresponds to an MIR AGN contribution approximate to 2-3x greater than that found in ISOCAM 15 mu m studies that used X-ray AGN identifications. Based on our spectroscopically selected AGN sample, we also investigate the merits of Infrared Array Camera (IRAC) color selection for AGN identification. Our comparison reveals that although there is considerable overlap, a significant fraction of spectroscopic AGNs are not identifiable based on their MIR colors alone. Both the measured completeness and reliability of the IRAC color selections are found to be strongly dependent on the MIR flux limit. Finally, our spectroscopic AGN sample implies as much as a 3x higher AGN surface density at high redshift (z > 1.2) than that of recent optical surveys at comparable optical flux limits, suggestive of a population of heavily obscured, optical/UV reddened AGNs.</P>