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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>
High-energy Emissions from the Pulsar/Be Binary System PSR J2032+4127/MT91 213
Takata, J.,Tam, P. H. T.,Ng, C. W.,Li, K. L.,Kong, A. K. H.,Hui, C. Y.,Cheng, K. S. American Astronomical Society 2017 The Astrophysical journal Vol.836 No.2
<P>PSR. J2032+4127 is a radio-loud gamma-ray-emitting pulsar; it is orbiting around a high-mass Be type star with a very long orbital period of 25-50 years, and is approaching periastron, which will occur in late 2017/early 2018. This system comprises a young pulsar and a Be type star, which is similar to the so-called gamma-ray binary PSR. B1259-63/LS2883. It is expected therefore that PSR. J2032+4127 shows an enhancement of high-energy emission caused by the interaction between the pulsar wind and Be wind/disk around periastron. Ho et al. recently reported a rapid increase in the X-ray flux from this system. In this paper, we also confirm a rapid increase in the X-ray flux along the orbit, while the GeV flux shows no significant change. We discuss the high-energy emissions from the shock caused by the pulsar wind and stellar wind interaction and examine the properties of the pulsar wind in this binary system. We argue that the rate of increase of the X-ray flux observed by Swift indicates (1) a variation of the momentum ratio of the two-wind interaction region along the orbit, or (2) an evolution of the magnetization parameter of the pulsar wind with the radial distance from the pulsar. We also discuss the pulsar wind/Be disk interaction at the periastron passage, and propose the possibility of formation of an accretion disk around the pulsar. We model high-energy emissions through the inverse-Compton scattering process of the cold-relativistic pulsar wind off soft photons from the accretion disk.</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>
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 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>
A<i>NuSTAR</i>Observation of the Gamma-Ray Emitting Millisecond Pulsar PSR J1723-2837
Kong, A. K. H.,Hui, C. Y.,Takata, J.,Li, K. L.,Tam, P. H. T. American Astronomical Society 2017 The Astrophysical journal Vol.839 No.2
<P>We report on the first NuSTAR observation of the gamma-ray emitting millisecond pulsar binary PSR J1723-2837. X-ray radiation up to 79 keV is clearly detected, and the simultaneous NuSTAR and Swift spectrum is well described by an absorbed power law with a photon index of similar to 1.3. We also find X-ray modulations in the 3-10, 10-20, 20-79, and 3-79 keV bands at the 14.8. hr binary orbital period. All of these are entirely consistent with previous X-ray observations below 10 keV. This new hard X-ray observation of PSR J1723-2837 provides strong evidence that the X-rays are from the intrabinary shock via an interaction between the pulsar wind and the outflow from the companion star. We discuss how the NuSTAR observation constrains the physical parameters of the intrabinary shock model.</P>
<i>Swift</i>,<i>XMM</i>-<i>Newton</i>, and<i>NuSTAR</i>Observations of PSR J2032+4127/MT91 213
Li, K. L.,Kong, A. K. H.,Tam, P. H. T.,Hou, X.,Takata, J.,Hui, and C. Y. American Astronomical Society 2017 The Astrophysical journal Vol.843 No.2
<P>We report our recent Swift, NuSTAR, and XMM-Newton X-ray and Lijiang optical observations on PSR J2032 + 4127/MT91 213, the gamma-ray binary candidate with a period of 45-50 years. The coming periastron of the system was predicted to be in 2017 November, around which high-energy flares from keV to TeV are expected. Recent studies with Chandra and Swift X-ray observations taken in 2015/2016 showed that its X-ray emission has been brighter by a factors of similar to 10 than that before 2013, probably revealing some ongoing activities between the pulsar wind and the stellar wind. Our new Swift/XRT lightcurve shows no strong evidence of a single vigorous brightening trend, but rather several strong X-ray flares on weekly to monthly timescales with a slowly brightening baseline, namely the low state. The NuSTAR and XMM-Newton observations taken during the flaring and the low states, respectively, show a denser environment and a softer power-law index during the flaring state, implying that the pulsar wind interacted with the stronger stellar winds of the companion to produce the flares. These precursors would be crucial in studying the predicted giant outburst from this extreme gamma-ray binary during the periastron passage in late 2017.</P>