Results for "W. C. G. Ho"

total 226979took 0.14s
Matter and Radiation in Superstrong Magnetic Fields and Thermal Emission from Neutron StarsFeb 07 2003Thermal surface emissions have now been detected from more than a dozen isolated neutron stars, including radio pulsars, radio-quiet neutron stars and magnetars. These detections can potentially provide important information on the interior physics, magnetic ... More
Transfer of Polarized Radiation in Strongly Magnetized Plasmas and Thermal Emission from Magnetars: Effect of Vacuum PolarizationNov 13 2002Feb 07 2003We present a theoretical study of radiative transfer in strongly magnetized electron-ion plasmas, focusing on the effect of vacuum polarization due to quantum electrodynamics. This study is directly relevant to thermal radiation from the surfaces of highly ... More
Opacities and spectra of hydrogen atmospheres of moderately magnetized neutron starsSep 26 2014There is observational evidence that central compact objects (CCOs) in supernova remnants have moderately strong magnetic fields $B\sim10^{11}$ G. Meanwhile, available models of partially ionized hydrogen atmospheres of neutron stars with strong magnetic ... More
Seismology of adolescent neutron stars: Accounting for thermal effects and crust elasticityFeb 23 2014Aug 20 2014We study the oscillations of relativistic stars, incorporating key physics associated with internal composition, thermal gradients and crust elasticity. Our aim is to develop a formalism which is able to account for the state-of-the-art understanding ... More
Atmospheres and radiating surfaces of neutron stars with strong magnetic fieldsMay 04 2016We review the current status of the theory of thermal emission from the surface layers of neutron stars with strong magnetic fields $B\sim 10^{10}-10^{15}$ G, including formation of the spectrum in a partially ionized atmosphere and at a condensed surface. ... More
Implications of an r-mode in XTE J1751-305: Mass, radius and spin evolutionMar 04 2014Mar 07 2014Recently Strohmayer and Mahmoodifar presented evidence for a coherent oscillation in the X-ray light curve of the accreting millisecond pulsar XTE J1751-305, using data taken by RXTE during the 2002 outburst of this source. They noted that a possible ... More
Buoyancy and g-modes in young superfluid neutron starsApr 28 2015We consider the local dynamics of a realistic neutron star core, including composition gradients, superfluidity and thermal effects. The main focus is on the gravity g-modes, which are supported by composition stratification and thermal gradients. We ... More
XMM-Newton observation of the highly magnetised accreting pulsar Swift J045106.8-694803: Evidence of a hot thermal excessSep 10 2013Several persistent, low luminosity (L_X 10^{34} erg s^{-1}), long spin period (P>100 s) High Mass X-ray Binaries have been reported with blackbody components with temperatures >1 keV. These hot thermal excesses have correspondingly small emitting regions ... More
More than meets the eye: magnetars in disguiseAug 06 2012Oct 31 2012It has recently been proposed that radio emission from magnetars can be evaluated using a "fundamental plane" in parameter space between pulsar voltage gap and ratio of X-ray luminosity Lx to rotational energy loss rate Edot. In particular, radio emission ... More
Central compact objects and their magnetic fieldsOct 26 2012Central compact objects (CCOs) are neutron stars that are found near the center of supernova remnants, and their association with supernova remnants indicates these neutron stars are young (<~ 10^4 yr). Here we review the observational properties of CCOs ... More
Constraining the Geometry of the Neutron Star RX J1856.5-3754May 31 2007RX J1856.5-3754 is one of the brightest, nearby isolated neutron stars, and considerable observational resources have been devoted to its study. In previous work, we found that our latest models of a magnetic, hydrogen atmosphere matches well the entire ... More
NSMAXG: A new magnetic neutron star spectral model in XSPECNov 21 2013The excellent sensitivity of X-ray telescopes, such as Chandra and XMM-Newton, is ideal for the study of cooling neutron stars, which can emit at these energies. In order to exploit the wealth of information contained in the high quality data, a thorough ... More
Gravitational waves within the magnetar model of superluminous supernovae and gamma-ray burstsJun 01 2016Sep 13 2016The light curve of many supernovae (SNe) and gamma-ray bursts (GRBs) can be explained by a sustained injection of extra energy from its possible central engine, a rapidly rotating strongly magnetic neutron star (i.e. magnetar). The magnetic dipole radiation ... More
Superfluid effects on gauging core temperatures of neutron stars in low-mass X-ray binariesAug 31 2011Oct 06 2011Neutron stars accreting matter from low-mass binary companions are observed to undergo bursts of X-rays due to the thermonuclear explosion of material on the neutron star surface. We use recent results on superfluid and superconducting properties to show ... More
Evolution of a buried magnetic field in the central compact object neutron starsFeb 23 2011The central compact objects are a newly-emerging class of young neutron stars near the centre of supernova remnants. From X-ray timing and spectral measurements, their magnetic fields are determined to be ~ 10^10-10^11 G, which is significantly lower ... More
Magnetic field growth in young glitching pulsars with a braking indexJun 12 2015Jul 08 2015In the standard scenario for spin evolution of isolated neutron stars, a young pulsar slows down with a surface magnetic field B that does not change. Thus the pulsar follows a constant B trajectory in the phase space of spin period and spin period time ... More
Optical-Flow based Self-Supervised Learning of Obstacle Appearance applied to MAV LandingSep 04 2015Aug 17 2017Monocular optical flow has been widely used to detect obstacles in Micro Air Vehicles (MAVs) during visual navigation. However, this approach requires significant movement, which reduces the efficiency of navigation and may even introduce risks in narrow ... More
Optical-Flow based Self-Supervised Learning of Obstacle Appearance applied to MAV LandingSep 04 2015Jun 16 2016Monocular motion cues have been widely used by Micro Air Vehicles (MAVs) to detect obstacles during visual navigation. However, this approach requires significant movement, which reduces the efficiency of navigation and may even introduce risks in narrow ... More
Hunting for Orphaned Central Compact Objects among Radio PulsarsJul 20 2015Central compact objects (CCOs) are a handful of young neutron stars found at the center of supernova remnants (SNRs). They show high thermal X-ray luminosities but no radio emission. Spin-down rate measurements of the three CCOs with X-ray pulsations ... More
Nonideal strongly magnetized plasmas of neutron stars and their electromagnetic radiationDec 05 2005We study the equation of state, polarization and radiation properties for nonideal, strongly magnetized plasmas which compose outer envelopes of magnetic neutron stars. Detailed calculations are performed for partially ionized hydrogen atmospheres and ... More
Partially ionized atmospheres of neutron stars with strong magnetic fieldsJan 21 2005We construct hydrogen atmosphere models for strongly magnetized neutron stars in thermodynamic equilibrium, taking into account partial ionization. The presence of bound states affects the equation of state, absorption coefficients, and polarizability ... More
Electromagnetic polarization in partially ionized plasmas with strong magnetic fields and neutron star atmosphere modelsMay 20 2004Polarizability tensor of a strongly magnetized plasma and the polarization vectors and opacities of normal electromagnetic waves are studied for the conditions typical of neutron star atmospheres, taking account of partial ionization effects. Vacuum polarization ... More
Pulsar glitches: The crust is not enoughJul 03 2012Pulsar glitches are traditionally viewed as a manifestation of vortex dynamics associated with a neutron superfluid reservoir confined to the inner crust of the star. In this Letter we show that the non-dissipative entrainment coupling between the neutron ... More
Constraining the Mass and Radius of Neutron Stars in Globular ClustersSep 15 2017We analyze observations of eight quiescent low-mass X-ray binaries in globular clusters and combine them to determine the neutron star mass-radius curve and the equation of state of dense matter. We determine the effect that several uncertainties may ... More
Discovery of Radio Outbursts in the Active Nucleus of M81May 06 1999The low-luminosity active galactic nucleus of M81 has been monitored at centimeter wavelengths since early 1993 as a by-product of radio programs to study the radio emission from Supernova 1993J. The extensive data sets reveal that the nucleus experienced ... More
Modelling the observable behaviour of SXP 5.05Apr 12 2019SXP 5.05 is a Be/X-ray binary with a neutron star companion located in the Small Magellanic Cloud. It was first detected in 2013, and later that year, SXP 5.05 underwent a massive optical and X-ray outburst. This outburst dwarfs any other optical event ... More
Spin period change and the magnetic fields of neutron stars in Be X-ray binaries in the Small Magellanic CloudNov 18 2013Nov 27 2013We report on the long-term average spin period, rate of change of spin period and X-ray luminosity during outbursts for 42 Be X-ray binary systems in the Small Magellanic Cloud. We also collect and calculate parameters of each system and use these data ... More
A Young Stellar Cluster in the Nucleus of NGC 4449Oct 26 2000Dec 02 2000We have obtained 1-2 A resolution optical Echellette spectra of the nuclear star cluster in the nearby starburst galaxy NGC 4449. The light is clearly dominated by a very young (6-10 Myr) population of stars. For our age dating, we have used recent population ... More
Deep X-ray Observations of the Young High-Magnetic-Field Radio Pulsar J1119-6127 and Supernova Remnant G292.2-0.5Nov 12 2012High-magnetic-field radio pulsars are important transition objects for understanding the connection between magnetars and conventional radio pulsars. We present a detailed study of the young radio pulsar J1119-6127, which has a characteristic age of 1900yr ... More
Neutron star atmosphere composition: the quiescent, low-mass X-ray binary in the globular cluster M28Mar 26 2012Using deep Chandra observations of the globular cluster M28, we study the quiescent X-ray emission of a neutron star in a low-mass X-ray binary in order to constrain the chemical composition of the neutron star atmosphere and the equation of state of ... More
Atmospheres and Spectra of Strongly Magnetized Neutron Stars II: Effect of Vacuum PolarizationJan 22 2002Dec 17 2002We study the effect of vacuum polarization on the atmosphere structure and radiation spectra of neutron stars with surface magnetic fields B=10^14-10^15 G, as appropriate for magnetars. Vacuum polarization modifies the dielectric property of the medium ... More
Spectral Features in the Thermal Emission from Isolated Neutron Stars: Dependence on Magnetic Field StrengthsFeb 04 2004We study several effects that influence the strength of the proton cyclotron and atomic features in the thermal spectra of magnetic neutron stars. We show that it is possible for vacuum polarization to strongly suppress the spectral lines when the magnetic ... More
Ejector and propeller spin-down: How might a superluminous supernova millisecond magnetar become the 6.67 hr pulsar in RCW103Aug 10 2016Sep 09 2016The X-ray source 1E 161348-5055 in the supernova remnant RCW 103 recently exhibited X-ray activity typical of magnetars, i.e. neutron stars with magnetic fields > 10^14-10^15 G. However, 1E 161348-5055 has an observed period of 6.67 hr, in contrast to ... More
Modelling mid-Z element atmospheres for strongly-magnetized neutron starsNov 04 2006Feb 23 2007We construct models for strongly-magnetized neutron star atmospheres composed of mid-Z elements (carbon, oxygen and neon) with magnetic fields B=10^{12}-10^{13} G and effective temperatures Teff=(1-5)*10^6 K; this is done by first addressing the physics ... More
A Neutron Star with a Carbon Atmosphere in the Cassiopeia A Supernova RemnantNov 04 2009The surface of hot neutron stars is covered by a thin atmosphere. If there is accretion after neutron star formation, the atmosphere could be composed of light elements (H or He); if no accretion takes place or if thermonuclear reactions occur after accretion, ... More
Atmospheres and Spectra of Strongly Magnetized Neutron StarsApr 11 2001Nov 22 2001We construct atmosphere models for strongly magnetized neutron stars with surface fields $B\sim 10^{12}-10^{15}$ G and effective temperatures $T_{\rm eff}\sim 10^6-10^7$ K. The atmospheres directly determine the characteristics of thermal emission from ... More
Resonant Tidal Excitations of Rotating Neutron Stars in Coalescing BinariesDec 07 1998Apr 08 1999In a coalescing neutron star-neutron star (NS-NS) or neutron star-black hole (NS-BH) binary, oscillation modes of the NS can be resonantly excited by the companion during the final minutes of the inspiral. The resonant energy transfer between the orbit ... More
Resonant Conversion of Photon Modes Due to Vacuum Polarization in a Magnetized Plasma: Implications for X-Ray Emission from MagnetarsAug 08 2001Oct 18 2001It is known that vacuum polarization can modify the photon propagation modes in the atmospheric plasma of a strongly magnetized neutron star. A resonance occurs when the effect of vacuum polarization on the photon modes balances that of the plasma. We ... More
R-Mode Oscillations and Spindown of Young Rotating Magnetic Neutron StarsDec 15 1999Jun 29 2000Recent work has shown that a young, rapidly rotating neutron star loses angular momentum to gravitational waves generated by unstable r-mode oscillations. We study the spin evolution of a young, magnetic neutron star including both the effects of gravitational ... More
Modeling Phase-resolved Observations of the Surfaces of Magnetic Neutron StarsOct 09 2007Recent observations by XMM-Newton detected rotational pulsations in the total brightness and spectrum of several neutron stars. To properly interpret the data, accurate modeling of neutron star emission is necessary. Detailed analysis of the shape and ... More
Comment on ``The Effect of Vacuum Polarization ... in Strongly Magnetized Plasmas'' by Ozel (astro-ph/0203449)Apr 11 2002We have recently shown that in a highly magnetized neutron star atmospheric plasma, vacuum polarization can induce resonant conversion of photon polarization modes via a mechanism analogous to MSW neutrino oscillation. In a recent paper Ozel has dismissed ... More
Measuring the Cooling of the Neutron Star in Cassiopeia A with all Chandra X-ray Observatory DetectorsJun 14 2013Aug 31 2013The thermal evolution of young neutron stars (NSs) reflects the neutrino emission properties of their cores. Heinke et al. (2010) measured a 3.6+/-0.6% decay in the surface temperature of the Cassiopeia A (Cas A) NS between 2000 and 2009, using archival ... More
Direct Observation of the Cooling of the Cassiopeia A Neutron StarJul 27 2010The cooling rate of young neutron stars gives direct insight into their internal makeup. Although the temperatures of several young neutron stars have been measured, until now a young neutron star has never been observed to decrease in temperature over ... More
Polarized X-Ray Emission from Magnetized Neutron Stars: Signature of Strong-Field Vacuum PolarizationMar 27 2003Aug 18 2003In the atmospheric plasma of a strongly magnetized neutron star, vacuum polarization can induce a Mikheyev-Smirnov-Wolfenstein like resonance across which a X-ray photon may (depending on its energy) convert from one mode into the other, with significant ... More
Rotational evolution of young pulsars due to superfluid decouplingAug 15 2012Apr 09 2013Pulsars are rotating neutron stars that are seen to slow down, and the spin-down rate is thought to be due to magnetic dipole radiation. This leads to a prediction for the braking index n, which is a combination of spin period and its first and second ... More
The radius of the quiescent neutron star in the globular cluster M13Feb 28 2018X-ray spectra of quiescent low-mass X-ray binaries containing neutron stars can be fit with atmosphere models to constrain the mass and the radius. Mass-radius constraints can be used to place limits on the equation of state of dense matter. We perform ... More
Variability in LINERsSep 19 2000A small number of LINERs have been seen to display variable H-alpha emission with a very broad, double-peaked profile. Recent observations with the Hubble Space Telescope indicate that such emission may be a common attribute of LINERs. The double-peaked ... More
An Intermediate-Mass Black Hole in the Dwarf Seyfert 1 Galaxy POX 52Oct 15 2003We describe new observations of POX 52, a previously known but nearly forgotten example of a dwarf galaxy with an active nucleus. While POX 52 was originally thought to be a Seyfert 2 galaxy, the new data reveal an emission-line spectrum very similar ... More
The Black Hole Masses and Host Galaxies of BL Lac ObjectsSep 26 2002We have measured the central stellar velocity dispersion in the host galaxies of 11 BL Lac objects with redshifts z <= 0.125. The range of velocity dispersions, 170-370 km/s, is similar to that of nearby radio galaxies. Using the correlation between stellar ... More
Adaptive Control Strategy for Constant Optical Flow Divergence LandingSep 21 2016Bio-inspired methods can provide efficient solutions to perform autonomous landing for Micro Air Vehicles (MAVs). Flying insects such as honeybees perform vertical landings by keeping flow divergence constant. This leads to an exponential decay of both ... More
A Study of the Direct-Fitting Method for Measurement of Galaxy Velocity DispersionsSep 26 2002We have measured the central stellar velocity dispersions of 33 nearby spiral and elliptical galaxies, using a straightforward template-fitting algorithm operating in the pixel domain. The spectra, obtained with the Double Spectrograph at Palomar Observatory, ... More
Stellar Velocity Dispersion and Black Hole Mass in the Blazar Markarian 501Jan 04 2002The recently discovered correlation between black hole mass and stellar velocity dispersion provides a new method to determine the masses of black holes in active galaxies. We have obtained optical spectra of Markarian 501, a nearby gamma-ray blazar with ... More
Multiwavelength monitoring and X-ray brightening of Be X-ray binary PSR J2032+4127/MT91 213 on its approach to periastronSep 20 2016The radio and gamma-ray pulsar PSR J2032+4127 was recently found to be in a decades-long orbit with the Be star MT91 213, with the pulsar moving rapidly toward periastron. This binary shares many similar characteristics with the previously unique binary ... More
Multiwavelength monitoring and X-ray brightening of Be X-ray binary PSR J2032+4127/MT91 213 on its approach to periastronSep 20 2016Oct 25 2016The radio and gamma-ray pulsar PSR J2032+4127 was recently found to be in a decades-long orbit with the Be star MT91 213, with the pulsar moving rapidly towards periastron. This binary shares many similar characteristics with the previously unique binary ... More
A systematic study of soft X-ray pulse profiles of magnetars in quiescenceMar 04 2019Magnetars are neutron stars with extremely high surface magnetic fields. They show diverse X-ray pulse profiles in the quiescent state. We perform a systematic Fourier analysis of their soft X-ray pulse profiles. We find that most magnetars have a single-peaked ... More
Biodegradable Polylactic Acid (PLA) Microstructures for Scaffold ApplicationsFeb 21 2008In this research, we present a simple and cost effective soft lithographic process to fabricate PLA scaffolds for tissue engineering. In which, the negative photoresist JSR THB-120N was spun on a glass subtract followed by conventional UV lithographic ... More
A Search for "Dwarf" Seyfert Nuclei. VI. Properties of Emission-Line Nuclei in Nearby GalaxiesOct 02 2002We use the database from Paper III to quantify the global and nuclear properties of emission-line nuclei in the Palomar spectroscopic survey of nearby galaxies. We show that the host galaxies of Seyferts, LINERs, and transition objects share remarkably ... More
A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host GalaxiesApr 11 1997We have completed an optical spectroscopic survey of the nuclear regions (r < 200 pc) of a large sample of nearby galaxies. Although the main objectives of the survey are to search for low-luminosity active galactic nuclei and to quantify their luminosity ... More
Low-Luminosity Seyfert NucleiJul 23 1996We describe a new sample of Seyfert nuclei discovered during the course of an optical spectroscopic survey of nearby galaxies. The majority of the objects, many recognized for the first time, have luminosities much lower than those of classical Seyferts ... More
Radiative Muon Capture by He-3Dec 06 2001Jun 18 2002The rate of the nuclear reaction $^3He+\mu^- \to ^3H+\gamma+\nu_{\mu}$ has been calculated using both the elementary particle model (EPM) approach and the impulse approximation (IA) approach. Using the EPM approach, the exclusive statistical radiative ... More
Distributed Randomized Gradient-Free Mirror Descent Algorithm for Constrained OptimizationMar 11 2019This paper is concerned with multi-agent optimization problem. A distributed randomized gradient-free mirror descent (DRGFMD) method is developed by introducing a randomized gradient-free oracle in the mirror descent scheme where the non-Euclidean Bregman ... More
The Influence of Bars on Nuclear ActivityApr 11 1997We test ideas on fueling of galactic nuclei by bar-driven inflow by comparing the detection rate and intensity of nuclear H II regions and AGNs among barred and unbarred galaxies in a sample of over 300 spirals selected from our recent optical spectroscopic ... More
Consensus over a Random Network Generated by i.i.d. Stochastic MatricesApr 21 2010Our goal is to find a necessary and sufficient condition on the consensus over a random network, generated by i.i.d. stochastic matrices. We show that the consensus problem in three different convergence modes (almost surely, in probability, and in L1) ... More
Distributed Dimensionality Reduction Fusion Estimation with Communication Delays in Cyber-Physical SystemsFeb 09 2018This paper studies the distributed dimensionality reduction fusion estimation problem with communication delays for a class of cyber-physical systems (CPSs). The raw measurements are preprocessed in each sink node to obtain the local optimal estimate ... More
A New Approach to Linear/Nonlinear Distributed Fusion Estimation ProblemAug 29 2017Jul 19 2018Disturbance noises are always bounded in a practical system, while fusion estimation is to best utilize multiple sensor data containing noises for the purpose of estimating a quantity--a parameter or process. However, few results are focused on the information ... More
BVRI Photometry of SupernovaeAug 18 2001Nov 08 2001We present optical photometry of one Type IIn supernova (1994Y) and nine Type Ia supernovae (1993Y, 1993Z, 1993ae, 1994B, 1994C, 1994M, 1994Q, 1994ae, and 1995D). SN 1993Y and SN 1993Z appear to be normal SN Ia events with similar rates of decline, but ... More
A Search for "Dwarf" Seyfert Nuclei. V. Demographics of Nuclear Activity in Nearby GalaxiesApr 11 1997We use the sample of emission-line nuclei derived from a recently completed optical spectroscopic survey of nearby galaxies to quantify the incidence of local (z = 0) nuclear activity. Consistent with previous studies, we find detectable amounts of ionized ... More
Optimal Distributed Stochastic Mirror Descent for Strongly Convex OptimizationOct 15 2016In this paper we consider convergence rate problems for stochastic strongly-convex optimization in the non-Euclidean sense with a constraint set over a time-varying multi-agent network. We propose two efficient non-Euclidean stochastic subgradient descent ... More
Optimal Distributed Stochastic Mirror Descent for Strongly Convex OptimizationOct 15 2016Aug 22 2018In this paper we consider convergence rate problems for stochastic strongly-convex optimization in the non-Euclidean sense with a constraint set over a time-varying multi-agent network. We propose two efficient non-Euclidean stochastic subgradient descent ... More
The Narrow-Line Regions of LINERs as Resolved with the Hubble Space TelescopeOct 20 1999LINERs exist in the nuclei of a large fraction of luminous galaxies, but their connection with the AGN phenomenon has remained elusive. We present Hubble Space Telescope narrowband [O III]5007 and H-alpha+[N II] emission-line images of the central regions ... More
Properties of H II Regions in the Centers of Nearby GalaxiesApr 11 1997As part of an optical spectroscopic survey of nearby, bright galaxies, we have identified a sample of over 200 emission-line nuclei having optical spectra resembling those of giant extragalactic H II regions. Such "H II nuclei," powered by young, massive ... More
Evolution of cooperation in multilevel public goods games with community structuresMar 02 2011In a community-structured population, public goods games (PGG) occur both within and between communities. Such type of PGG is referred as multilevel public goods games (MPGG). We propose a minimalist evolutionary model of the MPGG and analytically study ... More
Model X-ray Spectra of Magnetic Neutron Stars with Hydrogen AtmospheresFeb 20 2008Apr 11 2008We construct partially ionized hydrogen atmosphere models for magnetized neutron stars in radiative equilibrium with fixed surface fields between B=10^12 and 2x10^13 G and effective temperatures logT_eff=5.5-6.8, as well as with surface B and T_eff distributions ... More
Cosmic recycling of millisecond pulsarsFeb 21 2011Apr 07 2011We compare the rotation rate of neutron stars in low-mass X-ray binaries (LMXBs) with the orbital period of the binaries. We find that, while short orbital period LMXBs span a range of neutron star rotation rates, all the long period LMXBs have fast rotators. ... More
Degrees of entanglement for multipartite systemsMay 22 2012Jan 30 2013We propose a unified mathematical scheme, based on a classical tensor isomorphism, for characterizing entanglement that works for pure states of multipartite systems of any number of particles. The degree of entanglement is indicated by a set of absolute ... More
Constraining the physics of the r-mode instability in neutron stars with X-ray and UV observationsJan 10 2012Rapidly rotating Neutron Stars in Low Mass X-ray Binaries (LMXBs) may be an interesting source of Gravitational Waves (GWs). In particular, several modes of stellar oscillation may be driven unstable by GW emission, and this can lead to a detectable signal. ... More
Revealing the physics of r-modes in low-mass X-ray binariesJul 25 2011Aug 30 2011We consider the astrophysical constraints on the gravitational-wave driven r-mode instability in accreting neutron stars in low-mass X-ray binaries. We use recent results on superfluid and superconducting properties to infer the core temperature in these ... More
Dynamical onset of superconductivity and retention of magnetic fields in cooling neutron starsNov 22 2017A superconductor of paired protons is thought to form in the core of neutron stars soon after their birth. Minimum energy conditions suggest magnetic flux is expelled from the superconducting region due to the Meissner effect, such that the neutron star ... More
A Search for Rapid Photometric Variability in Symbiotic BinariesApr 02 2001We report on our survey for rapid (time scale of minutes) photometric variability in symbiotic binaries. These binaries are becoming an increasingly important place to study accretion onto white dwarfs since they are candidate Type Ia supernovae progenitors. ... More
Magnetars: super(ficially) hot and super(fluid) coolDec 06 2011Aug 24 2012We examine to what extent the inferred surface temperature of magnetars in quiescence can constrain the presence of a superfluid in the neutron star core and the role of magnetic field decay in the core. By performing detailed simulations of neutron star ... More
Variability of Sagittarius A* - Flares at 1 MillimeterFeb 04 2003Feb 11 2003We report the results from recent observations of Sgr A* at short-/sub-millimeter wavelengths made with the partially finished Sub-Millimeter Array (SMA) on Mauna Kea. A total of 25 epochs of observations were carried out over the past 15 months in 2001 ... More
Structure of Sagittarius A* at 86 GHz using VLBI Closure QuantitiesFeb 13 2001At radio wavelengths, images of the compact radio source Sagittarius A* (Sgr A*) in the Galactic Center are scatter broadened with a lambda^2 dependence due to an intervening ionized medium. We present VLBI observations of Sgr A* at 86 GHz using a six ... More
The Broad-Line and Narrow-Line Regions of the LINER NGC 4579Aug 17 2000We report the discovery of an extremely broad H-alpha emission line in the LINER nucleus of NGC 4579. From ground-based observations, the galaxy was previously known to contain a Type 1 nucleus with a broad H-alpha line of FWHM = 2300 km/s and FWZI ~ ... More
Lense-Thirring precession in ULXs as a possible means to constrain the neutron star equation-of-stateNov 20 2017The presence of neutron stars in at least three ultraluminous X-ray sources is now firmly established and offers an unambiguous view of super-critical accretion. All three systems show long-timescale periods (60-80 days) in the X-rays and/or optical, ... More
Efficient and accurate treatment of electron correlations from first-principlesJun 30 2014We present an efficient \textit{ab initio} method for calculating the electronic structure and total energy of strongly correlated electron systems. The method extends the traditional Gutzwiller approximation for one-particle operators to the evaluation ... More
Discovery of a binary icosahedral quasicrystal in Sc$_12$Zn$_88$Oct 14 2009We report the discovery of a new binary icosahedral phase in a Sc-Zn alloy obtained through solution-growth, producing millimeter-sized, facetted, single grain, quasicrystals that exhibit different growth morphologies, pentagonal dodecahedra and rhombic ... More
POX 52: A Dwarf Seyfert 1 Galaxy With An Intermediate-Mass Black HoleFeb 04 2004We describe new optical images and spectra of POX 52, a dwarf galaxy with an active nucleus that was originally detected in the POX objective-prism survey. While POX 52 was originally thought to be a Seyfert 2 galaxy, the new data reveal an emission-line ... More
A Search for Ultraviolet Emission from LINERsOct 28 1997We have obtained Hubble Space Telescope WFPC2 2200 A and optical V-band images of 20 low-luminosity active galactic nuclei, most of which are spectroscopically classified as LINERs, in order to search for a possible photoionizing continuum. Six (30%) ... More
The XMM-Newton view of AGN with intermediate mass black holesDec 09 2008We have observed with XMM-Newton four radiatively efficient active type 1 galaxies with black hole masses < 10^6 Msun, selected optically from the SDSS. We show here that their soft X-ray spectrum exhibits a soft excess with the same characteristics as ... More
An algorithm for decoherence analyses of lights through three-dimensional periodic microstructuresApr 03 2011A transfer-matrix algorithm is presented herein as a beginning to study the transmission characteristics of coherent light through three-dimensional periodic microstructures, in which the structures are treated as two-dimensional-layer stacks and multiple ... More
A Tidal Flare Candidate in Abell 1795Jul 24 2013As part of our ongoing archival X-ray survey of galaxy clusters for tidal flares, we present evidence of an X-ray transient source within 1 arcmin of the core of Abell 1795. The extreme variability (a factor of nearly 50), luminosity (> 2 x 10^42 erg ... More
Black Hole Demography from Nearby Active Galactic NucleiJan 24 2004A significant fraction of local galaxies show evidence of nuclear activity. I argue that the bulk of this activity, while energetically not remarkable, derives from accretion onto a central massive black hole. The statistics of nearby active galactic ... More
What Powers the Compact Radio Emission in Nearby Elliptical and S0 Galaxies?Aug 12 1998Many nearby early-type (elliptical and S0) galaxies contain weak (milli-Jansky level) nuclear radio sources on scales a few hundred parsecs or less. The origin of the radio emission, however, has remained unclear, especially in volume-limited samples ... More
The CO Tully-Fisher Relation and Implications for the Host Galaxies of High-Redshift QuasarsJul 23 2007The integrated line width derived from CO spectroscopy provides a powerful tool to study the internal kinematics of extragalactic objects, including quasars at high redshift, provided that the observed line width can be properly translated to more conventionally ... More
Radiatively Inefficient Accretion in Nearby GalaxiesJun 22 2009We use new central stellar velocity dispersions and nuclear X-ray and Halpha luminosities for the Palomar survey of nearby galaxies to investigate the distribution of nuclear bolometric luminosities and Eddington ratios for their central black holes (BHs). ... More
Nuclear Activity in Nearby GalaxiesMar 15 2008A significant fraction of nearby galaxies show evidence of weak nuclear activity unrelated to normal stellar processes. Recent high-resolution, multiwavelength observations indicate that the bulk of this activity derives from black hole accretion with ... More
The Central Engines of Low-Luminosity AGNsMar 03 2003I summarize the main characteristics of AGNs in nearby galaxies and present a physical picture of their central engines.
Prepotential approach to solvable rational potentials and exceptional orthogonal polynomialsApr 18 2011Aug 06 2011We show how all the quantal systems related to the exceptional Laguerre and Jacobi polynomials can be constructed in a direct and systematic way, without the need of shape invariance and Darboux-Crum transformation. Furthermore, the prepotential need ... More
Prepotential approach to solvable rational extensions of Harmonic Oscillator and Morse potentialsMay 18 2011Dec 21 2011We show how the recently discovered solvable rational extensions of Harmonic Oscillator and Morse potentials can be constructed in a direct and systematic way, without the need of supersymmetry, shape invariance, Darboux-Crum and Darboux-B\"acklund transformations ... More
XMM-Newton Survey of a Distance-limited Sample of Seyfert Galaxies: Preliminary Spectral ResultsMar 17 2003An unbiased estimate of the average intrinsic X-ray properties and column density distribution of Seyfert galaxies in the local Universe is crucial to validate unified models of active galactic nuclei (AGNs) and to synthesis models for the X-ray background. ... More