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At least 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Photoluminescence investigations on Sm3+ ions doped borate glasses for tricolor w-LEDs and lasers

Highlights: • Borate glasses with Sm3+ ions were synthesized by melt quenching technique. • Under 402 nm excitation Borate glasses show reddish orange luminescence. • Energy transfer through cross-relaxation leads to fall in decay time of Sm3+ ions. • I-H model confirms energy transfer between Sm3+ ions as dipole-dipole in nature. • 1 mol% Sm3+ ions in these glasses are apt for red photonic device applications. - Abstract: This work describes mainly the optical absorption, photoluminescence (PL) and decay spectral properties of Sm{sup 3+} ions doped borate glasses to understand their possible usage in tricolor w-LEDs and lasers.The XRD spectrum recorded for an un-doped glass confirms glassy nature of the as prepared glass. The Judd-Ofelt (J-O) intensity parameters evaluated from experimental oscillator strengths were used in estimating the various radiative parameters. Under 402 nm excitation, the PL spectra exhibit intense emission at 600 nm for which the decay spectral profiles were recorded.The decay profiles are converting from single exponential to non-exponential with increase in Sm{sup 3+} ion concentration ensuing decrease in experimental lifetimes which may be attributed to the efficient energy transfer through cross-relaxation process. The non-exponential decay curves fitted to I-H model reveals the interaction between the Sm{sup 3+} ions as dipole-dipole in nature. From the evaluated emission cross-sections, quantum efficiency, branching ratios and CIE co-ordinates, it is concluded that 1 mol% Sm{sup 3+} ions in these glasses are aptly suitable to fabricate reddish-orange luminescent devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Photoluminescence properties and efficient energy transfer of Ce3+/Eu2+ activated K2Ba7Si16O40 phosphors

Highlights: • K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}:Ce{sup 3+}/Eu{sup 2+} phosphors have been synthesized by a high temperature solid-state method with CO atmosphere. • The resonance-type energy transfer by dipole-dipole interaction from Ce{sup 3+} to Eu{sup 2+} in K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} is demonstrated. • The critical distance between Ce{sup 3+} and Eu{sup 2+} ions is calculated to be 25.06 Å. • The thermal activation energy of K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} is calculated to be 0.26 eV. - Abstract: Ce{sup 3+}/Eu{sup 2+} activated K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} phosphors have been synthesized via a high-temperature solid-state method with CO atmosphere. Under ultraviolet (UV) light pump, the photoluminescence (PL) spectra of K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: Ce{sup 3+} is composed of a broadband from 300 nm to 500 nm ascribed to the spin-allowed 5d–4f transition of Ce{sup 3+} ions. The optimal concentration is 8% for Ce{sup 3+} single doped K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} due to the ernergy dispersion between Ce{sup 3+} ions and the critical distance between Ce{sup 3+} ions is 15.05 Å. K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: Eu{sup 2+} emits a broad green emission peaking at 498 nm. The spectral overlap between the emission of Ce{sup 3+} and the excitation of Eu{sup 2+} suggests the resonance-type energy transfer from Ce{sup 3+} to Eu{sup 2+}, which is further demonstrated by the decay curves of K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: 8 mol% Ce{sup 3+}, m Eu{sup 2+}. The critical distance between Ce{sup 3+} and Eu{sup 2+} ions is calculated to be 25.06 Å by Dexter’s theory. Furthermore, the energy transfer mechanism is dipole-dipole interaction. In addition, the thermal activation energy is calculated to be 0.26 eV. The CIE coordinates can be tuned from blue to green by increasing Eu{sup 2+} ions. All results suggest that K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: Ce{sup 3+}, Eu{sup 2+} is potentially useful for near-UV pumped white LEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Exotic modes of excitation in proton rich nuclei

The framework of relativistic energy density functional has been applied in description of excitation phenomena in nuclei close to the proton drip line. In particular, low-lying dipole excitations have been studied using relativistic quasiparticle random phase approximation, based on effective Lagrangians with density dependent meson nucleon couplings. In the isovector dipole channel, the occurrence of pronounced low-lying dipole peaks is predicted, corresponding to the proton pygmy dipole resonance. Since this exotic mode still awaits its experimental confirmation, systematic calculations have been conducted within a pool of neutron deficient nuclei, in order to identify the best possible candidates for measurements.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Dynamic processes and polarizability of sodium atom in Debye plasmas

Dynamic processes including excitation and ionization, and spectrum parameters including the oscillator strengths, dipole polarizabilities from the orbital 3s,3p of sodium atom embedded in weakly coupled plasma are investigated in the entire energy range of a non-relativistic regime. The interaction between the valence electron and the atomic core is simulated by a model potential, and the plasma screening of the Coulomb interaction between charged particles is described by the Debye-Hückel model. The screening of Coulomb interactions reduces the number of bound states, decreases their binding energies, broadens their radial distribution of electron wave functions, and significantly changes the continuum wave functions including the amplitudes and phase-shift. These changes strongly affect the dipole matrix elements between the bound-bound and bound-continuum states, and even the oscillator strengths, the photo-ionization cross sections and the dipole polarizabilities. The plasma screening effect changes the interaction between the valence electron and the atomic core into a short-range potential. The energy behaviors of photo-ionization cross sections are unfolded, for instance, its low-energy behavior (obeying Wigner threshold law), and the appearance of multiple shape and virtual-state resonances when the upper bound states emerge into the continuum. The Combet-Farnoux and Cooper minima in the photo-ionization cross sections are also investigated, and here, the Cooper minima appear not only for the l→l+1 channel but also for l→l−1 one, different from that of hydrogen-like ions in a Debye plasma, which appear only in the l→l+1 channel. The total static electric dipole polarizabilities monotonously and dramatically increase with the plasma screening effect increasing, which are similar to those of hydrogen-like ions and lithium atom. Comparison of calculated results for the oscillator strength, the photo-ionization cross section and polarizability with the results of other authors, when available, is made.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Most spin-1/2 transition-metal ions do have single ion anisotropy

The cause for the preferred spin orientation in magnetic systems containing spin-1/2 transition-metal ions was explored by studying the origin of the easy-plane anisotropy of the spin-1/2 Cu{sup 2+} ions in CuCl{sub 2}·2H{sub 2}O, LiCuVO{sub 4}, CuCl{sub 2}, and CuBr{sub 2} on the basis of density functional theory and magnetic dipole-dipole energy calculations as well as a perturbation theory treatment of the spin-orbit coupling. We find that the spin orientation observed for these spin-1/2 ions is not caused by their anisotropic spin exchange interactions, nor by their magnetic dipole-dipole interactions, but by the spin-orbit coupling associated with their crystal-field split d-states. Our study also predicts in-plane anisotropy for the Cu{sup 2+} ions of Bi{sub 2}CuO{sub 4} and Li{sub 2}CuO{sub 2}. The results of our investigations dispel the mistaken belief that magnetic systems with spin-1/2 ions have no magnetic anisotropy induced by spin-orbit coupling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Far field emission profile of pure wurtzite InP nanowires

We report on the far field emission profile of pure wurtzite InP nanowires in comparison to InP nanowires with predominantly zincblende crystal structure. The emission profile is measured on individual nanowires using Fourier microscopy. The most intense photoluminescence of wurtzite nanowires is collected at small angles with respect to the nanowire growth axis. In contrast, zincblende nanowires present a minimum of the collected light intensity in the direction of the nanowire growth. Results are explained by the orientation of electric dipoles responsible for the photoluminescence, which is different from wurtzite to zincblende. Wurtzite nanowires have dipoles oriented perpendicular to the nanowire growth direction, whereas zincblende nanowires have dipoles oriented along the nanowire axis. This interpretation is confirmed by both numerical simulations and polarization dependent photoluminescence spectroscopy. Knowledge of the dipole orientation in nanostructures is crucial for developing a wide range of photonic devices such as light-emitting diodes, photodetectors, and solar cells.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Order and correlation contributions to the entropy of hydrophobic solvation

The entropy of hydrophobic solvation has been explained as the result of ordered solvation structures, of hydrogen bonds, of the small size of the water molecule, of dispersion forces, and of solvent density fluctuations. We report a new approach to the calculation of the entropy of hydrophobic solvation, along with tests of and comparisons to several other methods. The methods are assessed in the light of the available thermodynamic and spectroscopic information on the effects of temperature on hydrophobic solvation. Five model hydrophobes in SPC/E water give benchmark solvation entropies via Widom’s test-particle insertion method, and other methods and models are tested against these particle-insertion results. Entropies associated with distributions of tetrahedral order, of electric field, and of solvent dipole orientations are examined. We find these contributions are small compared to the benchmark particle-insertion entropy. Competitive with or better than other theories in accuracy, but with no free parameters, is the new estimate of the entropy contributed by correlations between dipole moments. Dipole correlations account for most of the hydrophobic solvation entropy for all models studied and capture the distinctive temperature dependence seen in thermodynamic and spectroscopic experiments. Entropies based on pair and many-body correlations in number density approach the correct magnitudes but fail to describe temperature and size dependences, respectively. Hydrogen-bond definitions and free energies that best reproduce entropies from simulations are reported, but it is difficult to choose one hydrogen bond model that fits a variety of experiments. The use of information theory, scaled-particle theory, and related methods is discussed briefly. Our results provide a test of the Frank-Evans hypothesis that the negative solvation entropy is due to structured water near the solute, complement the spectroscopic detection of that solvation structure by identifying the structural feature responsible for the entropy change, and point to a possible explanation for the observed dependence on length scale. Our key results are that the hydrophobic effect, i.e. the signature, temperature-dependent, solvation entropy of nonpolar molecules in water, is largely due to a dispersion force arising from correlations between rotating permanent dipole moments, that the strength of this force depends on the Kirkwood g-factor, and that the strength of this force may be obtained exactly without simulation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Ion aggregation in high salt solutions. III. Computational vibrational spectroscopy of HDO in aqueous salt solutions

The vibrational frequency, frequency fluctuation dynamics, and transition dipole moment of the O—D stretch mode of HDO molecule in aqueous solutions are strongly dependent on its local electrostatic environment and hydrogen-bond network structure. Therefore, the time-resolved vibrational spectroscopy the O—D stretch mode has been particularly used to investigate specific ion effects on water structure. Despite prolonged efforts to understand the interplay of O—D vibrational dynamics with local water hydrogen-bond network and ion aggregate structures in high salt solutions, still there exists a gap between theory and experiment due to a lack of quantitative model for accurately describing O—D stretch frequency in high salt solutions. To fill this gap, we have performed numerical simulations of Raman scattering and IR absorption spectra of the O—D stretch mode of HDO in highly concentrated NaCl and KSCN solutions and compared them with experimental results. Carrying out extensive quantum chemistry calculations on not only water clusters but also ion-water clusters, we first developed a distributed vibrational solvatochromic charge model for the O—D stretch mode in aqueous salt solutions. Furthermore, the non-Condon effect on the vibrational transition dipole moment of the O—D stretch mode was fully taken into consideration with the charge response kernel that is non-local polarizability density. From the fluctuating O—D stretch mode frequencies and transition dipole vectors obtained from the molecular dynamics simulations, the O—D stretch Raman scattering and IR absorption spectra of HDO in salt solutions could be calculated. The polarization effect on the transition dipole vector of the O—D stretch mode is shown to be important and the asymmetric line shapes of the O—D stretch Raman scattering and IR absorption spectra of HDO especially in highly concentrated NaCl and KSCN solutions are in quantitative agreement with experimental results. We anticipate that this computational approach will be of critical use in interpreting linear and nonlinear vibrational spectroscopies of HDO molecule that is considered as an excellent local probe for monitoring local electrostatic and hydrogen-bonding environment in not just salt but also other confined and crowded solutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Spin polarization transfer by the radical pair mechanism

In a three-site representation, we study a spin polarization transfer from radical pair spins to a nearby electron or nuclear spin. The quantum dynamics of the radical pair spins is governed by a constant exchange interaction between the radical pair spins which have different Zeeman frequencies. Radical pair spins can recombine to the singlet ground state or to lower energy triplet states. It is then shown that the coherent dynamics of the radical pair induces spin polarization on the nearby third spin in the presence of a magnetic field. The spin polarization transfer depends on the difference between Zeeman frequencies, the singlet and triplet recombination rates, and on the exchange and dipole-dipole interactions between the different spins. In particular, the sign of the polarization depends on the exchange coupling between radical pair spins and also on the difference between singlet and triplet recombination rate constants.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Electronic structure investigation of atomic layer deposition ruthenium(oxide) thin films using photoemission spectroscopy

Analyzing and manipulating the electronic band line-up of interfaces in novel micro- and nanoelectronic devices is important to achieve further advancement in this field. Such band alignment modifications can be achieved by introducing thin conformal interfacial dipole layers. Atomic layer deposition (ALD), enabling angstrom-precise control over thin film thickness, is an ideal technique for this challenge. Ruthenium (Ru{sup 0}) and its oxide (RuO{sub 2}) have gained interest in the past decade as interfacial dipole layers because of their favorable properties like metal-equivalent work functions, conductivity, etc. In this study, initial results of the electronic structure investigation of ALD Ru{sup 0} and RuO{sub 2} films via photoemission spectroscopy are presented. These experiments give insight into the band alignment, growth behavior, surface structure termination, and dipole formation. The experiments were performed in an integrated vacuum system attached to a home-built, stop-flow type ALD reactor without exposing the samples to the ambient in between deposition and analysis. Bis(ethylcyclopentadienyl)ruthenium(II) was used as precursor and oxygen as reactant. The analysis chamber was outfitted with X-ray photoemission spectroscopy (LIXPS, XPS). The determined growth modes are consistent with a strong growth inhibition situation with a maximum average growth rate of 0.21 Å/cycle for RuO{sub 2} and 0.04 Å/cycle for Ru.{sup 0} An interface dipole of up to −0.93 eV was observed, supporting the assumption of a strongly physisorbed interface. A separate experiment where the surface of a RuO film was sputtered suggests that the surface is terminated by an intermediate, stable, non-stoichiometric RuO{sub 2}/OH compound whose surface is saturated with hydroxyl groups.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Sub- and super-luminar propagation of structures satisfying Poynting-like theorem for incompressible generalized hydrodynamic fluid model depicting strongly coupled dusty plasma medium

The strongly coupled dusty plasma has often been modelled by the Generalized Hydrodynamic (GHD) model used for representing visco-elastic fluid systems. The incompressible limit of the model which supports transverse shear wave mode is studied in detail. In particular, dipole structures are observed to emit transverse shear waves in both the limits of sub- and super-luminar propagation, where the structures move slower and faster than the phase velocity of the shear waves, respectively. In the sub-luminar limit the dipole gets engulfed within the shear waves emitted by itself, which then backreacts on it and ultimately the identity of the structure is lost. However, in the super-luminar limit the emission appears like a wake from the tail region of the dipole. The dipole, however, keeps propagating forward with little damping but minimal distortion in its form. A Poynting-like conservation law with radiative, convective, and dissipative terms being responsible for the evolution of W, which is similar to “enstrophy” like quantity in normal hydrodynamic fluid systems, has also been constructed for the incompressible GHD equations. The conservation law is shown to be satisfied in all the cases of evolution and collision amidst the nonlinear structures to a great accuracy. It is shown that monopole structures which do not move at all but merely radiate shear waves, the radiative term, and dissipative losses solely contribute to the evolution of W. The dipolar structures, on the other hand, propagate in the medium and hence convection also plays an important role in the evolution of W.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Dual polarized receiving steering antenna array for measurement of ultrawideband pulse polarization structure

To measure simultaneously two orthogonal components of the electromagnetic field of nano- and subnano-second duration, an antenna array has been developed. The antenna elements of the array are the crossed dipoles of dimension 5 × 5 cm. The arms of the dipoles are connected to the active four-pole devices to compensate the frequency response variations of a short dipole in the frequency band ranging from 0.4 to 4 GHz. The dipoles have superimposed phase centers allowing measuring the polarization structure of the field in different directions. The developed antenna array is the linear one containing four elements. The pattern maximum position is controlled by means of the switched ultrawideband true time delay lines. Discrete steering in seven directions in the range from −40° to +40° has been realized. The error at setting the pattern maximum position is less than 4°. The isolation of the polarization exceeds 29 dB in the direction orthogonal to the array axis and in the whole steering range it exceeds 23 dB. Measurement results of the polarization structure of radiated and scattered pulses with different polarization are presented as well.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Communication: Proton NMR dipolar-correlation effect as a method for investigating segmental diffusion in polymer melts

A simple and fast method for the investigation of segmental diffusion in high molar mass polymer melts is presented. The method is based on a special function, called proton dipolar-correlation build-up function, which is constructed from Hahn Echo signals measured at times t and t/2. The initial rise of this function contains additive contributions from both inter- and intramolecular magnetic dipole-dipole interactions. The intermolecular contribution depends on the relative mean squared displacements (MSDs) of polymer segments from different macromolecules, while the intramolecular part reflects segmental reorientations. Separation of both contributions via isotope dilution provides access to segmental displacements in polymer melts at millisecond range, which is hardly accessible by other methods. The feasibility of the method is illustrated by investigating protonated and deuterated polybutadiene melts with molecular mass 196 000 g/mol at different temperatures. The observed exponent of the power law of the segmental MSD is close to 0.32 ± 0.03 at times when the root MSD is in between 45 Å and 75 Å, and the intermolecular proton dipole-dipole contribution to the total proton Hahn Echo NMR signal is larger than 50% and increases with time.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

A mathematical model of extremely low frequency ocean induced electromagnetic noise

Magnetic Anomaly Detection (MAD) system uses the principle that ferromagnetic objects disturb the magnetic lines of force of the earth. These lines of force are able to pass through both water and air in similar manners. A MAD system, usually mounted on an aerial vehicle, is thus often employed to confirm the detection and accomplish localization of large ferromagnetic objects submerged in a sea-water environment. However, the total magnetic signal encountered by a MAD system includes contributions from a myriad of low to Extremely Low Frequency (ELF) sources. The goal of the MAD system is to detect small anomaly signals in the midst of these low-frequency interfering signals. Both the Range of Detection (R{sub d}) and the Probability of Detection (P{sub d}) are limited by the ratio of anomaly signal strength to the interfering magnetic noise. In this paper, we report a generic mathematical model to estimate the signal-to-noise ratio or SNR. Since time-variant electro-magnetic signals are affected by conduction losses due to sea-water conductivity and the presence of air-water interface, we employ the general formulation of dipole induced electromagnetic field propagation in stratified media [1]. As a first step we employ a volumetric distribution of isolated elementary magnetic dipoles, each having its own dipole strength and orientation, to estimate the magnetic noise observed by a MAD system. Numerical results are presented for a few realizations out of an ensemble of possible realizations of elementary dipole source distributions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

BROADBAND SPECTROSCOPY USING TWO SUZAKU OBSERVATIONS OF THE HMXB GX 301-2

We present the analysis of two Suzaku observations of GX 301-2 at two orbital phases after the periastron passage. Variations in the column density of the line-of-sight absorber are observed, consistent with accretion from a clumpy wind. In addition to a cyclotron resonance scattering feature (CRSF), multiple fluorescence emission lines were detected in both observations. The variations in the pulse profiles and the CRSF throughout the pulse phase have a signature of a magnetic dipole field. Using a simple dipole model we calculated the expected magnetic field values for different pulse phases and were able to extract a set of geometrical angles, loosely constraining the dipole geometry in the neutron star. From the variation of the CRSF width and energy, we found a geometrical solution for the dipole, making the inclination consistent with previously published values.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

CAN WE PREDICT THE GLOBAL MAGNETIC TOPOLOGY OF A PRE-MAIN-SEQUENCE STAR FROM ITS POSITION IN THE HERTZSPRUNG-RUSSELL DIAGRAM?

Zeeman-Doppler imaging studies have shown that the magnetic fields of T Tauri stars can be significantly more complex than a simple dipole and can vary markedly between sources. We collect and summarize the magnetic field topology information obtained to date and present Hertzsprung-Russell (H-R) diagrams for the stars in the sample. Intriguingly, the large-scale field topology of a given pre-main-sequence (PMS) star is strongly dependent upon the stellar internal structure, with the strength of the dipole component of its multipolar magnetic field decaying rapidly with the development of a radiative core. Using the observational data as a basis, we argue that the general characteristics of the global magnetic field of a PMS star can be determined from its position in the H-R diagram. Moving from hotter and more luminous to cooler and less luminous stars across the PMS of the H-R diagram, we present evidence for four distinct magnetic topology regimes. Stars with large radiative cores, empirically estimated to be those with a core mass in excess of {approx}40% of the stellar mass, host highly complex and dominantly non-axisymmetric magnetic fields, while those with smaller radiative cores host axisymmetric fields with field modes of higher order than the dipole dominant (typically, but not always, the octupole). Fully convective stars above {approx}> 0.5 M{sub Sun} appear to host dominantly axisymmetric fields with strong (kilo-Gauss) dipole components. Based on similarities between the magnetic properties of PMS stars and main-sequence M-dwarfs with similar internal structures, we speculate that a bistable dynamo process operates for lower mass stars ({approx}< 0.5 M{sub Sun} at an age of a few Myr) and that they will be found to host a variety of magnetic field topologies. If the magnetic topology trends across the H-R diagram are confirmed, they may provide a new method of constraining PMS stellar evolution models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE SPIN-DOWN OF PSR J0821-4300 AND PSR J1210-5226: CONFIRMATION OF CENTRAL COMPACT OBJECTS AS ANTI-MAGNETARS

Using XMM-Newton and Chandra, we measure period derivatives for the second and third known pulsars in the class of central compact objects (CCOs) in supernova remnants, proving that these young neutron stars have exceptionally weak dipole magnetic field components. For the 112 ms PSR J0821-4300 in Puppis A, P-dot = (9.28{+-}0.36) Multiplication-Sign 10{sup -18}. Its proper motion, {mu} = 61 {+-} 9 mas yr{sup -1}, was also measured using Chandra. This contributes a kinematic term to the period derivative via the Shklovskii effect, which is subtracted from P-dot to derive dipole B{sub s} = 2.9 Multiplication-Sign 10{sup 10} G, a value similar to that of the first measured CCO, PSR J1852+0040 in Kes 79, which has B{sub s} = 3.1 Multiplication-Sign 10{sup 10} G. Antipodal surface hot spots with different temperatures and areas are deduced from the X-ray spectrum and pulse profiles. Paradoxically, such nonuniform surface temperature appears to require strong crustal magnetic fields, probably toroidal or quadrupolar components much stronger than the external dipole. A spectral feature, consisting of either an emission line at Almost-Equal-To 0.75 keV or an absorption line at Almost-Equal-To 0.46 keV, is modulated in strength with the rotation. It may be due to a cyclotron process in a magnetic field on the surface that is slightly stronger than the dipole deduced from the spin-down. We also timed anew the 424 ms PSR J1210-5226, resolving previous ambiguities about its spin-down rate. Its P-dot is (2.22 {+-} 0.02) Multiplication-Sign 10{sup -17}, corresponding to B{sub s} = 9.8 Multiplication-Sign 10{sup 10} G. This is also compatible with a cyclotron resonance interpretation of its prominent absorption line at 0.7 keV and its harmonics. These results deepen the mystery of the origin and evolution of CCOs: Why are their numerous descendants not evident?.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Modeling the X-rays from the central compact object PSR J1852+0040 in Kesteven 79: Evidence for a strongly magnetized neutron star

I present modeling of the X-ray pulsations from the central compact object (CCO) PSR J1852+0040 in the Galactic supernova remnant Kesteven 79. In the context of thermal surface radiation from a rotating neutron star (NS), a conventional polar cap model can reproduce the broad, large-amplitude X-ray pulse only with a 'pencil plus fan' beam emission pattern, which is characteristic of ≳ 10{sup 12} G NS atmospheres, much greater than the ∼10{sup 10} G external dipole field inferred from the pulsar spin-down rate. This discrepancy can be explained by an axially displaced dipole. For other beaming patterns, it is necessary to invoke high-aspect-ratio emitting regions that are greatly longitudinally elongated, possibly due to an extremely offset dipole. For all assumed emission models, the existence of strong internal magnetic fields (≳ 10{sup 14} G) that preferentially channel internal heat to only a portion of the exterior is required to account for the implied high-temperature contrast across the stellar surface. This lends further observational evidence in support of the 'hidden' strong magnetic field scenario, in which CCOs possess submerged magnetic fields that are substantially stronger than the external dipole field, presumably due to burial by fallback of supernova ejecta. I also conduct phase-resolved X-ray spectroscopy and find no evidence for prominent spin-phase-dependent absorption features that could be produced by cyclotron absorption/scattering.

79 ASTRONOMY AND ASTROPHYSICS↗