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Applying the timing tools of kilohertz quasi-periodic oscillations (kHz QPOs) and cross-correlations, we study the influence of the magnetosphere-disk relation on the X-ray radiation process of GX 17+2. First, as the spectral state track of X-ray emission evolves along the horizontal branch (HB), the magnetosphere-disk radii of the source derived by kHz QPOs shrink from r ∼ 24 km to r ∼ 18 km, while its average X-ray intensities in ≤10 keV and in ≥10 keV show the opposite evolutional trends. Moreover, this branch has been detected with the anti-correlations between the low-/high-energy (e.g., 2–5 keV/16–30 keV) X-rays. We suggest that in HB there may exist an X-ray radiation transfer process at the disk radii near the neutron star (NS), i.e., ∼5–10 km away from the surface, which probably originates from the interaction between the corona or jet with high-energy X-rays and accretion disk with low-energy X-rays. Second, as the source evolves along the normal branch (NB) and along the flaring branch (FB), their average X-ray intensities in all ∼2–30 keV show the monotonously decreasing and monotonously increasing trends, respectively. In addition, these two branches are both dominated by the positive correlations between the low- and high-energy (e.g., 2–5 keV/16–30 keV) X-rays. Moreover, the evolution along NB is accompanied by the shrinking of the magnetosphere-disk radii from r ∼ 18 km to r ∼ 16 km. We ascribe these phenomena to that as the shrinking of the accretion disk radius, the piled up accretion matter around the NS surface may trigger the radiation that produces both the low- and high-energy X-rays simultaneously, and then form the branches of NB and FB.

PSR B1237+25, whose mean pulse profile has five components, is a well-known star to study pulsar emission geometries. We conducted mode changing and modulation analysis on this pulsar using FAST data at 1.25 GHz with a bandwidth of 400 MHz. We observed and identified three emission modes of this pulsar: a quiet normal mode that has little or no core activity with distinctive 2.8-period subpulse modulation on its outer cone, a flare normal mode in which the core is highly active and an abnormal mode in which the core is active and the last component is weak. We found that the core activity cuts off the position angle traverse in flare normal mode and leads to a position angle jumping in abnormal mode. We also found that there exists a quasi-periodical modulation on the outer conal components. Such modulation shows an irregular wave-like pattern, and has a weak correlation with the core component. We discuss the likely origin of such a modulation, and argue that this modulation can be interpreted as precession of the emission cones around the magnetic axis.

LIGO-Virgo has observed the gravitational waves (GWs) from the coalescence of binary black hole (BBH) and binary neutron star (BNS) during O1 and O2, and the ones from NS-BH are expected to be hunted in the operating O3 run. The population properties and mass distribution of NS-BH mergers are poorly understood now, thus researchers simulated their chirp mass ( ℳ ) distribution by a synthetic model, in which the BHs and NSs were inferred by LIGO-Virgo (O1/O2), and obtained the values in the range of 2.1 M ⊙ < ℳ < 7.3 M ⊙ . In this paper, we further simulate the GW frequency (f GW) distribution of NS-BH mergers by the above-stated synthetic model, with a basic binary system model through the Monte Carlo method. Our results predict that the median with 90% credible intervals is 165 − 64 + 475 Hz in the case of Schwarzschild BH when the system just before merger, and this GW frequency is expected to increase several times in the merger stage, which is lying in the frequency band of LIGO-Virgo, i.e., about 15 Hz to a few kHz. Our results provide an important reference for hunting the NS-BH mergers by the on-going O3 run of LIGO-Virgo.

So far among the nineteen pairs of detected double neutron star (DNS) systems, it is a usual fact that the first-born recycled pulsar is detected, however the youngest DNS system PSR J1906+0746, with the characteristic age of 113 kyr, is one of the three detected DNS as a non-recycled and second-born NS, which is believed to be formed by an electron capture or a low energy ultra-stripped iron core-collapse supernova (SN) explosion. The SN remnant around PSR J1906+0746 is too dim to be observed by optical telescopes, then its x-ray flux limit has been given by Chandra. A reference pulsar PSR J1509-5850 with the young characteristic age of 154 kyr was chosen as an object of comparison, which has an SN remnant observed by Chandra and is believed to be formed by iron core SN explosion. We impose a restriction on the maximum kinetic energy of electron-capture (EC) SN explosion that induces the formation of PSR J1906+0746. The estimated result is (4–8)×1050 erg (1 erg = 10−7 J), which is consistent with that of the published simulations of the EC process, i.e., a lower value than that of the conventional iron core SN explosion of (1–2) × 1051 erg. As suggested, EC process for NS formation is pertained to the subluminous type Ic SN by the helium star with ONeMg core, thus for the first time we derived the kinetic energy of EC SN explosion of DNS, which may be reconciled with the recent observation of type Ic SN 2014ft with kinetic energy of 2 × 1050 erg.

We investigated the pulsar radio luminosity (L), emission efficiency (ratio of radio luminosity to its spin-down power E ˙ ), and death line in the magnetic field (B) versus spin period (P) diagram. We found that the dependence of pulsar radio luminosity on its spin-down power ( L − E ˙ ) is very weak, shown as L ∼ E ˙ 0.06 , which deduces an equivalent inverse correlation between emission efficiency and spin-down power as ξ ∼ E ˙ − 0.94 . Furthermore, we examined the distributions of radio luminosity of millisecond and normal pulsars and found that for the similar spin-down powers, the radio luminosity of millisecond pulsars is about one order of magnitude lower than that of the normal pulsars. The analysis of pulsar radio flux suggests that these correlations are not due to a selective effect but are intrinsic to the pulsar radio emission physics. Their radio radiations may be dominated by the different radiation mechanisms. The cut-off phenomenon of currently observed radio pulsars in B – P diagram is usually referred as the “pulsar death line”, which corresponds to E ˙ ≈ 10 30 erg s−1 and is obtained by the cut-off voltage of electron acceleration gap in the polar cap model of pulsar proposed by Ruderman and Sutherland. Observationally, this death line can be inferred by the actual observed pulsar flux S ≥ 1mJy and 1 kpc distance, together with the maximum radio emission efficiency of 1%. However, the observation data show that the 37 pulsars pass over the death line, including the recently observed two pulsars with long periods of 23.5 s and 12.1 s, which violate the prediction of the polar cap model. At present, the actual observed pulsar flux can reach 0.01mJy by FAST telescope. This will arise the observational limit of spin-down power of pulsars as low as E ˙ ≈ 10 28 erg s−1. This means that the new death line is downward shifted two orders of magnitude, which might be favorably referred as the “observational limit–line”. Accordingly, the pulsar theoretical model for the cut-off voltage of gap should be heavily modified.

We analyze the properties of the binary millisecond pulsars (BMSPs), detected at radio and gamma-ray wavelengths, and further probe their correlations with the binary orbital parameters and companion masses to trace the possible evolutionary histories. We find that the BMSPs with the lowest-mass companions, (0.006-0.06)M-circle dot, have short orbital periods P-orb = 3.37 ms) than the radio-only BMSPs ( = 4.73ms). We propose that the latter systems are a later evolutionary phase of the former ones.

The brightest optical flash from a gamma-ray burst (GRB) was, briefly, a naked-eye object. Several other GRBs have produced optical transients only slightly fainter. We argue that, based upon the recently accumulated data from hundreds of GRB transients, many such optical events should have been visible to the unaided eye in the course of human history. The most likely repositories of such observations are historical records from the Orient, and we have located and discuss a number of candidates. We also consider the value of such observations, should any very likely ones be uncovered, to modern astrophysics., 9 pages, 3 figures

Large scale, high density boron carbide nanowires have been synthesized by using an improved carbothermal reduction method with B/B2O3/C powder precursors under an argon flow at 1100°C. The boron carbide nanowires are 5–10 μm in length and 80–100 nm in diameter. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) characterizations show that the boron carbide nanowire has a B4C rhombohedral structure with good crystallization. The Raman spectrum of the as-grown boron carbide nanowires is consistent with that of a B4C structure consisting of B11C icosahedra and C-B-C chains. The room temperature photoluminescence spectrum of the boron carbide nanowires exhibits a visible range of emission centred at 638 nm.

This paper reports that the large-scale single crystalline boron carbide nanobelts have been fabricated through a simple carbothermal reduction method with B/B2O3/C/Fe powder as precursors at 1100°C. Transmission electron microscopy and selected area electron diffraction characterizations show that the boron carbide nanobelt has a B4C rhomb-centred hexagonal structure with good crystallization. Electron energy loss spectroscopy analysis indicates that the nanobelt contains only B and C, and the atomic ratio of B to C is close to 4:1. High resolution transmission electron microscopy results show that the preferential growth direction of the nanobelt is [101]. A possible growth mechanism is also discussed.

This paper reports that a simple chemical vapour deposition method has been adopted to fabricate large scale, high density boron nanocones with thermal evaporation of B/B2O3 powders precursors in an Ar/H2 gas mixture at the synthesis temperature of 1000–1200°C. The lengths of boron nanocones are several micrometres, and the diameters of nanocone tops are in a range of 50–100 nm. transmission electron microscopy and selected area electron diffraction indicate that the nanocones are single crystalline α-tetragonal boron. The vapour–liquid–solid mechanism is the main formation mechanism of boron nanocones. One broad photoluminescence emission peak at the central wavelength of about 650 nm is observed under the 532 nm light excitation. Boron nanocones with good photoluminescence properties are promising candidates for applications in optical emitting devices.

A single ZnO nanowire with intrinsic oxygen vacancies is utilized to fabricate four-contact device with focus ion beam lithography technique. Cathodoluminescent spectra indicate strong near-UV and green emission at both room temperature and low temperatures. Experimental measurement shows the temperature-dependent conductivity of the ZnO nanowire at low temperatures (below 100 K). The further theoretical analysis confirms that weak localization plays an important role in the electrical transport, which is attributed to the surface states induced by plenty of oxygen vacancies in ZnO nanowire.

High density boron carbide nanowires are grown by an improved carbon thermal reduction technique. Transmission electron microscopy and electron energy lose spectroscopy of the sample show that the synthesized nanowires are B4 C with good crystallization. The field emission measurement for an individual boron nanowire is performed by using a Pt tip installed in the focused ion beam system. A field emission current with enhancement factor of 106 is observed and the evolution process during emission is also carefully studied. Furthermore, a two-step field emission with stable emission current density is found from the high-density nanowire film. Our results together suggest that boron carbide nanowires are promising candidates for electron emission nanodevices.

This paper reports high temperature liquid phase synthesis of Pd nanowires using chemically modified porous anodic aluminium oxide as template. In this synthesis process, oleic acid is used to modify the inner wall of the pores and Pd2+ complex with oleylamine is filled into the channel of the template. The complex is then reduced to give oleylamine-capped Pd nanowires. This paper suggests that oleic acid can improve the environment of inner wall of the pores, leading to the formation of uniform Pd nanowires. The synthetic process can be extended to make other types of nanowires.

The morphology and properties of nanostructures are significantly influenced by the chemical coordination during their growth procedure. Using small molecule N-vinyl pyrolidone as stabilizer, this paper introduces a new strategy for synthesis of palladium nanospheres, which has a novel surface plasmon resonance band in the visible range. An aggregation growth mode was observed in the growth process. More specifically, the growth rate increases with increasing concentration of stabilizer. The absorption in visible region suggests new optical applications for these Pd nanospheres, such as photocatalysis, photothermal heating and surface enhanced Raman scattering.

We present X-ray spectral analyses of the low-mass X-ray binary Cir X-1 during X-ray dips, using the Rossi X-ray Timing Explorer (RXTE) data. Each dip was divided into several segments, and the spectrum of each segment was fitted with a three-component blackbody model, in which the first two components are affected by partial covering and the third one is unaffected. A Gaussian emission line is also included in the spectral model to represent the Fe K alpha line at similar to 6.4keV. The fitted temperatures of the two partially covered components are about 2 keV and I keV, while the uncovered component has a temperature of similar to 0.5-0.6keV. The equivalent blackbody emission radius of the hottest component is the smallest and that of the coolest component is the largest. During the dips the fluxes of the two hot components are linearly correlated, while that of the third component does not show any significant variation. The Fe line flux remains constant, within the errors, during the short dips. However, during the long dips the line flux varies significantly and is positively correlated with the fluxes of the two hot components. These results suggest: (1) that the temperature of the X-ray emitting region decreases with radius, (2) that the Fe Ka line emitting region is close to the hot continuum emitting region, and (3) that the size of the Fe line emitting region is larger than that of the obscuring matter causing the short dips but smaller than the region of that causing the long dips.

MHD Alfven wave oscillation for the interpretation of the twin kilohertz Quasi Periodic Oscillations (kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries (LMXBs) is proposed, and the upper kHz QPO frequency coincides with the Keplerian frequency. The model concludes that the kHz QPO frequencies inversely depend on the disk radius, and the theoretical relation between the upper frequency (v2) and the lower frequency (v1) is v1 ~ v22, which is similar to the measured empirical relation. The separation between the twin frequencies decreases (increases) with increasing the kHz QPO frequency if the lower kHz frequency is more (less) than ~ 400 Hz.

For the bright neutron star low-mass X-ray binary Sco X-1, we analyzed all updated frequencies of the twin kilohertz quasi-periodic oscillations (kHz QPOs), their correlations and distributions. We found that the frequency separation of the kHz QPO peaks appears not to be a constant, rather, it decreases with increasing inferred mass accretion rate. We show that the currently available data of Sco X-1 by Rossi X-ray Timing Explorer are inconsistent with the proposals of the beat model that the frequency separation is a constant. Our conclusions are consistent with those of some previous researchers and we discuss further implications for the kilohertz QPO models.

Large-scale silver nanowires with controlled aspect ratio were synthesized via reducing silver nitrate with 1, 2-propanediol in the presence of poly (vinyl pyrrolidone) (PVP). Scanning electron microscopy, transmission electron microscopy and x-ray powder diffraction were employed to characterize these silver nanowires. The diameter of the silver nanowires can be readily controlled in the range of 100 to 400 nm by varying the experimental conditions. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy results show that there exists no chemical bond between the silver and the nitrogen atoms. The interaction between PVP and silver nanowires is mainly through the oxygen atom in the carbonyl group.

In the framework of parallelism general relativity, the torsion axial-vector in the rotating gravitational field is studied in terms of the alternative Kerr tetrad. In the case of the weak field and slow rotation approximation, we obtain that the torsion axial-vector possesses the dipole-like structure. Furthermore, the effect of massive neutrino spin precession in this field is mentioned.

A model, without adjustable parameters, describing the size-dependent phonon frequency of semiconductor nanocrystals is established based on the size-dependent force constant and thus the size-dependent bond length and bond energy of nanocrystals. This model shows frequency shifts as the size of the crystals decreases. Our predictions agree with the results of experiments for the blue shift of TiO2 nanoparticles, Si and InP quantum dots. The model will be useful for understanding the origins of the phonon behaviour of nanocrystals and the effect of the thermodynamic parameters on the phonon frequency.

Monodispersive CoPt nanoparticles in sizes of about 2.2 nm are synthesized by superhydride reduction of CoCl2 and PtCl2 in diphenyl ether. The as-prepared nanoparticles show a chemically disordered A1 structure and are superparamagnetic. Thermal annealing transforms the A1 structure into chemically ordered L10 structure and the particles are ferromagnetic at room temperature.

The effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier is investigated theoretically and experimentally. The complex Ginzburg–Landau equation and adaptive split-step Fourier method are used to simulate the propagation of pulses with different pulse widths in the fiber amplifier, and the results show that a longer pulse is more profitable in near-infrared supercontinuum generation if the central wavelength of the input laser lies in the normal dispersion region of the gain fiber. A four-stage master oscillator power amplifier configuration is adopted and the output spectra under picosecond and nanosecond input pulses are compared with each other. The experimental results are in good accordance with the simulations which can provide some guidance for further optimization of the system.