arXiv subjects

J. Wang

Publications and source records attributed to J. Wang.

At least 361 records · Page 20Linked to original sources

arXiv2012

Radio properties of H2O maser host galaxies

The 6 cm and 20 cm radio continuum properties of all 85 galaxies with reported 22 GHz H2O maser emission and luminosity distance D > 0.5 Mpc are studied. For the total of 55 targets for which both 6 cm and 20 cm measurements exist and for the subsample of 42 sources with masers related to active galactic nuclei (AGN), a spectral index could be determined from an assumed power-law dependence. The mean value of the resulting spectral index is in both cases 0.66+-0.07. Comparing radio properties of the maser galaxies with a sample of Seyferts without detected H2O maser, we find that (1) the spectral indices agree within the error limits, and (2) maser host galaxies have higher nuclear radio continuum luminosities, exceeding those of the comparison sample by factors of order 5. Only considering the subsample of galaxies with masers associated with AGN, there seems to be a trend toward rising maser luminosity with nuclear radio luminosity (both at 6 cm and 20 cm). However, when accounting for the Malmquist effect, the correlation weakens to a level, which is barely significant. Overall, the study indicates that nuclear radio luminosity is a suitable indicator to guide future AGN maser searches and to enhance detection rates, which are otherwise quite low (<10%).

astro-ph.CO↗

arXiv2012

Moderate Galaxy-Galaxy Lensing

We study moderate gravitational lensing where a background galaxy is magnified substantially, but not multiply imaged, by an intervening galaxy. We focus on the case where both the lens and source are elliptical galaxies. The signatures of moderate lensing include isophotal distortions and systematic shifts in the fundamental plane and Kormendy relation, which can potentially be used to statistically determine the galaxy mass profiles. These effects are illustrated using Monte Carlo simulations of galaxy pairs where the foreground galaxy is modelled as a singular isothermal sphere model and observational parameters appropriate for the Large Synoptic Survey Telescope (LSST). The range in radius probed by moderate lensing will be larger than that by strong lensing, and is in the interesting regime where the density slope may be changing.

astro-ph.CO↗

arXiv2011

Reversible modulation and ultrafast dynamics of THz resonances in strongly photoexcited metamaterials

We demonstrate an ultrafast reversible modulation of resonant terahertz (THz) response in strongly photoexcited metamaterials. The transient spectral-temporal response of the dipole transition ~1.6 THz exhibits a distinct non-monotonic variation as a function of pump fluence. The transition energy shift, strength, spectral width and density-dependent ultrafast relaxation manifest a remarkable re-emergence of the resonances after initial quenching. Our simulation, incorporating the first-order diffraction from the photoinduced transient grating, reproduces the salient features, providing a new avenue for designing nonlinear and frequency-agile THz modulators.

cond-mat.mtrl-sci↗

arXiv2011

Coded Single-Tone Signaling and Its Application to Resource Coordination and Interference Management in Femtocell Networks

Resource coordination and interference management is the key to achieving the benefits of femtocell networks. Over-the-air signaling is one of the most effective means for distributed dynamic resource coordination and interference management. However, the design of this type of signal is challenging. In this paper, we address the challenges and propose an effective solution, referred to as coded single-tone signaling (STS). The proposed coded STS scheme possesses certain highly desirable properties, such as no dedicated resource requirement (no overhead), no near-and-far effect, no inter-signal interference (no multi-user interference), low peak-to-average power ratio (deep coverage). In addition, the proposed coded STS can fully exploit frequency diversity and provides a means for high quality wideband channel estimation. The coded STS design is demonstrated through a concrete numerical example. Performance of the proposed coded STS and its effect on cochannel traffic channels are evaluated through simulations.

cs.IT↗

arXiv2011

Dynamics of Fluctuations of Localized Waves

We follow the temporal evolution of mesoscopic intensity fluctuations and correlation in strongly localized samples. We find an initial burst in relative transmission fluctuations in random one dimensional (1D) samples due to fluctuations in the arrival time of ballistic transmission. Relative fluctuations subsequently rise, then drop to a minimum at a time t_m, after which they increase rapidly in 1D simulations and quasi-1D (Q1D) measurements. For t > 3t_m, results in 1D and Q1D samples converge towards predictions of a dynamic single parameter scaling model. These results reflect the changing number of modes participating appreciably in transmission as the impact of longer lived modes grows with time delay.

cond-mat.dis-nn↗

arXiv2011

Strong Response of the very broad h$β$ Emission Line in Luminous Radio-Quite Quasar pg1416-129

We report new spectroscopic observations performed in 2010 and 2011 for luminous radio-quite quasar PG 1416-129. Our new spectra with high quality cover both H$β$ and H$α$ regions, and show negligible line profile variation within a timescale of one year. The two spectra allow us to study the variability of the Balmer line profile by comparing the spectra with the previous ones taken at 10 and 20 years ago. By decomposing the broad Balmer emission lines into two Gaussian profiles, our spectral analysis suggests a strong response to the continuum level for the very broad component, and significant variations in both bulk blueshift velocity/FWHM and flux for the broad component. The new observations additionally indicate flat Balmer decrements (i.e., too strong H$β$ emission) at the line wings, which is hard to be reproduced by recent optically thin models. With these observations we argue that a separate inner optically thin emission-line region might not be necessary in the object to reproduce the observed line profiles.

astro-ph.CO↗

arXiv2011

Letter of Intent: The Hyper-Kamiokande Experiment --- Detector Design and Physics Potential ---

We propose the Hyper-Kamiokande (Hyper-K) detector as a next generation underground water Cherenkov detector. It will serve as a far detector of a long baseline neutrino oscillation experiment envisioned for the upgraded J-PARC, and as a detector capable of observing -- far beyond the sensitivity of the Super-Kamiokande (Super-K) detector -- proton decays, atmospheric neutrinos, and neutrinos from astronomical origins. The baseline design of Hyper-K is based on the highly successful Super-K, taking full advantage of a well-proven technology. (to be continued)

hep-ex↗

arXiv2011

Search for the Rare Decays KL->pi0pi0mu+mu- and KL->pi0pi0X0->pi0pi0mu+mu-

The KTeV E799 experiment has conducted a search for the rare decays KL->pi0pi0mu+mu- and KL->pi0pi0X0->pi0pi0mu+mu-, where the X0 is a possible new neutral boson that was reported by the HyperCP experiment with a mass of (214.3 pm 0.5) MeV/c^{2}. We find no evidence for either decay. We obtain upper limits of Br(KL->pi0pi0X0->pi0pi0mu+mu-) < 1.0 x 10^{-10} and Br(KL->pi0pi0mu+mu-) < 9.2 x 10^{-11} at the 90% confidence level. This result rules out the pseudoscalar X0 as an explanation of the HyperCP result under the scenario that the \bar{d}sX0 coupling is completely real.

hep-ex↗

arXiv2011

All-optical four-state magnetization reversal in (Ga,Mn)As ferromagnetic semiconductors

Using density matrix equations of motion and a tight-binding band calculation, we predict all-optical switching between four metastable magnetic states of (III,Mn)As ferromagnets. This switching is initiated non-thermally within 100fs, during nonlinear coherent photoexcitation. For a single optical pulse, magnetization reversal is completed after $\sim$100 ps and controlled by the coherent femtosecond photoexcitation. Our predicted switching comes from magnetic nonlinearities triggered by a femtosecond magnetization tilt that is sensitive to un--adiabatic light--induced spin interactions.

physics.optics↗

arXiv2011

Evolution of [OIII]5007 emission-line profiles in narrow emission-line galaxies

The AGN-host co-evolution issue is investigated here by focusing on the evolution of the [\ion{O}{3}]$\lambda5007$ emission-line profile. In order to simultaneously measure both [\ion{O}{3}] line profile and circumnuclear stellar population in individual spectrum, a large sample of narrow emission-line galaxies is selected from the MPA/JHU SDSS DR7 catalog. By requiring that 1) the [\ion{O}{3}] line signal-to-noise ratio is larger than 30, 2) the [\ion{O}{3}] line width is larger than the instrumental resolution by a factor of 2, our sample finally contains 2,333 Seyfert galaxies/LINERs (AGNs), 793 transition galaxies, and 190 starforming galaxies. In additional to the commonly used profile parameters (i.e., line centroid, relative velocity shift and velocity dispersion), two dimensionless shape parameters, skewness and kurtosis, are used to quantify the line shape deviation from a pure Gaussian function. We show that the transition galaxies are systematically associated with narrower line widths and weaker [\ion{O}{3}] broad wings than the AGNs, which implies that the kinematics of the emission-line gas is different in the two kinds of objects. By combining the measured host properties and line shape parameters, we find that the AGNs with stronger blue asymmetries tend to be associated with younger stellar populations. However, the similar trend is not identified in the transition galaxies. The failure is likely resulted from a selection effect in which the transition galaxies are systematically associated with younger stellar populations than the AGNs. The evolutionary significance revealed here suggests that both NLR kinematics and outflow feedback in AGNs co-evolve with their host galaxies.

astro-ph.CO↗

arXiv2011

Lunar Exosphere Influence on Lunar-based Near-ultraviolet Astronomical Observations

The potential effect of the lunar exosphere on the near-ultraviolet sky background emission is predicted for Lunar-based Ultraviolet Telescope (LUT: a funded Chinese scientific payload for the Chang'e-III mission). Using the upper limit on the OH concentration inferred from the recent MIP CHACE results, our calculations show that the sky brightness due to the illuminated exosphere is $<8.7\ \mathrm{photon\ s^{-1}\ cm^{-2}\ arcsec^{-2}}$ within the wavelength range 245-340 nm. By evaluating the signal-to-noise ratios of observations of an AB=13 mag point source at a series of sky background levels, our analysis indicates that the detection performance of LUT can be moderately degraded by the lunar exosphere emission in most cases. An AB=13 mag point source can still be detected by the telescope at a signal-to-noise ratio more than 8 when the OH concentration is less than $2\times10^8\ \mathrm{molecules\ cm^{-3}}$. However, the effect on the performance is considerable when the exosphere is as dense as suggested by CHACE.

astro-ph.EP↗

arXiv2011

Spectroscopic and Photometric Observations of Unidentified Ultraviolate Variable Objects in GUVV-2 Catalog

An NUV-optical diagram made for sources from the secend Galaxy Evolution Explorer (GALEX) Ultraviolet Variability (GUVV-2) Catalog provide us a method to tentatively classify the unknown GUVV2 sources by their NUV-optical magnitudes. On the purpose of testing the correctness and generality of the method, we carry out a program on the spectroscopic observations of the unidentified GUVV2 sources. The spectroscopic identification for these 37 sources are 19 type -A to -F stars, 10 type -G to -K stars and 7 M dwarf stars together with an AGN. We also present the light curves in R-band for two RR Lyrae star candidates selected from the NUV-optical diagram, both of which perform cyclic variations. Combining there light curves and colors, we classify them as RR Lyrae stars. To confirm the results, we shows a color-color diagram for the 37 newly spectroscopically identified objects compared with the previously identified ones, which manifests good consistence with our former results, indicating that the ultroviolet variable sources can be initially classified by their NUV/optical color-color diagram.

astro-ph.SR↗

arXiv2011

Gamma-ray Burst Prompt Emission: Jitter Radiation in Stochastic Magnetic Field Revisited

We revisit the radiation mechanism of relativistic electrons in the stochastic magnetic field and apply it to the high-energy emissions of gamma-ray bursts (GRBs). We confirm that jitter radiation is a possible explanation for GRB prompt emission in the condition of a large electron deflection angle. In the turbulent scenario, the radiative spectral property of GRB prompt emission is decided by the kinetic energy spectrum of turbulence. The intensity of the random and small-scale magnetic field is determined by the viscous scale of the turbulent eddy. The microphysical parameters $ε_e$ and $ε_B$ can be obtained. The acceleration and cooling timescales are estimated as well. Due to particle acceleration in magnetized filamentary turbulence, the maximum energy released from the relativistic electrons can reach a value of about $10^{14}$ eV. The GeV GRBs are possible sources of high-energy cosmic-ray.

astro-ph.HE↗

arXiv2011

Study of measured pulsar masses and their possible conclusions

We study the statistics of 61 measured masses of neutron stars (NSs) in binary pulsar systems, including 18 double NS (DNS) systems, 26 radio pulsars (10 in our Galaxy) with white dwarf (WD) companions, 3 NSs with main-sequence companions, 13 NSs in X-ray binaries, and one undetermined system. We derive a mean value of M = 1.46 +/- 0.30 solar masses. When the 46 NSs with measured spin periods are divided into two groups at 20 milliseconds, i.e., the millisecond pulsar (MSP) group and others, we find that their mass averages are, respectively, M=1.57 +/- 0.35 solar masses and M=1.37+/- 0.23 solar masses. In the framework of the pulsar recycling hypothesis, this suggests that an accretion of approximately 0.2 solar mass is sufficient to spin up a neutron star and place it in the millisecond pulsar group. An empirical relation between the accreting mass and MSP spin period is ΔM=0.43 (solar mass)(P/1 ms)^{-2/3}. UNlike the standard recycling process, if a MSP is formed by the accretion induced collapse (AIC) of a white dwarf with a mass less than Chandrasekha limit, e.g. 1.35 solar mass, then the binary MSPs involved in AICs is not be higher than 20%, which imposes a constraint on the AIC origin of MSPs.

astro-ph.HE↗

arXiv2011

A model for upper kHz QPO coherence of accreting neutron star

{We investigate the coherence of the twin kilohertz quasi-periodic oscillations (kHz QPOs) in the low-mass X-ray binary (LMXB) theoretically. The profile of upper kHz QPO, interpreted as Keplerian frequency, is ascribed to the radial extent of the kHz QPO emission region, associated with the transitional layer at the magnetosphere-disk boundary, which corresponds to the coherence of upper kHz QPO. The theoretical model for Q-factor of upper kHz QPO is applied to the observational data of five Atoll and five Z sources, and the consistence is implied.

astro-ph.HE↗

arXiv2010

Spin Period Evolution of Recycled Pulsar in Accreting Binary

We investigate the spin-period evolutions of recycled pulsars in binary accreting systems. Taking both the accretion induced field decay and spin-up into consideration, we calculate their spin-period evolutions influenced by the initial magnetic-field strengths, initial spin-periods and accretion rates, respectively. The results indicate that the minimum spin-period (or maximum spin frequency) of millisecond pulsar (MSP) is independent of the initial conditions and accretion rate when the neutron star (NS) accretes $\sim> 0.2\ms$. The accretion torque with the fastness parameter and gravitational wave (GW) radiation torque may be responsible for the formation of the minimum spin-period (maximum spin frequency). The fastest spin frequency (716 Hz) of MSP can be inferred to associate with a critical fastness parameter about $ω_{c}=0.55$. Furthermore, the comparisons with the observational data are presented in the field-period ($B-P$) diagram.

astro-ph.HE↗

arXiv2010

Gamma-Ray Burst Afterglows as Analogues of High Frequency-Peaked BL Lac Objects

The spectral properties from radio to optical bands are compared between the 18 optically bright Gamma-ray burst afterglows and well established power-spectrum sequence in Blazars. The comparison shows that the afterglows are well agreement with the well known Blazar sequence (i.e., the $νL_ν(\mathrm{5GHz})$-$α_{\mathrm{RO}}$ correlation, where $α_{\mathrm{RO}}$ is the broad-band spectral slope from radio to optical bands). The afterglows are, however, clustered at the low luminosity end of the sequence, which is typically occupied by high frequency-peaked BL Lac objects. The correlation suggests that Gamma-ray burst afterglows share the similar emission process with high frequency-peaked BL Lac objects. We further identify a deviation at a significance level larger than 2$σ$ from the sequence for three typical optically "dark" bursts. The deviation favors a heavy extinction in optical bands for the "dark" bursts. The extinction $A_V$ is estimated to be larger than 0.5-0.6 magnitude from the $νL_ν(\mathrm{5GHz})$-$α_{\mathrm{RO}}$ sequence.

astro-ph.CO↗

arXiv2010

Precise Measurements of Direct CP Violation, CPT Symmetry, and Other Parameters in the Neutral Kaon System

We present precise tests of CP and CPT symmetry based on the full dataset of K to pipi decays collected by the KTeV experiment at Fermi National Accelerator Laboratory during 1996, 1997, and 1999. This dataset contains 16 million K to 2pi0 and 69 million K to pi+pi- decays. We measure the direct CP violation parameter Re(epsilon'/epsilon) = (19.2 pm 2.1)x10-4. We find the KL-KS mass difference Deltam = (5270 pm 12)x10^6 hbar/s and the KS lifetime tauS = (89.62 pm 0.05)x10-12 s. We also measure several parameters that test CPT invariance. We find the difference between the phase of the indirect CP violation parameter, epsilon, and the superweak phase, phi_epsilon - phi_SW = (0.40 pm 0.56) degrees. We measure the difference of the relative phases between the CP violating and CP conserving decay amplitudes for K to pi+pi- (phi+-) and for K to 2pi0 (phi00), Delta phi = (0.30 pm 0.35) degrees. From these phase measurements, we place a limit on the mass difference between K0 and K0bar, DeltaM < 4.8 x 10-19 GeV/c^2 at 95% C.L. These results are consistent with those of other experiments, our own earlier measurements, and CPT symmetry.

hep-ex↗