H. G. Wang

Radio variability properties for radio sources

In this paper, we used the database of the university of Michigan Radio Astronomy Observatory (UMRAO) at three (4.8 GHz, 8.0 GHZ, and 14.5 GHz) radio frequency to analyze the radio light curves by the power spectral analysis method in search of possible periodicity. The analysis results showed that the radio sources display astrophysically meaningful periodicity ranging from 2.2 to 20.8 years in their light curves at the three frequencies. We also calculated the variability parameters and investigated the correlations between the variability parameter and the flux density. For the variability parameters, we found that the parameters at higher frequency are higher than those in the lower frequency. In addition, the variability parameters of BL Lacertae objects are larger than those of flat-spectrum radio quasars. suggesting that they are more variable than flat spectrum radio quasars.

The inner annular gap for pulsar radiation: gamma-ray and radio emission

The inner annular gap (IAG), a new type of inner gap whose magnetic field lines intersect the null charge surface (NCS), is proposed to explain γ-ray and radio emission from pulsars. The IAG can be an important source for high-energy particles. The particles can radiate between the NCS and the IAG. Some observational characteristics in both γ-ray and radio bands, such as the Crab-like, Vela-like, and Geminga-like γ-ray emission beams, can be reproduced by the numerical method. It is predicted that the view angle ζ should be larger than the inclination angle (ζ > α), otherwise the γ-ray radiation will have little possibility to be observed. Whether the IAG (or cap) is sparking (or free flow) depends on the surface binding energy of the pulsar. Instead of neutron star models, the scenario of the IAG is favorable for bare strange star models, because bare strange stars can easily satisfy the requisite condition to form an IAG for both pulsars (Ω 0).

A study of multifrequency polarization pulse profiles of millisecond pulsars

We present high signal-to-noise ratio, multifrequency polarization pulse profiles for 24 millisecond pulsars that are being observed as part of the Parkes Pulsar Timing Array project. The pulsars are observed in three bands, centred close to 730, 1400 and 3100 MHz, using a dual-band 10 cm/50 cm receiver and the central beam of the 20-cm multibeam receiver. Observations spanning approximately six years have been carefully calibrated and summed to produce high S/N profiles. This allows us to study the individual profile components and in particular how they evolve with frequency. We also identify previously undetected profile features. For many pulsars we show that pulsed emission extends across almost the entire pulse profile. The pulse component widths and component separations follow a complex evolution with frequency; in some cases these parameters increase and in other cases they decrease with increasing frequency. The evolution with frequency of the polarization properties of the profile is also non-trivial. We provide evidence that the pre- and post-cursors generally have higher fractional linear polarization than the main pulse. We have obtained the spectral index and rotation measure for each pulsar by fitting across all three observing bands. For the majority of pulsars, the spectra follow a single power-law and the position angles follow a lambda(2) relation, as expected. However, clear deviations are seen for some pulsars. We also present phase-resolved measurements of the spectral index, fractional linear polarization and rotation measure. All these properties are shown to vary systematically over the pulse profile.

Testing Pulsar Radiation Models Using an α-Weak-Dependent Altitude Ratio

It is found that pulsar radiation altitude ratios between different radio frequencies are weak-dependent on the inclination angle α. This is proved via series expansion techniques and illustrated by using pulsar examples of PSR B0329+54, B1508+55, B2016+28, B1133+16, and B2319+60. It is emphasized that this α-weak-dependent radiation altitude ratio offers a good tool to test pulsar radiation models. We use the measured altitude ratios to constrain the parameter space for the Ruderman-Sutherland model and the inverse Compton scattering model. It is found that the Ruderman-Sutherland model is not compatible with the measured altitude ratios, while the results are compatible with the inverse Compton scattering model. The potential possible applications of this method in studying pulsar timing and in studying pulsar high energy radiation are also discussed.

Pulsar kicks and γ-ray burst

The consistence of the distributions of pulsars kick velocities from the model of GRB and from the pulsar observations is tested based on the supernova-GRB (

Low bounds for pulsar γ‐ray radiation altitudes

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Interstellar Scintillation observations for PSR B0355+54

-ray burst) association and under the assumption that the GRB asymmetric explosions produce pulsars. The deduced distribution of kick velocity from the model of GRB and the observed kick distribution of radio pulsars are checked by K-S test. These two distributions are found to come from a same parent population. This result may indicate that GRBs could be really related to supernova, and that the asymmetry of GRB associated with supernova would cause the kick of pulsars.

Low bounds for pulsar γ-ray radiation altitudes: Pulsar γ-ray radiation low bounds

Determining radiation location observationally plays a very important role in testing the pulsar radiation models. One-photon pair production in the strong magnetic field,

Radio Variability Properties of a Sample of 168 Radio Sources: Periodicity Analysis

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Inner Annular Gap and Related Topics

, is one of the important physical processes in pulsar radiation mechanisms. Photons near pulsar surface with sufficient energy will be absorbed in the magnetosphere and the absorption optical depth for these GeV