arXiv subjects

H. G. Wang

Publications and source records attributed to H. G. Wang.

47 records · Page 3Linked to original sources

arXiv2006

To Constrain the Parameter Space of the ICS Model

The pulse profile of pulsar gives geometric information about pulsar's radiation model. After investigating the pulse profiles of PSR B1642-03 and PSR B0950+08, we calculate the ratios of beam width and the emission height between different frequencies. We find that the ratios are almost constants as inclination angle $α$ changes from $0^{\circ}$ to $90^{\circ}$. The ratios can be used to test pulsar's radiation model. In particular it can well constrain the parameter space of the inverse Compton scattering (ICS) model. These constrained parameters indicate some physical implication for the ICS model.

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arXiv2006

Optical Photometrical Observations and Variability for Quasar 4C 29.45

We reported the result of long term optical variability of the blazar 4C 29.45 (QSO 1156+295, Ton 599), carried out optical photometric observations in Johnson V, Cousins RI passbands during April 1997 to March 2002 using the 1.56 meter telescope of the Shanghai Astronomical Observatory (SHAO) at Sheshan, China, compiled the post-1974 optical photometric data of the blazar by combining our new observations with the published optical data, and found maximum variations in different passbands: $Δ$U = 4.41 mag, $Δ$B = 5.55 mag, $Δ$V = 4.53 mag, $Δ$R = 5.80 mag, and $Δ$I = 5.34 mag. The average color indices are: U$-$B = $-0.54\pm$0.18 mag, B$-$V = 0.56$\pm$0.21 mag, B$-$R = 0.93$\pm$0.18 mag, B$-$I = 1.51$\pm$0.24 mag, V$-$R = 0.44$\pm$0.15 mag and V$-$I = 1.03$\pm$0.23 mag. The post-1974 data give us an excellent opportunity to search for the existence of possible periodicity in the light curve. In search for periodicity in the R passband light curve, we performed Jurkevich test and power spectral (Fourier) analysis methods, and CLEANest algorithms to remove false signals. We found possible periods of 3.55 and 1.58 years. The possible mechanism for the periodic variability was discussed.

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arXiv2004

A model for the challenging "bi-drifting" phenomenon in PSR J0815+09

A new drifting pulsar, PSR J0815+09, was discovered in the Arecibo drift-scan searches. An intriguing feature of this source is that within the four pulse components in the integrated pulse profile, the sub-pulse drifting direction in the two leading components is opposite from that in the two trailing components. In view that the leading theoretical model for pulsar sub-pulse drifting can only interpret one-direction sub-pulse drifting, the observed "bi-drifting" phenomenon from PSR J0815+09 poses a great challenge to the pulsar theory. The inner annular gap (IAG), a new type of inner particle accelerator, was recently proposed to explain both $γ$-ray and radio emission from pulsars. Here we show that the coexistence of the IAG and the conventional inner core gap (ICG) offers a natural interpretation to the bi-drifting phenomenon. In particular, the peculiar drifting behavior in PSR J0815+09 can be reproduced within the inverse Compton scattering (ICS) model for pulsar radio emission.

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arXiv2004

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 $γ$-ray emission beams of Crab-like, Vela-like and Geminga-like, can be reproduced by 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 inner annular gap (or cap) is sparking (or free flow) depends on the surface binding energy of the pulsar. In stead 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 ($\vecΩ\cdot \vec{B}<0$) and anti-pulsars ($\vecΩ\cdot \vec{B}>0$).

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arXiv2003

An accretion disk model for periodic timing variations of pulsars

The long-term, highly periodic and correlated variations in both the pulse shape and the rate of slow-down of two isolated pulsars (PSRs) PSR B1828-11 and PSR B1642-03 were discovered recently. This phenomenon may provide evidence for "free precession" as suggested in the literature. Some authors presented various kinds of models to explain this phenomenon within the framework of free precession. Here we present an accretion disk model for this precession phenomenon instead. Under reasonable parameters, the observed phenomenon can be explained by an isolated pulsar with a fossil disk. This may link radio pulsars and anomalous X-ray pulsars (AXPs) and present an indirect evidence for the existence of the fossil disk in nature.

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arXiv2003

A Joint model for radio and gamma-ray emission from pulsars

Although pulsars can radiate electromagnetic wave from radio to gamma ray bands, we still have no a united model to understand the multi-band emission. In this paper the effort for a joint model is presented. The inverse Compton scattering (ICS) and a second acceleration process near the null charge surface are involved to account for the radio and the gama-ray emission, respectively. Various kind of pulse profiles and other observational properties can be reproduced.

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arXiv2003

Radio and gamma-ray emission from pulsars

The radiation of pulsars have been observed for many years. A few pulsars are discovered to have both radio and gamma-ray emission. Many models on pulsar radiation have been developed, but so far we are still lacking an elaborate model which can explain the emission from radio to gamma-rays in detail. In this paper we present a joint model for radio and gamma-ray emission, in which both the dominate emission mechanisms are inverse Compton scattering. The pulse profiles at radio and gamma-ray bands are reproduced for the Crab-like, Vela-like and Geminga-like pulsars, in good agreement with observations.

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arXiv2002

A note on the discovery of absorption features in 1E 1207.4-5209

In a paper by Sanwal et al. (2002), it is supposed to be very difficult to interpret the absorption features in term of cyclotron lines. However, we would like to address here that the possibility of the absorption being cyclotron resonance can not be ruled out.We propose that the isolate neutron star, 1E 1207.4-5209 in the center of supernova remnant PKS 1209-51/52, has a debris disk and is in a propeller phase, with an accretion rate 6x10^{-11} M_solar/year.

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arXiv2002

Possible evidence for the pulsed X-ray emission from outer gap in PSR B1937+21?

The fastest millisecond pulsar PSR B1937+21 presents an interpulse separated from the main pulse by nealy 180^o at radio frequencies. Recently, the ASCA observations (Takahashi et al. 2001) detected pulsed X-ray emission from this pulsar. Only a single narrow X-ray pulse is observed, which is coincident with the radio interpulse in phase. We investigate the possible origin of the pulsed X-rays from the polar cap (PC) accelerators or the outer gap (OG) accelerators in the frame of PC model and OG model, respectively, by assuming a dipolar magnetic field structure and the same radio emission pattern from its poles for the pulsar. The OG model can naturally explain the main observational facts. For the PC model, the coincidence between the X-ray pulse and the radio interpulse can not be reproduced in the assumed case. However when considering possible deviation from our assumption, PC model may still be valid for this pulsar in some cases.

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arXiv2002

How fast could a proto-pulsar rotate?

According to two estimated relations between the initial period and the dynamo-generated magnetic dipole field of pulsars, we calculate the statistical distributions of pulsar initial periods. It is found that proto-pulsars are very likely to have rotation periods between 20 and 30 ms, and that most of the pulsars rotate initially at a period < 60 ms.

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arXiv2001

Energy Loss of Particles in Pulsar Radio Emission Region

Extremely relativistic particles play an important role in various radiative mechanisms of pulsar radio as well as high-energy emission. It is thus very essential to estimate the Lorentz factor of these particles in the radiation regions both observationally and theoretically. In this paper, according to the frequency dependence of component separation and considering some radiation processes, we obtain the Lorentz factor and its variation in the radiation region observationally for seven multi-frequency observed pulsars. It is found that the Lorentz factor decays substantially in the emission region, and the decay can not be well understood by all known energy loss processes. This result hints that there are some unknown processes which are responsible to loosing energy effectively.

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