arXiv subjects

G. J. Qiao

Publications and source records attributed to G. J. Qiao.

59 records · Page 4Linked to original sources

arXiv1998

A strange star model for GRO J1744-28

A model is suggested for the bursting x-ray pulsar, GRO J1744-28, where the compact object of the pulsar is proposed to be a strange matter star with crusts. It is suggested that two envelope crusts shield the two polar caps of an accreting strange stars owing to strong polar-cap magnetic fields. GRO J1744-28 might not have a unified crust, but two polar crusts. Bursts are the result of phase transition of polar crusts if one accreting crust is heavier than that the Coulomb force can support. It is shown that there should be phase-lags when bursting crust is expanded about one hundred meters. Many calculated properties of this model, such as the phase-lags, the bursting luminosity and the characteristic photon energy, are in agreement with observations.

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arXiv1998

Circular polarization in pulsar integrated profiles

We present a systematic study of the circular polarization in pulsar integrated profiles, based on published polarization data. For core components, we find no significant correlation between the sense-change of circular polarization and the sense of linear position angle variation. Circular polarization is not restricted to core components and, in some cases, reversals of circular polarization sense are observed across the conal emission. In conal double profiles, the sense of circular polarization is found to be correlated with the sense of position-angle variation. Pulsars with a high degree of linear polarization often have one hand of circular polarization across the whole profile. For most pulsars, the sign of circular polarization is the same at 50-cm and 20-cm wavelength, and the degree of polarization is similar, albeit with a wide scatter. However, at least two cases of frequency-dependent sign reversals are known. This diverse behaviour may require more than one mechanism to generate circular polarization.

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arXiv1998

Two-photon annihilation in the pair formation cascades in pulsar polar caps

The importance of the photon-photon pair production process ($γ+ γ^{\prime}\to e^{+}+e^{-}$) to form pair production cascades in pulsar polar caps is investigated within the framework of the Ruderman-Sutherland vacuum gap model. It is found that this process is unimportant if the polar caps are not hot enough, but will play a non-negligible role in the pair formation cascades when the polar cap temperatures are in excess of the critical temperatures, $T_{cri}$, which are around $4\times 10^6K$ when $P=0.1$s and will slowly increase with increasing periods. Compared with the $γ-B$ process, it is found that the two-photon annihilation process may ignite a central spark near the magnetic pole, where $γ-B$ sparks can not be formed due to the local weak curvatures. This central spark is large if the gap is dominated by the ``resonant ICS mode''. The possible connection of these central sparks with the observed pulsar ``core'' emission components is discussed.

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arXiv1998

Is Gamma-ray Absorption by Induced Electric Fields Important in the Pulsar Magnetospheres?

Although the unified formula for gamma-ray absorption process involving both the magnetic field and a perpendicular electric field derived by Daugherty & Lerche (1975) is correct, we argued in this paper that their conclusion that the induced electric fields are important in the pair formation process in the pulsar magnetospheres is wrong and misleading. The key point is that usually the direction of a gamma photon at the emission point observed in the laboratory frame should be (v/c, 0, [1-(v/c)^2]^{1/2}) rather than (0, 0, 1), where v is the co-rotating velocity. This emission direction is just the one which results in zero attenuation coefficient of the gamma photon. Calculation shows that after the photon has moved a distance, its direction lead to the result that the induced electric field is also of minor importance. Thus only gamma-B process is the important mechanism for the pair production in the pulsar magnetospheres. The implications of the modification by ejecting the induced electric field are also discussed.

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arXiv1997

An inverse Compton scattering (ICS) model of pulsar emission

Core and conal emission beams of radio pulsars have been identified observationally (Rankin 1983,1993; Lyne and Manchester 1988), In the inner gap model (Ruderman and Sutherland 1975, hereafter RS75), the gap continually breaks down (sparking) by forming electron-positron pairs on a time scale of a few microseconds (RS75). This makes a large amplitude low frequency wave to be produced and which would be scattered by relativistic particles moving out from the gap. Under this assumption, Qiao (1988a,1992) presented an Inverse Compton Scattering (ICS) model for both core and conal emissions. This paper presented a development of the model. Retardation and aberration effects due to different radiation components emitted from different heights are considered. The luminosity of pulsar radio emission via the ICS process is discussed. Coherent emission by bunches of particles is adopted and which is adequate to explain pulsar radiation. The theoretical results are in agreement with observations very well.

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