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1.
本文讨论了光线的狭义相对论性偏折、光行时间差和磁场拖曳对脉冲到达相位的综合影响。在辐射束中的核、内锥以及外锥的辐射高度有差别时,观测得到的平均脉冲中的各个成份的位置也会发生改变,导致平均脉冲的不对称。分析了脉冲星ＰＳＲ１４５１６８ 和ＰＳＲＪ０４３７４７１５ 资料,发现它们的平均脉冲属于两种不同的不对称性。用相位综合漂移理论解释了这两种不对称性。  相似文献   

2.
It is of great importance to study pulsar beam shape if we are concerned with emission theories and pulsar birth rate.Both observations and the ICS model show that different emission components are emitted from different heights.The relative longitude phase shifts due to different heights of the emission components and the toridal velocity of the electrons are considered in this paper.Several pos-sible observational effects arising from the phase shift are presented.The emission beams may not have circular cross section although the emission region may be symmetric with respect to the magnetic axis.  相似文献   

3.
Based on dividing the profile into a number of absolute phase intervals,the phase-resolved spectra (PHRS) are derived from published time-aligned average profiles at radio frequencies over two decades for the classic conal-double pulsar B1133 16. The relative spectral index,defined as the difference between the spectral indices of a reference and the given arbitrary phase interval,is obtained by power-law fit at each phase interval. The derived phase-resolved spectra show an "M-like" shape,of which the leading part and trailing part are approximately symmetrical. The basic feature of the PHRS is that the spectrum first flat-tens then steepens as the pulse phase sweeps from the profile center to the profile edges. The PHRS provide a coherent explanation of the major features of profile evolution of B1133 16,namely,the pulse width shrinkage with increasing frequency and the frequency evolution of the relative intensity between the leading and trailing conal components,and the bridge emission. The PHRS may be an indicator for emission spectral variation across the pulsar magnetosphere. Possible mapping from PHRS to emission-location-dependent spectral vari-ation is presented,and some intrinsic mechanisms are discussed.  相似文献   

4.
The induced Compton scattering of radio emission off the particles of the ultrarelativistic electron–positron plasma in the open field line tube of a pulsar is considered. We examine the scattering of a bright narrow radio beam into the background over a wide solid angle and specifically study the scattering in the transverse regime, which holds in a moderately strong magnetic field and gives rise to the scattered component nearly antiparallel to the streaming velocity of the scattering particles. Making use of the angular distribution of the scattered intensity and taking into account the effect of rotational aberration in the scattering region, we simulate the profiles of the backscattered components as applied to the Crab pulsar. It is suggested that the interpulse (IP), the high-frequency interpulse (IP') and the pair of so-called high-frequency components (HFC1 and HFC2) result from the backward scattering of the main pulse (MP), precursor (PR) and low-frequency component (LFC), respectively. The components of the high-frequency profiles, the IP' and HFCs, are interpreted for the first time. The HFC1 and HFC2 are argued to be a single component split by the rotational aberration close to the light cylinder. It is demonstrated that the observed spectral and polarization properties of the profile components of the Crab pulsar as well as the giant pulse phenomenon outside the MP can be explained in terms of our model.  相似文献   

5.
We have investigated the Quasi Periodic Oscillation (QPO) properties of the transient accreting X-ray pulsar XTE J1858 + 034 during the second outburst of this source in April–May 2004. We have used observations made with the Proportional Counter Array (PCA) of the Rossi X-ray Timing Explorer (RXTE) during May 14–18, 2004, in the declining phase of the outburst. We detected the presence of low frequency QPOs in the frequency range of 140–185 mHz in all the RXTE-PCA observations. We report evolution of the QPO parameters with the time, X-ray flux, and X-ray photon energy. Though a correlation between the QPO centroid frequency and the instantaneous X-ray flux is not very clear from the data, we point out that the QPO frequency and the one day averaged X-ray flux decreased with time during these observations. We have obtained a clear energy dependence of the RMS variation in the QPOs, increasing from about 3% at 3 keV to 6% at 25 keV. The X-ray pulse profile is a single peaked sinusoidal, with pulse fraction increasing from 20% at 3 keV to 45% at 30keV. We found that, similar to the previous outburst, the energy spectrum is well fitted with a model consisting of a cut-off power law along with an iron emission line.  相似文献   

6.
We report on 685-MHz observations of PSR J1823–3021A using the Parkes radio telescope. A total of 120 giant pulses (GPs) were found by searching for spiky emission at 16-μs time resolution. The energies of these pulses follow a power law that has a very steep exponent of −3.1. This means that the emission mechanism that gives rise to the GPs almost always produces pulses that only have moderate energies. The profile formed by adding all the GPs has components that are narrower and more widely separated than the profile formed from all pulses. Aberration and retardation of emission from a corotating volume mean that components emitted at high altitude will have asymmetric phases compared to those emitted at low altitude. By assuming that the components of the pulse profile form conal pairs, we use this effect to limit the GPs to be emitted no higher than 4 km above ordinary emission. The arrival times of the GPs are well modelled by Poisson statistics at time-scales around 100 s. We report a GP with spikes of emission at the phases of both components. The probability of two independent GPs occurring within a single pulse period is     , so an interpretation can be conjectured that the two pulses are not independent. This may mean that the magnetosphere can remain in a state that is susceptible to discrete 'giant' emission events for as long as 2 ms.  相似文献   

7.
Observations of mean or average pulse profiles and their polarization give us much information on the shape of pulsar beams. The observed polarization variations, profile symmetry and frequency dependence of profile shape strongly suggest that the emission beam is conical and emitted from the vicinity of a magnetic pole. Central and outer parts of the beam have somewhat different properties, but the evidence is that they are emitted by the same basic mechanism. Recent observations suggest that the highly polarized pulse components seen in young pulsars may be emitted at a large angle to the magnetic axis.  相似文献   

8.
We update the systematic studies of circular polarization in integrated pulse profiles by Han et al. Data of circular polarization profiles are compiled. Sense reversals can occur in core or cone components, or near the intersection between components. The correlation between the sense of circular polarization and the sense of position angle variation for conal-double pulsars is confirmed with a much large database. Circular polarization of some pulsars has clear changes with frequency. Circular polarization of millisecond pulsars is marginally different from that of normal pulsars.  相似文献   

9.
The magnetospheric locations of pulsar radio emission region are not well known. The actual form of the so-called radius-to-frequency mapping should be reflected in the aberration–retardation (A/R) effects that shift and/or delay the photons depending on the emission height in the magnetosphere. Recent studies suggest that in a handful of pulsars the A/R effect can be discerned with respect to the peak of the central core emission region. To verify these effects in an ensemble of pulsars, we launched a project analysing multifrequency total intensity pulsar profiles obtained from the new observations from the Giant Meterwave Radio Telescope (GMRT), Arecibo Observatory (AO) and archival European Pulsar Network (EPN) data. For all these profiles, we measure the shift of the outer cone components with respect to the core component, which is necessary for establishing the A/R effect. Within our sample of 23 pulsars, seven show the A/R effects, 12 of them (doubtful cases) show a tendency towards this effect, while the remaining four are obvious counterexamples. The counterexamples and doubtful cases may arise from uncertainties in the determination of the location of the meridional plane and/or the core emission component. Hence, it appears that the A/R effects are likely to operate in most pulsars from our sample. We conclude that in cases where those effects are present the core emission has to originate below the conal emission region.  相似文献   

10.
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 wavelengths, 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.  相似文献   

11.
New Giant Metre-Wave Radio Telescope (GMRT) observations of the five-component pulsar B1857−26 provide detailed insight into its pulse-sequence modulation phenomena for the first time. The outer conal components exhibit a 7.4-rotation period, longitude-stationary modulation. Several lines of evidence indicate a carousel circulation time     of about 147 stellar rotations, characteristic of a pattern with 20 beamlets. The pulsar nulls some 20 per cent of the time, usually for only a single pulse, and these nulls show no discernible order or periodicity. Finally, the pulsar's polarization-angle traverse raises interesting issues: if most of its emission comprises a single polarization mode, the full traverse exceeds 180°; or if both polarization modes are present, then the leading and the trailing halves of the profiles exhibit two different modes. In either case, the rotating-vector model fails to fit the polarization-angle traverse of the core component.  相似文献   

12.
The inner vacuum gap model has become the foundation stone of most theories on pulsar radio emission. The fundamental picture of this model is the sparking, which was conjectured to be induced by magnetic absorption of background gamma photons. However, a question is, can the sparking be triggered in the millisecond pulsars (MSPs) with magnetic fields (B) only about 108 G? We investigate this problem by including the pair production above the inner gap. Under the assumption that the magnetic field is dipolar, our results show the background gamma-ray emission can not be the key factor that triggers the sparking, at least not in MSPs with B - 108 G, if the temperature in the polar cap region is only so high as is observed (< 4 × 106 K). Some other mechanisms are required.  相似文献   

13.
We present polarization profiles at 1.4 and 3.1 GHz for 14 young pulsars with characteristic ages less than 75 kyr. Careful calibration ensures that the absolute position angle of the linearly polarized radiation at the pulsar is obtained. In combination with previously published data, we draw three main conclusions about the pulse profiles of young pulsars. (i) Pulse profiles are simple and consist of either one or two prominent components. (ii) The linearly polarized fraction is nearly always in excess of 70 per cent. (iii) In profiles with two components, the trailing component nearly always dominates, only the trailing component shows circular polarization and the position angle swing is generally flat across the leading component and steep across the trailing component.
Based on these results, we can make the following generalizations about the emission beams of young pulsars. (i) There is a single, relatively wide cone of emission from near the last open field lines. (ii) Core emission is absent or rather weak. (iii) The height of the emission is between 1 and 10 per cent of the light cylinder radius.  相似文献   

14.
We present a calculation of a three-dimensional pulsar magnetosphere model to explain high-energy emission from the Geminga pulsar with a thick outer gap. High-energy γ -rays are produced by primary accelerated particles with a power-law energy distribution through curvature radiation inside the outer gap. We also calculate the emission pattern, pulse profile and phase-resolved spectra of high-energy γ -rays of the Geminga pulsar, and find that its pulse profile is consistent with the observed one if the magnetic inclination and viewing angle are ∼50° and ∼86° respectively. We describe the relative phases among soft (thermal) X-rays, hard (non-thermal) X-rays, and γ -rays. Our results indicate that X-ray and γ -ray emission from the Geminga pulsar may be explained by the single thick outer gap model. Finally, we discuss the implications of the radio and optical emission of the Geminga pulsar.  相似文献   

15.
Radio-quiet γ-ray pulsars like Geminga may account for a number of the unidentified EGRET sources in the Galaxy. The number of Geminga-like pulsars is very sensitive to the geometry of both the γ-ray and radio beams. Recent studies of the shape and polarization of pulse profiles of young radio pulsars have provided evidence that their radio emission originates in wide cone beams at altitudes that are a significant fraction (1–10%) of their light cylinder radius. Such wide radio emission beams will be visible at a much larger range of observer angles than the narrow core components thought to originate at lower altitude. Using 3D geometrical modeling that includes relativistic effects from pulsar rotation, we study the visibility of such radio cone beams as well as that of the γ-ray beams predicted by slot gap and outer gap models. From the results of this study, one can obtain revised predictions for the fraction of Geminga-like, radio quiet pulsars present in the γ-ray pulsar population.   相似文献   

16.
We show that the proportionately spaced emission bands in the dynamic spectrum of the Crab pulsar fit the oscillations of the square of a Bessel function whose argument exceeds its order. This function has already been encountered in the analysis of the emission from a polarization current with a superluminal distribution pattern: a current whose distribution pattern rotates (with an angular frequency ω) and oscillates (with a frequency  Ω > ω  differing from an integral multiple of ω) at the same time. Using the results of our earlier analysis, we find that the dependence on frequency of the spacing and width of the observed emission bands can be quantitatively accounted for by an appropriate choice of the value of the single free parameter  Ω/ω  . In addition, the value of this parameter, thus implied by Hankins & Eilek's data, places the last peak in the amplitude of the oscillating Bessel function in question at a frequency  (∼Ω3/ω2)  that agrees with the position of the observed ultraviolet peak in the spectrum of the Crab pulsar. We also show how the suppression of the emission bands by the interference of the contributions from differing polarizations can account for the differences in the time and frequency signatures of the interpulse and the main pulse in the Crab pulsar. Finally, we put the emission bands in the context of the observed continuum spectrum of the Crab pulsar by fitting this broad-band spectrum (over 16 orders of magnitude of frequency) with that generated by an electric current with a superluminally rotating distribution pattern.  相似文献   

17.
The shape of pulsar radio beams   总被引：1，自引：0，他引：1  
Using all available multicomponent radio pulse profiles for pulsars with medium to long periods and good polarization data, we have constructed a two-dimensional image of the mean radio beam shape. This shows a peak near the centre of the beam but is otherwise relatively uniform with only mild enhancements in a few regions. This result supports the patchy beam model for emission beams, in which the mean beam shape represents the properties of the emission mechanism and observed pulse components result from emission sources distributed randomly across the beam.  相似文献   

18.
研究了高斯辐射成分在可视点所画出轨迹上的分布,这个可视点因脉冲星的转动而作非匀速度运动.通过假设辐射区域围绕磁轴均匀分布,一个高斯辐射成分便对应于可视轨迹划过的一个辐射区域.因为演示辐射区域在可视轨迹上是不均匀的分布,因此高斯成分沿轨迹也是不均匀的,而高斯成分的密度在磁轴与视线距离最近时为最大.高斯成分的分布取决于脉冲星的两个角度:旋转轴和视线之间的夹角,以及磁轴和旋转轴之间的倾角.基于此模型,一个脉冲星平均轮廓中观察到的多个高斯成分便对应于可视轨迹在特定的转动相位范围内的辐射区域.演示了脉冲星旋转的近侧和远侧的相位,分别对应的主脉冲和中间脉冲,两者高斯成分的数量和分布是不同的.而且还发现,沿可视轨迹上的辐射区域总数与围绕磁轴的辐射区域的总数是不同,并且预测的辐射区域数目会因忽略可见点的运动而明显不同.拟合表明脉冲星轮廓的高斯成分的形状和数量可能与实际构成轮廓的成分的形状和数量不同.以PSR B0826–34的辐射为例,并假设辐射来自单一磁极.  相似文献   

19.
Pulsar B1929+10 is remarkable on a number of grounds. Its narrow primary components exhibit virtually complete and highly stable linear polarisation, which can be detected over most of its rotation cycle. Various workers have been lured by the unprecedented range over which its linear polarisation angle can be determined, and more attempts have been made to model its emission geometry than perhaps for any other pulsar. Paradoxically, there is compelling evidence to interpret the pulsar’s emission geometryboth in terms of an aligned configuration whereby its observed radiation comes from a single magnetic-polar emission regionand in terms of a nearly orthogonal configuration in which we receive emission from regions near each of its two poles. Pulsar 1929+10 thus provides a fascinating context in which to probe the conflict between these lines of interpretation in an effort to deepen our understanding of pulsar radio emission. Least-squares fits to the polarisation-angle traverse fit poorly near the main pulse and interpulse and have an inflection point far from the centre of the main pulse. This and a number of other circumstances suggest that the position-angle traverse is an unreliable indicator of the geometry in this pulsar, possibly in part because its low level ‘pedestal’ emission makes it impossible to properly calibrate a Polarimeter which correlates orthogonal circular polarisations. Taking the interpulse and main-pulse comp. II widths as indicators of the magnetic latitude, it appears that pulsar 1929+10 has anα value near 90‡ and thus has a two-pole interpulse geometry. This line of interpretation leads to interesting and consistent results regarding the geometry of the conal components. Features corresponding to both an inner and outer cone are identified. In addition, it appears that pulsar 1929+10–and a few other stars–have what we are forced to identify as a ‘furtherin’ cone, with a conal emission radius of about2.3‡/P 1/2 Secondarily, 1929+10’s nearly complete linear polarisation provides an ideal opportunity to study how mechanisms of depolarisation function on a pulse-to-pulse basis. Secondary-polarisation-mode emission appears in significant proportion only in some limited ranges of longitude, and the subsequent depolarization is studied using different mode-separation techniques. The characteristics of the two polarisation modes are particularly interesting, both because the primary mode usually dominates the secondary so completely and because the structure seen in the secondary mode appears to bear importantly on the question of the pulsar’s basic emission geometry. New secondary-mode features are detected in the average profile of this pulsar which appear independent of the main-pulse component structure and which apparently constitute displaced modal emission. Individual pulses during which the secondary-mode dominates the primary one are found to be considerably more intense than the others and largely depolarised. Monte-Carlo modeling of the mode mixing in this region, near the boundary of comps. II and III, indicates that the incoherent interference of two fully and orthogonally polarised modes can adequately account for the observed depolarisation. The amplitude distributions of the two polarisation modes are both quite steady: the primary polarisation mode is well fitted by a χ2 distribution with about nine degrees of freedom; whereas the secondary mode requires a more intense distribution which is constant, but sporadic.  相似文献   

20.
徐钧  韩金林  王陈 《天文学报》2011,52(3):180-189
脉冲宽度的测量方法有几种.最常用的脉冲宽度有Wpp（两峰值点的间距）、W50（最高峰值强度50%处的宽度）和W10（最高峰值强度10%处的宽度）.另外,还有测量两个最外成分各自强度50%处的宽度Wc50和各自强度10%处的宽度Wc10.利用16颗双锥峰脉冲星和7颗核锥三峰脉冲星样本在1.4 GHz的脉冲轮廓数据,测量了5种脉冲宽度.利用有磁倾角α和撞击角β数据的脉冲星,导出了对应的辐射束半径ρ,并验证其与脉冲星周期P之间的关系ρ∝P-0.5.通过比较5种脉冲宽度导出的ρ与P关系的好坏,发现最外成分之间的宽度比前面3种宽度更好,其中Wc50宽度得出的相关关系最好.由此认为Wc50是最能反映辐射束宽度的测量值.还讨论了脉冲轮廓的对称性,发现后随的锥辐射成分与先导的锥辐射成分相比,更靠近核心辐射成分,两个锥辐射成分的宽度在统计上基本相同.  相似文献   

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