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1.
Using the standard equation for the slowdown of a neutron star, we derive a formula for the braking index via integration rather than the conventional differentiation. The new formula negates the need to measure the second time derivative of the rotation frequency, ν¨ . We show that the method gives similar braking indices for PSR B1509−58 and the Crab pulsar to those already in the literature. We point out that our method is useful for obtaining the braking indices of moderate-aged pulsars without the need for long, phase-connected timing solutions. We applied the method to 20 pulsars and discuss the implications of the results. We find that virtually all the derived braking indices are dominated by the effects of (unseen) glitches, the recovery from which corrupts the value of ν˙ . However, any real, large, positive braking index has implications for magnetic field decay and offers support to recent models of pulsar evolution.  相似文献   

2.
We present the discovery and follow-up observations of 142 pulsars found in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. These new discoveries bring the total number of pulsars found by the survey to 742. In addition to tabulating spin and astrometric parameters, along with pulse width and flux density information, we present orbital characteristics for 13 binary pulsars which form part of the new sample. Combining these results from another recent Parkes multibeam survey at high Galactic latitudes, we have a sample of 1008 normal pulsars which we use to carry out a determination of their Galactic distribution and birth rate. We infer a total Galactic population of  30 000 ± 1100  potentially detectable pulsars (i.e. those beaming towards us) having 1.4-GHz luminosities above 0.1 mJy kpc2. Adopting the Tauris & Manchester beaming model, this translates to a total of  155 000 ± 6000  active radio pulsars in the Galaxy above this luminosity limit. Using a pulsar current analysis, we derive the birth rate of this population to be  1.4 ± 0.2  pulsars per century. An important conclusion from our work is that the inferred radial density function of pulsars depends strongly on the assumed distribution of free electrons in the Galaxy. As a result, any analyses using the most recent electron model of Cordes & Lazio predict a dearth of pulsars in the inner Galaxy. We show that this model can also bias the inferred pulsar scaleheight with respect to the Galactic plane. Combining our results with other Parkes multibeam surveys we find that the population is best described by an exponential distribution with a scaleheight of 330 pc. Surveys underway at Parkes and Arecibo are expected to improve the knowledge of the radial distribution outside the solar circle, and to discover several hundred new pulsars in the inner Galaxy.  相似文献   

3.
The initial period of a pulsar is an important factor in our understanding of the formation of neutron stars and of the nature of the equation of state of neutron star matter.Up to now this quantity can only be obtained for a few pulsars for which accurate age and braking index are known.Based on the theory of the offcenter dipole emission,in which pulsars obtain theiry high velocities depending on the initial periods,we calculate the initial period using the proper motion data,Because the orbital velocity of the progenitor and asymmetric kick in the supernova explosion may also contribute to the observed velocity of the pusar,the derived values of initial periods are lower limits.For normal pulsars,the initial periods are in the range of 0.6～2.6ms.For the millisecond pulsars,the initial periods are comparable to their current periods,and the ratio between the initial period and the current period increases with the decrease of the current period.For PSR B1937 21 with the shortest period of 1.56ms,the ratio is 0.77.  相似文献   

4.
In this contribution we present our preliminary investigation on pulsar sensitivity of the Large Area Telescope, the main instrument aboard the GLAST mission. In particular we concentrated our attention to pulsars located at low galactic latitudes. We created a set of simulated pulsars having different fluxes in an array of galactic coordinates separated by a distance greater than the LAT Point Spread Function in order to avoid confusion between adjacent sources. Galactic gamma-ray sky background as used during the second LAT Data Challenge (DC2) is also included. We then run an automatic routine for testing periodicity for all the pulsars considering an opportune timing solution. In this way we can obtain a map of the sensitivity of the periodic searches for different fluxes and for various Galactic latitudes. Some assumptions have been made by simulating the pulsar sources, but this study is a first step toward an estimate for pulsed emission sensitivity of the GLAST LAT. The pulsed flux sensitivity profile we generate could also be input to a population synthesis code of Galactic pulsars in order to obtain more accurate predictions of the number of expected pulsar detections by GLAST. On behalf of the GLAST LAT Collaboration.  相似文献   

5.
We present results of our pulsar population synthesis of normal and millisecond pulsars in the Galactic plane. Over the past several years, a program has been developed to simulate pulsar birth, evolution and emission using Monte Carlo techniques. We have added to the program the capability to simulate millisecond pulsars, which are old, recycled pulsars with extremely short periods. We model the spatial distribution of the simulated pulsars by assuming that they start with a random kick velocity and then evolve through the Galactic potential. We use a polar cap/slot gap model for γ-ray emission from both millisecond and normal pulsars. From our studies of radio pulsars that have clearly identifiable core and cone components, in which we fit the polarization sweep as well as the pulse profiles in order to constrain the viewing geometry, we develop a model describing the ratio of radio core-to-cone peak fluxes. In this model, short period pulsars are more cone-dominated than in our previous studies. We present the preliminary results of our recent study and the implications for observing these pulsars with GLAST and AGILE.   相似文献   

6.
The computation of theoretical pulsar populations has been a major component of pulsar studies since the 1970s. However, the majority of pulsar population synthesis has only regarded isolated pulsar evolution. Those that have examined pulsar evolution within binary systems tend to either treat binary evolution poorly or evolve the pulsar population in an ad hoc manner. Thus, no complete and direct comparison with observations of the pulsar population within the Galactic disc has been possible to date. Described here is the first component of what will be a complete synthetic pulsar population survey code. This component is used to evolve both isolated and binary pulsars. Synthetic observational surveys can then be performed on this population for a variety of radio telescopes. The final tool used for completing this work will be a code comprised of three components: stellar/binary evolution, Galactic kinematics and survey selection effects. Results provided here support the need for further (apparent) pulsar magnetic field decay during accretion, while they conversely suggest the need for a re-evaluation of the assumed typical millisecond pulsar formation process. Results also focus on reproducing the observed     diagram for Galactic pulsars and how this precludes short time-scales for standard pulsar exponential magnetic field decay. Finally, comparisons of bulk pulsar population characteristics are made to observations displaying the predictive power of this code, while we also show that under standard binary evolutionary assumption binary pulsars may accrete much mass.  相似文献   

7.
Analysis of the arrival directions of extensive air showers (EASs) detected on the EAS MSU array and the prototype of the EAS-1000 array has revealed a region of enhanced flux of cosmic rays with PeV energies toward the pulsars PSR J1840+5640 and LAT PSR J1836+5925 at a confidence level up to 4.5σ. The first pulsar was discovered almost 30 years ago and is a well-studied old radio pulsar at a distance of 1.7 kpc from the Solar system. The second pulsar belongs to a new class of pulsars discovered by the Fermi Gamma-Ray Observatory whose pulsations are seen neither in the X-ray nor in the radio bands, but only in the gamma-ray energy range (gamma-ray-only pulsars). In our opinion, the existence of a region of enhanced cosmic-ray flux in the data sets obtained on two different arrays suggests that the pulsars can make a noticeable contribution to the flux of Galactic cosmic rays with PeV energies.  相似文献   

8.
We consider the contribution to the Galactic diffuse γ-ray emission from unresolved γ-ray pulsars. Based on the thick outer gap model, Monte Carlo methods are used to simulate the properties (period, distance, magnetic field, etc.) of the Galactic population of rotation-powered pulsars the gamma-ray flux of which is lower than the threshold sensitivity of the EGRET detector on the Compton Gamma-Ray Observatory . Furthermore, the contribution to the Galactic diffuse γ-ray spectrum from the unresolved γ-ray pulsars is calculated. Our results indicate that the unresolved γ-ray pulsars contribute ∼5 to ∼10 per cent to the measured Galactic diffuse γ-ray emission if the birth rate of neutron stars in the Galaxy is 1 to 2 per century, and that these pulsars contribute significantly to the observed Galactic diffuse γ-ray emission above 1 GeV. Comparing the model spectrum with the observed spectrum, we show that the unresolved γ-ray pulsars contribute very little to the diffuse emission at lower energies but can account for ∼50 per cent of the observed spectrum above 1 GeV if the product of the birth rate of neutron stars and the γ-ray beaming fraction is about unity. Such a large pulsar contribution can explain the difference (∼60 per cent) between the intensity of the Galactic diffuse emission as measured by EGRET above 1 GeV and model predictions based on cosmic ray–matter interaction only.  相似文献   

9.
毫秒脉冲星定时研究进展   总被引：1，自引：0，他引：1  
毫秒脉冲星守时的理论和方法研究己取得重要进展,利用现有2颗毫秒脉冲星约10yr的计时观测资料分析得到的 TAI-PT,其长期稳定度为 2×10－14。采用合适的长期稳定度算法,由多颗毫秒脉冲星计时观测可以建立综合脉冲星时间尺度。它可以成为与原子时系统比较的重要手段,并对原子时长期稳定度的改进做出贡献。介绍了该领域研究的基本状况,重点对毫秒脉冲星守时的理论方法,综合脉冲星时间及与原子时的关系等进行了讨论和评述。对由双星系统内毫秒脉冲星的轨道运动定义的双星脉冲星时也做了介绍。  相似文献   

10.
We make a statistical analysis of the periodsP and period-derivativesP of pulsars using a model independent theory of pulsar flow in theP-P diagram. Using the available sample ofP andP values, we estimate the current of pulsars flowing unidirectionally along theP-axis, which is related to the pulsar birthrate. Because of radio luminosity selection effects, the observed pulsar sample is biased towards lowP and highP. We allow for this by weighting each pulsar by a suitable scale factor. We obtain the number of pulsars in our galaxy to be 6.05−2.80 +3.32 × 105 and the birthrate to be 0.048−0.011 +0.014 pulsars yr−1 galaxy−1. The quoted errors refer to 95 per cent confidence limits corresponding to fluctuations arising from sampling, but make no allowance for other systematic and random errors which could be substantial. The birthrate estimated here is consistent with the supernova rate. We further conclude that a large majority of pulsars make their first appearance at periods greater than 0.5 s. This ‘injection’, which runs counter to present thinking, is probably connected with the physics of pulsar radio emission. Using a variant of our theory, where we compute the current as a function of pulsar ‘age’ (1/2P/P), we find support for the dipole braking model of pulsar evolution upto 6 × 106 yr of age. We estimate the mean pulsar braking index to be 3.7−0.8 +0.8.  相似文献   

11.
We present results of a population synthesis study of radio-loud and radio-quiet γ-ray pulsars from the Galactic plane and the Gould Belt. The simulation includes the Parkes multibeam pulsar survey, realistic beam geometries for radio and γ-ray emission from neutron stars and the new electron density model of Cordes and Lazio. Normalizing to the number of radio pulsars observed by a set of nine radio surveys, the simulation suggests a neutron star birth rate of 1.4 neutron stars per century in the Galactic plane. In addition, the simulation predicts 19 radio-loud and 7 radio-quiet γ-ray pulsars from the plane that EGRET should have observed as point sources. Assuming that during the last 5 Myr the Gould Belt produced 100 neutron stars, only 10 of these would be observed as radio pulsars with three radio-loud and four radio-quiet γ-ray pulsars observed by EGRET. These results are in general agreement with the recent number of about 25 EGRET error boxes that contain Parkes radio pulsars. Since the Gould Belt pulsars are relatively close by, the selection of EGRET radio-quiet γ-ray pulsars strongly favors large impact angles, β, in the viewing geometry where the off-beam emission from curvature radiation provides the γ-ray flux. Therefore, the simulated EGRET radio-quiet γ-ray pulsars, being young and nearby, most closely reflect the current shape of the Gould Belt suggesting that such sources may significantly contribute to the EGRET unidentified γ-ray sources correlated with the Gould Belt.  相似文献   

12.
The evolution of high-and low-mass X-ray binaries (HMXB and LMXB) into different types of binary radio pulsars, the ‘high-mass binary pulsars’(HMBP) and ‘low-mass binary pulsars’ (LMBP) is discussed. The HMXB evolve either into Thorne-Zytkow objects or into short-period binaries consisting of a helium star plus a neutron star (or a black hole), resembling Cygnus X-3. The latter systems evolve (with or without a second common-envelope phase) into close binary pulsars, in which the companion of the pulsar may be a massive white dwarf, a neutron star or a black hole ( some final systems may also consist of two black holes). A considerable fraction of the systems may also be disrupted in the second supernova explosion. We discuss the possible reasons why the observed numbers of double neutron stars and of systems like Cyg X-3 are several orders of magnitude lower than theoretically predicted. It is argued that the observed systems form the tip of an iceberg of much larger populations of unobserved systems, some of which may become observable in the future. As to the LMBP, we consider in some detail the origins of systems with orbital periods in the range 1–20 days. We show that to explain their existence, losses of orbital angular momentum (e.g., by magnetic braking) and in a number of cases: also of mass, have to be taken into account. The masses of the low-mass white dwarf companions in these systems can be predicted accurately. We notice a clear correlation between spin period and orbital period for these systems, as well as a clear correlation between pulsar magnetic field strength and orbital period. These relations strongly suggest that increased amounts of mass accreted by the neutron stars lead to increased decay of their magnetic fields: we suggest a simple way to understand the observed value of the ‘bottom’ field strengths of a few times 108 G. Furthermore, we find that the LMBP-systems in which the pulsar has a strong magnetic field (> 1011 G) have an about two orders of magnitude larger birth rate (i.e., about 4 × 10-4 yr-1 in the Galaxy) than the systems with millisecond pulsars (which have B < 109 G). Using the observational fact that neutron stars receive a velocity kick of ∼450 km/s at birth, we find that some 90% of the potential progenitor systems of the strong-field LMBP must have been disrupted in the Supernovae in which their neutron stars were formed. Hence, the formation rate of the progenitors of the strong-field LMBP is of the same order as the galactic supernova rate (4 × 10-3 yr-1). This implies that a large fraction of all Supernovae take place in binaries with a close low-mass (< 2.3 M⊙) companion.  相似文献   

13.
韩金林 《天文学进展》2001,19(2):201-204
脉冲星的偏振信息是理解脉冲星辐射区的重要手段，利用澳大利亚的64m射电望远镜进行大量的脉冲星观测，得到了一批脉冲星的偏振轮廓和偏振参数，编辑了几乎所有发表的脉冲星轮廓资料，系统总结了脉冲星圆偏辐射的规律，为理论上解释脉冲星辐射这一重要难题提供观测依据和物理限制，利用脉冲星作为探针，研究了银河系磁场结构和模型，确定了银河系BS磁场模型，发现了银河系上下反对称的环向磁场，并首次对星系尺度的发电机类型进行判别，证认出A0型发电机运行于银河系，发现了银晕中的垂直磁场和M31及银盘中的非常延展的磁场，探测到NGC2997星系中由内到外的旋涡磁场，并提出可能有两种发电机在这个星系的不同区域运行。  相似文献   

14.
The behaviour of pulsars at low radio-frequencies (below ≈ 50 MHz) remains poorly understood mainly due to very limited observational data on pulsars at these frequencies. We report here our measurements of pulse profiles at 34.5 MHz of 8 pulsars using the Gauribidanur Radio Telescope. None of the 8 pulsars show any significant interpulse emission at this frequency which conflicts with an earlier claim from 25 MHz observations. With the exception of one pulsar (PSR 0943 + 10) all the observed pulsars show turnovers at frequencies above 35 MHz in their spectra. We also report our attempts to study the short and long term variations in the pulsar signals at this low frequency.  相似文献   

15.
A model of pulsars is discussed in which formation of a polar diagram of the radiation is influenced by the motion of the source around a neutron star with a velocity close to that of light. For a power-law frequency-spectrum of the radiation and isotropy of the diagram in a system of coordinates rotating with the source, the width of the observed pulse is shown to be independent of frequency.The proposed explanation of the second period characteristics of type CP 1919 pulsars is based on the effect of relativistic motion of the radiation source. The positions are established (relative to the axis of rotation of the star) of the local sources of radiation in the optical and in the radio ranges for the pulsar NP 0532. It is shown how the polarization characteristics of the optical radiation of this pulsar may be connected with the effects of relativistic orbiting of the source of radiation about the star.  相似文献   

16.
Using reasonable assumptions, we derive the distribution function of pulsar space velocities from the distribution of pulsar heights above the Galactic plane. We find that for 137 pulsars of the north Galactic hemisphere, the space velocity distribution is discrete, and forms two separate groups. We estimate the velocity ranges and the mean pulsar velocity of each group.Translated from Astrofizika, Vol. 37, No. 2, pp. 245–254, April–June, 1994.  相似文献   

17.
为了解释间歇脉冲星PSR B1931+24在射电噪比射电宁静状态下更大的自转减慢率和模拟蟹状星云脉冲星的自转演化,建立同时考虑了具有不同加速电势的核区和环区的环加速间隙下的星风制动模型.其中对于PSR B1931+24通过计算得到它的磁场强度和磁倾角,并且预言了其理论制动指数.对于蟹状星云脉冲星,通过计算得到它的磁场强度和磁倾角,还计算得到其制动指数随周期的演化和它在周期-周期导数图上的自转演化.相比于真空加速间隙、外加速间隙等,环加速间隙也同样能够适用于星风制动模型.  相似文献   

18.
For pulsars in globular clusters, we suggest using observations of the relativistic time delay of their radiation in the gravitational field of a massive body (the Shapiro effect) located close to the line of sight to detect and identify invisible compact objects and to study the distribution of both visible and dark matter in globular clusters and different components of the Galaxy. We have derived the dependences of the event probability on the Galactic latitude and longitude of sources for two models of the mass distribution in the Galaxy: the “classical” Bahcall—Soneira model and the more recent Dehnen—Binney model. Using three globular clusters (M15, 47 Tuc, Terzan 5) as an example, we show that the ratios of the probability of the events due to the passages of massive Galactic objects close to the line of sight to the parameter f 2 for pulsars in the globular clusters 47 Tuc and M 15 are comparable to those for close passages of massive objects in the clusters themselves and are considerably higher than those for the cluster Terzan 5. We have estimated the rates of such events. We have determined the number of objects near the line of sight toward the pulsar that can produce a modulation of its pulse arrival times characteristic of the effect under consideration; the population of brown dwarfs in the Galactic disk, whose concentration is comparable to that of the disk stars, has been taken into account for the first time.  相似文献   

19.
We measured a sample of 150 pulsar rotation measures (RMs) using the 20-cm receiver of the Parkes 64-m radio telescope. 46 of the pulsars in our sample have not had their RM values previously published, whereas 104 pulsar RMs have been revised. We used a novel quadratic fitting algorithm to obtain an accurate RM from the calibrated polarization profiles recorded across 256 MHz of receiver bandwidth. The new data are used in conjunction with previously known dispersion measures and the NE2001 electron-density model to study models of the direction and magnitude of the Galactic magnetic field.  相似文献   

20.
Shemar & Lyne have previously presented observations and an analysis of 32 glitches and their subsequent relaxations observed in a total of 15 pulsars. These data are brought together in this paper with those published by other authors. We show quantitatively how glitch activity decreases linearly with decreasing rate of slow-down. As indicated previously from studies of the Vela pulsar, the analysis suggests that 1.7 per cent of the moment of inertia of a typical neutron star is normally contained in pinned superfluid which releases its excess angular momentum at the time of a glitch. There is a broad range of glitch amplitude and there is a strong indication that pulsars with large magnetic fields suffer many small glitches while others show a smaller number of large glitches. Transient effects following glitches are very marked in young pulsars and decrease linearly with decreasing rate of slow-down, suggesting that the amount of loosely pinned superfluid decreases with age. We suggest that the low braking index of the Vela and Crab pulsars cannot be caused by a decreasing moment of inertia and should be attributed to step increases in the effective magnetic moment of the neutron star at the glitches.  相似文献   

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