共查询到20条相似文献，搜索用时 46 毫秒
1.
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
2.
M. Kramer D.C. Backer J.M. Cordes T.J.W. Lazio B.W. Stappers S. Johnston 《New Astronomy Reviews》2004,48(11-12):993
The sensitivity of the SKA enables a number of tests of theories of gravity. A Galactic Census of pulsars will discover most of the active pulsars in the Galaxy beamed toward us. In this census will almost certainly be pulsar–black hole binaries as well as pulsars orbiting the super-massive black hole in the Galactic centre. These systems are unique in their capability to probe the ultra-strong field limit of relativistic gravity. These measurements can be used to test the Cosmic Censorship Conjecture and the No-Hair theorem.The large number of millisecond pulsars discovered with the SKA will also provide a dense array of precision clocks on the sky. These clocks will act as the multiple arms of a huge gravitational wave detector, which can be used to detect and measure the stochastic cosmological gravitational wave background that is expected from a number of sources. 相似文献
3.
It is expected that specific globular clusters (GCs) can contain up to a hundred of millisecond pulsars. These pulsars can accelerate leptons at the shock waves originated in collisions of the pulsar winds and/or inside the pulsar magnetospheres. Energetic leptons diffuse gradually through the GC Comptonizing stellar and microwave background radiation. We calculate the GeV–TeV γ-ray spectra for different models of injection of leptons and parameters of the GCs assuming reasonable, of the order of 1 per cent, efficiency of energy conversion from the pulsar winds into the relativistic leptons. It is concluded that leptons accelerated in the GC cores should produce well localized γ-ray sources which are concentric with these GCs. The results are shown for four specific GCs (47 Tuc, Ter 5, M13 and M15), in which significant population of millisecond pulsars have been already discovered. We argue that the best candidates, which might be potentially detected by the present Cherenkov telescopes and the planned satellite telescopes (AGILE, GLAST), are 47 Tuc on the Southern hemisphere, and M13 on the Northern hemisphere. We conclude that detection (or non-detection) of GeV–TeV γ-ray emission from GCs by these instruments put important constraints on the models of acceleration of leptons by millisecond pulsars. 相似文献
4.
R. N. Manchester 《Astrophysics and Space Science》2005,297(1-4):101-108
A total of eight gamma-ray sources are identified with pulsars and these include some of the strongest gamma-ray sources in
the sky. About 20 of the unidentified gamma-ray sources are very likely to be associated with currently known pulsars and
there is little doubt that many of the others, at least those at low Galactic latitudes, will ultimately be identified with
pulsars. How many of these and future gamma-ray detections will be detectable at radio wavelengths depends on the details
of the radio and gamma-ray beaming. There is good evidence that the radio beams in young and millisecond pulsars are very
wide, implying that most gamma-ray pulsars will be detectable in the radio band. 相似文献
5.
There are indications now that globular clusters contain a large number of low magnetic field millisecond pulsars. Since millisecond
pulsars are expected to emit γ-rays due to curvature radiation, it is likely that globular clusters will themselves be sources
of γ-rays bright enough to be detectable by present day instruments. Using the expression derived by Scharlemann, Arons &
Fawley (1978) of the energy acquired by the electrons moving along the open magnetic field lines of the pulsars we have calculated
the likely luminosity of γ-rays from globular clusters. We discuss our results in the light of the calculations reported in
the literature based on some of the other models. 相似文献
6.
A. G. Lyne R. N. Manchester D. R. Lorimer M. Bailes N. D'Amico T. M. Tauris S. Johnston J. F. Bell & L. Nicastro 《Monthly notices of the Royal Astronomical Society》1998,295(4):743-755
A survey of the entire southern sky for millisecond and low-luminosity pulsars using the ATNF Parkes radio telescope has now been completed. The survey detected 298 pulsars, of which 101 were previously unknown. The new pulsars include 17 millisecond pulsars. This is the largest sample of both normal and millisecond pulsars detected in any survey. Combining our sample with other recent surveys in the Northern Hemisphere, we present a statistical study of the populations of both normal and millisecond pulsars. We find that the improved statistics allow us to estimate the number and birth-rate of both types of pulsar down to a 400-MHz luminosity limit of 1 mJy kpc2 . The local surface densities of potentially observable normal pulsars and millisecond pulsars are both about 30 kpc−2 , corresponding to ∼ 30000 potentially observable pulsars of each type in the Galaxy. Once beaming effects are taken into consideration we estimate that the active population of normal pulsars is ∼ 160000. Although there is evidence for flattening of the luminosity function of normal pulsars, this is not evident for millisecond pulsars which probably have a substantial population with luminosities below 1 mJy kpc2 . After correcting for beaming effects, we estimate that a normal pulsar is born with a luminosity greater than 1 mJy kpc2 between once every 60 and 330 yr in the Galaxy. The birth-rate of millisecond pulsars is at least 3 × 10−6 yr−1 above the same luminosity limit. Modelling the observed transverse speeds of millisecond pulsars using a dynamical simulation, we find their mean birth velocity to be 130 ± 30 km s−1 , significantly lower than that of the normal pulsars. 相似文献
7.
Population synthesis is used to model the number of neutron stars in globular clusters that are observed as low-mass X-ray sources and millisecond radio pulsars. The dynamical interactions between binary and single stars in a cluster are assumed to take place only with a continuously replenished “background” of single stars whose properties keep track of the variations in parameters of the cluster as a whole and the evolution of single stars. We use the hypothesis that the neutron stars forming in binary systems from components with initial masses of ～8–12 M ⊙ during the collapse of degenerate O-Ne-Mg cores through electron captures do not acquire a high space velocity. The remaining neutron stars (from single stars with masses >8 M ⊙ or from binary components with masses >12 M ⊙) are assumed to be born with high space velocities. According to this hypothesis, a sizeable fraction of the forming neutron stars remain in globular clusters (about 1000 stars in a cluster with a mass of 5 × 105 M ⊙). The number of millisecond radio pulsars forming in such a cluster in the case of accretion-driven spinup in binary systems is found to be ～10, in agreement with observations. Our modeling also reproduces the observed shape of the X-ray luminosity function for accreting neutron stars in binary systems with normal and degenerate components and the distribution of spin periods for millisecond pulsars. 相似文献
8.
Contribution to diffuse gamma-rays in the Galactic Centre region from unresolved millisecond pulsars
W. Wang Z. J. Jiang K. S. Cheng 《Monthly notices of the Royal Astronomical Society》2005,358(1):263-269
Diffuse gamma-rays in the Galactic Centre region have been studied. We propose that there exists a population of millisecond pulsars in the Galactic Centre, which emit GeV gamma-rays through synchrotron-curvature radiation as predicted by outer gap models. These GeV gamma-rays from unresolved millisecond pulsars probably contribute to the diffuse gamma-ray spectrum detected by EGRET which displays a break at a few GeV. We have used a Monte Carlo method to obtain simulated samples of millisecond pulsars in the Galactic Centre region covered by EGRET (∼ 15) according to the different period and magnetic field distributions from observed millisecond pulsars in the Galactic field and globular clusters, and superposed their synchrotron-curvature spectra to derive the total GeV flux. Our simulated results suggest that there probably exist about 6000 unresolved millisecond pulsars in the region of angular resolution of EGRET, the emissions of which could contribute significantly to the observed diffuse gamma-rays in the Galactic Centre. 相似文献
9.
Vyacheslav E. Zavlin 《Astrophysics and Space Science》2007,308(1-4):297-307
Millisecond pulsars represent an evolutionarily distinct group among rotation-powered pulsars. Outside the radio band, the soft X-ray range (～0.1–10 keV) is most suitable for studying radiative mechanisms operating in these fascinating objects. X-ray observations revealed diverse properties of emission from millisecond pulsars. For the most of them, the bulk of radiation is of a thermal origin, emitted from small spots (polar caps) on the neutron star surface heated by relativistic particles produced in pulsar acceleration zones. On the other hand, a few other very fast rotating pulsars exhibit almost pure nonthermal emission generated, most probably, in pulsar magnetospheres. There are also examples of nonthermal emission detected from X-ray nebulae powered by millisecond pulsars, as well as from pulsar winds shocked in binary systems with millisecond pulsars as companions. These and other most important results obtained from X-ray observations of millisecond pulsars are reviewed in this paper, as well as results from the search for millisecond pulsations in X-ray flux of the radio-quite neutron star RX J1856.5-3754. 相似文献
10.
脉冲星时间特征和多星计时观测 总被引：1，自引：0，他引：1
在评介脉冲星时研究发展趋势的基础上,讨论了基于毫秒脉冲星自转的脉冲星时间的短期特征和长期稳定度,并对影响其稳定度的因素作了初步分析.50m射电望远镜计时观测的目的之一就是综合脉冲星时研究.对于50m望远镜计时观测的选星和由多星观测进行综合脉冲星时研究中的数据分析问题进行了讨论. 相似文献
11.
Radio flux-density measurements for a large sample of millisecond pulsars at a low frequency of 102 MHz are presented. Using higher frequency measurements, we construct their spectra in the frequency range from 102 MHz to 4.8 GHz, the widest one studied to date. The spectra of millisecond and normal pulsars have been found to differ. The spectra of millisecond pulsars have no low-frequency turnover typical of normal pulsars. The absence of a low-frequency turnover in the spectrum suggests that the emitting regions of millisecond and normal pulsars differ in geometry, which we interpret by deviation of the magnetic field from a dipole one or by compactness of the emitting region. 相似文献
12.
The gravitational radiation from millisecond pulsars owing to glitches in their angular velocity is examined. It is assumed
that the energy transferred from interior superfluid regions to the crust of a neutron star is converted into gravitational
wave energy by damping oscillations of the matter in the star. The gravitational wave intensity and amplitude are calculated
for fourteen millisecond pulsars. Gravitational radiation can explain the observed spin-down of millisecond pulsars and an
estimate is given for the magnetic field at which the proposed mechanism predominates in the spin-down of these pulsars.
__________
Translated from Astrofizika, Vol. 51, No. 3, pp. 479–486 (August 2008). 相似文献
13.
14.
The rotation periods, surface magnetic field strengths, as well as the spatial distribution of the several kinds of pulsars discovered sofar are analyzed statistically. It is revealed that the spatial distribution of the millisecond pulsars is more dispersive than that of the normal radio pulsars. And that the spatial distribution of the pulsars in low-mass X-ray binaries (LMXBs) is also more dispersive than that of the pulsars in high-mass X-ray binaries (HMXBs). The distribution of rotation periods of the isolated millisecond pulsars has a peak at 4.7ms, and the corresponding peak values for the normal radio pulsars and the millisecond pulsars in binaries are 0.6 s and 3.5ms, respectively. The surface magnetic field strengths of the FERMI pulsars (the gamma-ray pulsars observed by the Large Area Telescope/Fermi Gamma-ray Space Telescope) and normal pulsars are all concentrated around 1012 Gs. It is found also that some young high-energy pulsars are associated with supernova remnants. In combination with the formation and evolution models of pulsars, we have made some remarks on the characteristics of these distributions. 相似文献
15.
Peter L. Gonthier Sarah A. Story Brian D. Clow Alice K. Harding 《Astrophysics and Space Science》2007,309(1-4):245-251
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
16.
D. R. Lorimer M. A. McLaughlin D. J. Champion I. H. Stairs 《Monthly notices of the Royal Astronomical Society》2007,379(1):282-288
We present 3 yr of timing observations for PSR J1453+1902, a 5.79-ms pulsar discovered during a 430-MHz drift-scan survey with the Arecibo telescope. Our observations show that PSR J1453+1902 is solitary and has a proper motion of 8 ± 2 mas yr−1 . At the nominal distance of 1.2 kpc estimated from the pulsar's dispersion measure, this corresponds to a transverse speed of 46 ± 11 km s−1 , typical of the millisecond pulsar population. We analyse the current sample of 55 millisecond pulsars in the Galactic disc and revisit the question of whether the luminosities of isolated millisecond pulsars are different from their binary counterparts. We demonstrate that the apparent differences in the luminosity distributions seen in samples selected from 430-MHz surveys can be explained by small-number statistics and observational selection biases. An examination of the sample from 1400-MHz surveys shows no differences in the distributions. The simplest conclusion from the current data is that the spin, kinematic, spatial and luminosity distributions of isolated and binary millisecond pulsars are consistent with a single homogeneous population. 相似文献
17.
P. L. Gonthier R. Van Guilder A. K. Harding I. A. Grenier C. A. Perrot 《Astrophysics and Space Science》2005,297(1-4):71-80
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
18.
R. Orduña C. Baixeras A. Carramiñana V. Fonseca 《Astrophysics and Space Science》2005,297(1-4):377-383
Most of the unidentified gamma ray sources detected near the Galactic plane by EGRET aboard CGRO are expected to be gamma
ray pulsars. We present a study about the detectability and identification of some unidentified EGRET sources with the MAGIC
telescope. We list some unidentified gamma ray sources from the third EGRET catalogue to be detected with MAGIC taking into
account some important conditions such as the variability parameter of the source, spectral index, inclusion in the GeV catalogue
(ApJ 488, 1997, p. 872) and possible associations with known X-ray/radio sources located within the error box of the unidentified
gamma ray source. We show the required observation time of these gamma ray pulsar candidates to be detected by MAGIC telescope
considering reasonable values of cut-off energy. To be more realistic, we have chosen the zenith angle corresponding to the
source culmination in the simulation of the effective area A since the observation time is function of the effective area.
In addition to this study, it is very important to consider the extrapolated EGRET flux at MAGIC energies above 30 GeV of
the gamma ray pulsar candidates taking the MAGIC sensitivity. 相似文献
19.
We have obtained deep 6, 20 and 90 cm observation of two of the richest globular clusters in the galaxy, Terzan 5 and Liller
1. In addition to the well known eclipsing pulsar, PSR1744-24A, our 20 cm image of Terzan 5 displays numerous point sources
within 30″, or 4 core radii of the cluster center. The density of these objects rises rapidly toward the core, where an elongated
region of emission is found. This feature may be due to the presence of a higher density of point sources than can be resolved
by the 1″ resolution of our data. Observations at 6 and 90 cm show that the brightest individual sources, as well as the extended
emission, possess the steep spectra expected of pulsars. Furthermore, we find that the strength of the sources in the 20 cm
image agrees well with the standard pulsar luminosity function. The total luminosity and number of objects observed in Terzan
5 suggest that this cluster may contain 100 pulsars — probably more than any other Galactic cluster. Although we do not resolve
individual sources in Liller 1, comparison of our images with other observations suggests that we are again observing the
sum of emission from a number of objects. The 90 cm flux densities of Terzan 5 and Liller 1 are 35 and 9 mJy, respectively,
implying that a number of bright pulsars in these clusters have been hidden from pulsed searches, perhaps by a combination
of dispersion smearing, scattering and doppler broadening. 相似文献
20.
Zhao-Xia Han Li Zhang Department of Physics Yunnan University Kunming National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Kunming 《中国天文和天体物理学报》2005,5(3):256-264
The variability of γ-ray sources listed in the third EGRET catalog is studied using three variability indices. These indices are found to be statistically equivalent if the observed data are sufficiently accurate. Using the three indices,30 EGRET point sources which are positionally coincident with pulsars and 40 persistent unidentified sources at low latitudes are analyzed for their variability status. It is found that 14 of the 30 point sources may have genuine or plausible associations with pulsars, and 16 of the 40 persistent unidentified sources are possible pulsar candidates. 相似文献