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1.
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
2.
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
3.
We study the contribution of young pulsars, with characteristic ages of less than 106 yr, to the diffuse γ-ray emission from the Large Magellanic Cloud (LMC). Based on the outer gap model for γ-ray emission proposed by Zhang & Cheng and pulsar properties in the LMC given by Hartmann, Brown & Schnepf, we simulate the properties of the young pulsars in the LMC. We show that γ-rays produced by the pulsars in the LMC may make an important contribution to the diffuse γ-rays in the LMC, especially in the high-energy range. We calculate the γ-ray energy spectrum of the pulsars in the LMC and show that the γ-ray component contributed by the pulsars to the diffuse γ-rays in the high-energy range (above ∼1 GeV) becomes dominant. We expect that none of the young pulsars should be detectable as an individual point source of γ-ray emission by EGRET. We also expect that pulsar contribution above ∼1 GeV in the SMC is very important. 相似文献
4.
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.
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Translated from Astrofizika, Vol. 51, No. 3, pp. 479–486 (August 2008). 相似文献
5.
We use a new self-consistent model to derive the conversion efficiency from rotation power to γ-ray power for pulsars (εth ). Our result indicates that εth ∝τ6/7 P 2 , where τ and P are the characteristic age and period of the pulsar, which shows that although the efficiency increases with the characteristic age of the pulsar, it also depends on the pulsar period. We test our model results with the survey of high-energy γ-rays from pulsars by EGRET. Our model not only successfully explains the efficiency of the confirmed γ-ray pulsars but also explains why the γ-ray efficiency of millisecond pulsars is so low. 相似文献
6.
We have attempted to devise a scheme by which it may be possible to identify pulsars which are likely to be γ-ray pulsars.
We apply this test to a representative population of pulsars and identify the likely candidates for γ emission. We also discuss
some individual cases including the Crab and Vela pulsars. 相似文献
7.
Melvyn B. Davies & Brad M. S. Hansen 《Monthly notices of the Royal Astronomical Society》1998,301(1):15-24
We investigate the conditions by which neutron star retention in globular clusters is favoured. We find that neutron stars formed in massive binaries are far more likely to be retained. Such binaries are likely to then evolve into contact before encountering other stars, possibly producing a single neutron star after a common envelope phase. A large fraction of the single neutron stars in globular clusters are then likely to exchange into binaries containing moderate-mass main-sequence stars, replacing the lower-mass components of the original systems. These binaries will become intermediate-mass X-ray binaries (IMXBs), once the moderate-mass star evolves off the main sequence, as mass is transferred on to the neutron star, possibly spinning it up in the process. Such systems may be responsible for the population of millisecond pulsars (MSPs) that has been observed in globular clusters. Additionally, the period of mass-transfer (and thus X-ray visibility) in the vast majority of such systems will have occurred 5–10 Gyr ago, thus explaining the observed relative paucity of X-ray binaries today, given the MSP population. 相似文献
8.
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
9.
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
10.
A prolonged timing of millisecond pulsars has revealed low-frequency uncorrelated (infrared) noise, presumably of astrophysical
origin, in the pulse arrival time (PAT) residuals for some of them. Currently available pulsar timing methods allow the statistical
parameters of this noise to be reliably measured by decomposing the PAT residual function into orthogonal Fourier harmonics.
In most cases, pulsars in globular clusters show a low-frequency modulation of their rotational phase and spin rate. The relativistic
time delay of the pulsar signal in the curved spacetime of randomly distributed and moving globular cluster stars (the Shapiro
effect) is suggested as a possible cause of this modulation. Extremely important (from an astrophysical point of view) information
about the structure of the globular cluster core, which is inaccessible to study by other observational methods, could be
obtained by analyzing the spectral parameters of the low-frequency noise caused by the Shapiro effect and attributable to
the random passages of stars near the line of sight to the pulsar. Given the smallness of the aberration corrections that
arise from the nonstationarity of the gravitational field of the randomly distributed ensemble of stars under consideration,
a formula is derived for the Shapiro effect for a pulsar in a globular cluster. The derived formula is used to calculate the
autocorrelation function of the low-frequency pulsar noise, the slope of its power spectrum, and the behavior of the σz statistic that characterizes the spectral properties of this noise in the form of a time function. The Shapiro effect under
discussion is shown to manifest itself for large impact parameters as a low-frequency noise of the pulsar spin rate with a
spectral index of n = −1.8 that depends weakly on the specific model distribution of stars in the globular cluster. For small impact parameters,
the spectral index of the noise is n = −1.5. 相似文献
11.
Xiaohu Yang H. J. Mo Frank C. van den Bosch Simone M. Weinmann Cheng Li Y. P. Jing 《Monthly notices of the Royal Astronomical Society》2005,362(2):711-726
Some massive binaries should contain energetic pulsars which inject relativistic leptons from their inner magnetospheres and/or pulsar wind regions. If the binary system is compact enough, then these leptons can initiate inverse Compton (IC) e± pair cascades in the anisotropic radiation field of a massive star. γ-rays can be produced in the IC cascade during its development in a pulsar wind region and above a shock in a massive star wind region where the propagation of leptons is determined by the structure of a magnetic field around the massive star. For a binary system with specific parameters, we calculate phase-dependent spectra and fluxes of γ-rays escaping as a function of the inclination angle of the system and for different assumptions on injection conditions of the primary leptons (their initial spectra and location of the shock inside the binary). We conclude that the features of γ-ray emission from such massive binaries containing energetic pulsars should allow us to obtain important information on the acceleration of particles by the pulsars, and on interactions of a compact object with the massive star wind. Predicted γ-ray light curves and spectra in the GeV and TeV energy ranges from such binary systems within our Galaxy and Magellanic Clouds should be observed by future AGILE and GLAST satellites and low-threshold Cherenkov telescopes, such as MAGIC, HESS, VERITAS or CANGAROO III. 相似文献
12.
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
13.
14.
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
15.
We consider the possibility of detecting intermediate-mass (103–104 M ⊙) black holes, whose existence at the centers of globular clusters is expected from optical and infrared observations, using precise pulse arrival timing for the millisecond pulsars in globular clusters known to date. For some of these pulsars closest to the cluster centers, we have calculated the expected delay times of pulses as they pass in the gravitational field of the central black hole. The detection of such a time delay by currently available instruments for the known pulsars is shown to be impossible at a black hole mass of 103 M ⊙ and very problematic at a black hole mass of 104 M ⊙. In addition, the signal delay will have a negligible effect on the pulsar periods and their first derivatives compared to the current accuracy of their measurements. 相似文献
16.
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
17.
We estimate the contribution of millisecond pulsars to the diffuse gamma-ray background of the Galaxy, and show that a significant
fraction of the Galactic background may originate from them. A small number of the unidentified COS-B point sources may, in
fact, be millisecond pulsars. It is argued that several hundred millisecond pulsars may be detectable as point sources by
the GRO satellite
A preliminary version of these results was presented at the NATO Advanced Study Institute on Neutron stars, AGNs and Jets,
Erice, September 5–17, 1988.
On leave from Raman Research Institute, Bangalore, India. 相似文献
18.
Spherically symmetric stellar clusters (compact galactic nuclei and globular clusters), far advanced toward the state of complete
statistical equilibrium in the course of evolution, are investigated. The equation of state of such systems (a polytrope with
an index k = 0.5) is derived and their main characteristics are calculated. It is shown that compact galactic nuclei must
consist mainly of rapidly rotating neutron stars and white dwarfs. It is demonstrated that pulsars may be created by the evaporation
of neutron stars from the nucleus of our Galaxy. The number of such pulsars is ~3.106.
Translated from Astrofizika, Vol. 41, No. 1, pp. 41–50, January-March, 1998. 相似文献
19.
K. Mannheim 《Astrophysics and Space Science》1998,264(1-4):471-479
The propagation of γ-rays through metagalactic space is associated with pair creation and subsequent inverse-Compton scattering
off low-energy background radiation. As a consequence, γ-rays of very high energy emitted by remote sources are reprocessed
into the window from 10 MeV to 30 GeV conserving the injected energy. Any cosmologically distributed population of γ-ray sources
therefore contributes to the diffuse γ-ray background in this energy band which is well-determined from recent observations
with the Compton Gamma Ray Observatory (CGRO). Since the γ-rays trace accelerated particles, the observed flux of diffuse
γ-rays also constrains the global efficiency for particle acceleration. Radio galaxies can account for the γ-ray background
if their particle acceleration efficiency considerably exceeds ∼ 18% implying that particle acceleration is an essential part
of the thermodynamics in these sources.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
Alice K. Harding Isabelle A. Grenier Peter L. Gonthier 《Astrophysics and Space Science》2007,309(1-4):221-230
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