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1.
We impose the requirement that the spatial distribution of pulsars deduced from their dispersion measures using a model of
the galactic electron density (n
e
) should be consistent with cylindrical symmetry around the galactic centre (assumed to be 10 kpc from the Sun). Using a carefully
selected subsample of the pulsars detected by the II Molonglo Survey (II MS), we test a number of simple models and conclude
that (i) the effective mean 〈ne〉) for the whole galaxy is 0.037-0.012
+0.020 cm-3, (ii) the scale height of electrons is greater than 300 pc and probably about 1 kpc or more, and (iii) there is little evidence
for variation of ne with galactic radius RGC for RGc ≳ 5 kpc. Further, we make a detailed analysis of the contribution to ne from H II regions. Combining the results of a number of relatively independent calculations, we propose a model for the galactic
electron density of the formn
e
(z) = 0.030 + 0.020 exp (- |z|/70) cm-3 where z(pc) is the height above the galactic plane and the second term describes the contribution from H II regions. We believe
the statistical uncertainties in the parameters of this model are quite small. 相似文献
2.
Radio luminosities of pulsars depend on their periods and derivatives of periods. The parameters of these dependences and the independent distances for 288 pulsars are determined. Known dispersion measures are used for determination of the mean electron densities in the direction of pulsars. The results obtained are used for investigation of the large-scale distribution of electron concentration in the galaxy. The maximum value of that distribution is found at a distance of 9 kpc from the galactic center in the Sagittarius arm. In the interarm regions electron density decreases roughly exponentially.Published in Astrofizika, Vol. 38, No. 4, pp. 587–592, October–December, 1995. 相似文献
3.
Based on a large volume of statistical data it is shown that the spatial distributions of radio pulsars in the galaxy with
characteristic ages T ≤ 10
6
years and T > 106 years differ significantly. The overwhelming majority of the pulsars with T ≤ 10
6
years lie within a narrow band of width 400 pc around the galactic plane. A large portion of the pulsars with T > 106 years is concentrated outside this zone. In the case of younger pulsars, a larger fraction of them lies within the confines
of the above mentioned zone. It is also shown that pulsars with T ≤ 10
6
years and the remnants of supernova explosions have essentially the same spatial distribution. These facts support the existence
of a relationship between pulsars and supernova remnants, as well as the acquisition of high spatial velocities by pulsars
during their birth.
__________
Translated from Astrofizika, Vol. 49, No. 1, pp. 103–110 (February 2006). 相似文献
4.
A method that is independent of the model for the distribution of free electrons in the galaxy is proposed for revealing possible oscillations of pulsars in the direction perpendicular to the galactic plane. Oscillations of pulsars in this direction with a half period of approximately 108 years on the scale of characteristic ages are found by this method, which is independent of the distance scale. 相似文献
5.
In accordance with the data on the Faraday rotation, angular coordinates, and dispersion measurements and distances of 38 pulsars, the strengthB=2.1±1.1 G and directionl=99°±24°,b0° of the large-scale galactic magnetic field and the mean electron density in the galactic discN
e=0.03±0.01 cm–3 are determined. A comparison with the results of a study of the measures of rotation of extragalactic radio sources enabled us to estimate the characteristic half-width of the distribution of the electron density on the Z-coordinate (h400 ps). The characteristic size of galactic magnetic field flucturations is shown to be =100–150 ps. 相似文献
6.
The spatial distributions of pulsars with ages of less than 106 years and more than 106 years are shown to be quite different. The spatial distributions of pulsars with ages of less than 106 years and of the remnants of supernova outbursts are essentially the same. They lie near the galactic plane in a thin zone of width 400 pc. The overwhelming majority of pulsars with ages exceeding 106 years lie outside this zone. These facts suggest a genetic relationship between pulsars and supernova remnants. The spatial distribution of pulsars with different emission periods also supports this point. 相似文献
7.
Faraday rotation data on 40 pulsars are used in a detailed study of the magnetic field and its fluctuations in the direction of the spiral arm of Sagittarius. These results mostly agree with standard models for the galactic magnetic field. A magnetic field on the order of 3.2 G is directed from galactic longitude l
0=55° (toward the sun). However, an asymmetry has been found in the degrees of rotation relative to a plane lying in the southern hemisphere parallel to the galactic plane and at a distance of 50-60 pc from it. All the pulsars with measures of dispersion greater than 30 pc·cm-3 and lying to the north of this plane have positive measures of rotation which increase linearly with distance, while the pulsars lying to the south of this plane have unusually absolutely low negative measures of rotation. We propose that the spiral arm of Sagittarius lies entirely to the north of this plane, while the negative measures of rotation of the pulsars below this plane are caused by the magnetic field of the halo of the southern hemisphere of the galaxy. The magnetic field in the arm of Sagittarius is regular to a great extent and its fluctuating component is roughly half the regular component. 相似文献
8.
We have developed a method of searching for the connections between the isolated radio pulsars and supernova remnants, based on the analysis of their kinematic characteristics. We investigate fairly young (τ ch ≲ 106 yr) radio pulsars with known proper motions and estimated distances (dispersion measures), and supernova remnants located no more than 1–2 kpc away from them. Using a standard empirical radial velocity distribution, we have constructed 100–200 thousand trajectories for each of these pulsars, tracing back their possible motion in the Galactic gravitational field on a time-scale of a few million years. The probabilities of their close encounters with the SNRs at epochs consistent with the age of the pulsar are analyzed. When these probabilities exceed considerably their reference values, obtained by assuming a purely random encounter between the objects, we conclude that the pulsars may have originated in the SNRs under consideration. Out of eight preselected pairs of pulsar-SNR association candidates, two pairs, J 1829-1751 / G16.2-2.7 and J 1833-0827 / G24.7-0.6 may have a common origin with a high probability. 相似文献
9.
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
10.
An empirical relation which relates the 408 MHz galactic continuum background temperature (408GCBT) to dispersion measures, position and radio-luminosity of 325 pulsars is obtained by means of multple stepwise regression analysis. This relation showns that pulsars may be considered as galactic probes for the distribution of 408GCBT and interstellar electron density (IED) in interstellar medium (ISM).Peculiar pulsars (O-C±2.5) point out galactic regions where the observedT
408 are higher (or lower) andn
e
lower (or higher) than the averaged ones.Normal pulsars (–2.5T
408 andn
e
are in agreement, on, the average.Standard pulsars (O-C±0.05) show galactic regions where observed and computedT
408 andn
e
are in good agreement. Recent models of pulsar disk systems, suggested by Michel and Dessler (1981) could justify the conclusions drawn for peculiar pulsars having O-C>2.5. 相似文献
11.
The galactic distribution of pulsars and shell remnants of supernovae (SN) as investigated on the basis of newly-estimated parameters. Special attention was paid to taking into account all possible selection effects and an attempt was made to reveal a statistically-pure ensemble of objects. On the basis of this ensemble we studied the radial andz-distribution of pulsars and supernova remnants (SNR).It is shown that the radial distribution of both objects is considered to have an annular structure with the maximum surface density at a distance of 4.5–5.3 kpc (if the distance of the Sun from the galactic centre is assumed to be equal to 8.5 kpc). The scle-height of the progenitors of SNRs is not more than 110 pc and only 15% of the SNRs, whose progenitors may also be massive runaway stars, are situated at 300 pc. The mean application of the pulsars is not more than 300 pc which agrees with the hypothesis about the genetic connection with type-II SN outbursts at the kinematic aget
k5×106 yr and thez-component of spatial velocity beingV
z=120 km s–1.The possible precursors of type-I SNRs by the shape of their radial distribution in late spirals and the various model calculations given in the literature, are also discussed. 相似文献
12.
It is shown that the drift waves near the light cylinder can cause the modulation of emission with periods of order several
seconds. These periods explain the intervals between successive pulses observed in AXPs, SGRs and radio pulsars with long
periods. The model under consideration gives the possibility to calculate real rotation periods P of host neutron stars. It is shown that P≤1 s for the investigated objects. The magnetic fields at the surface of the neutron star are of order 1011–1013 G and equal to the fields usual for the known radio pulsars.
相似文献
13.
The values of the proper motions of 36 pulsars are analysed. It is shown that the birthplaces of pulsars are located within the OB-associations and/or in the galactic arms. Eleven cases of pulsar formation in associations, and fourteen cases of formation in the galactic arms, have been established. More precise parameters of pulsars — such as: distances, ages, spatial velocity components —, and the spatial velocity distribution of pulsars is constructed. 相似文献
14.
The radio luminosities of pulsars are given as functions of their period and the time variation of the period. The parameters
of that dependence are calculated and independent distances are determined for pulsars. The average electron densities toward
the pulsars are determined from the known dispersion measures. The results obtained are used to study the large-scale electron
density distribution in the Galaxy. The distribution maximum lies in the vicinity of the Sagittarius spiral arm. The electron
density falls off exponentially in the regions between spiral arms.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
The diffuse soft X-ray background in 0.07∼ 2.0 keV has been observed along a small circle with the angular width of 10– covering
b=—57– ∼ 77– and crossing the galactic plane at l=125– and 283–. Observed spectra are well fitted with models emitted from a thin hot gas with two or multi-temperature components
and attenuated by a slab or interspersed neutral gas clouds. However the multi-temperature component model has some difficulties
to explain the diffuse component expected from observations of OVI absorption lines. The two temperature component model with
interspersed clouds consistently interprets a physical state of the hot interstellar medium. It turned out that the hot interstellar
medium interspersed with neutral clouds of a representative hydrogen column density of 1× 1020 cm-2has two temperature components (105.8 K,(1.2-4.5)× 106 K) and a disk-like distribution with the thickness of 580(± 100). {(p/k)/104cm-3 K} -2 pc at the pressure of p/k cm-3 K along the galactic plane. Its pressure (p/k) is obtained to be 1.4(+0.7,-0.5)× 104cm-3 K, assuming that hot gases responsible for the diffuse soft X-rays and OVI ions are in pressure equilibrium. This interpretation
qualitatively agrees with the theoretical prediction proposed by McKee and Ostriker.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
The results of flux pulsar radioemission measurements at meter wavelengths, made at Pushchino Radio Astronomical Observatory
of the Lebedev Physical Institute, are presented. Flux densities at 102, 85, 61 and 39 MHz have been measured for 85, 29,
37 and 23 pulsars correspondingly. Some of them were performed at all frequencies simultaneously.
On the basis of these data and high frequencies data obtained by other authors, spectra of 52 pulsars were plotted. In practically
all investigated pulsars we have detected a turn-over frequency at which the flux density of pulsar radioemission attained
its maximum. Its mean value isv
m
=130±80 MHz. Averaged on many pulsars, the spectral index is negative in the 39–61 MHz frequency range
and passes through zero at frequencies of about 100 MHz, becoming positive in the 100–400 MHz frequency range. It was noticed
that the spectral index in the 100–400 MHz interval depends upon such pulsar periods as α100−=0.7logp+0.9. Using the spectra, more precise radio luminosities of pulsars have been computed. 相似文献
17.
T. G. Mdzinarishvili T. M. Borchkhadze R. M. Dzigvashvili N. G. Kogoshvili 《Astrophysics》1998,41(2):157-160
The spatial distribution of pulsars in the solar neighborhood is investigated on the basis of the recent catalog of Taylor,
Manchester, and Lyne. It is shown that “old” pulsars with an age τ > 2.106 yr, like “young ” ones, are indicators of fragments of the Galaxy’s spiral structure. It is concluded that if the distance
scale adopted in the catalog is accurate, the peculiar velocities of the pulsars with the most accurate distances must be
far lower than those adopted up to now.
Translated from Astrofizika, Vol. 41, No. 2, pp. 245–250, April-June, 1998. 相似文献
18.
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
19.
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
20.
P. R. Vishwanath 《Journal of Astrophysics and Astronomy》2002,23(1-2):45-51
The field of Very High Energy (VHE) gamma ray astronomy using the Atmospheric Cerenkov Technique has entered an interesting
phase with detection of various galactic and extragalactic sources. Among galactic sources, only the Crab nebula has been
established as a standard candle. Most observations on pulsars are in agreement as to the necessity for the GeV spectra to
steepen at < 200 GeV. While the Imaging method for increase of sensitivity has been successful with many results, an alternate
technique —Wavefront Sampling Technique- is also being used by an increasing number of experiments. The recently commissioned experiment at Pachmarhi (PACT) in India
is presented as an example of this technique. Preliminary results from this experiment show detection of VHE γ-ray emission
from (a) the Crab nebula at a high significance and (b) Crab and Geminga pulsars at > 1.5 TeV which could be the second component of the Outer Gap pulsar models. 相似文献