首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 699 毫秒
1.
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   

2.
Our paper is dedicated to the problem of anomalous values of braking indices n obs and spin frequency second derivatives [(n)\ddot]\ddot \nu of isolated radio pulsars. Observations of these objects for over 40 years have shown that in addition to the complex short-term irregular component in the evolution of the pulsars’ frequency, secular values of its second derivative are orders of magnitude greater than the predicted theoretical ones, and in a good half of cases—they are even negative. We earlier attributed this behavior of secular values of the second derivative to the presence of a cyclic component in the secular evolution of ν(t), with a characteristic recurrence time of thousands to tens of thousand years. We continue to develop this hypothesis based on a more detailed statistical analysis of the characteristics of 297 isolated radio pulsars: we analyze the model of these objects spin-down, consisting of two components, monotonic and cyclic, and determine their parameters. We demonstrate that the monotonic spin-down component is described by the classical magnetodipolar power law with an braking index of about 3, while the large amplitude of the cyclic component causes a significant variation of the observed spin-down rate ([(n)\dot] )(\dot \nu ) (with respect to magnetodipolar one), and fully determines the anomalous values of [(n)\ddot]\ddot \nu and n obs. An important consequence of the existence of a cyclic component of the pulsar rotational variations is the difference between their characteristic ages and respective secular values (by about 0.5–5 times). This allows to explainthe observed discrepancy of the characteristic and physical ages of some objects, as well as very large, up to 108 years, characteristic ages of some old pulsars. The paper argues that the cyclic component of the observed spin-down is due to the long-term precession of neutron stars around their magnetic axes, which, in particular, may be driven by the anomalous braking torque. In the model of purely magnetodipolar braking this torque is a consequence of emission in the near field zone.  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.
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   

5.
A method is proposed for constructing a map of the electron density distribution in the galactic plane. Data on the dispersion measures DM of more than 1500 pulsars and their distances, found by an independent method, are used. The independent distances of the pulsars are estimated using an empirical relation of the form L=γP α Ṗ β W δ between the radio luminosity L of the pulsars and their periods P, the rate of change Ṗ. of their periods, and the half width W of their pulses. A map of the electron density distribution in the galactic plane within a ±400 pc layer is provided. __________ Translated from Astrofizika, Vol. 49, No. 2, pp. 277–287 (May 2006).  相似文献   

6.
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   

7.
We have measured the decorrelation frequency (f v ) and decorrelation time (t v ) for 15 pulsars. We show by combining our data with those of others thatfv∫ DM-1.79±0.14 andt v ∫ DM-0.80±0.15 up to a dispersion measure (DM) of about 60 cm3 pc. The combined data set does not form a complete sample, but the relations obtained from our measurements on 14 pulsars, which form almost a complete sample up to 41 cm3 pc, are consistent with the above relations, suggesting that these relations are not seriously affected by selection effects. The relations are broadly in agreement with those expected from a homogeneous interstellar medium and are in disagreement with earlier conclusions by others that these relations steepen even for low-DM pulsars. The agreement suggests that the local interstellar medium is homogeneous at least up to a distance of about 2 kpc.  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.
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   

10.
It is usually assumed that the dipole radiation at the spin frequency Wd is the only source of braking torque on pulsars (the POG hypothesis), but certain observations cast doubt on this. In this paper, we discuss the effect of elctromagnetic braking near the light cylinder Wem without using the POG hypothesis. We found Wem ∝ P?3.2 (P is the pulsar period), and the total power Lt ∝ P?3.2 (if Lt ∝ Wem). A correlation analysis between Lt and Pn for a sample of 15 pulsars gives n = ?3.1, in agreement with our theoretical expectations.Our analysis based on observations shows that Wem is important or even dominant in some cases. In these cases, the evolutionary path (Fig.2) is very different from that given in /4/ where Wd is assumed to be dominant. The actual braking mechanism could be a superposition of the two (Fig.3).The gap in the P ～ P? diagram found by Ferguson /5/ for a sample of 80-odd pulsars persists in a larger sample of 199 pulsars. This gap, if real, implies that, for a certain range of parameter values, a neutron star is unstable, while it is stable on either side of the range.  相似文献   

11.
Selection effects are a major source of error in statistical studies of pulsar data since the observed sample is a biased subset of the full galactic pulsar population. It is important to identify all selection effects and make a reasonable model before attempting to determine pulsar properties. Here we discuss a hitherto neglected selection effect which is a function of the periodP of the pulsar. We find that short-P pulsars are more difficult to detect, particularly if their dispersion measures are high. We also discuss a declination-dependent selection effect in the II Molonglo Survey (II MS), and find some evidence for the existence of both selection effects in the pulsar data from this survey. We discuss the implications of these additional selection effects for the recently proposed ‘injection’ of pulsars whereby pulsars seem to switch on only at longerP. Using the II MS data we calculate that the observability of pulsars withP between 0.0 s and 0.5 s is about 18 per cent less with the new selection effects than hitherto believed; the mean correction is 6 per cent forP between 0.5 s and 1.0 s. We conclude that injection is not qualitatively affected by these corrections.  相似文献   

12.
The Hertzsprung-Russell diagram of the Large Magellanic Cloud compiled recently by Fitzpatrick & Garmany (1990) shows that there are a number of supergiant stars immediately redward of the main sequence although theoretical models of massive stars with normal hydrogen abundance predict that the region 4.5 ≤ logT eff ≤ 4.3 should be un-populated (“gap”). Supergiants having surface enrichment of helium acquired for example from a previous phase of accretion from a binary companion, however, evolve in a way so that the evolved models and observed data are consistent — an observation first made by Tuchman & Wheeler (1990). We compare the available optical data on OB supergiants with computed evolutionary tracks of massive stars of metallicity relevant to the LMC with and without helium-enriched envelopes and conclude that a large fraction (≈ 60 per cent) of supergiant stars may occur in binaries. As these less evolved binaries will later evolve into massive X-ray binaries, the observed number and orbital period distribution of the latter can constrain the evolutionary scenarios of the supergiant binaries. The distributions of post main sequence binaries and closely related systems like WR + O stars are bimodal-consisting of close and wide binaries in which the latter type is numerically dominating. When the primary star explodes as a supernova leaving behind a neutron star, the system receives a kick and in some cases can lead to runaway O-stars. We calculate the expected space velocity distribution for these systems. After the second supernova explosion, the binaries in most cases, will be disrupted leading to two runaway neutron stars. In between the two explosions, the first born neutron star’s spin evolution will be affected by accretion of mass from the companion star. We determine the steady-state spin and radio luminosity distributions of single pulsars born from the massive stars under some simple assumptions. Due to their great distance, only the brightest radio pulsars may be detected in a flux-limited survey of the LMC. A small but significant number of observable single radio pulsars arising out of the disrupted massive binaries may appear in the short spin period range. Most pulsars will have a low velocity of ejection and therefore may cluster around the OB associations in the LMC.  相似文献   

13.
The observeduvby and Hα indices of member stars of the Hyades and Praesepe clusters have been analysed in detail for rotation effects. The Alpha Persei, Pleiades and the Centaurus subgroup of the Scorpio—Centaurus association have been reanalysed using the observed indices instead of the extinction-corrected indices used earlier. The observed rotation effects from the analysis of these cluster data are found to be in excellent agreement with the theoretical predictions of Collins & Sonneborn (1977). We have also analysed the α,c and (u − b) values of the member stars of NGC 1976, 2264, 2287, 2422, 4755,1C 2391, IC 2602 and IC 4665 for rotation effects. The results are found to be consistent with the theoretical predictions. The observed slopes of the rotation effects were used to determine the zero rotation main sequence values of the intermediate band photometric indices for selected clusters. We also corrected the observed indices for each star in each cluster using the theoretical predictions of Collins and Sonneborn and derived the ZRMS values for each cluster. The agreement between the two determinations is found to be good. The various ZRMS curves were utilised to derive the ZRZAMS values. A preliminary calibration of the absolute visual magnitudes as a function of α valid for ZRZAMS has also been derived. The ZRMS values of the intermediate band photometric indices for different clusters and the ZRZAMS values are listed as a function of α. on leave from Assumption College, Changanacherry, Kerala.  相似文献   

14.
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   

15.
Using a well-known method for calculating the propagation of waves in an inhomogeneous medium, we have managed to reduce the problem of wave propagation in pulsar magnetospheres to a system of two ordinary differential equations that allow the polarization characteristics of the radio emission to be quantitatively described for any magnetic field structure and an arbitrary density profile of the outflowing plasma. We confirm that for ordinary pulsars (period P ∼ 1 s, magnetic field B 0 ∼ 1012 G, particle production multiplicity parameter λ ∼ 104), the polarization is formed inside the light cylinder at a distance of the order of a thousand neutron star radii. For reasonable magnetic field strengths and plasma densities on the emission propagation path, the degree of circular polarization is found to be ∼5–20%, in good agreement with observations.  相似文献   

16.
We present the Wide-field Infrared Survey Explorer (WISE) photometric data of 158 Fermi-detected BL Lacs and investigate the nature of their mid-infrared (MIR) continuum emission. In the [3.4]-[4.6]-[12] μm color–color diagram, nearly all their colors lie within the WISE Blazar strip (WBS), which is an effective diagnostic tool to separate sources dominated by non-thermal radiation from those dominated by thermal radiation. This feature indicates that their MIR emission is predominantly non-thermal. This argument is further supported by the strong radio-MIR flux correlation. We derive their MIR spectral indices and compare them with the near-infrared (NIR) spectral indices. We find that there is a prevalent steepening from MIR spectrum to NIR spectrum. The low-frequency-peaked BL Lacs (LBLs) have on average a larger MIR spectral index and a higher MIR luminosity than the high-frequency-peaked BL Lacs (HBLs), and the intermediate-frequency-peaked BL Lacs (IBLs) appear to bridge them. The MIR-γ-ray flux correlation is highly significant. A strong positive correlation is also found between the MIR and γ-ray spectral indices. The γ-ray-MIR loudness is significantly correlated with the synchrotron peak frequency. Finally we propose that the γ-rays are highly associated with the MIR emission from the jet, and the γ-ray emission is likely from the synchrotron self-Compton process for the Fermi-detected BL Lacs in our sample.  相似文献   

17.
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   

18.
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   

19.
Y. Liu  J. Zhao 《Solar physics》2009,260(2):289-298
Using one-minute cadence time-series full disk magnetograms taken by the SOHO/MDI, we have studied the magnetic field elements at high latitude (poleward of 65° in latitude). It is found that an average lifetime of the magnetic field elements is 16.5 h during solar minimum, much longer than that during solar maximum (7.3 h). During solar minimum, number of the magnetic field elements with the dominant polarity is about 3 times as that of the opposite polarity elements. Their lifetime is 21.0 h on average, longer than that of the opposite polarity elements (2.3 h). It is also found that the lifetime of the magnetic field elements is related with their size, consistent with the magnetic field elements in the quiet sun at low latitude found by Hagenaar et al. (Astrophys. J. 511:932, 1999). During solar maximum, the polar regions are equally occupied by magnetic field elements with both polarities, and their lifetimes are roughly the same on average. No evidence shows there is a correlation between the lifetime and size of the magnetic field elements. Using an image cross-correlation method, we also measure the solar rotation rate at high latitude, up to 85° in latitude. The rate is ω=2.914−0.342sin 2 φ−0.482sin 4 φ μrad s−1 sidereal. It agrees with previous studies using the spectroscopic and image cross-correlation methods, and also agrees with the results using the element tracking method when the sample of the tracked magnetic field elements is large. The consistency of those results strongly suggests that this rate at high latitude is reliable.  相似文献   

20.
The on-going Parkes multibeam survey has been astoundingly successful (Manchesteret al. 2001), and its discovery of over 600 pulsars has opened up new avenues for probing the Galaxy’s electron content and magnetic field. Here we report on recent observations made with the Arecibo 305-m telescope, where 80 distant, high dispersion measure pulsars (of which 35 are from the multibeam survey) were studied at multiple frequency bands in the range 0.4–2.4 GHz, in order to determine their scattering properties, rotation measures and spectral indices. The results will be used to meet a variety of science goals; viz., creating an improved model of the electron density, mapping out the Galactic magnetic field, and modeling the pulsar population.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号