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1.
The latest observational data are analyzed to investigate their consistency with two known models for anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs): the magnetar and drift models. The results of spectral measurements disagree with the predictions of theories that assume the presence of super-strong magnetic fields on AXPs and SGRs and associated processes for the generation of electron-positron plasma in the upper layers of the neutron-star magnetosphere. We present arguments against the use of magnetic-dipole braking for these objects. The rotational periods P, period derivatives dP/dt, and magnetic fields B of known AXPs and SGRs are calculated for the drift model. The mean values of these parameters in the sample used are 〈P〉 = 108 ms and 〈log B s [G]〉 = 12.08. Overall, the measured profiles, polarizations, and spectra can be brought into agreement with the drift model.  相似文献   

2.
Parameters of 100 radio pulsars detected outside the radio range (he pulsars) are compared with those of pulsars radiating only in the radio (n pulsars). The periods of he pulsars are, on average, appreciably shorter than those of n pulsars: 〈P〉 = 0.10 and 0.56 s, respectively. The distribution of the magnetic field at the light cylinder is shifted toward higher magnetic fields for the pulsars with high-energy radiation, compared to the distribution for pulsars radiating only in the radio. The magnetic fields at the light cylinder are 〈B lc〉 = 9×103 G for he radio pulsars, and 〈Blc〉 = 56 G formost purely radio pulsars. This suggests the generation of high-energy nonthermal radiation in radio pulsars at the peripheries of their magnetospheres. The distribution of the spin-energy loss rate dE/dt is uniform for he pulsars, and is characterized by a higher average value \(\left( {\left\langle {\log \frac{{dE}} {{dt}}} \right\rangle = 35.53} \right) \) , compared to n pulsars, \(\left( {\left\langle {\log \frac{{dE}} {{dt}}} \right\rangle = 32.60} \right) \) . The spatial distribution of he pulsars is nonuniform: they form two well separated clouds.  相似文献   

3.
A new model is put forward to explain the observed features of anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs). It is shown that drift waves can be excited in the magnetosphere of a neutron star with a rotational period of P～0.1 s, surface magnetic field Bs～1012 G, and angle between the rotational axis and magnetic moment β<10°. These waves lead to the formation of radiation pulses with a period of Pdr～10 s. The rate of loss of rotational energy by such a star (～1037 erg/s) is sufficient to produce the observed increase in the period \((\dot P \sim 10^{ - 10} )\), the X-ray luminosities of AXPs and SGRs (～1034–1036 erg/s), and an injection of relativistic particles into the surrounding supernova remnant. A modulation of the constant component of the radiation with a period of P～0.1 s is predicted. In order for SGRs to produce gamma-ray bursts, an additional source of energy must be invoked. Radio pulsars with periods of Pobs>5 s can be described by the proposed model; in this case, their rotational periods are considerably less than Pobs and the observed pulses are due to the drift waves.  相似文献   

4.
The question of why the observed periods of anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) cluster in the range 2–12 s is discussed. The possibility that AXPs and SGRs are the descendants of high-mass X-ray binaries that have disintegrated in core-collapse supernova explosions is investigated. The spin periods of neutron stars in high-mass X-ray binaries evolve towards the equilibrium period, which is a few seconds, on average. After the explosion of its massive companion, the neutron star becomes embedded in a dense gaseous envelope, and accretion from this envelope leads to the formation of a residual magnetically levitating disk. It is shown that the expected mass of the disk in this case is 10?7–10?8 M⊙, which is sufficient to support accretion at the rate 1014–1015 g/s over a few thousand years. During this period, the star manifests itself as an isolated X-ray pulsar with a number of parameters similar to those of AXPs and SGRs. The periods of such pulsars can cluster if the lifetime of the residual disk does not exceed the spin-down timescale of the neutron star.  相似文献   

5.
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6.
The integrated radio luminosities of 311 long-period (P > 0.1 s) and 27 short-period (P < 0.1 s) pulsars have been calculated using a new compilation of radio spectra. The luminosities are in the range 1027 ? 1030 erg/s for 88% of the long-period pulsars and 1028 ? 1031 erg/s for 88% of the short-period pulsars. We find a high correlation between the luminosity L and the estimate L 1 = S 400 d 2 from the catalog of Taylor et al. The factor η for the transformation of the rotational energy of the neutron star into radio emission increases-decreases with increasing period for long-period and short-period pulsars. The mean value of η is ?3.73 for the long-period and ?4.85 for short-period pulsars. No dependence was found between L and the pulsar’s kinematic age t k = |z|/〈v z〉, where |z| and 〈v z〉 = 300 km/s are the pulsars’ height above the plane of the Galaxy and mean velocity. A dependence of L on the rate of rotational energy losses ? was found for both groups of pulsars. It is shown that L ∝ ? 1/3 for the entire sample. The pulsar luminosity function is constructed, and the total number and birth rate of pulsars in the Galaxy are calculated.  相似文献   

7.
A comparative analysis of various parameters of pulsars with short (P < 0.1 s) and long (P > 0.1 s) periods is carried out. There is no correlation between the radio and gamma-ray luminosities of the pulsars and their surfacemagnetic fields, but there is a correlation between the X-ray luminosity and the surfacemagnetic field. A dependence of the X-ray and gamma-ray luminosities on the magnetic field at the light cylinder is also found. This result provides evidence for the formation of hard, non-thermal emission at the periphery of the magnetosphere. An appreciable positive correlation between the luminosity and the rate of rotational energy loss by the neutron star is observed, supporting the idea that all radio pulsars have the same basic source of energy. The efficiency of the transformation of rotational energy into radiation is significantly higher in long-period pulsars. The dependence of the pulse width on the pulsar period is steeper for pulsars with short periods than for those with long periods. The results obtained support earlier assertions that there are differences in the processes generating the emission in pulsars with P < 0.1 s and those with P > 0.1 s.  相似文献   

8.
We present the results of a comparative statistical analysis of the integrated radio luminosities of millisecond and normal pulsars and their dependences on other parameters of the pulsars. The analysis is based on our own measurements of the flux densities, spectra, and integrated radio luminosities of the millisecond pulsars, as well as data from the literature used to determine the integrated radio luminosities for 545 pulsars, 50 of them millisecond pulsars. Despite large differences in their periods P, period derivatives $\dot P$ , magnetic fields B, and ages τ, the integrated radio luminosities of the millisecond and normal pulsars and their dependences on other parameters are approximately the same. The integrated radio luminosity depends on the parameter B/P 2, which is proportional to the potential difference in the polar-cap gap; this may indicate that the radio energy of pulsars is determined by the energy of primary particles accelerated in the polar-cap gap. Secular decreases in the radio luminosities of both normal and millisecond pulsars were also detected.  相似文献   

9.
We analyze possible origins of the observed high rotational and spatial velocities of radio pulsars. In particular, these can be understood if all radio pulsars originate in close binary systems with orbital periods of 0.1–100 days, with the neutron star being formed by a type Ib,c supernova. The high spatial velocities of pulsars (v p up to 1000 km/s) reflect the high Keplerian velocities of the components of these binaries, while their short periods of rotation (P p < 4 s) are due to the rapid rotation of the presupernova helium-star components with masses of 2.5–10 M⊙, which is synchronous with their orbital rotation. Single massive stars or components in wide binaries are likely to produce only slowly rotating (P p > 4 s) neutron stars or black holes, which cannot be radio pulsars. As a result, the rate of formation of radio pulsars should be a factor of a few lower than the rate of type II and type Ib,c supernovae estimated from observations. This scenario for the formation of radio pulsars is supported by (i) the bimodal spatial velocity distribution of radio pulsars; (ii) the coincidence of the observed spatial velocities of radio pulsars with the orbital velocities of the components of close binaries with nondegenerate helium presupernovae; (iii) the correlation between the orbital and rotational periods for 22 observed radio pulsars in binaries with elliptical orbits; and (iv) the similarity of the observed rate of formation of radio pulsars and the rate of type Ib,c supernovae.  相似文献   

10.
The parameters of radio pulsars in binary systems and globular clusters are investigated. It is shown that such pulsars tend to have short periods (of the order of several milliseconds). Themagnetic fields of most of the pulsars considered are weak (surface fields of the order of 108?109 G). This corresponds to the generally accepted view that short-period neutron stars are spun up by angular momentum associated with the stellar wind from a companion. However, the fields at the light cylinders in these objects are two to three orders of magnitude higher than for the main population of single neutron stars. The dependence of the pulse width on the period does not differ from the corresponding dependences for single pulsars, assuming the emission is generated inside the polar cap, at moderate distances from the surface or near the light cylinder. The radio luminosities of pulsars in binary systems do not show the correlation with the rate of loss of rotational energy that is characteristic for single pulsars, probably due to the influence of accreting matter from a companion. Moreover, accretion apparently decreases the power of the emergent radiation, and can explain the observed systematic excess of the radio luminosity of single pulsars compared to pulsars in binary systems. The distributions and dependences presented in the article support generally accepted concepts concerning the processes occurring in binary systems containing neutron stars.  相似文献   

11.
The formation of neutron stars in the closest binary systems (P orb<12 h) gives the young neutron star/pulsar a high rotational velocity and energy. The presence of a magnetic field of 3×1011–3×1013 G, as is observed for radio pulsars, enables the neutron star to transfer ～1051 erg of its rotational energy to the envelope over a time scale of less than an hour, leading to a magnetorotational supernova explosion. Estimates indicate that about 30% of all type-Ib,c supernovae may be the products of magnetorotational explosions. Young pulsars produced by such supernovae should exhibit comparatively slow rotation (P rot>0.01 s), since a large fraction of their rotational angular momentum is lost during the explosion. The magnetorotational mechanism for the ejection of the envelope is also reflected by the shape of the envelope. It is possible that the Crab radio pulsar is an example of a product of a magnetorotational supernova. A possible scenario for the formation of the close binary radio pulsar discovered recently by Lyne et al. is considered.  相似文献   

12.
Various mechanisms for the loss of angular momentum of neutron stars are analyzed. Theoretical predictions about the evolution of the period are compared with the observed distribution of pulsars on the log\(\dot P\)log(P) diagram. Pulsars with short periods (P≤0.1 s) cannot be fit well by any of the models considered. Their braking index is n=?1, which requires the development of a new braking mechanism. The evolution of pulsars with P>1.25 s is described by the law \(\dot P \propto P^2\), probably due to processes internal to the neutron stars. The observational data for pulsars with 0.1<P≤1.25 s can be fit with a hybrid model incorporating internal processes and magnetic-dipole losses. The magnetic fields in pulsar catalogs should be recomputed in accordance with the results obtained. For example, the magnetic fields obtained for two magnetars with P=5.16 s and P=7.47 s are B s =1.7×1013 and 2.9×1013 G, which are lower than the critical field Bcr=4.4×1013 G. For a substantial fraction of pulsars, their characteristic ages \(\tau = P/2\dot P\) cannot serve as measures of their real ages.  相似文献   

13.
The luminosity L of radio pulsars due to synchrotron radiation by the primary beam at the magnetosphere periphery is derived. There is a strong correlation between the observed optical luminosities of radio pulsars and the parameter $\dot P/P^4$ (where P is the pulsar period). This correlation predicts appreciable optical emission from several dozen pulsars, in particular, from all those with P<0.1 s. Agreement with optical observations can be achieved for Lorentz factors of the secondary plasma γp=2–13. Plasma with such energies can be produced only when the magnetic-field structure near the neutron-star surface deviates substantially from a dipolar field. The peak frequency of the synchrotron spectrum should shift toward higher values as the pulsar period P decreases; this is, in agreement with observational data for 27 radio pulsars for which emission has been detected outside the radio band.  相似文献   

14.
Previously developed methods for estimating the angle β between the spin axis of a neutron star and its magnetic moment together with observational data for anomalous X-ray pulsars (AXPs) indicate that these objects are nearly aligned rotators, and that the drift model can be applied to them. The magnetospheres of aligned rotators are appreciably more extended than in pulsars with large values of β. With such extents for the magnetosphere, the conditions for the generation of transverse waves via the cyclotron instability are satisfied. The expected spectrum of the resulting radiation is very steep (its spectral index is α > 3), consistent with the observed radio spectra of known AXPs (α > 2). A large magnetosphere also favors the appearance of appreciable pitch angles for relativistic electrons, and therefore the generation of synchrotron emission. The maximum of this emission falls in the microwave range. This mechanism provides appreciable fluxes at frequencies of tens of gigahertz and can explain the observed enhanced AXP radiation in this range.  相似文献   

15.
The arrival directions of extensive air showers with energies 4×1019<E≤3×1020 eV detected by the AGASA, Yakutsk, Haverah Park, and Fly’s Eye arrays are analyzed in order to identify possible sources of cosmic rays with these energies. We searched for active galactic nuclei, radio galaxies, and X-ray pulsars within 3-error boxes around the shower-arrival directions and calculated the probabilities of objects being in the 3 error boxes by chance. These probabilities are small in the case of Seyfert galaxies with redshifts z<0.01 and BL Lac objects, corresponding to P>3σ (σ is the parameter of Gaussian distribution). The Seyfert galaxies are characterized by moderate luminosities (L<1046 erg/s) and weak radio and X-ray emission. We also analyzed gamma-ray emission at energies E>1014 eV recorded by the Bolivian and Tian Shan arrays. The source identifications suggest that the gamma rays could have been produced in interactions of cosmic rays with the microwave background radiation and subsequent electromagnetic cascades in intergalactic space. We estimate the strength of intergalactic magnetic fields outside galaxy clusters to be B≤8.7×10?10 G.  相似文献   

16.
We report the results of a search for spatial and spectral fluctuations of the cosmic microwave background in the region of the North celestial pole carried out at 6.2 cm using the RATAN-600 radio telescope in 1999–2000. The spatial spectrum is flat and has no features exceeding ΔT/T =10?3 in a ～1 MHz frequency band for spatial periods from 0.5′ to 16′. If this estimate is adopted as an upper limit for emission associated with the first rotational transition of primordial LiH at z=90.7, we obtain an upper limit for the LiH abundance of about 3×10?14 for protocluster masses of about 1013 M ⊙.  相似文献   

17.
The similarities in certain empirical relations derived for active galactic nuclei (AGN) and radio pulsars support the idea that the energy release in the jets of AGN is electrodynamical, associated with the presence of a massive central object (MCO) and circumnuclear, magnetized Keplerian disk. For example, in both types of object, the radio luminosities are proportional to characteristic time scales—for precession for AGN or rotation for pulsars—to the 0.8 power. In this approach to studying the nature of the activity, the $\dot P - P$ relation for pulsars can be considered analogous to the P r-M MCO relation for AGN, which has the form P 5GHz (W/Hz)=2.73 log(M MCO/M ⊙)?2.87.  相似文献   

18.
Low-frequency pulsations of 22 and 37 GHz microwave radiation detected during solar flares are analyzed. Several microwave bursts observed at the Metsähovi Radio Observatory are studied with time resolutions of 100 and 50 ms. A fast Fourier transformation with a sliding window and the Wigner-Ville method are used to obtain frequency-time diagrams for the low-frequency pulsations, which are interpreted as natural oscillations of coronal magnetic loops; the dynamical spectra of the pulsations are synthesized for the first time. Three types of low-frequency fluctuations modulating the flare microwave radiation can be distinguished in the observations. First, there are fast and slow magneto-acoustic oscillations with periods of 0.5–0.8 s and 200–280 s, respectively. The fast magneto-acoustic oscillations appear as trains of narrow-band signals with durations of 100–200 s, a positive frequency drift dν/dt=0.25 MHz/min, and frequency splitting δν=0.01–0.05 Hz. Second, there are natural oscillations of the coronal magnetic loops as equivalent electrical circuits. These oscillations have periods of 0.5–10 s and positive or negative frequency drift rates dν/dt=8×10?3 Hz/min or dν/dt=?1.3×10?2 Hz/min, depending on the phase of the radio outburst. Third, there are modulations of the microwave radiation by short periodic pulses with a period of 20 s. The dynamical spectra of the low-frequency pulsations supply important information about the parameters of the magnetic loops: the ratio of the loop radius to its length r/L≈0.1, the plasma parameter β≈10?3, the ratio of the plasma densities outside and inside the loop ρe/ρi≈10?2, and the electrical current flowing along the loop I≈1012 A.  相似文献   

19.
Data on the profiles and polarization of the 10- and 20-cm emission of radio pulsars are used to calculate the angle β between the rotational axis of the neutron star and its magnetic moment. It is shown that, for these calculations, it is sufficient to use catalog values of the pulse width at the 10% level W 10, since the broadening of the observed pulses due to the transition to the full width W 0 and narrowing of the pulses associated with the emission of radiation along tangents to the field lines approximately cancel each other out. The angles β 1 are calculated for 283 pulsars at 20 cm and 132 pulsars at 10 cm, assuming that the line of sight passes through the center of the emission cone. The mean values of these angles are small and similar for the two wavelengths (〈β 1〉 = 18° at λ = 10 cm and 〈β 1〉 = 14° at λ = 20 cm). The angle β 2 is estimated for several dozen pulsars for the case when the orientation of the angle to the line of sight is arbitrary. The mean value of β 2 at 10 cm is found to be 〈β 2〉 = 33.9° if the maximum derivative of the polarization position angle C is positive and 〈β 2〉 = 52.1° ifC < 0. We find at 20 cm 〈β 2〉 = 33.9° ifC > 0 and 〈β2〉 = 54.1° ifC < 0. The values at the two wavelengths are equal within the errors, and close to the β 2 value obtained earlier at 30 cm (〈β 2〉 = 36.4° if C >0 and 〈β2〉 = 49.1° if C < 0). The mean 〈β 2〉 for the entire set of data can be taken to be 43.5°. The period dependence of the pulse width W(P) √ P −0.25 differs from the relation that is usually used in the polar-cap model, W(P) √ P −0.5. This difference could be associated with the rate of development of plasma instabilities near the surface of the neutron star (in the region where high-frequency radiation is generated). The role of the quadrupole component of the magnetic field is not important here. There is no dependence of the angle β on the pulsar age (z distance, luminosity L, or characteristic age τ = P/(2dP/dt)) for the studied sample.  相似文献   

20.
Photographic plates of the Harvard Observatory stacks have been used to obtain 1261 brightness estimates for the low-amplitude Cepheid FF Aql (P = 4.47 days). Combined with published visual, photoelectric, and CCD observations, these data enable the construction of an O-C diagram spanning 122 years. The resulting O-C diagram is parabola-shaped, enabling the determination of quadratic brightness elements for the first time. The evolutionary rate of increase of the period, dP/dt = 0.072 ± 0.011 s/year, is in agreement with theoretical computations for the third crossing of the instability strip. The available data, reduced using the technique of by Eddington and Plakidis, reveal the presence of small, random period fluctuations, ? = 0.0061d ± 0.0044d, that do not distort the evolutionary trend of the O-C residuals.  相似文献   

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