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1.
There are indications that less than 10–3 of the spin-down energy of the millisecond pulsar PSR 1937+214 emerges as electromagnetic radiation. The implications of this result are discussed. The surface magnetic field would then be 107 G, making the pulsar optically undetectable, and casting aspersions on the accretion disc spin-up neutron star models for the pulsar. The pulsar should have an equatorial ellipticity 10–9, which can be accounted for if the equatorial magnetic field departs from axisymmetry by one part in 103.  相似文献   

2.
The curvature -quanta emitted in the pulsar magnetospheres tangentially to the curved lines of force of the magnetic field are shown to be later canalized along the magnetic field—if it is strong enough,B0.1B cr =4×1012G—by gradually converting into a mutually bound electron-positron pair, i.e. a positronium atom. This happens before the photon reaches the threshold of free-pair creation. The positronium thus arising is stable against the ionizing action of the electric field near the pulsar unless it reaches a critical value about 4×107 CGSE forB1013G. This prevents the screening of the electric field up to the distances from the pulsar, where the magnetic field is already below the value of 0.1B cr and the free pair creation may become essential. This effect provides, at least within the Arons model, a higher theoretical estimate for the total luminosity of pulsars whose field at the surfaceB s exceeds 0.1B cr as compared with the conventional one.  相似文献   

3.
The high energy particles emitted by a pulsar prevent the accretion of the interstellar matter onto the star. However, during the life of a pulsar the energy output decreases and after elapsing of critical timet cr the pulsar mechanism is obviously inhibited and matter may penetrate through the radius of capturer a . It is proposed that a possible accumulation of this matter in the regionrr c , wherer c is the corotational radius, is followed by a sudden fall onto the stellar surface. Short bursts of high energy photons may be expected as a result. A possible explanation of recently observed gamma-ray bursts by this mechanism is discussed.  相似文献   

4.
It has been suggested by Usov (1992) that accreting white dwarfs, collapsing to neutron stars may be the sources of the gamma-ray bursts observed at cosmological distances, provided they rotate very fast and have enormously high magnetic fields. In this model the burst's duration is given by the ratio of pulsar kinetic energy and magneticdipole luminosity, so that in order to account for the shortest ( 0.1 s) bursts, the pulsars must rotate very fast (with periodP 0.5 ms) and have magnetic fields of 1016 - 1017 G. Though the high pulsar frequency was anticipated (Qadir and Rafique, 1986) and has been shown to be plausible (Abramowicz, 1990), the extremely high magnetic fields seem anomalous as observed neutron stars have fields below 1013 G.The problem with Usov's proposal is reduced by incorporating the relativistic corrections for fast rotating magnetic dipoles (Belinskyet al., 1994) or magnetic stars (De Paolis and Qadir, 1994). These corrections substantially enhance the radiation efficiency due to the existence of a magnetic synchrotron effect so that the magnetic field required for the explanation of the shortest gamma-ray bursts is strongly reduced. As such the model becomes much more plausible.  相似文献   

5.
Electrostatic drift wave in a hot rotating and strongly magnetized electron-positron pulsar plasma is considered. Using relativistic two fluid equations a pair of coupled nonlinear equations is derived. It is shown that the wave can propagate in the form of two-dimensional dipolar vortices at ultrarelativistic temperature (Tmc 2) of the plasma. The latter may affect the energy transport in the hot plasma, which can lead to a new turbulent state in the pulsar magnetosphere.  相似文献   

6.
The model of the pulsar magnetosphere filled with massless charged particles (rest massm=0) is considered. Such a representation is valid in the case, when e mc 2, where is a characteristic potential difference in the pulsar magnetosphere. This inequality takes place almost everywhere in the pulsar magnetosphere. The gas of charged massless particles can be found in two different phases: (1) dynamical phase (DP), when the particles move with nonvanishing energy along some base lines, determined by the electromagnetic field only, (2) statical phase (SP), when the particles have vanishing energy =0. Even in the simplest axially-symmetric case the pulsar magnetosphere occurs to be divided into regions of different types: (a) the accelerating regions (DP-regions), containing only DP, (b) the capture regions, containing only SP, (c) leaky capture regions, where DP moves through SP. The leaky capture regions are the active regions, which are responsible for the pulsar radio-emission, In the paper the mathematical technique of the massless approximation has been developed. The properties of the capture region has been investigated. The problem of axially-symmetric pulsar magnetosphere has been stated mathematically. The massless approximation permits to substitute some differential equations by the algebraic ones, and to simplify the statement of the problem.  相似文献   

7.
We investigate the effect of asymmetric supernova explosions on the orbital parameters of binary systems with a compact component. We relate such explosions to the origin of binary pulsars. The degree of asymmetry of the explosion is represented by the kick velocity gained by the exploding star due to the asymmetric mass ejection. The required kick velocity to produce the observed parameters of the binary pulsar PSR 1913+16 should be larger than 80 km s–1 if the mass of the exploding star is larger than 4M . We examine the mean survival probability of the binary system (<f>) for various degrees of asymmetry in the explosion. The rare occurrence of a binary pulsar does not necessarily imply that such a probability is low since not all pulsars have originated in a binary system. Assuming the birth rate of pulsars derived by Taylor and Manchester (1977), we derive that <f> would be as high as 0.25. Such values of <f> can be obtained if the mass of the exploding stars is, in general, not large (10M ).  相似文献   

8.
The mechanism of the large-scale magnetic field generation in the Crab Nebula is proposed. The basis for the considered fast mechanism is the model of the central region of Crab Nebula amorphous part having the form of slightly divergent double-layer disk consisting of the relativistic electron-positron plasma.The nebula toroidal magnetic field generation occurs in the double-layer disk in the immediate neighbourhood of the light cylinder of pulsar PSR 0531+21 due to the differential rotation by means of dynamo-mechanism. The generated field is transferred into the nebula by the pulsar wind which forms the double-layer disk.By use of the known parameters of pulsar PSR 0531+21, the considered mechanism yields the strength of magnetic fieldB=10–3 G observed in the nebula. The disk structure must be destroyed toward the edges of the nebula.  相似文献   

9.
A theory of pulsar radio emission generation, in which the observed waves are produced directly by the maser-type plasma instabilities on the anomalous cyclotron-Cherenkov resonance and the Cherenkov-drift resonance , is capable of explaining the main observational characteristics of pulsar radio emission. The instabilities are due to the interaction of the fast particles of the primary beam and from the tail of the distribution with the normal modes of a strongly magnetized one-dimensional electron-positron plasma. The waves emitted at these resonances are vacuum-like electromagnetic waves that may leave the magnetosphere directly. The cyclotron-Cherenkov instability is responsible for core emission pattern and the Cherenkov-drift instability produces conal emission. The conditions for the development of the cyclotron-Cherenkov instability are satisfied for the both typical and millisecond pulsars provided that the streaming energy of the bulk plasma is not very high γ p = 5 ÷ 10. In a typical pulsar the cyclotron-Cherenkov and Cherenkov-drift resonances occur in the outer parts of magnetosphere at r res ≈ 109cm. This theory can account for various aspects of pulsar phenomenology including the morphology of the pulses, their polarization properties and spectral behavior. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

10.
The model of the pulsar magnetosphere filled with massless charged particles (rest massm=0) is considered. The gas of charged massless particles can be found in two different phases: (1) dynamical phase (DP), when the particles move with nonvanishing energy along some base line, determined by the electromagnetic field only, (2) statical phase (SP), when the particles have vanishing energy =0. The pulsar magnetosphere occurs to be divided into regions of different types: (a) the accelerating regions (DP-regions) containing only DP, (b) the capture regions, containing only SP, (3) leaky capture regions, where DP moves through SP. The leaky capture regions are the active regions, which are responsible for the pulsar radioemission. In the case of oblique magnetic moment the equation for the capture surface has been obtained. The capture region is formed around this surface. Expressions for jumps of the electromagnetic field, the current density and the charge density on the capture region boundary have been obtained. The problem of the pulsar magnetosphere is stated mathematically in the case of oblique magnetic moment and ejection of only electrons.  相似文献   

11.
The 24-year-old pulsar problem is reconsidered. New results are obtained by replacing the assumption of steady-state discharges near the polar caps by oscillatory discharges, and by creating the neutral-excess pair plasma via inverse-Compton collisions rather than via curvature radiation. As a result, the electrons and positrons which compose the pulsar wind have different bulk velocities and an oscillating space density, and (strong) coherent curvature radiation is implied (without invoking the excitation of instabilities, and contrary to existing proofs of its impossibility). The magnetospheres of young pulsars are likely to have considerable higher-order multipole components, in particular octupole. Radiation transfer through the pulsar magnetosphere results in fan beams whose polarization is dictated by the bottom of the radiation zone, hence, looks like curvature radiation from dipole-like polar caps.Wind generation depends mainly on the quantityB2 which takes similar values for the ms pulsars; the latter compensate for (somewhat) weaker fields by wider polar caps and smaller curvature radii.  相似文献   

12.
The synchrotron mechanism of radiation from the Crab pulsar has been investigated on the assumption that the mechanism acts in a source moving with relativistic velocity round a neutron star. A detailed matching has been made of the theoretical spectra of synchrotron radiation from relativistic electrons with the results of measurements of the radiation flux from the Crab pulsar in the infrared, optical and X-ray ranges. The parameters of the radiating region (intensity of the magnetic field, source dimensions, density and lifetime of radiating electrons) have been found. They are expressed through the ratio of the energy density of the magnetic field in the source to that of radiating electrons. The level of Compton-radiation in this region is estimated. Possible values of at which the level will correspond to the available results of measurements of the-radiation flux from the Crab pulsar are given. An estimate is presented for the surface magnetic field of the neutron star which does not contradict those obtained from considerations of the magnetic flux conservation when compressing the object up to the neutron star dimensions.  相似文献   

13.
We have discussed, in general, the important physical parameters, likemaximum mass, radius, and the minimum rotation period of self-bound,causally consistent, and pulsationally stable neutron stars (Q-starmodels) by using a realistic stiff EOS (such that, the speed of sound,v P N, or nP=K(E-E a ) n, where K 1 and n =1/(1-2N);where P and E represent respectively, the pressure and theenergy-density, and E a is the value of E at the surface (r = a) of the configuration) within the two constraints imposed by: (i) The minimumrotation period, P rot, for the pulsar known to date corresponds to1.558 ms, and (ii) The maximum number density anywhere inside thestructure for the models described as Q-stars cannot exceed 1nucleon/fm3. By using the empirical formula given by Koranda,Stergioulas and Friedman (1997) (KSF-formula), and imposing constraint(i), we have obtained an upper bound of M max 7.76 M radius a 32.5 km, and the central energy-density around 2.17 ×1014 g cm-3 (for n =1.01). Constraint (ii) provides the minimumrotation period, P rot 0.489 ms for the maximum mass M max 2.4 M, and the central energy-density around 2.20 ×1015 g cm-3 (for n =1.01). The speed of sound at the centre ofthese models approaches 99% of the speed of light `c' (in thevacuum) and vanishes at the surface of the configuration together withpressure. If we relax the maximum Kepler frequency imposed by the fastestrotating pulsar known to date (constraint (i)), in view of certainobservational effects and theoretical evidences, and allow the present EOSto produce larger rotation rates than the 1.558 ms pulsar, the maximummass of the non-rotating model drops down to a value 7.2 M .The higher values of masses ( 7 M ) and radii (31-32 km) obtained in this study imply that these models may representthe massive compact objects like Cyg X-1, Cyg XR-1, LMC X-3, and otherswhich are known as black hole candidates (BHCs). This study also suggestthat the strongest contender for black hole at present might be recurrentnova V404 Cyg (mass estimate 8 -12 M ).  相似文献   

14.
The production of magnetic monopoles-antimonopoles pairs is expected in the interactions of highly energetic particles in the outer gaps of a pulsar. We estimate upper limit for production of monopoles withm g 104 GeV c –2 ine + e – interactions of the order ee 10–32 cm–2.  相似文献   

15.
Radio observations of the Lyrid meteor shower obtained by a forward scatter radio system (Bologna-Lecce) in 1994 are analysed and discussed. The shower maximum appeared at solar longitude 31.0°(1950.0) and a distinct displacement between the maxima of the short-duration (< 1s) and long-duration ( 1s) echoes is observed. The shower has displayed a high activity, but no exceptional burst similar to that one observed in 1982, was recorded. It has been shown that the shower activity continues down to the smallest particle size of which existence in a meteoroid stream means their recent origin.  相似文献   

16.
Theoretical distributions of pulsar dispersion measures (times sinb II) are computed for various assumed pulsar spatial distributions above (and below) the galactic plane, assuming a distribution for the ionized gas. The statistics on the twelve high-latitude pulsars lead to the conclusion that the pulsar distribution inz is at least as broad as the distribution of the ionized gas. The value derived for the local mean interstellar electron density in the galactic plane is 0.12 cm–3 and is interpreted to be due to a uniform ionized intercloud medium.Interstellar absorption of radio waves at low frequencies and cosmic X-rays at low energies are considered with regard to irregularities in the distribution of ionized gas. It is shown that if the obervations are made with a wide angle receiver the effective absorption optical deph is –2/2 where is the mean value and is the dispersion in . This relation assumes is much larger than . Analysis of recent low-frequency radio measurements from a satellite-borne receiver, however, leads to the conclusion that effects of irregulatirities are large.  相似文献   

17.
This article describes in detail a burst from PSR 0950+08 on July 29, 1992. This event was observed by two radio telescopes (separated by ~ 200 km) operating at 103 MHz. There exists a very convincing indirect evidence that at the same time the pulsar also emitted large X-ray flux. The X-ray flux during the event compares with that during a solar X-ray flare. During the event the Sun was extraordinarily quiet as the solar X-ray flux 3 · 10–7 W/m2 only was observed. The cause for the burst is quite unknown and may be complex. However, a possibility of accretion of a comet-like object by pulsar may provide reasonable explanation of the observations. These results open some interesting questions about the pulsar physics.  相似文献   

18.
《Astroparticle Physics》2008,29(4):243-256
A method is developed to search for air showers initiated by photons using data recorded by the surface detector of the Auger Observatory. The approach is based on observables sensitive to the longitudinal shower development, the signal risetime and the curvature of the shower front. Applying this method to the data, upper limits on the flux of photons of 3.8×10-3, above , are derived, with corresponding limits on the fraction of photons being 2.0%, 5.1%, and 31% (all limits at 95% c.l.). These photon limits disfavor certain exotic models of sources of cosmic rays. The results also show that the approach adopted by the Auger Observatory to calibrate the shower energy is not strongly biased by a contamination from photons.  相似文献   

19.
The activity of the Leonid shower in the years 1944–1953 was derived from visual records obtained at the Skalnaté Pleso Observatory, using the zenithal exponent = 1.47 in the reduction factor cos z R.  相似文献   

20.
The two Earth-like mass objects orbiting a 6.2-ms pulsar, PSR1257+25, have survived more than one year of close scrutiny aimed at verifying their existence and remain the most serious candidates to become the first planets detected beyond the Solar System. The analysis of systematic timing measurements of the pulsar made over a 2.5-year period continues to require the presence of two planets with the minimum masses of 3.4M and 2.8M and the corresponding distances from PSR1257+12 of 0.36 AU and 0.47 AU to correctly predict the pulse arrival times. The presently available 3µs rms accuracy of this procedure leaves little room for significant contributions to the pulsar's timing from any mechanisms other than the Keplerian motion. A detection of the effect of planetary perturbations on pulse arrival times which is commonly accepted as the most convincing way to furnish a 100% proof of the reality of pulsar planets is already possible at a 2 level. Intensive searches for millisecond pulsars now under way at various observatories are expected to address a very intriguing question of the frequency of occurrence of neutron star planetary systems.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.  相似文献   

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