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1.
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   

2.
Ultrarelativistic electrons must be being accelerated in the Crab Nebula to maintain the synchrotron spectrum. Sufficient power to maintain the synchrotron spectrum is supplied by an observed damping of compressional motions in the central region of the nebula (the wisps of Baade). An acceleration mechanism which involves compressional motions, the gyrorelaxation effect and the removal of pitch angle anisotropies by the generation of hydromagnetic waves is formulated and applied to a model of the Crab Nebula with acceleration confined to a central region. This can account for the power supplied to the electrons, the overall shape of the spectrum and allows acceleration up to energies corresponding to the synchrotron emission of hard X-rays. The acceleration process tends to flatten an initial energy spectrum.  相似文献   

3.
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   

4.
A map of Rosette Nebula in continuum absorption is made at 34.5 MHz using the Decameter Wave Radio Telescoe at Gauribidanur, India, with a resolution of 26×40, is presented. These observations are combined with the 2700 MHz measurements of Grahamet al. (1982) to derive the electron temperature distribution across the nebula. It is found that the temperatures in the southeastern parts of the nebula are around 5000 K and increase up to 8000 K towards the northwestern regions. It is suggested that the lower electron temperatures in the southeastern regions are due to the presence of more dust there compared to other regions in the nebula.  相似文献   

5.
Rotational stability condition is applied to the PSR 1937+214 pulsar, suggesting that its rapid rotational rate may be close to the limit of rotational stability. This application implies additional bounds on the mass, radius, and moment of inertia of neutron star models, which depend on the theory of gravitation and the equation of state of cold superdense matter. Results obtained for various equations of state and theories of gravitation are used to set limits on the surface magnetic field and slow down rate of pulsar models.  相似文献   

6.
Conclusions Our chief result is the proof that pulsars can possess a quasi-steady-state magnetosphere with temperature T104–106. The magnetosphere can be maintained in this state in its part nearest the star if the plasma is heated by radiation from the star (except for P 0531, for which such radiation is nearlyinsignificant). Plasma in the main part of the magnetosphere is maintained in such a hot state as a result of Joule heat due to drift currents. Radiation from the magnetosphere of P 0531 is found basically in the optical spectrum, though the intensity is several orders of magnitude less than the observed value, so that it does not correspond to the observed optical emission from the pulsar in the Crab nebula.Erevan State University. Translated from Astrofizika, Vol. 12, No. 2, pp. 339–349, April–June, 1976.  相似文献   

7.
The magnetic field in the neutron-proton-electron (npe) layer of a neutron star is caused by quasi-stationary vortex current of superconducting and normal protons relative to the normal electrons. The same current generates the radio emission due to the Josephson effect. The radiation propagates in the magnetically-active medium and goes out the crust through the cracks to the magnetosphere (npe-layer is optically thick layer). As a result the hot radiospots on the star surface develop and a resulting polarized radiation pattern near the magnetic poles is formed. The cross-section of this radiation pattern gives the observed pulse structure of the pulsar. The variations of quasi-stationary vortex current can result in the amplitude-frequency variations of the radiation spectrum due to specific properties of the radiation mechanism. From this we have the variations of the fine spectrum structure, pulse amplitude and pulse structure and the correlation of them with the spectral index variations of pulsars in this model.  相似文献   

8.
We investigate the global evolution of a turbulent protoplanetary disk incorporating the effects of Maxwell stress due to a large-scale magnetic field permeating the disk. A magnetic field is produced continuously by an dynamo and the resultant Maxwell stress assists the viscous stress in p roviding the means for disk evolution. The most striking feature of magnetized disk evolution is the presence of the surface density bulge located in the magnetic gap, the region of the disk where the degree of ionization is too low to allow for coupli ng between the magnetic field and the gas. The bulge persists for a time of the order of 105–106 yr. The presence and persistence of the surface density bulge may have important implications for the process of planet formation and the overall characteristics of resultant planetary systems.Operated by USRA under contract No. NASW-4574 with NASA.  相似文献   

9.
Nonlinear propagation of strong low-frequency waves, as emitted by pulsars or compact galactic nuclei at their rotation frequencies, in a magnetized plasma is investigated. It is shown that even rather small amplitude waves can drive electrons to ultrarelativistic energies. In the limit when the electrons are ultrarelativistic but the ions are immobile, two types of circularly polarized waves (i.e., ± modes) are excited. In the wave zone of the Crab pulsar, both the electric field ( 3 V m–1) and the wavelength (108 m) of the - mode are larger, by an order of magnitude, than those of the + wave mode. Both ± modes can become modulationally unstable due to their nonlinear interaction with density fluctuations induced by the electrostatic waves.  相似文献   

10.
BVR data for the middle-aged radio pulsar PSR 0656+14 obtained on January 20-21, 1996 at the 6-m telescope of the Special Astrophysical Observatory are presented. The brightness of a star-like object coincident with the position of the VLA radio source in the Cousins B filter is B 25.1, with eff = 4448Å, adjacent to the HST F130LP long-pass filter. The relatively large V and R fluxes (3 or > 10-30 ergs cm-2 s-2 Hz-1) provide evidence that the optical emission of this pulsar is non-thermal up to 6600 Å. Most probably, in the UV-optical (BVR) spectral range, a power-law spectrum is super-imposed on the thermal-like emission of the neutron star surface, which could be related to the mechanism of the pulsar activity itself.  相似文献   

11.
The possible discovery of three new -ray pulsars PSR 0656+14, PSR 0950+08, and PSR 1822-09 (Ma, Lu, Yu, and Young, 1993) in data obtained with the COS-B experiment is reinvestigated using a refined technique for pulsar light curve analysis. The results of this study do not confirm the previously claimed -ray pulsar nature of any of these pulsars. Even when using the standard epoch folding technique in conjunction with energy-dependent acceptance cones, we do not detect pulsed -ray emission from these sources. We suspect that insufficient position accuracy is the cause for the discrepancy between our results and those of Maet al. (1993). We do not rule out that any one of the three candidates, or all of them, is in fact a -ray pulsar, but their spin properties must differ from those derived by Maet al. (1993). More work is needed to determine the correct high-energy properties of these three sources.  相似文献   

12.
The spherical-harmonic-Fourier analysis of the Sun's magnetic field inferred from the Greenwich sunspot data is refined and extended to include the full length (1874–1976) of the data on the magnetic tape provided by H. Balthasar. Perspective plots and grey level diagrams of the SHF power spectra for the odd and the even degree axisymmetric modes are presented. Comparing these with spectra obtained from two simulated data sets with random redistribution within the wings in the butterfly diagrams, we conclude that there is no clear evidence for the existence of any relation between the harmonic degree and the temporal frequency of the power concentrations of the inferred field. Apart from the power ridge in the narrow frequency band at 1/21.4 y –1, and low ridges at odd multiples of this frequency, there are no other spectral features. This strongly suggests that the solar magnetic cycle consists of some global oscillations of the Sun forced at a frequency 1/21.4 y –1 and, perhaps, weak resonances at its odd harmonics. The band width of the forcing frequency seems to be much less than 1/107 y –1. In case the global oscillations are torsional MHD, the significance of their parity and power peak is pointed out.  相似文献   

13.
Sunspot associated H-flares and microwave bursts occurring during the period 1972 to 1974 have been examined in relation to the magnetic strength and configurations of the sunspots and sunspot groups (abbreviated as spots). Important results obtained are: (i) percentage occurrences of flares exceeds those of microwave bursts up to a magnetic field strength of 2000 G while the reverse is true for higher field strength of spots, (ii) flare productivity (average number of flares per spot) and also burst productivity are comparatively higher in the case of and types of spots than in the case of other types of spots, (iii) the above productivities are predominantly high when magnetic configuration of spots changes during their life time, and (iv) impulsive type of microwave bursts are more associated with spots having changing type of magnetic configuration.  相似文献   

14.
The effect of a magnetic field on a thermal instability has been studied in a radiatively cooling region behind an interstellar shock of moderate propagation velocity ( 10 km s–1). It is shown that the presence of a magnetic field of a few microgauss is very effective in preventing the thermal instability from building-up density concentrations. In the absence of the magnetic field, the shock-induced thermal instability will amplify a pre-shock density inhomogeneity by more than an order of magnitude. However, in the field's presence, the amplified density contrast is shown to be only a factor 2. Implications for the trace of a sweeping broom in the Pleiades nebula are discussed.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.  相似文献   

15.
Infrared maps are used to propose that the bird is the former windzone of a blue giant which is presently radio-illuminated by PSR 1757-24. The pulsar is still deep inside its supernova shell; its space velocity is large but not excessive.  相似文献   

16.
A mechanism explaining the generation of the helium-enriched plasma-condensation colud (HAE-events) behind the front of shock waves associated with mass-ejecting flares is presented. The mechanism is based on the occurence of physical conditions, analogous to those in a Wilson cloud chamber in a magnetic field, behind the front of a flare-generated shock wave propagation out into interplanetary space. Consequently, if the solar atmosphere above the flare active region is saturated with ejected helium plasma, conditions are created for the forming of the helium-enriched plasma-condensation colud in the temperature-depressed region behind the shock wave front.  相似文献   

17.
We examine three major possible interpretations of observed reconfigurations of coronal X-ray and XUV emitting structures on a scale comparable to the size of the structures themselves. One possibility is that little change in the large-scale magnetic field configuration is associated with the change in emission. The other two possibilities are processes by which the magnetic field structure can change.We demonstrate that large changes in visibility in X-rays or XUV lines can be associated with relatively minor changes in the coronal magnetic field by showing the behavior of magnetic interconnections between individual active regions in a complex of activity observed by the S-054 X-ray spectrographic telescope on Skylab. While the large-scale interconnections are continuously present for at least several days, individual loops in these structures are visible for only relatively short times (1 day).The two theoretical possibilities which we discuss are frozen-in motion of the fields, and field line reconnection. We emphasize that reconnection occurs in regions much smaller than telescopic resolution. Because there are no measurements of the magnetic field in the corona in projection against the disk, existing observations are generally not sufficient to show in detail howmuch reconnection has occurred.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

18.
The size of the hard X-ray source in the Crab Nebula was observed with scintillation counters on board two balloons at a lunar occulatation on 24 January, 1975. The Gaussian width of the source is 34 (+17, –14) and the center thereof is offset from the pulsar by 6±4 at position angle 102°. The observed time profile can also be fitted to an alternative model of two line sources whose intensities are 48% at 11 and 25.5% at 7 on both sides of the pulsar.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.  相似文献   

19.
The exact solutions for the equilibrium of rotating gaseous disk with poloidal magnetic field are obtained. The stability of the disk with respect to uniform expansion and contraction is investigated by means of the variational principle. It is shown that if the equilibrium is determined by gravitational and magnetic forces only, the disk is in neutral equilibrium with respect to perturbations of the form r=r. The instability to short-waves perturbations is studied by the quasi-classical method. The analysis shows that if the magnetic field isH>2G, where is the surface density, then these perturbations are stabilized. The configurations of the electrical field induced by the rotation of magnetized disk are found. In conclusion, the questions of the evolution of the disk are discussed in connection with the quasar model when pulsar-like radiation is taken into account.  相似文献   

20.
The scientific performance evaluation of a photon countingimaging system is presented. The detector is constituted by an ICCD camera with RbTe photocathode(optimized for UV radiation), and dedicated electronics for the acquisition and analysis ofthe events. For each photon event on the CCD, a real-time centroid calculation is performed, inorder to reach spatial resolution down to 25 m FWHM. The system has been tested usingthe 182 cm telescope of the Asiago Observatory.A standard stars field through U Johnson filter,and the Crab pulsar (PSR 0531+21) were observed. From the photometric data, relative magnitudes of the standard stars have been derived, showing a goodlinearity of the detector in the range of flux under consideration, as expected fromprevious laboratory measurements.The pulsar's data have been processed by FFT and epoch foldingtechniques to testthe detector's timing performances in the highest resolutionmode (4.512 ms).These observations show that a space resolved time analysis ofperiodic sources can be performed with 10-7 s accuracy.  相似文献   

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