Angles between the rotational axis and magnetic moment in 80 pulsars from observations near 1 GHz     

I. F. Malov  E. B. Nikitina 《Astronomy Reports》2011,55(1):19-30

Data on the pulse structure and variations of the linear polarization angle at frequencies near 1 GHz have been used to estimate the angles β between the rotational axis and magnetic moment of the neutron stars assocaited with 80 pulsars. The calculations applied several methods. The minimum values of β were estimated from the observed pulse width W ₁₀ at the 10% level for the entire sample. Maximum estimates of β were obtained for six sources with small polarization position angle derivatives. Equations for the angle β were derived for various forms of the observed profile, and solutions obtained for 34 pulsars. The β values calculated using different methods are compared. For three pulsars with known interpulses, the obtained values of β demonstrate that two (PSR B1055-52 and PSR 1822-09) are aligned rotators, whereas the other (PSR B1702-19) is an orthogonal rotator. A search for interpulses and interpulse emission in PSRB1641-45, PSR1642-03, and PSR 1944+17 is necessary, and a search for an interpulse at 180° from the main pulse is required in PSR B2321-61.  相似文献   

The radio emission of anomalous pulsars     

I. F. Malov 《Astronomy Reports》2014,58(3):139-144

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   

The pulsar PSR B1931+24 as an orthogonal rotator     

I. F. Malov 《Astronomy Reports》2007,51(6):477-480

The angles of the magnetic moment μ and the line of sight L to the rotation axis Ω are estimated for the pulsar PSR B1921+24, which displays “on” and “off” periods in its radio emission. It is shown that this object is an orthogonal rotator, i.e., the angle β between μ and Ω is equal to 88°.2 and the angle between L and Ω is ζ = 98.7°, and that its rotation period should be twice the usually adopted value (P = 1.626 s). One possible reason for the peculiarities of this pulsar could be the precession of a relic disk in the equatorial region of the object. Further observations (in particular, in the infrared) are required to confirm the existence of such a disk. Polarization data for other pulsars whose radiation switches on and off (transients) are also required, to determine if they are likewise orthogonal rotators. Calculations for PSR B0656+14 show that β ∼ 20°, and the sharp increase of its pulse intensities is due to intrinsic reasons, and is not associated with a relic disk. Original Russian Text ? I.F. Malov, 2007, published in Astronomicheskiĭ Zhurnal, 2007, Vol. 84, No. 6, pp. 531–535.  相似文献   

Do magnetars really exist?     

I. F. Malov 《Astronomy Reports》2012,56(1):29-34

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The space velocities of radio pulsars     

A. A. Loginov  E. B. Nikitina  I. F. Malov 《Astronomy Reports》2016,60(2):193-203

Known models proposed to explain the high space velocities of pulsars based on asymmetry of the transport coefficients of different sorts of neutrinos or electromagnetic radiation can be efficient only in the presence of high magnetic fields (to 10¹⁶ G) or short rotation periods for the neutron stars (of the order of 1 ms). This current study shows that the observed velocities are not correlated with either the pulsar periods or their surface magnetic fields. The initial rotation periods are estimated in a model for the magnetedipolar deceleration of their spin, aßsuming that the pulsar ages are equal to their kinematic ages. The initial period distribution is bimodal, with peaks at 5 ms and 0.5 s, and similar to the current distribution of periods. It is shown that asymmetry of the pulsar electromagnetic radiation is insufficient to give rise to additional acceleration of pulsars during their evolution after the supernova explosion that gave birth to them. The observations testify to deceleration of the motion, most likely due to the influence of the interstellar medium and interactions with nearby objects. The time scale for the exponential decrease in the magnetic field τ_D and in the angle between the rotation axis and magnetic moment τ_ß are estimated, yielding τ_β = 1.4 million years. The derived dependence of the transverse velocity of a pulsar on the angle between the line of sight and the rotation axis of the neutron star corresponds to the expected dependence for acceleration mechanisms associated with asymmetry of the radiation emitted by the two poles of the star.  相似文献   

A new model of a magnetar     

I. F. Malov  G. Z. Machabeli  V. M. Malofeev 《Astronomy Reports》2003,47(3):232-239

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 B_s～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 P_dr～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 P_obs>5 s can be described by the proposed model; in this case, their rotational periods are considerably less than P_obs and the observed pulses are due to the drift waves.  相似文献   

Differences in the parameters of radio pulsars with short and long periods     

A. A. Loginov  I. F. Malov 《Astronomy Reports》2014,58(10):733-745

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   

Synchrotron spectra of short-period pulsars     

F. Malov 《Astronomy Reports》2001,45(2):138-143

A model with synchrotron radiation near the light cylinder is proposed to explain the observed spectra of short-period pulsars (P≤0.1 s). These spectra can be described if a power-law energy distribution of the emitting electrons with exponent γ=2–8 is assumed. For most pulsars, the peak frequency ν_m is below 10 MHz. The ν_m(γ) dependence is derived, and shows that the peak frequencies for pulsars with spectral indices α<1.5 may fall in the observable range. In particular, ν_m may be ν_m ～ 100 MHz for PSR J0751 + 1807 and PSR J1640 + 2224. The observed radio spectrum of Geminga (PSR J0633 + 1746) can be described by a synchrotron model with a monoenergetic or Maxwellian distribution of relativistic electrons and a small angle β between the spin axis and magnetic moment (β ～ 10°).  相似文献   

Magnetic fields of radio pulsars     

E.?B.?Nikitina  I.?F.?MalovEmail author 《Astronomy Reports》2017,61(7):591-611

The mechanism of magnetodipole braking of radio pulsars is used to calculate new values of the surface magnetic fields of neutron stars. The angles β between the spin axes and magnetic moments of the neutron stars were estimated for 376 radio pulsars using three different methods. It is shown that small inclinations of magnetic axes dominate. The equatorial magnetic fields for the considered sample of pulsars are calculated using the β values obtained. As a rule, these magnetic fields are a factor of a few higher than the corresponding values in known catalogs.  相似文献   

Detection of new pulsars at 111 MHz     

S. A. Tyul’bashev  V. S. Tyul’bashev  V. V. Oreshko  S. V. Logvinenko 《Astronomy Reports》2016,60(2):220-232

The first results of a search for pulsars using the Large Phased Array of the Lebedev Physical Institute at 111 MHz for right ascensions 0^h-24^h and declinations 21°-42° are reported. Data with a time resolution of 100 ms in six frequency channels within a 2.5-MHz frequency band have been processed. Thirty-four pulsars have been detected, of which seventeen were observed on this telescope earlier; ten known pulsars had not been observed earlier. Seven new pulsars have been discovered.  相似文献   

Polarization of individual pulses of radio pulsars at the low frequencies 40, 60, and 103 MHz     

S. A. Suleimanova  V. D. Pugachev 《Astronomy Reports》2002,46(4):309-326

Measurements of the linear polarization of individual pulses at 40, 60, and 103 MHz are presented for ten pulsars. The degree and position angle of a linear polarization were measured with a temporal resolution of 1–7 ms, and the longitudinal distributions of these parameters were constructed for each pulsar at one or more of these frequencies. These are the first such measurements for pulsars B0031-07, B0320 + 39, B0628-28, and B2217 + 47. Apart from B0628-28, all the pulsars are characterized by the simultaneous presence of orthogonal polarization modes in at least one component of the integral profile. The secondary polarization mode increases at frequencies ≤100 MHz for pulsars whose integrated pulses contain pairs of conal components (B0031-07, B0329 + 54, B0834 + 06, B1133 + 16, B2020 + 28). This is manifested both as an expansion of the longitudinal range where the secondary polarization mode is observed and an increase in its contribution to the emission at a given longitude. New data confirming the dependence of the linear polarization of individual pulses on the intensity and mode of the pulsar emission have been obtained.  相似文献   

The geometry of radio pulsar magnetospheres     

I. F. Malov  E. B. Nikitina 《Astronomy Reports》2011,55(10):878-889

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   

A spindown mechanism for short-period radio pulsars     

I. F. Malov 《Astronomy Reports》2004,48(4):337-341

It is shown that a model with accretion in a “quasi-propeller” mode can explain the observed spindown of pulsars with periods P<0.1 s. The mean accretion rate for 39 selected objects is \(\dot M = 5.6 \times 10^{ - 11} M_ \odot /year\). If \(\dot M\) is constant during the pulsar’s lifetime, the neutron star will stop rotating after 10⁷ years. The mean magnetic field at the neutron-star surface calculated in this model, \(\bar H_0 = 6.8 \times 10^8 G\), is consistent to an order of magnitude with the values of H₀ for millisecond pulsars from known catalogs. However, the actual value of H₀ for particular objects can differ from the catalog values by appreciable factors, and these quantities must be recalculated using more adequate models. The accretion disk around the neutron star should not impede the escape of the pulsar’s radiation, since this radiation is generated near the light cylinder in pulsars with P<0.1 s. Pulsars such as PSR 0531+21 and PSR 0833-45 have probably spun down due to the effect of magnetic-dipole radiation. If the difference in the braking indices for these objects from n=3 is due to the effect of accretion, the accretion rate must be of the order of 10¹⁸ g/s.  相似文献   

Distribution of regions of emission at different frequencies in pulsar magnetospheres     

I. F. Malov  E. B. Nikitina 《Astronomy Reports》2012,56(9):693-701

It is shown that the observed width of the emission profile W ₁₀ and the maximum derivative C of the polarization position angle for the mean profile of a pulsar can be used to calculate the ratio n of the emission-cone radius ?? to the minimum distance between the line of sight and the center of this cone fairly accurately. Estimates of n obtained earlier by eye based on the shape of the emission profiles are close to these more accurate values for pulsars from a catalog at a frequency near 1 GHz. Values of n are calculated for several dozen pulsars using data at 10 and 20 cm. In the standard model, the ratio of n at two frequencies is equal to the ratio of the squares of the distances from the center of the neutron star to the emission levels at the two frequencies. Statistical dependences of the profile width on the pulsar period for these wavelengths and a model assuming emission at the local plasma frequency are used to determine the absolute values of these distances. These estimates display good consistency and yield distances to the emission levels of the order of several tens of neutron-star radii. The calculations take into account possible variation of the dimensions of the polar cap associated with the inclination of the emission cone to the rotational axis of the pulsar; i.e., the influence of the angle ?? between the magnetic moment and rotational axis of the neutron star. Values of ?? calculated earlier for the pulsar sample considered are used for this analysis.  相似文献   

Peculiarities of radio pulsars with emission outside the radio range     

I. F. Malov  M. A. Timirkeeva 《Astronomy Reports》2014,58(9):611-618

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 〈B_lc〉 = 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   

Parameters of radio pulsars in binary systems and globular clusters     

A. A. Loginov  I. F. Malov 《Astronomy Reports》2017,61(2):115-121

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   

Rotational periods and other parameters of magnetars     

I. F. Malov 《Astronomy Reports》2006,50(5):398-404

The rotational periods P, period derivatives dP/dt, and magnetic fields B in the region where the emission of anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) is generated are calculated using a model that associates the emission of these objects with the existence of drift waves at the periphery of the magnetosphere of a neutron star. The values obtained for these parameters are P = 11?737 ms, dP/dt = 3.7 × 10^?16?5.5 × 10^?12, and log B (G) = 2.63?6.25. We find a dependence between the X-ray luminosity of AXPs and SGRs, L _x, and the rate at which they lose rotational energy, dE/dt, which is similar to the L _x(dE/dt) dependence for radio pulsars with detected X-ray emission. Within the errors, AXPs/SGRs and radio pulsars with short periods (P < 0.1 s) display the same slopes for their log(dP/dt)-log P relations and for the dependence of the efficiency of their transformation of rotational energy into radiation on their periods. A dipole model is used to calculate the surface magnetic fields of the neutron stars in AXPs and SGRs, which turn out to be, on average, comparable to the surface fields of normal radio pulsars (〈log B _s (G)〉 = 11.90).  相似文献   

Properties of pulsars with short and long periods     

Loginov  A. A.  Malov  I. F. 《Astronomy Reports》2015,59(11):1053-1061

A comparative analysis has been conducted for the timescale on which the observed radio emission of pulsars is switched off (nulling fraction), the polarization parameters, and the residual deviations in the pulse arrival times for pulsars with periods P >0.1 s and P <0.1 s. For the former group of pulsars, the greater the energy injected into the magnetosphere from internal layers of the neutron star, the smaller the nulling fraction; in the latter group, nullings are not observed at all. Mode switches are also observed only in pulsarswith long pulse-to-pulse intervals (P >1 s), and in many objects they are correlatedwith the presence of nullings. The degree of polarization grows with decreasing period, and is systematically higher in objects with P <0.1 s than in long-period pulsars. The relative deviations of the pulse arrival times are, on average, appreciably smaller for pulsars with P >0.1 s. The observed differences in the parameters of pulsars with short and long periods can be understood if the radiation of pulsars with P <0.1 s is generated near the light cylinder.

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Classification of radio pulsars using the principle-components method     

A. A. Loginov  I. F. Malov 《Astronomy Reports》2013,57(12):1001-1013

The principle-components method is used as a basis to analyze the distributions of known radio pulsars in spaces of eigenvectors of correlation matrices for various samples of pulsars and classification parameters (from 4 to 11 parameters characterizing the physical and kinematic properties of the objects). Pulsars with periods P < 0.1 s form a separate cluster, far from the cluster formed by “normal” pulsars with P ～ 1 s, in all the studied spaces. These two groups also differ appreciably in their other parameters (period derivatives, magnetic fields, pulse widths). In particular, the spatial velocities of short-period pulsars (106 km/s) are appreciably lower than those displayed by long-period pulsars (334 km/s). The distributions of the pulsars at southern (Z < 0) and northern (Z > 0) Galactic latitudes do not differ; i.e., there is no anisotropy in the motions in these two directions perpendicular to the Galactic plane, or in the corresponding distributions of the pulsar parameters.  相似文献   

Effect of microstructure and weathering on the strength anisotropy of porous rhyolite     

《Engineering Geology》2002,63(1-2):39-47

To study the effect of microstructure and weathering on the strength anisotropy of rock, unconfined compressive strength (UCS) tests were carried out on three porous rhyolites having the same original lithology, but different weathering periods of 2600, 20,000 and 40,000 years. The rock is mainly composed of glassy groundmass, with flow structure. UCS tests were undertaken on a series of samples at 15° intervals, from right angles to the flow structure (β=90°) to parallel (β=0°), where β is the angle between the direction of the applied load and the direction of the flow structure. The test results show that UCS-values are maximum when β=0–30° and minimum when β=60–90°. This differs from previous reports for layered anisotropic rocks such as sandstone, sandy shale, schist etc., for which, UCS-values are maximum at β=0 or 90°. It is also found that UCS-values for β=60–90° reduce rapidly in the initial stage of weathering (the first 20,000 years), while for β=0–30°, the reduction rate increases after 20,000 years. This shows that the effect of weathering on strength anisotropy is not uniform, but depends on the weathering processes of the microstructures of the rock.  相似文献