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 15 毫秒
1.
We present results of our pulsar population synthesis of normal and millisecond pulsars in the Galactic plane. Over the past several years, a program has been developed to simulate pulsar birth, evolution and emission using Monte Carlo techniques. We have added to the program the capability to simulate millisecond pulsars, which are old, recycled pulsars with extremely short periods. We model the spatial distribution of the simulated pulsars by assuming that they start with a random kick velocity and then evolve through the Galactic potential. We use a polar cap/slot gap model for γ-ray emission from both millisecond and normal pulsars. From our studies of radio pulsars that have clearly identifiable core and cone components, in which we fit the polarization sweep as well as the pulse profiles in order to constrain the viewing geometry, we develop a model describing the ratio of radio core-to-cone peak fluxes. In this model, short period pulsars are more cone-dominated than in our previous studies. We present the preliminary results of our recent study and the implications for observing these pulsars with GLAST and AGILE.   相似文献   

2.
The shape of pulsar radio beams   总被引：1，自引：0，他引：1  
Using all available multicomponent radio pulse profiles for pulsars with medium to long periods and good polarization data, we have constructed a two-dimensional image of the mean radio beam shape. This shows a peak near the centre of the beam but is otherwise relatively uniform with only mild enhancements in a few regions. This result supports the patchy beam model for emission beams, in which the mean beam shape represents the properties of the emission mechanism and observed pulse components result from emission sources distributed randomly across the beam.  相似文献   

3.
We have used the 76-m Lovell, 94-m equivalent Westerbork Synthesis Radio Telescope (WSRT) and 100-m Effelsberg radio telescopes to investigate the simultaneous single-pulse properties of the radio emitting magnetar Anomalous X-ray Pulsar (AXP) XTE J1810−197 at frequencies of 1.4, 4.8 and 8.35 GHz during 2006 May and July. We study the magnetar's pulse-energy distributions which are found to be very peculiar as they are changing on time-scales of days and cannot be fit by a single statistical model. The magnetar exhibits strong spiky single giant-pulse-like subpulses, but they do not fit the definition of the giant pulse or giant micropulse phenomena. Measurements of the longitude-resolved modulation index reveal a high degree of intensity fluctuations on day-to-day time-scales and dramatic changes across pulse phase. We find the frequency evolution of the modulation index values differs significantly from what is observed in normal radio pulsars. We find that no regular drifting subpulse phenomenon is present at any of the observed frequencies at any observing epoch. However, we find a quasi-periodicity of the subpulses present in the majority of the observing sessions. A correlation analysis indicates a relationship between components from different frequencies. We discuss the results of our analysis in light of the emission properties of normal radio pulsars and a recently proposed model which takes radio emission from magnetars into consideration.  相似文献   

4.
We present a geometric study of the radio and γ-ray pulsar B1055−52 based on recent observations at the Parkes radio telescope. We conclude that the pulsar's magnetic axis is inclined at an angle of 75° to its rotation axis and that both its radio main pulse and interpulse are emitted at the same height above their respective poles. This height is unlikely to be higher or much lower than 700 km, a typical value for radio pulsars.
It is argued that the radio interpulse arises from emission formed on open fieldlines close to the magnetic axis which do not pass through the magnetosphere's null (zero-charge) surface. However, the main pulse emission must originate from fieldlines lying well outside the polar cap boundary beyond the null surface, and farther away from the magnetic axis than those of the outer gap region where the single γ-ray peak is generated. This casts doubt on the common assumption that all pulsars have closed, quiescent, corotating regions stretching to the light cylinder.  相似文献   

5.
Pulsars play a crucial astrophy sical role as highly energetic compact radio, X-ray and gammaray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope(LAT) on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars: log B_(lc)(G) are 3.60-3.95 and 1.75 correspondingly. Moreover,their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average: log E(erg s~(-1)) = 35.37-35.53 and 32.64. The correlation between gammaray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand,the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.  相似文献   

6.
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   

7.
Pulsar radio emission beams have been studied observationally for a long time, and the suggestion is that they consist of the so-called core and conal components. To reproduce these components is a challenge for any emission model, and that the pulse profile of pulsars changes with frequency presents even a greater challenge. Assuming a local surface magnetic structure (to produce the core or central beam) and a global dipole magnetic field (to produce the conal beams), Gil & Krawczyk (1997) applied curvature radiation to the pulse profile simulation of PSR J0437-4715 (hereafter the GK model). Here we present an alternative multi-frequency simulation of the same profiles within the framework of the Inverse Compton Scattering (ICS) model. It is obtained from our simulation (1) that besides the core, the inner cone and the outer cone, there is an outer-outer cone; (2) that the emission components of the core and cones evolve strongly with frequency. Some important differences between the ICS model and the  相似文献   

8.
We report on a sensitive survey for radio pulsar wind nebulae (PWN) towards 27 energetic and/or high-velocity pulsars. Observations were carried out at 1.4 GHz using the Very Large Array and the Australia Telescope Compact Array and utilized pulsar-gating to search for off-pulse emission. These observing parameters resulted in a considerably more sensitive search than previous surveys and could detect PWN over a much wider range of spatial scales (and hence ambient densities and pulsar velocities). However, no emission clearly corresponding to a PWN was discovered. Based on these non-detections we argue that the young and energetic pulsars in our sample have winds which are typical of young pulsars, but produce unobservable PWN because they reside in low-density ( n ∼0.003 cm−3) regions of the interstellar medium. However, non-detection of PWN around older and less energetic pulsars can only be explained if the radio luminosity of their winds is less than 10−5 of their spin-down luminosity, implying an efficiency at least an order of magnitude smaller than that seen for young pulsars.  相似文献   

9.
Scintillation of pulsar radio emission provides information about the interstellar medium along the path to the pulsar and the velocities of pulsars. It also affects the precision of pulse timing observations. Using a pulsar timing system developed at the Urumqi Astronomical Observatory25 m telescope, we observed diffractive scintillation dynamic spectra for several strong northern pulsars. This paper introduces the observing system and discusses the observational results. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

10.
The connection between the radio emission from “lightnings” produced by the absorption of high-energy photons from the cosmic gamma-ray background in a neutron star magnetosphere and radio bursts from rotating ratio transients (RRATs) is investigated. The lightning length reaches 1000 km; the lightning radius is 100 m and is comparable to the polar cap radius. If a closed magnetosphere is filled with a dense plasma, then lightnings are efficiently formed only in the region of open magnetic field lines. For the radio emission from a separate lightning to be observed, the polar cap of the neutron star must be directed toward the observer and, at the same time, the lightning must be formed. The maximum burst rate is related to the time of the plasma outflow from the polar cap region. The typical interval between two consecutive bursts is ∼100 s. The width of a single radio burst can be determined both by the width of the emission cone formed by the lightning emitting regions at some height above the neutron star surface and by a finite lightning lifetime. The width of the phase distribution for radio bursts from RRATs, along with the integrated pulse width, is determined by the width of the bundle of open magnetic field lines at the formation height of the radio emission. The results obtained are consistent with the currently available data and are indicative of a close connection between RRATs, intermittent pulsars, and extreme nullers.  相似文献   

11.
Two investigations of millisecond pulsar radiation are discussed: average total intensity pulse morphology and individual pulse to pulse fluctuations. The average emission profiles of millisecond pulsars are compared with those of slower pulsars in the context of polar cap models. In general the full widths of pulsar emission regions continue to widen inversely with periodP as P-(0.30-0.5) as expected for dipole polar cap models. Many pulse components are very narrow. The period scaling of pulsar profiles -separations and widths -can tell us about the angular distribution of radiating currents. An investigation of individual pulses from two millisecond pulsars at 430 MHz shows erratic pulse to pulse variations similar to that seen in slow pulsars. PSR B1937+21 displays occasional strong pulses that are located in the trailing edge of the average profile with relative flux densities in the range of 100 to 400. These are similar to the giant pulses seen in the Crab pulsar.  相似文献   

12.
Polarization observations of 66 southern pulsars   总被引：1，自引：0，他引：1  
Mean pulse profiles and polarization parameters at 435, 660 or 1500 MHz obtained using the ATNF Parkes radio telescope are presented for 66 southern pulsars. About half of these pulsars were discovered in the Parkes southern pulsar survey and most have no previously published polarization parameters. Where possible, beam impact parameters and inclination angles are computed assuming a circular beam geometry and the rotating-vector model. Implications of the results for models of the pulse emission mechanism are briefly discussed.  相似文献   

13.
The magnetospheric locations of pulsar radio emission region are not well known. The actual form of the so-called radius-to-frequency mapping should be reflected in the aberration–retardation (A/R) effects that shift and/or delay the photons depending on the emission height in the magnetosphere. Recent studies suggest that in a handful of pulsars the A/R effect can be discerned with respect to the peak of the central core emission region. To verify these effects in an ensemble of pulsars, we launched a project analysing multifrequency total intensity pulsar profiles obtained from the new observations from the Giant Meterwave Radio Telescope (GMRT), Arecibo Observatory (AO) and archival European Pulsar Network (EPN) data. For all these profiles, we measure the shift of the outer cone components with respect to the core component, which is necessary for establishing the A/R effect. Within our sample of 23 pulsars, seven show the A/R effects, 12 of them (doubtful cases) show a tendency towards this effect, while the remaining four are obvious counterexamples. The counterexamples and doubtful cases may arise from uncertainties in the determination of the location of the meridional plane and/or the core emission component. Hence, it appears that the A/R effects are likely to operate in most pulsars from our sample. We conclude that in cases where those effects are present the core emission has to originate below the conal emission region.  相似文献   

14.
Pulsars are fast rotating neutron stars with a strong magnetic field, that emit over a wide frequency range. In spite of all efforts during the 40 years after the discovery of pulsars, the mechanism of their radio emission so far remains unknown. We propose a new approach to solving this problem for a subset of pulsars with a high-frequency cutoff of the spectrum from the Pushchino catalogue (the “Pushchino” sample). We provide a theoretical explanation of the observed dependence of the high-frequency cutoff on the pulsar period, and we predict the dependence of the cutoff position from the magnetic field. This explanation is based on a new mechanism for electron radio emission in pulsars. Namely, radiation occurs in the inner (polar) gap, when electrons are accelerated in the electric field that is increasing from zero level at the star surface. In this case the acceleration of electrons passes through a maximum and goes to zero when the electron velocity approaches the speed of light. All the radiated power is located within the radio frequency band. The averaging of radiation intensity over the polar cap, with some natural assumptions of the coherence of the radiation, leads to the observed spectra. It also leads to an acceptable estimate of the power of radio emission.  相似文献   

15.
We present results of a population synthesis study of radio-loud and radio-quiet γ-ray pulsars from the Galactic plane and the Gould Belt. The simulation includes the Parkes multibeam pulsar survey, realistic beam geometries for radio and γ-ray emission from neutron stars and the new electron density model of Cordes and Lazio. Normalizing to the number of radio pulsars observed by a set of nine radio surveys, the simulation suggests a neutron star birth rate of 1.4 neutron stars per century in the Galactic plane. In addition, the simulation predicts 19 radio-loud and 7 radio-quiet γ-ray pulsars from the plane that EGRET should have observed as point sources. Assuming that during the last 5 Myr the Gould Belt produced 100 neutron stars, only 10 of these would be observed as radio pulsars with three radio-loud and four radio-quiet γ-ray pulsars observed by EGRET. These results are in general agreement with the recent number of about 25 EGRET error boxes that contain Parkes radio pulsars. Since the Gould Belt pulsars are relatively close by, the selection of EGRET radio-quiet γ-ray pulsars strongly favors large impact angles, β, in the viewing geometry where the off-beam emission from curvature radiation provides the γ-ray flux. Therefore, the simulated EGRET radio-quiet γ-ray pulsars, being young and nearby, most closely reflect the current shape of the Gould Belt suggesting that such sources may significantly contribute to the EGRET unidentified γ-ray sources correlated with the Gould Belt.  相似文献   

16.
Absorption of radio emission through normal cyclotron resonance within pulsar magnetospheres is considered. The optical depth for cyclotron damping is calculated using a plasma distribution with an intrinsically relativistic spread. We argue that such a broad distribution is plausible for pulsar plasmas and that it implies that a class of pulsars that should have cyclotron damping extends to include young pulsars with shorter periods and stronger magnetic fields. There is no obvious observational evidence for disruption of radio pulses, which implies that the optical depth cannot be too large. We propose that cyclotron resonance may cause marginal absorption of radio emission. It is shown that such marginal absorption produces potentially observable asymmetric features for double-peak pulse profiles with wide separation, with one peak tending to be suppressed.  相似文献   

17.
We discuss the correlations between the luminosities of radio pulsars in various frequency ranges and the magnetic fields on the light cylinder. These correlations suggest that the observed emission is generated in outer layers of the pulsar magnetospheres by the synchrotron mechanism. To calculate the distribution functions of the relativistic particles in the generation region, we use a model of quasilinear interactions between the waves excited by cyclotron instability and particles of the primary beam and the secondary electron—positron plasma. We derive a formula for calculating the X-ray luminosity L x of radio pulsars. A strong correlation was found between L x and the parameter \(\dot P_{ - 15} /P^{3.5}\), where P is the neutron-star rotation period, in close agreement with this formula. The latter makes it possible to predict the detection of X-ray emission from more than a hundred (114) known radio pulsars. We show that the Lorentz factors of the secondary particles are small (γ p = 1.5–8.5), implying that the magnetic field near the neutron-star surface in these objects is multipolar. It follows from our model that almost all of the millisecond pulsars must emit X-ray synchrotron radiation. This conclusion differs from predictions of other models and can be used to test the theory under consideration. The list of potential X-ray radiators presented here can be used to search for X-ray sources with existing instruments.  相似文献   

18.
Known classes of radio wavelength transients range from the nearby stellar flares and radio pulsars to the distant Universe γ‐ray burst afterglows. Hypothesized classes of radio transients include analogs of known objects, e.g., extrasolar planets emitting Jovian‐like radio bursts and giant‐pulse emitting pulsars in other galaxies, to the exotic, prompt emission from γ‐ray bursts, evaporating black holes, and transmitters from other civilizations. A number of instruments and facilities are either under construction or in early observational stages and are slated to become available in the next few years. With a combination of wide fields of view and wavelength agility, the detection and study of radio transients will improve immensely. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
We present the results of modelling of the radio spectrum evolution and dispersion measure variations of PSR B1259–63, a pulsar in a binary system with Be star LS 2883.We base our model on a hypothesis that the observed variations of the spectrum are caused by thermal free-free absorption occurring in the pulsar surroundings. We reproduce the observed pulsar spectral shapes in order to examine the influence of the stellar wind of LS 2883 and the equatorial disc on the pulsar’s radiation.The simulations of the pulsar’s radio emission and its consequent free-free absorption give us an insight into the impact of stellar wind and equatorial disc of LS 2883 has on the shapes of PSR B1259–63 radio spectra, providing an evidence for the connection between gigahertz-peaked spectra phenomenon and the close environment of the pulsar. Additionally, we supplement our model with an external absorbing medium, which results in a good agreement between simulated and observational data.  相似文献   

20.
This review describes the observational properties of radio pulsars, fast rotating neutron stars, emitting radio waves. After the introduction we give a list of milestones in pulsar research. The following chapters concentrate on pulsar morphology: the characteristic pulsar parameters such as pulse shape, pulsar spectrum, polarization and time dependence. We give information on the evolution of pulsars with frequency since this has a direct connection with the emission heights, as postulated in the radius to frequency mapping (RFM) concept. We deal successively with the properties of normal (slow) pulsars and of millisecond (fast-recycled) pulsars. The final chapters give the distribution characteristics of the presently catalogued 1300 objects.Received: 5 December 2003, Published online: 15 April 2004 Correspondence to: Richard Wielebinski  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