共查询到20条相似文献，搜索用时 31 毫秒
1.
Xiao-Peng You Jin-lin Han National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2006,6(2):237-246
We update the systematic studies of circular polarization in integrated pulse profiles by Han et al. Data of circular polarization profiles are compiled. Sense reversals can occur in core or cone components, or near the intersection between components. The correlation between the sense of circular polarization and the sense of position angle variation for conal-double pulsars is confirmed with a much large database. Circular polarization of some pulsars has clear changes with frequency. Circular polarization of millisecond pulsars is marginally different from that of normal pulsars. 相似文献
2.
Peter L. Gonthier Sarah A. Story Brian D. Clow Alice K. Harding 《Astrophysics and Space Science》2007,309(1-4):245-251
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
3.
Alice K. Harding Isabelle A. Grenier Peter L. Gonthier 《Astrophysics and Space Science》2007,309(1-4):221-230
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
4.
In this paper, we describe pulsar observations at decametric wavelengths using the Gauribidanur Radio Telescope made subsequent
to our earlier measurements (Deshpande & Radhakrishnan 1992). To improve the time-resolution in our measurements of pulse
profiles, we have used the ‘swept-frequency dedispersion’ method with some modifications to suit its application at such low
radio frequencies. We also present a new scheme that simplifies the calibration of the receiver gain characteristics. We present
average profiles on four pulsars from these improved measurements at 34.5 MHz. 相似文献
5.
6.
A. Noutsos A. Karastergiou M. Kramer S. Johnston B. W. Stappers 《Monthly notices of the Royal Astronomical Society》2009,396(3):1559-1572
We have detected significant rotation measure (RM) variations for nine bright pulsars, as a function of pulse longitude. An additional sample of 10 pulsars showed a rather constant RM with phase, yet a small degree of RM fluctuation is visible in at least three of those cases. In all cases, we have found that the rotation of the polarization position angle across our 1.4 GHz observing band is consistent with the λ2 law of interstellar Faraday rotation. We provide for the first time convincing evidence that RM variations across the pulse are largely due to interstellar scattering, although we cannot exclude that magnetospheric Faraday rotation may still have a minor contribution; alternative explanations of this phenomenon, like erroneous de-dispersion and the presence of non-orthogonal polarization modes, are excluded. If the observed, phase-resolved RM variations are common amongst pulsars, then many of the previously measured pulsar RMs may be in error by as much as a few tens of rad m−2 . 相似文献
7.
The behaviour of pulsars at low radio-frequencies (below ≈ 50 MHz) remains poorly understood mainly due to very limited observational
data on pulsars at these frequencies. We report here our measurements of pulse profiles at 34.5 MHz of 8 pulsars using the
Gauribidanur Radio Telescope. None of the 8 pulsars show any significant interpulse emission at this frequency which conflicts
with an earlier claim from 25 MHz observations. With the exception of one pulsar (PSR 0943 + 10) all the observed pulsars
show turnovers at frequencies above 35 MHz in their spectra. We also report our attempts to study the short and long term
variations in the pulsar signals at this low frequency. 相似文献
8.
We quantify the level of polarization of the atmosphere due to Zeeman splitting of oxygen in the Earth’s magnetic field and compare it to the level of polarization expected from the polarization of the cosmic microwave background radiation. The analysis focuses on the effect at mid-latitudes and at large angular scales. We find that from stratospheric balloon borne platforms and for observations near 100 GHz the atmospheric linear and circular polarized intensities are about 10−12 and 100 × 10−9 K, respectively, making the atmosphere a negligible source of foreground. From the ground the linear and circular polarized intensities are about 10−9 and 100 × 10−6 K, making the atmosphere a potential source of foreground for the CMB E (B) mode signal if there is even a 1% (0.01%) conversion of circular to linear polarization in the instrument. 相似文献
9.
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
10.
Polarization observations of 66 southern pulsars 总被引：1，自引：0，他引：1
R. N.Manchester J. L.Han G. J.Qiao 《Monthly notices of the Royal Astronomical Society》1998,295(2):280-298
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
11.
R. N. Manchester 《Journal of Astrophysics and Astronomy》1995,16(2):107-117
Observations of mean or average pulse profiles and their polarization give us much information on the shape of pulsar beams.
The observed polarization variations, profile symmetry and frequency dependence of profile shape strongly suggest that the
emission beam is conical and emitted from the vicinity of a magnetic pole. Central and outer parts of the beam have somewhat
different properties, but the evidence is that they are emitted by the same basic mechanism. Recent observations suggest that
the highly polarized pulse components seen in young pulsars may be emitted at a large angle to the magnetic axis. 相似文献
12.
P. L. Gonthier R. Van Guilder A. K. Harding I. A. Grenier C. A. Perrot 《Astrophysics and Space Science》2005,297(1-4):71-80
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
13.
Polarimetric observations of 300 pulsars have been conducted with the 76-m Lovell telescope at Jodrell Bank at radio frequencies centred around 230, 400, 600, 920, 1400 and 1600 MHz. More than half of the pulsars have no previously published polarization profiles and this compilation represents about three times the sum of all previously published pulsar polarization data. A selection of integrated polarization profiles is provided. Tables of pulse widths and the degree of both linear and circular polarization are given for all pulsars, and these act as an index for all the data, which are available by anonymous ftp in numerical and graphical form. 相似文献
14.
15.
We offer two possible explanations to account for the characteristics of integrated pulse profiles, in particular their degree
of complexity, their variation from pulsar to pulsar, their stability, and the tendency of complex profiles to be associated
with older pulsars.
It is proposed that the pulse structure could be a reflection of surface irregularities at the polar caps, and it is shown
how the surface relief can affect the number of positrons released into the magnetosphere which are subsequently responsible
for the observed radio radiation. The electrons produced in the vacuum break-down in the gap carry enough energy to allow
creating such a surface relief in ∼ 106 years, and one way in which this could be achieved is discussed.
Alternatively, the presence of multipole components in the magnetic fields of older pulsars could lead to significant variations
in the curvature of the field lines across the gap, and hence to structure in the integrated pulse profiles. An assessment
of the two hypotheses from observed pulse profiles seems to favour the polar cap relief picture.
An erratum to this article is available at . 相似文献
16.
在本文中先简要介绍了８０年代以来射电脉冲星方面的观测进展，然后详细介绍了射电脉冲星的第一手观测资料，包括空间分布，传播特性，时间特性，脉冲轮廓与偏振以及频谱特性等，并详细综述观测资料对我们提供的信息及给我们的启示，为理论模型的建立和检验提供了基础。 相似文献
17.
We have made a statistical analysis on the subpulse width, the mean pulse width and the rate of change of polarization angle in pulsars. We obtained a number of empirical relations showing how these radio emission characteristics are related to the magnetic inclination and discussed the physical implications of the relations. 相似文献
18.
D. R. Lorimer A. J. Faulkner A. G. Lyne R. N. Manchester M. Kramer M. A. McLaughlin G. Hobbs A. Possenti I. H. Stairs F. Camilo M. Burgay N. D'Amico A. Corongiu F. Crawford 《Monthly notices of the Royal Astronomical Society》2006,372(2):777-800
We present the discovery and follow-up observations of 142 pulsars found in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. These new discoveries bring the total number of pulsars found by the survey to 742. In addition to tabulating spin and astrometric parameters, along with pulse width and flux density information, we present orbital characteristics for 13 binary pulsars which form part of the new sample. Combining these results from another recent Parkes multibeam survey at high Galactic latitudes, we have a sample of 1008 normal pulsars which we use to carry out a determination of their Galactic distribution and birth rate. We infer a total Galactic population of 30 000 ± 1100 potentially detectable pulsars (i.e. those beaming towards us) having 1.4-GHz luminosities above 0.1 mJy kpc2 . Adopting the Tauris & Manchester beaming model, this translates to a total of 155 000 ± 6000 active radio pulsars in the Galaxy above this luminosity limit. Using a pulsar current analysis, we derive the birth rate of this population to be 1.4 ± 0.2 pulsars per century. An important conclusion from our work is that the inferred radial density function of pulsars depends strongly on the assumed distribution of free electrons in the Galaxy. As a result, any analyses using the most recent electron model of Cordes & Lazio predict a dearth of pulsars in the inner Galaxy. We show that this model can also bias the inferred pulsar scaleheight with respect to the Galactic plane. Combining our results with other Parkes multibeam surveys we find that the population is best described by an exponential distribution with a scaleheight of 330 pc. Surveys underway at Parkes and Arecibo are expected to improve the knowledge of the radial distribution outside the solar circle, and to discover several hundred new pulsars in the inner Galaxy. 相似文献
19.
K. E. McGowan M. J. Coe M. Schurch V. A. McBride J. L. Galache W. R. T. Edge R. H. D. Corbet S. Laycock A. Udalski D. A. H. Buckley 《Monthly notices of the Royal Astronomical Society》2007,376(2):759-770
We investigate the X-ray and optical properties of a sample of X-ray bright sources from the Small Magellanic Cloud (SMC) Wing Survey. We have detected two new pulsars with pulse periods of 65.8 s (CXOU J010712.6−723533) and 700 s (CXOU J010206.6−714115), and present observations of two previously known pulsars RX J0057.3−7325 (SXP101) and SAX J0103.2−7209 (SXP348). Our analysis has led to three new optical identifications for the detected pulsars. We find long-term optical periods for two of the pulsars, CXOU J010206.6−714115 and SXP101, of 267 and 21.9 d, respectively. Spectral analysis of a subset of the sample shows that the pulsars have harder spectra than the other sources detected. By employing a quantile-based colour–colour analysis we are able to separate the detected pulsars from the rest of the sample. Using archival catalogues we have been able to identify counterparts for the majority of the sources in our sample. Combining this with our results from the temporal analysis of the Chandra data and archival optical data, the X-ray spectral analysis, and by determining the X-ray to optical flux ratios we present preliminary classifications for the sources. In addition to the four detected pulsars, our sample includes two candidate foreground stars, 12 probable active galactic nuclei, and five unclassified sources. 相似文献
20.
Altan Baykal Ça&#;da&#; &#;nam M. Ali Alpar Jean in 'T Zand Tod Strohmayer 《Monthly notices of the Royal Astronomical Society》2001,327(4):1269-1272
Using X-ray data from the Rossi X-ray Timing Explorer , we report the pulse timing results of the accretion-powered, high-mass X-ray binary pulsar 4U 1907+09, covering a time-span of almost two years. We measured three new pulse periods in addition to the previously measured four pulse periods. We are able to connect pulse arrival times in phase for more than a year. The source has been spinning down almost at a constant rate, with a spin-down rate of for more than 15 yr. Residuals of pulse arrival times yield a very low level of random-walk noise, with a strength of ∼ on a time-scale of 383 d, which is 40 times lower than that of the high-mass X-ray binary pulsar Vela X-1. The noise strength is only a factor of 5 greater than that of the low-mass X-ray binary pulsar 4U 1626−67. The low level of the timing noise and the very stable spin-down rate of 4U 1907+09 make this source unique among the high-mass X-ray binary pulsars, providing another example, in addition to 4U 1626−67, of long-term quiet spin down from an accreting source. These examples show that the extended quiet spin-down episodes observed in the anomalous X-ray pulsars 1RXS J170849.0−400910 and 1E 2259+586 do not necessarily imply that these sources are not accreting pulsars. 相似文献