排序方式： 共有18条查询结果，搜索用时 15 毫秒
1.
X. P. You G. Hobbs W. A. Coles R. N. Manchester R. Edwards M. Bailes J. Sarkissian J. P. W. Verbiest W. van Straten A. Hotan S. Ord F. Jenet N. D. R. Bhat A. Teoh 《Monthly notices of the Royal Astronomical Society》2007,378(2):493-506
We present an analysis of the variations seen in the dispersion measures (DMs) of 20-ms pulsars observed as part of the Parkes Pulsar Timing Array project. We carry out a statistically rigorous structure function analysis for each pulsar and show that the variations seen for most pulsars are consistent with those expected for an interstellar medium characterized by a Kolmogorov turbulence spectrum. The structure functions for PSRs J1045−4509 and J1909−3744 provide the first clear evidence for a large inner scale, possibly due to ion–neutral damping. We also show the effect of the solar wind on the DMs and show that the simple models presently implemented into pulsar timing packages cannot reliably correct for this effect. For the first time we clearly show how DM variations affect pulsar timing residuals and how they can be corrected in order to obtain the highest possible timing precision. Even with our presently limited data span, the residuals (and all parameters derived from the timing) for six of our pulsars have been significantly improved by correcting for the DM variations. 相似文献
2.
S. Johnston R. Taylor M. Bailes N. Bartel C. Baugh M. Bietenholz C. Blake R. Braun J. Brown S. Chatterjee J. Darling A. Deller R. Dodson P. Edwards R. Ekers S. Ellingsen I. Feain B. Gaensler M. Haverkorn G. Hobbs A. Hopkins C. Jackson C. James G. Joncas V. Kaspi V. Kilborn B. Koribalski R. Kothes T. Landecker A. Lenc J. Lovell J.-P. Macquart R. Manchester D. Matthews N. McClure-Griffiths R. Norris U.-L. Pen C. Phillips C. Power R. Protheroe E. Sadler B. Schmidt I. Stairs L. Staveley-Smith J. Stil S. Tingay A. Tzioumis M. Walker J. Wall M. Wolleben 《Experimental Astronomy》2008,22(3):151-273
3.
M. Toscano J. S. Sandhu M. Bailes R. N. Manchester M. C. Britton S. R. Kulkarni S. B. Anderson B. W. Stappers 《Monthly notices of the Royal Astronomical Society》1999,307(4):925-933
We present improved timing parameters for 13 millisecond pulsars (MSPs), including nine new proper motion measurements. These new proper motions bring to 23 the number of MSPs with measured transverse velocities. In light of these new results we present and compare the kinematic properties of MSPs with those of ordinary pulsars. The mean transverse velocity of MSPs was found to be 85±13 km s−1 , a value consistent with most models for the origin and evolution of MSPs and approximately a factor of 4 lower than that of ordinary pulsars. We also find that, in contrast to young ordinary pulsars, the vast majority of which are moving away from the Galactic plane, almost half of the MSPs are moving towards the plane. This near-isotropy would be expected of a population that has reached dynamic equilibrium. Accurate measurements of MSP velocities have allowed us to correct their measured spin-down rates for Doppler acceleration effects, and thereby derive their intrinsic magnetic field strengths and characteristic ages. We find that close to half of our sample of MSPs have a characteristic age comparable to or greater than the age of the Galactic disc. 相似文献
4.
W. M. Yan R. N. Manchester G. Hobbs W. van Straten J. E. Reynolds N. Wang M. Bailes N. D. R. Bhat S. Burke-Spolaor D. J. Champion A. Chaudhary W. A. Coles A. W. Hotan J. Khoo S. Oslowski J. M. Sarkissian D. R. B. Yardley 《Astrophysics and Space Science》2011,335(2):485-498
We report on variations in the mean position angle of the 20 millisecond pulsars being observed as part of the Parkes Pulsar Timing Array (PPTA) project. It is found that the observed variations are dominated by changes in the Faraday rotation occurring in the Earth??s ionosphere. Two ionospheric models are used to correct for the ionospheric contribution and it is found that one based on the International Reference Ionosphere gave the best results. Little or no significant long-term variation in interstellar RM was found with limits typically about 0.1 rad?m?2?yr?1 in absolute value. In a few cases, apparently significant RM variations over timescales of a few 100 days or more were seen. These are unlikely to be due to localised magnetised regions crossing the line of sight since the implied magnetic fields are too high. Most probably they are statistical fluctuations due to random spatial and temporal variations in the interstellar electron density and magnetic field along the line of sight. 相似文献
5.
Richard A. Stern Eric C. Syme Alan H. Bailes Stephen B. Lucas 《Contributions to Mineralogy and Petrology》1995,119(2-3):117-141
Geochemical and isotopic (Nd, Sr) data are reported on Paleoproterozoic (1904–1864 Ma), maficintermediate (<63% SiO2), arc metavolcanic rocks from the Flin Flon greenstone belt, Manitoba and Saskatchewan. Major element criteria permit subdivision of the rocks into tholeiitic (TH), calc-alkaline (CA), alkaline, and boninitic (BO) magma series. Subaqueously erupted, TH and related CA basalt-basaltic andesite, and rare high-Ca boninites dominated between 1904 Ma and 1890 Ma. The TH rocks are similar to modern island are tholeiites, having low high-field-strength element (HFSE) and rare earth element (REE) abundances, and chondrite-normalized light REE depletion to slight enrichment. The boninites have even lower HFSE and REE abundances (1–2X chondrites). Along with their extreme ratios of refractory incompatible elements (e.g., high Al/Ti, Ti/Zr, low Ti/V, Zr/Y), these features indicate that the arc mantle source was strongly depleted, probably residual after MORB or back-arc basin basalt extraction. Elevated Th/Yb, Ba/La, La/Nb values, and the spread in Nd isotopic compositions (initial Nd=–0.4 to +4.8) suggest recycling of small amounts (0–8%) of Archean and possibly older Proterozoic crust via sediment subduction and, locally, intracrustal contamination. Calcalkaline andesite-rhyolite and rare shoshonite and trachyandesite, erupted between 1890 Ma and 1864 Ma, are more strongly light REE enriched and have comparatively higher HFSE abundances, and higher Zr/Y and Nb/Y values. The rocks have strong arc trace element signatures (e.g., high Th/Nb, La/Nb), and initial Nd values (+2.3 to +4.6) indicate that depleted mantle contributions to the magmas continued to be dominant. The geochemistry and geology of these younger volcanic rocks suggest a mature island arc setting in which the arc lithosphere was thicker than in the previous period, and a more fertile sub-arc mantle source was tapped. The pre-1890 Ma volcanism occurred in one or more separate arcs, probably characterized by rapid subduction of oceanic lithosphere, relatively thin, tholeiitic arc crust, and extensive backarc basin formation. In contrast, post-1890 Ma volcanism is dominantly calc-alkaline to (rarely) alkaline, and is interpreted to reflect crustal thickening due to longterm growth of arc edifice(s) and tectonic thickening associated with intraoceanic arc-arc (>1870 Ma) collision and subsequent intra-arc deformation. 相似文献
6.
D'Amico Stappers Bailes Martin Bell Lyne & Manchester 《Monthly notices of the Royal Astronomical Society》1998,297(1):28-40
The Parkes survey of the entire southern sky for millisecond and other low-luminosity pulsars has now been completed. The survey system and initial results were described by Manchester et al. and the final results and population studies are described by Lyne et al. A total of 298 pulsars were detected, including 101 new discoveries of which 17 were millisecond pulsars. Here we report on timing observations at Parkes and Jodrell Bank of the 84 long-period (non-millisecond) pulsars discovered in the survey, including timing solutions for 78 of them. Pulse profiles and arrival times were obtained at several different frequencies over intervals of more than a year, yielding a position, period, period derivative and dispersion measure for each pulsar. Pulse profiles at frequencies near 400 MHz and 600 or 1400 MHz are presented for most of the observed pulsars. Significant timing noise was detected for five pulsars and a glitch was observed in the period of PSR J1123–6259. 相似文献
7.
High-precision baseband timing of 15 millisecond pulsars 总被引：1，自引：0，他引：1
A. W. Hotan M. Bailes S. M. Ord 《Monthly notices of the Royal Astronomical Society》2006,369(3):1502-1520
8.
9.
The Swinburne intermediate-latitude pulsar survey 总被引：1，自引：0，他引：1
R.T. Edwards † M. Bailes W. van Straten M.C. Britton 《Monthly notices of the Royal Astronomical Society》2001,326(1):358-374
We have conducted a survey of intermediate Galactic latitudes using the 13-beam 21-cm multibeam receiver of the Parkes 64-m radio telescope. The survey covered the region enclosed by 5°<| b |<15° and −100°< l <50° with 4702 processed pointings of 265 s each, for a total of 14.5 d of integration time. 13 2×96‐channel filterbanks provided 288 MHz of bandwidth at a centre frequency of 1374 MHz, one-bit sampled every 125 μs and incurring ∼ DM/13.4 cm−3 pc samples of dispersion smearing. The system was sensitive to slow and most millisecond pulsars in the region with flux densities greater than approximately 0.3–1.1 mJy . Offline analysis on the 64-node Swinburne workstation cluster resulted in the detection of 170 pulsars of which 69 were new discoveries. Eight of the new pulsars, by virtue of their small spin periods and period derivatives, may be recycled and have been reported elsewhere. The slow pulsars discovered are typical of those already known in the volume searched, being of intermediate to old age. Several pulsars experience pulse nulling and two display very regular drifting subpulses. We discuss the new discoveries and provide timing parameters for the 48 slow pulsars for which we have a phase-connected solution. 相似文献
10.
Paul D. Kiel Jarrod R. Hurley Matthew Bailes James R. Murray 《Monthly notices of the Royal Astronomical Society》2008,388(1):393-415
The computation of theoretical pulsar populations has been a major component of pulsar studies since the 1970s. However, the majority of pulsar population synthesis has only regarded isolated pulsar evolution. Those that have examined pulsar evolution within binary systems tend to either treat binary evolution poorly or evolve the pulsar population in an ad hoc manner. Thus, no complete and direct comparison with observations of the pulsar population within the Galactic disc has been possible to date. Described here is the first component of what will be a complete synthetic pulsar population survey code. This component is used to evolve both isolated and binary pulsars. Synthetic observational surveys can then be performed on this population for a variety of radio telescopes. The final tool used for completing this work will be a code comprised of three components: stellar/binary evolution, Galactic kinematics and survey selection effects. Results provided here support the need for further (apparent) pulsar magnetic field decay during accretion, while they conversely suggest the need for a re-evaluation of the assumed typical millisecond pulsar formation process. Results also focus on reproducing the observed diagram for Galactic pulsars and how this precludes short time-scales for standard pulsar exponential magnetic field decay. Finally, comparisons of bulk pulsar population characteristics are made to observations displaying the predictive power of this code, while we also show that under standard binary evolutionary assumption binary pulsars may accrete much mass. 相似文献