The Parkes Southern Pulsar Survey — II. Final results and population analysis     

A. G. Lyne  R. N. Manchester  D. R. Lorimer  M. Bailes  N. D'Amico  T. M. Tauris  S. Johnston  J. F. Bell  & L. Nicastro 《Monthly notices of the Royal Astronomical Society》1998,295(4):743-755

A survey of the entire southern sky for millisecond and low-luminosity pulsars using the ATNF Parkes radio telescope has now been completed. The survey detected 298 pulsars, of which 101 were previously unknown. The new pulsars include 17 millisecond pulsars. This is the largest sample of both normal and millisecond pulsars detected in any survey. Combining our sample with other recent surveys in the Northern Hemisphere, we present a statistical study of the populations of both normal and millisecond pulsars. We find that the improved statistics allow us to estimate the number and birth-rate of both types of pulsar down to a 400-MHz luminosity limit of 1 mJy kpc². The local surface densities of potentially observable normal pulsars and millisecond pulsars are both about 30 kpc⁻², corresponding to ∼ 30000 potentially observable pulsars of each type in the Galaxy. Once beaming effects are taken into consideration we estimate that the active population of normal pulsars is ∼ 160000. Although there is evidence for flattening of the luminosity function of normal pulsars, this is not evident for millisecond pulsars which probably have a substantial population with luminosities below 1 mJy kpc². After correcting for beaming effects, we estimate that a normal pulsar is born with a luminosity greater than 1 mJy kpc² between once every 60 and 330 yr in the Galaxy. The birth-rate of millisecond pulsars is at least 3 × 10⁻⁶ yr⁻¹ above the same luminosity limit. Modelling the observed transverse speeds of millisecond pulsars using a dynamical simulation, we find their mean birth velocity to be 130 ± 30 km s⁻¹, significantly lower than that of the normal pulsars.  相似文献   

A unifying view of the spectral energy distributions of blazars   总被引：3，自引：0，他引：3  

G. Fossati  L. Maraschi  A. Celotti  A. Comastri  & G. Ghisellini 《Monthly notices of the Royal Astronomical Society》1998,299(2):433-448

We collect data at well-sampled frequencies from the radio to the γ-ray range for the following three complete samples of blazars: the Slew survey, the 1-Jy samples of BL Lacs and the 2-Jy sample of flat-spectrum radio-loud quasars (FSRQs). The fraction of objects detected in γ-rays ( E  ≳ 100 MeV) is ∼ 17, 26 and 40 per cent in the three samples respectively. Except for the Slew survey sample, γ-ray detected sources do not differ either from other sources in each sample, or from all the γ-ray detected sources, in terms of the distributions of redshift, radio and X-ray luminosities or of the broad-band spectral indices (radio to optical and radio to X-ray). We compute average spectral energy distributions (SEDs) from radio to γ-rays for each complete sample and for groups of blazars binned according to radio luminosity, irrespective of the original classification as BL Lac or FSRQ. The resulting SEDs show a remarkable continuity in that (i) the first peak occurs in different frequency ranges for different samples/luminosity classes, with most luminous sources peaking at lower frequencies; (ii) the peak frequency of the γ-ray component correlates with the peak frequency of the lower energy one; (iii) the luminosity ratio between the high and low frequency components increases with bolometric luminosity. The continuity of properties among different classes of sources and the systematic trends of the SEDs as a function of luminosity favour a unified view of the blazar phenomenon: a single parameter, related to luminosity, seems to govern the physical properties and radiation mechanisms in the relativistic jets present in BL Lac objects as well as in FSRQs. The general implications of this unified scheme are discussed while a detailed theoretical analysis, based on fitting continuum models to the individual spectra of most γ-ray blazars, is presented in a separate paper.  相似文献   

The topology of the IRAS Point Source Catalogue Redshift Survey     

A. Canavezes  V. Springel  S. J. Oliver  M. Rowan-Robinson  O. Keeble  S. D. M. White  W. Saunders  G. Efstathiou  C. S. Frenk  R. G. McMahon  S. Maddox  W. Sutherland  & H. Tadros 《Monthly notices of the Royal Astronomical Society》1998,297(3):777-793

We investigate the topology of the new Point Source Catalogue Redshift Survey (PSCz) of IRAS galaxies by means of the genus statistic. The survey maps the local Universe with approximately 15 000 galaxies over 84.1 per cent of the sky, and provides an unprecedented number of resolution elements for the topological analysis. For comparison with the PSCz data we also examine the genus of large N -body simulations of four variants of the cold dark matter (CDM) cosmogony. The simulations are part of the Virgo project to simulate the formation of structure in the Universe. We assume that the statistical properties of the galaxy distribution can be identified with those of the dark matter particles in the simulations. We extend the standard genus analysis by examining the influence of sampling noise on the genus curve and introducing a statistic able to quantify the amount of phase correlation present in the density field, the amplitude drop of the genus compared to a Gaussian field with identical power spectrum. The results for PSCz are consistent with the hypothesis of random-phase initial conditions. In particular, no strong phase correlation is detected on scales ranging from 10 to 32 h ⁻¹ Mpc, whereas there is a positive detection of phase correlation at smaller scales. Among the simulations, phase correlations are detected in all models at small scales, albeit with different strengths. When scaled to a common normalization, the amplitude drop depends primarily on the shape of the power spectrum. We find that the constant-bias standard CDM model can be ruled out at high significance, because the shape of its power spectrum is not consistent with PSCz. The other CDM models with more large-scale power all fit the PSCz data almost equally well, with a slight preference for a high-density τCDM model.  相似文献   

Aeromagnetic And Aeroradiometric Response To Hydrothermal Alteration     

M.-L. Airo 《Surveys in Geophysics》2002,23(4):273-302

In Precambrian terrains all regional and most localintensive magnetic anomalies areproduced by magnetite. Monoclinic pyrrhotite isresponsible for some local, but oftenintensive, magnetic anomaly patterns. Both magnetiteand pyrrhotite are affected byhydrothermal alteration processes in various ways,resulting in changes either inabundance or in grain fabric. These changes arerecorded in the magnetic properties ofthe altered rock units and reflected in theiraeromagnetic signatures. Hydrothermalalteration in deformed bedrock zones is commonlycontrolled by structural or tectonicfeatures. Regional high-resolution aerogeophysicalsurveys can be utilized, in bothregional and detailed investigations, to map theoverall geological and tectonic settingor to estimate local changes in magnetic mineralogyand the relative abundance ofradionuclides.Magnetite is most commonly destroyed in alterationprocesses, such as biotitization,carbonation, sulfidization and silicification. Theprogressive destruction of magnetitebegins at grain margins and results first in broken and cracked grain texture and smallergrain size, then progresses to total disappearanceof magnetite. Alteration in magnetite-bearing rock units may be recognized by decreasedmagnetic intensity and by thebroken, disrupted magnetic pattern. The abundance ofmonoclinic pyrrhotite isenhanced by reducing hydrothermal fluids, and typicalcrystal anisotropy is developeddue to tectonic stress.The relative contents of radioelements are changedin the same hydrothermal processesand partly for the same reasons as the ferrimagneticminerals. Potassic alteration oftenresults in elevated K radiation particularly formafic rocks, and then anomalous K/Thratios along local shear or fracture zones may beindicative of gold-bearingmineralization. On the other hand, high U/Th ratioswithin metasedimentary units maypoint out prospects for sulphidization. Althoughvariation of U/Th ratios largely reflectsthe environmental conditions during primarydiagenesis or a later deformational phase,mainly the decrease in Th radiation close tosulphide mineralization seems to beresponsible for the elevated U/Th ratios.  相似文献   

Gradient profiling for the investigation of groundwater saturated fractures in hard rocks of Uttar Pradesh,India     

G. S. Yadav  Shashi Kant Singh 《Hydrogeology Journal》2008,16(2):363-372

Gradient profiling (GP) has been successfully utilized as a preliminary tool to identify fractured zones saturated with groundwater in hard-rock areas of Robertsganj, Sonebhadra district, Uttar Pradesh, India. Conducting geoelectrical sounding at randomly selected places may not provide fruitful results since fractures are sparsely distributed in hard rocks. In gradient profiling, current electrodes with large separation remain fixed while the potential dipole is moved between the current electrodes in the central one-third portion of the profile at a small station interval. A GP survey was conducted along seven profiles having different lengths in two small sectors of the study area. Low resistive zones have been identified which correspond to the fractured zones. A few geoelectrical soundings were carried out to investigate the depth and thickness of the fractured zones. Two test boreholes, one drilled in each sector, yielded continuous discharge of fresh water (18,000–24,000 L/h). The present study confirms the findings of previous work that the GP survey is a powerful initial technique that identifies the presence of a fractured zone, especially in a hard-rock area covered with a thin soil layer.  相似文献   

The second epoch Molonglo Galactic Plane Survey: compact source catalogue     

T. Murphy  T. Mauch  A. Green  R. W. Hunstead  B. Piestrzynska  A. P. Kels  P. Sztajer 《Monthly notices of the Royal Astronomical Society》2007,382(1):382-392

We present the first data release from the second epoch Molonglo Galactic Plane Survey (MGPS-2). MGPS-2 was carried out with the Molonglo Observatory Synthesis Telescope at a frequency of 843 MHz and with a restoring beam of 45 × 45      arcsec², making it the highest resolution large-scale radio survey of the southern Galactic plane. It covers the range  | b | < 10° and 245° < l < 365°  , and is the Galactic counterpart to the Sydney University Molonglo Sky Survey (SUMSS) which covers the whole southern sky with  δ≤−30° (| b | > 10°  ).
In this paper, we present the MGPS-2 compact source catalogue. The catalogue has 48 850 sources above a limiting peak brightness of 10 mJy beam⁻¹. Positions in the catalogue are accurate to 1–2 arcsec. A full catalogue including extended sources is in preparation. We have carried out an analysis of the compact source density across the Galactic plane and find that the source density is not statistically higher than the density expected from the extragalactic source density alone.
We also present version 2.0 of the SUMSS image data and catalogue which is now available online. The data consist of 629 4.3°× 4.3° mosaic images covering the 8100 deg² of sky with  δ≤−30° and | b | > 10°  . The catalogue contains 210 412 radio sources to a limiting peak brightness of 6 mJy beam⁻¹ at  δ≤−50°  and 10 mJy beam⁻¹ at  δ > −50°  . We describe the updates and improvements made to the SUMSS cataloguing process.  相似文献   

Optical identification of XMM sources in the Canada–France–Hawaii Telescope Legacy Survey     

C. S. Stalin  Patrick Petitjean  R. Srianand  A. J. Fox  F. Coppolani  A. Schwope 《Monthly notices of the Royal Astronomical Society》2010,401(1):294-306

  相似文献   

Rounding up the wanderers: optimizing coronagraphic searches for extrasolar planets     

Eric Agol 《Monthly notices of the Royal Astronomical Society》2007,374(4):1271-1289

  相似文献   

Searches for ultracompact dwarf galaxies in galaxy groups     

E. A. Evstigneeva  M. J. Drinkwater  R. Jurek  P. Firth  J. B. Jones  M. D. Gregg  S. Phillipps 《Monthly notices of the Royal Astronomical Society》2007,378(3):1036-1042

We present the results of a search for ultracompact dwarf galaxies (UCDs) in six different galaxy groups: Dorado, NGC 1400, 0681, 4038, 4697 and 5084. We searched in the apparent magnitude range  17.5 ≤ b _J≤ 20.5  (except NGC 5084:  19.2 ≤ b _J≤ 21.0  ). We found one definite plus two possible UCD candidates in the Dorado group and two possible UCD candidates in the NGC 1400 group. No UCDs were found in the other groups. We compared these results with predicted luminosities of UCDs in the groups according to the hypothesis that UCDs are globular clusters formed in galaxies. The theoretical predictions broadly agree with the observational results, but deeper surveys are needed to fully test the predictions.  相似文献   

The XMM-Large Scale Structure catalogue: X-ray sources and associated optical data. Version I     

M. Pierre  L. Chiappetti  F. Pacaud  A. Gueguen  C. Libbrecht  B. Altieri  H. Aussel  P. Gandhi †  O. Garcet  E. Gosset  L. Paioro  T. J. Ponman  A. M. Read  A. Refregier  J.-L. Starck  J. Surdej  I. Valtchanov  C. Adami  D. Alloin  A. Alshino  S. Andreon  M. Birkinshaw  M. Bremer  A. Detal  P.-A. Duc  G. Galaz  L. Jones  J.-P. Le Fèvre  O. Le Fèvre  D. Maccagni  A. Mazure  H. Quintana  H. J. A. Röttgering  P.-G. Sprimont  C. Tasse  G. Trinchieri  J. P. Willis 《Monthly notices of the Royal Astronomical Society》2007,382(1):279-290

  相似文献