The Experts below are selected from a list of 79701 Experts worldwide ranked by ideXlab platform
D R Lorimer - One of the best experts on this subject based on the ideXlab platform.
-
the Pulsar spectral index distribution
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: S D Bates, D R Lorimer, J P W VerbiestAbstract:The flux density spectra of radio Pulsars are known to be steep and, to first order, described by a power-law relationship of the form S_{\nu} \propto \nu^{\alpha}, where S_{\nu} is the flux density at some frequency \nu and \alpha is the spectral index. Although measurements of \alpha have been made over the years for several hundred Pulsars, a study of the intrinsic distribution of Pulsar spectra has not been carried out. From the result of Pulsar surveys carried out at three different radio frequencies, we use population synthesis techniques and a likelihood analysis to deduce what underlying spectral index distribution is required to replicate the results of these surveys. We find that in general the results of the surveys can be modelled by a Gaussian distribution of spectral indices with a mean of -1.4 and unit standard deviation. We also consider the impact of the so-called "Gigahertz-peaked spectrum" Pulsars. The fraction of peaked spectrum sources in the population with significant turn-over at low frequencies appears to be at most 10%. We demonstrate that high-frequency (>2 GHz) surveys preferentially select flatter-spectrum Pulsars and the converse is true for lower-frequency (<1 GHz) surveys. This implies that any correlations between \alpha and other Pulsar parameters (for example age or magnetic field) need to carefully account for selection biases in Pulsar surveys. We also expect that many known Pulsars which have been detected at high frequencies will have shallow, or positive, spectral indices. The majority of Pulsars do not have recorded flux density measurements over a wide frequency range, making it impossible to constrain their spectral shapes. We also suggest that such measurements would allow an improved description of any populations of Pulsars with 'non-standard' spectra.
-
Pulsar searches and timing with the square kilometre array
Astronomy and Astrophysics, 2009Co-Authors: R Smits, J M Cordes, M Kramer, B W Stappers, D R Lorimer, A. J. FaulknerAbstract:The square kilometre array (SKA) is a planned multi purpose radio telescope with a collecting area approaching 1 million square metres. One of the key science objectives of the SKA is to provide exquisite strong-field tests of gravitational physics by finding and timing Pulsars in extreme binary systems such as a Pulsar-black hole binary. To find out how three preliminary SKA configurations will affect a Pulsar survey, we have simulated SKA Pulsar surveys for each configuration. We estimate that the total number of Pulsars the SKA will detect, is around 14 000 normal Pulsars and 6000 millisecond Pulsars, using only the 1-km core and 30-mn integration time. We describe a simple strategy for follow-up timing observations and find that, depending on the configuration, it would take 1–6 days to obtain a single timing point for 14 000 Pulsars. Obtaining one timing point for the high-precision timing projects of the SKA, will take less than 14 h, 2 days, or 3 days, depending on the configuration. The presence of aperture arrays will be of great benefit here. We also study the computational requirements for beam forming and data analysis for a Pulsar survey. Beam forming of the full field of view of the single-pixel feed 15-m dishes using the 1-km core of the SKA requires about 2.2 × 10 15 operations per second. The corresponding data rate from such a Pulsar survey is about 4.7 × 10 11 bytes per second. The required computational power for a deep real time analysis is estimated to be 1.2 × 10 16 operations per second. For an aperture array or dishes equipped with phased array feeds, the survey can be performed faster, but the computational requirements and data rates will go up.
-
the parkes multibeam Pulsar survey vi discovery and timing of 142 Pulsars and a galactic population analysis
Monthly Notices of the Royal Astronomical Society, 2006Co-Authors: M A Mclaughlin, G Hobbs, M Kramer, A. G. Lyne, A. J. Faulkner, Rn Manchester, D R Lorimer, A. PossentiAbstract: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 kpc 2 . 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.
M A Mclaughlin - One of the best experts on this subject based on the ideXlab platform.
-
The NANOGrav Nine-Year Data Set: Measurement and Interpretation of Variations in Dispersion Measures
arXiv: High Energy Astrophysical Phenomena, 2016Co-Authors: M.l. Jones, M A Mclaughlin, Paul Demorest, Sourav Chatterjee, Zaven Arzoumanian, K. Crowter, L. Levin, J M Cordes, Timothy DolchAbstract:We analyze dispersion measure (DM) variations of 37 millisecond Pulsars in the 9-year NANOGrav data release and constrain the sources of these variations. Variations are significant for nearly all Pulsars, with characteristic timescales comparable to or even shorter than the average spacing between observations. Five Pulsars have periodic annual variations, 14 Pulsars have monotonically increasing or decreasing trends, and 13 Pulsars show both effects. Several Pulsars show correlations between DM excesses and lines of sight that pass close to the Sun. Mapping of the DM variations as a function of the Pulsar trajectory can identify localized ISM features and, in one case, an upper limit to the size of the dispersing region of 13.2 AU. Finally, five Pulsars show very nearly quadratic structure functions, which could be indicative of an underlying Kolmogorov medium. Four Pulsars show roughly Kolmogorov structure functions and another four show structure functions less steep than Kolmogorov. One Pulsar has too large an uncertainty to allow comparisons. We discuss explanations for apparent departures from a Kolmogorov-like spectrum, and show that the presence of other trends in the data is the most likely cause.
-
the north american nanohertz observatory for gravitational waves
Classical and Quantum Gravity, 2013Co-Authors: M A MclaughlinAbstract:The North American Nanohertz Observatory for Gravitational Waves is a collaboration of researchers who are actively engaged in using North American radio telescopes to detect and study gravitational waves (GWs) via Pulsar timing. To achieve this goal, we regularly observe millisecond Pulsars with the Arecibo and Green Bank telescopes and develop and implement new instrumentation and algorithms for searching for and observing Pulsars, calculating arrival times, understanding and correcting for propagation delays and sources of noise in our data and detecting and characterizing a variety of GW sources. We collaborate on these activities with colleagues in the International Pulsar Timing Array. We also educate students of all levels and the public about the detection and study of GWs via Pulsar timing.
-
the parkes multibeam Pulsar survey vi discovery and timing of 142 Pulsars and a galactic population analysis
Monthly Notices of the Royal Astronomical Society, 2006Co-Authors: M A Mclaughlin, G Hobbs, M Kramer, A. G. Lyne, A. J. Faulkner, Rn Manchester, D R Lorimer, A. PossentiAbstract: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 kpc 2 . 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.
-
The Gamma Ray Pulsar Population
The Astrophysical Journal, 2000Co-Authors: M A Mclaughlin, James M. CordesAbstract:We apply a likelihood analysis to Pulsar detections, Pulsar upper limits, and diffuse background measurements from the OSSE and EGRET instruments on the Compton Gamma Ray Observatory to constrain the luminosity law for gamma-ray Pulsars and some properties of the gamma-ray Pulsar population. We find that the dependence of luminosity on spin period and dipole magnetic field is much steeper at OSSE than at EGRET energies (50-200 keV and >100 MeV, respectively), suggesting that different emission mechanisms are responsible for low- and high-energy gamma-ray emission. Incorporating a spin-down model and assuming a Pulsar spatial distribution, we estimate the fraction of the Galactic gamma-ray background due to unidentified Pulsars and find that Pulsars may be an important component of the OSSE diffuse flux but are most likely not important at EGRET energies. Using measurements of the diffuse background flux from these instruments, we are able to place constraints on the braking index, initial spin period, and magnetic field of the Galactic Pulsar population and are also able to constrain the Pulsar birthrate to be between 1/25 yr-1 and 1/500 yr-1. Our results are based on a large gamma-ray beam, but they do not scale in a simple way with beam size. We estimate that about 20 of the 169 unidentified EGRET sources are probably gamma-ray Pulsars. We use our model to predict the Pulsar population that will be seen by future gamma-ray instruments and estimate that Gamma Ray Large Area Space Telescope will detect roughly 750 gamma-ray Pulsars as steady sources, only 120 of which are currently known radio Pulsars.
A. Possenti - One of the best experts on this subject based on the ideXlab platform.
-
Discovery of 28 Pulsars using new techniques for sorting Pulsar candidates
Monthly Notices of the Royal Astronomical Society, 2009Co-Authors: Michael Keith, Felivel Camilo, Michael Kramer, Ralph Eatough, Andrew Lyne, A. Possenti, R N ManchesterAbstract:Modern Pulsar surveys produce many millions of candidate Pulsars, far more than can be individually inspected. Traditional methods for filtering these candidates, based upon the signal-to-noise ratio of the detection, cannot easily distinguish between interference signals and Pulsars. We have developed a new method of scoring candidates using a series of heuristics which test for Pulsar-like properties of the signal. This significantly increases the sensitivity to weak Pulsars and Pulsars with periods close to interference signals. By applying this and other techniques for ranking candidates from a previous processing of the Parkes Multi-beam Pulsar Survey, 28 previously unknown Pulsars have been discovered. These include an eccentric binary system and a young Pulsar which is spatially coincident with a known supernova remnant.
-
the parkes multibeam Pulsar survey vi discovery and timing of 142 Pulsars and a galactic population analysis
Monthly Notices of the Royal Astronomical Society, 2006Co-Authors: M A Mclaughlin, G Hobbs, M Kramer, A. G. Lyne, A. J. Faulkner, Rn Manchester, D R Lorimer, A. PossentiAbstract: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 kpc 2 . 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.
-
The Parkes multibeam Pulsar survey – IV. Discovery of 180 Pulsars and parameters for 281 previously known Pulsars
Monthly Notices of the Royal Astronomical Society, 2004Co-Authors: George Hobbs, R N Manchester, Felivel Camilo, Michael Kramer, A. G. Lyne, Ingrid H. Stairs, Victoria M. Kaspi, A. J. Faulkner, Nicolo' D'amico, A. PossentiAbstract:The Parkes multibeam Pulsar survey has led to the discovery of more than 700 Pulsars. In this paper, we provide timing solutions, flux densities and pulse profiles for 180 of these new discoveries. Two Pulsars, PSRs J1736−2843 and J1847−0130, have rotational periods P > 6 s and are therefore among the slowest rotating radio Pulsars known. Conversely, with P = 1.8 ms, PSR J1843−1113 has the third-shortest period of Pulsars currently known. This Pulsar and PSR J1905+0400 (P = 3.8 ms) are both solitary. We also provide orbital parameters for a new binary system, PSR J1420−5625, which has P = 34 ms, an orbital period of 40 d and a minimum companion mass of 0.4 solar masses. The 10 ◦ -wide strip along the Galactic plane that was surveyed is known to contain 264 radio Pulsars that were discovered prior to the multibeam Pulsar survey. We have redetected almost all of these Pulsars and provide new dispersion measure values and flux densities at 20 cm for the redetected Pulsars.
-
The Parkes Multibeam Pulsar Survey - V. Finding binary and millisecond Pulsars
Monthly Notices of the Royal Astronomical Society, 2004Co-Authors: A. J. Faulkner, R N Manchester, Duncan R. Lorimer, Michael Kramer, Andrew Lyne, A. Possenti, George Hobbs, Ingrid H. Stairs, Maura Mclaughlin, Nicolo' D'amicoAbstract:The Parkes Multibeam Pulsar Survey is the most successful survey of the Galactic plane ever performed, finding over 600 Pulsars in the initial processing. We report on a reprocessing of all 40 000 beams with a number of algorithms, including conventional frequency-domain searches and an acceleration search for fast binary Pulsars. The very large volume of results coupled with the need to distinguish new candidates from known Pulsars and their many harmonics, often with multiple detections from different search algorithms, necessitated the development of a new graphical selection tool tightly linked to a web-based results data base. We discuss and demonstrate the benefits of these software systems, which are specifically designed for large survey projects. The results of this processing have been encouraging. We have discovered 128 new Pulsars, including 11 binary and 15 millisecond Pulsars; in addition to those previously found in the survey, we have thus far discovered 737 Pulsars. In this paper, we discuss the discoveries of PSR J1744-3922 (a 172-ms mildly recycled Pulsar in a 4.6-h orbit that exhibits nulling behaviour, not previously observed in recycled or binary objects), PSR J1802-2124 (an intermediate mass binary Pulsar) and PSR J1801-1417 (a solitary millisecond Pulsar).
-
The Parkes Multibeam Pulsar Survey – II. Discovery and timing of 120 Pulsars
Monthly Notices of the Royal Astronomical Society, 2002Co-Authors: D. J. Morris, R N Manchester, Felivel Camilo, A. Possenti, George Hobbs, A. G. Lyne, Ingrid H. Stairs, J. F. Bell, Victoria M. Kaspi, Nichi D. AmicoAbstract:The Parkes Multibeam Pulsar Survey is a sensitive survey of a strip of the Galactic plane with |b| < 5 ◦ and 260 ◦ < l < 50 ◦ at 1374 MHz. Here we report the discovery of 120 new Pulsars and subsequent timing observations, primarily using the 76-m Lovell radio telescope at Jodrell Bank. The main features of the sample of 370 published Pulsars discovered during the multibeam survey are described. Furthermore, we highlight two Pulsars: PSR J1734−3333, a young Pulsar with the second highest surface magnetic field strength among the known radio Pulsars, Bs = 5.4 × 10 13 G, and PSR J1830−1135, the second slowest radio Pulsar known,
P Esposito - One of the best experts on this subject based on the ideXlab platform.
-
the evolution of the γ and x ray luminosities of Pulsar wind nebulae
The Astrophysical Journal, 2009Co-Authors: F Mattana, A Pellizzoni, Mariarosaria Falanga, D Gotz, P Esposito, R. Terrier, A. De LucaAbstract:Pulsar wind nebulae are a prominent class of very high energy (E > 0.1 TeV) Galactic sources. Their -ray spectra are interpreted as due to inverse Compton scattering of ultrarelativistic electrons on the ambient photons, whereas the X-ray spectra are due to synchrotron emission. We investigate the relation between the - and-X-ray emission and the Pulsars’ spin-down luminosity and characteristic age. We find that the distance-independent - to X-ray flux ratio of the nebulae is inversely proportional to the spin-down luminosity, (∝ u E −1.9 ), while it appears proportional to the characteristic age, (∝ � 2.2 c ), of the parent Pulsar. We interpret these results as due to the evolution of the electron energy distribution and the nebular dynamics, supporting the idea of so-called relic Pulsar wind nebulae. These empirical relations provide a new tool to classify unidentified diffuse -ray sources and to estimate the spin-down luminosity and characteristic age of rotation powered Pulsars with no detected pulsation from the X- and −ray properties of the associated Pulsar wind nebulae. We apply these relations to predict the spin-down luminosity and characteristic age of four (so far unpulsing) candidate Pulsars associated to wind nebulae. Subject headings: Pulsars : general — radiation mechanisms: non-thermal — supernova remnants — X-rays : stars — gamma rays: observations
F Mattana - One of the best experts on this subject based on the ideXlab platform.
-
the evolution of the γ and x ray luminosities of Pulsar wind nebulae
The Astrophysical Journal, 2009Co-Authors: F Mattana, A Pellizzoni, Mariarosaria Falanga, D Gotz, P Esposito, R. Terrier, A. De LucaAbstract:Pulsar wind nebulae are a prominent class of very high energy (E > 0.1 TeV) Galactic sources. Their -ray spectra are interpreted as due to inverse Compton scattering of ultrarelativistic electrons on the ambient photons, whereas the X-ray spectra are due to synchrotron emission. We investigate the relation between the - and-X-ray emission and the Pulsars’ spin-down luminosity and characteristic age. We find that the distance-independent - to X-ray flux ratio of the nebulae is inversely proportional to the spin-down luminosity, (∝ u E −1.9 ), while it appears proportional to the characteristic age, (∝ � 2.2 c ), of the parent Pulsar. We interpret these results as due to the evolution of the electron energy distribution and the nebular dynamics, supporting the idea of so-called relic Pulsar wind nebulae. These empirical relations provide a new tool to classify unidentified diffuse -ray sources and to estimate the spin-down luminosity and characteristic age of rotation powered Pulsars with no detected pulsation from the X- and −ray properties of the associated Pulsar wind nebulae. We apply these relations to predict the spin-down luminosity and characteristic age of four (so far unpulsing) candidate Pulsars associated to wind nebulae. Subject headings: Pulsars : general — radiation mechanisms: non-thermal — supernova remnants — X-rays : stars — gamma rays: observations
