918 results on '"PULSAR detection"'
Search Results
152. Understanding the nature of the intriguing source X Persei: a deep look with a Suzaku observation.
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Maitra, Chandreyee, Raichur, Harsha, Pradhan, Pragati, and Paul, Biswajit
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NEUTRON stars , *BINARY systems (Astronomy) , *LUMINOSITY , *ACCRETION (Astrophysics) , *MAGNETIC field measurements ,PULSAR detection - Abstract
We present detailed broad-band timing and spectral analysis of the persistent, low luminosity and slowly spinning pulsar X Persei using a deep Suzaku observation of the source. The spectrum is unusually hard with a cyclotron resonance scattering feature (CRSF), the presence of which has been debated. By comparing the spectral models relevant for accretion-powered pulsars, we have obtained the best constraint on the broad-band spectral model of X Persei obtained so far. The CRSF is not confirmed in the average spectrum.We have also identified the presence of different intensity levels in the source with distinct changes in the pulse profile and the energy spectrum indicating changes in the accretion geometry. We further find evidence of a CRSF in the highest intensity levels at ~40 keV, indicating a magnetic field strength of 3.4 × 1012 G. [ABSTRACT FROM AUTHOR]
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- 2017
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153. A mathematical description of glitches in neutron stars.
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Mongiovì, Maria Stella, Russo, Francesco G., and Sciacca, Michele
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NEUTRON stars , *PULSATING stars , *STELLAR oscillations , *SOLAR oscillations , *STELLAR atmospheres ,PULSAR detection - Abstract
In a pulsar, there are gaps and difficulties in our knowledge of glitches, mainly because of the absence of information about the physics of the matter of the star. This has motivated several authors to suggest dynamical models that interpret most of the astronomical data. Many predictions are based on the assumption that the inner part is analogous to the structure of matter of superfluids. Here, we illustrate a new mathematical model, partially inspired by the dynamics of superfluid helium. We obtain two evolution equations for the angular velocities (of the crust and of superfluid), which are supported by another evolution equation for the average vortex line length per unit volume. This third equation is more delicate from an analytical perspective and is probably at the origin of glitches. We identify two stationary solutions, corresponding to the straight vortex regime and the turbulent regime. [ABSTRACT FROM AUTHOR]
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- 2017
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154. Interstellar scintillations of PSR B1919+21: space–ground interferometry.
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Shishov, V. I., Smirnova, T. V., Gwinn, C. R., Andrianov, A. S., Popov, M. V., Rudnitskiy, A. G., and Soglasnov, V. A.
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SCINTILLATION spectrometry , *SPECTRUM analysis , *SPECTROMETRY , *PULSATING stars , *RADIATION sources ,PULSAR detection - Abstract
We carried out observations of pulsar PSR B1919+21 at 324 MHz to study the distribution of interstellar plasma in the direction of this pulsar. We used the RadioAstron (RA) space radio telescope, together with two ground telescopes: Westerbork (WB) and Green Bank (GB). The maximum baseline projection for the space-ground interferometer was about 60 000 km. We show that interstellar scintillation of this pulsar consists of two components: diffractive scintillations from inhomogeneities in a layer of turbulent plasma at a distance z1 = 440 pc from the observer or homogeneously distributed scattering material to the pulsar; and weak scintillations from a screen located near the observer at z2 = 0.14 ± 0.05 pc. Furthermore, in the direction to the pulsar we detected a prism that deflects radiation, leading to a shift in observed source position. We show that the influence of the ionosphere can be ignored for the space-ground baseline. Analysis of the spatial coherence function for the space-ground baseline (RA-GB) yielded a scattering angle in the observer plane of ϑscat = 0.7 mas. An analysis of the time-frequency correlation function for weak scintillations yielded an angle of refraction in the direction to the pulsar ϑref, 0 = 110 ms and a distance to the prism zprism ≤ 2 pc. [ABSTRACT FROM AUTHOR]
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- 2017
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155. An investigation of pulsar searching techniques with the fast folding algorithm.
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Cameron, A. D., Barr, E. D., Champion, D. J., Kramer, M., and Zhu, W. W.
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DATA analysis , *ALGORITHMS , *FOURIER transform infrared spectroscopy , *BAYESIAN analysis ,PULSAR detection - Abstract
Here, we present an in-depth study of the behaviour of the fast folding algorithm (FFA), an alternative pulsar searching technique to the fast Fourier transform (FFT). Weaknesses in the FFT, including a susceptibility to red noise, leave it insensitive to pulsars with long rotational periods (P > 1 s). This sensitivity gap has the potential to bias our understanding of the period distribution of the pulsar population. The FFA, a time-domain based pulsar searching technique, has the potential to overcome some of these biases. Modern distributed-computing frameworks now allow for the application of this algorithm to all-sky blind pulsar surveys for the first time. However, many aspects of the behaviour of this search technique remain poorly understood, including its responsiveness to variations in pulse shape and the presence of red noise. Using a custom CPU-based implementation of the FFA, FFANCY, we have conducted an in-depth study into the behaviour of the FFA in both an ideal, white noise regime as well as a trial on observational data from the High Time Resolution Universe South Low Latitude pulsar survey, including a comparison to the behaviour of the FFT.We are able to both confirm and expand upon earlier studies that demonstrate the ability of the FFA to outperform the FFT under ideal white noise conditions, and demonstrate a significant improvement in sensitivity to long-period pulsars in real observational data through the use of the FFA. [ABSTRACT FROM AUTHOR]
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- 2017
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156. Evidence for an intermediate-mass black hole in the globular cluster NGC 6624.
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Perera, B. B. P., Stappers, B. W., Lyne, A. G., Bassa, C. G., Cognard, I., Guillemot, L., Kramer, M., Theureau, G., and Desvignes, G.
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GLOBULAR clusters , *STAR clusters , *BINARY black holes , *ASTRONOMY ,PULSAR detection - Abstract
PSR B1820--30A is located in the globular cluster NGC 6624 and is the closest known pulsar to the centre of any globular cluster. We present more than 25 yr of high-precision timing observations of this millisecond pulsar and obtain four rotational frequency time derivative measurements. Modelling these higher order derivatives as being due to orbital motion, we find solutions that indicate the pulsar is in either a low-eccentricity (0.33 ≲ e ≲ 0.4) smaller orbit with a low-mass companion (such as a main-sequence star, white dwarf, neutron star or stellar mass black hole) or a high-eccentricity (e ≳ 0.9) larger orbit with a massive companion. The cluster mass properties and the observed properties of 4U 1820-30 and the other pulsars in the cluster argue against the low-eccentricity possibility. The high-eccentricity solution reveals that the pulsar is most likely orbiting around an intermediate-mass black hole (IMBH) of mass >7500 M⊙ located at the cluster centre. A gravitational model for the globular cluster, which includes such a central BH, predicts an acceleration that is commensurate with that measured for the pulsar. It further predicts that the model-dependent minimum mass of the IMBH is ∼60 000 M⊙. Accounting for the associated contribution to the observed period derivative indicates that the γ-ray efficiency of the pulsar should be between 0.08 and 0.2. Our results suggest that other globular clusters may also contain central BHs and they may be revealed by the study of new pulsars found sufficiently close to their centres. [ABSTRACT FROM AUTHOR]
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- 2017
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157. Spectral and timing properties of IGR J00291+5934 during its 2015 outburst.
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Sanna, A., Pintore, F., Bozzo, E., Ferrigno, C., Papitto, A., Riggio, A., Di Salvo, T., Iaria, R., D'Aì, A., Egron, E., and Burderi, L.
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BINARY stars , *NEUTRON stars , *STELLAR oscillations , *STELLAR luminosity function ,PULSAR detection - Abstract
We report on the spectral and timing properties of the accreting millisecond X-ray pulsar IGR J00291+5934 observed by XMM-Newton and NuSTAR during its 2015 outburst. The source is in a hard state dominated at high energies by a Comptonization of soft 0 (~photons.9 keV) by an electron population with kTe ~30 keV, and at lower energies by a blackbody component with kT ~ 0.5 keV. A moderately broad, neutral Fe emission line and four narrow absorption lines are also found. By investigating the pulse phase evolution, we derived the best-fitting orbital solution for the 2015 outburst. Comparing the updated ephemeris with those of the previous outbursts, we set a 3σ confidence level interval -6.6 × 10-13 s s-1 < P orb < 6.5 × 10-13 s s-1 on the orbital period derivative. Moreover, we investigated the pulse profile dependence on energy finding a peculiar behaviour of the pulse fractional amplitude and lags as a function of energy. We performed a phase-resolved spectroscopy showing that the blackbody component tracks remarkably well the pulse profile, indicating that this component resides at the neutron star surface (hotspot). [ABSTRACT FROM AUTHOR]
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- 2017
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158. Detection methods for stochastic gravitational-wave backgrounds: a unified treatment.
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Romano, Joseph and Cornish, Neil.
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GRAVITATIONAL waves , *ASTROPHYSICS , *STOCHASTIC analysis , *BAYESIAN analysis , *DATA analysis ,PULSAR detection - Abstract
We review detection methods that are currently in use or have been proposed to search for a stochastic background of gravitational radiation. We consider both Bayesian and frequentist searches using ground-based and space-based laser interferometers, spacecraft Doppler tracking, and pulsar timing arrays; and we allow for anisotropy, non-Gaussianity, and non-standard polarization states. Our focus is on relevant data analysis issues, and not on the particular astrophysical or early Universe sources that might give rise to such backgrounds. We provide a unified treatment of these searches at the level of detector response functions, detection sensitivity curves, and, more generally, at the level of the likelihood function, since the choice of signal and noise models and prior probability distributions are actually what define the search. Pedagogical examples are given whenever possible to compare and contrast different approaches. We have tried to make the article as self-contained and comprehensive as possible, targeting graduate students and new researchers looking to enter this field. [ABSTRACT FROM AUTHOR]
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- 2017
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159. A multi-observatory database of X-ray pulsars in the Magellanic Clouds.
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Yang, J., Laycock, S. G. T., Drake, J. J., Coe, M. J., Fingerman, S., Hong, J., Antoniou, V., and Zezas, A.
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MAGELLANIC clouds , *X-ray astronomy , *STELLAR luminosity function , *STAR observations , *BINARY stars , *ACCRETION (Astrophysics) ,PULSAR detection - Abstract
Using hundreds of XMM-Newton and Chandra archival observations and nearly a thousand RXTE observations, we have generated a comprehensive library of the known pulsars in the Small and Large Magellanic Clouds (SMC and LMC). The pulsars are detected multiple times across the full parameter spaces of X-ray luminosity (LX =1031-38 erg s-1) and spin period (P<1 s to P>1,000 s), and the library enables time-domain studies at a range of energy scales. The high time resolution and sensitivity of the European Photon Imaging cameras are complemented by the angular resolution of Chandra and the regular monitoring of RXTE. Our processing pipeline uses the latest calibration files and software to generate a suite of useful products for each pulsar detection: event lists, high-time-resolution light curves, periodograms, spectra, and complete histories of Ṗ , the pulsed fraction, and so on, in the broad (0.2-12 keV), soft (0.2-2 keV), and hard (2-12 keV) energy bands. After combining the observations from these telescopes, we found that 27 pulsars show long-term spin up and 24 long-term spin down.We also used the faintest and brightest sources to map out the lower and upper boundaries of accretion-powered X-ray emission: the propeller line and the Eddington line, respectively. We are in the process of comparing the observed pulse profiles to geometric models of X-ray emission in order to constrain the physical parameters of the pulsars. Finally, we are preparing a public release of the library so that it can be used by others in the astronomical community. [ABSTRACT FROM AUTHOR]
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- 2017
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160. Follow-up of isolated neutron star candidates from the eROSITA survey.
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Pires, A. M., Schwope, A. D., and Motch, C.
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NEUTRON stars , *MAGNETARS , *OPEN clusters of stars , *MONTE Carlo method ,PULSAR detection - Abstract
Peculiar groups of X-ray emitting isolated neutron stars, which include magnetars, the "magnificent seven", and central compact objects in supernova remnants, escape detection in standard pulsar surveys. Yet, they constitute a key element in understanding the neutron star evolution and phenomenology. Their use in population studies in the galactic scale has been hindered by the rarity of their detection. The all-sky survey of the extended Roentgen Survey with an Imaging Telescope Array (eROSITA) on-board the forthcoming Spectrum-Roentgen-Gamma (SRG) mission has the unique potential to unveil the X-ray faint part of the population and constrain evolutionary models. To create a forecast for the 4-year all-sky survey, we perform Monte Carlo simulations of a population synthesis model, where we follow the evolutionary tracks of thermally emitting neutron stars in the Milky Way and test their detectability. In this paper, we discuss strategies for pinpointing the most promising candidates for follow-up observing campaigns using current and future facilities. [ABSTRACT FROM AUTHOR]
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- 2017
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161. Detection of the magnetar SGR J1745-2900 up to 291GHz with evidence of polarized millimetre emission.
- Author
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Torne, P., Desvignes, G., Eatough, R. P., Karuppusamy, R., Paubert, G., Kramer, M., Cognard, I., Champion, D. J., and Spitler, L. G.
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MAGNETARS , *MILLIMETER astronomy , *POLARIZATION (Nuclear physics) , *GALACTIC center ,PULSAR detection - Abstract
In 2015, Torne et al. reported detections of the magnetar SGR J1745-2900 up to 225 GHz (1.33 mm), which was the highest radio frequency detection of pulsar emission at that time. In this work, we present the results of new observations of the same magnetar with detections up to 291GHz (1.03mm), together with evidence of linear polarization in its millimetre emission. SGR J1745-2900 continues to show variability and is, on average, a factor ~4 brighter in the millimetre band than in our observations of 2014 July. The new measured spectrum is slightly inverted, with (α) = +0.4 ± 0.2 (for Sv ∝ vα). However, the spectrum does not seem to be well described by a single power law, which might be due to the intrinsic variability of the source, or perhaps a turn-up somewhere between 8.35 and 87GHz. These results may help us to improve our still incomplete model of pulsar emission and, in addition, they further support the search for and study of pulsars located at the Galactic Centre using millimetre wavelengths. [ABSTRACT FROM AUTHOR]
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- 2017
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162. On the difference between γ -ray-detected and non-γ -ray-detected pulsars.
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Rookyard, S. C., Weltevrede, P., Johnston, S., and Kerr, M.
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GAMMA ray detectors , *ENERGY dissipation , *MAGNETIC inclination , *MAGNETOSPHERE ,PULSAR detection - Abstract
We compare radio profile widths of young, energetic γ-ray-detected and non-γ-ray-detected pulsars. We find that the latter typically have wider radio profiles, with the boundary between the two samples exhibiting a dependence on the rate of rotational energy loss. We also find that within the sample of γ-ray-detected pulsars, radio profile width is correlated with both the separation of the main γ-ray peaks and the presence of narrow γ-ray components. These findings lead us to propose that these pulsars form a single population where the main factors determining γ-ray detectability are the rate of rotational energy loss and the proximity of the line of sight to the rotation axis. The expected magnetic inclination angle distribution will be different for radio pulsars with and without detectable γrays, naturally leading to the observed differences. Our results also suggest that the geometry of existing radio and outer-magnetosphere γ-ray emission models is at least qualitatively realistic, implying that information about the viewing geometry can be extracted from profile properties of pulsars. [ABSTRACT FROM AUTHOR]
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- 2017
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163. A Fast Detection Algorithm for the X-Ray Pulsar Signal.
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Liang, Hao and Zhan, Yafeng
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NAVIGATION , *GAUSSIAN distribution , *PROBABILITY theory , *POISSON distribution , *COMPUTER simulation ,PULSAR detection - Abstract
The detection of the X-ray pulsar signal is important for the autonomous navigation system using X-ray pulsars. In the condition of short observation time and limited number of photons for detection, the noise does not obey the Gaussian distribution. This fact has been little considered extant. In this paper, the model of the X-ray pulsar signal is rebuilt as the nonhomogeneous Poisson distribution and, in the condition of a fixed false alarm rate, a fast detection algorithm based on maximizing the detection probability is proposed. Simulation results show the effectiveness of the proposed detection algorithm. [ABSTRACT FROM AUTHOR]
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- 2017
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164. Autonomous Navigation of Mars Probes by Single X-ray Pulsar Measurement and Optical Data of Viewing Martian Moons.
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Ma, Pengbin, Wang, Tianshu, Jiang, Fanghua, Mu, Junshan, and Baoyin, Hexi
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MARS probes , *SATELLITES of Mars , *ORBIT determination , *KALMAN filtering ,PULSAR detection - Abstract
In order to achieve high accuracy of autonomous navigation for Mars probes, an integrated navigation method using X-ray pulsar measurement and optical data of viewing Martian moons is proposed. For single X-ray pulsar measurement on board a Mars probe, navigation accuracy is low due to its poor observability. On the other hand, Phobos and Deimos, two natural moons of Mars, are important optical navigation information sources available for Mars missions. However, the Martian moons ephemeris bias and the differences between barycentre and centre of brightness of Martian moons will result in low navigation accuracy. The method of integrated navigation using X-ray pulsar measurement and optical data of viewing Martian moons can overcome the defect and achieve accurate navigation. Two sequential orbit determination algorithms, Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF), are compared. The simulation results show this method can obtain high autonomous navigation accuracy during the phase of a probe orbiting Mars. [ABSTRACT FROM PUBLISHER]
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- 2017
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165. A Bayesian Classifier for X-Ray Pulsars Recognition.
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Liang, Hao, Zhan, Yafeng, and Duan, Chaowei
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SPACE vehicle attitude control systems , *POISSON processes , *BAYESIAN analysis , *MAXIMUM likelihood statistics ,PULSAR detection - Abstract
Recognition for X-ray pulsars is important for the problem of spacecraft’s attitude determination by X-ray Pulsar Navigation (XPNAV). By using the nonhomogeneous Poisson model of the received photons and the minimum recognition error criterion, a classifier based on the Bayesian theorem is proposed. For X-ray pulsars recognition with unknown Doppler frequency and initial phase, the features of every X-ray pulsar are extracted and the unknown parameters are estimated using the Maximum Likelihood (ML) method. Besides that, a method to recognize unknown X-ray pulsars or X-ray disturbances is proposed. Simulation results certificate the validity of the proposed Bayesian classifier. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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166. Detecting pulsars with interstellar scintillation in variance images.
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Dai, S., Johnston, S., Bell, M. E., Coles, W. A., Hobbs, G., Ekers, R. D., and Lenc, E.
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RADIO sources (Astronomy) , *RADIO telescopes , *ASTROPHYSICS , *FIELD theory (Physics) ,PULSAR detection - Abstract
Pulsars are the only cosmic radio sources known to be sufficiently compact to show diffractive interstellar scintillations. Images of the variance of radio signals in both time and frequency can be used to detect pulsars in large-scale continuum surveys using the next generation of synthesis radio telescopes. This technique allows a search over the full field of view while avoiding the need for expensive pixel-by-pixel high time resolution searches. We investigate the sensitivity of detecting pulsars in variance images. We show that variance images are most sensitive to pulsars whose scintillation time-scales and bandwidths are close to the subintegration time and channel bandwidth. Therefore, in order to maximize the detection of pulsars for a given radio continuum survey, it is essential to retain a high time and frequency resolution, allowing us to make variance images sensitive to pulsars with different scintillation properties. We demonstrate the technique with Murchision Widefield Array data and show that variance images can indeed lead to the detection of pulsars by distinguishing them from other radio sources. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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167. Towards practical autonomous deep-space navigation using X-Ray pulsar timing.
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Shemar, Setnam, Fraser, George, Heil, Lucy, Hindley, David, Martindale, Adrian, Molyneux, Philippa, Pye, John, Warwick, Robert, and Lamb, Andrew
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SPACE vehicles , *X-ray spectrometers , *TELESCOPES ,PULSAR detection - Abstract
We investigate the feasibility of deep-space navigation using the highly stable periodic signals from X-ray pulsars in combination with dedicated instrumentation on the spacecraft: a technique often referred to as 'XNAV'. The results presented are based on the outputs from a study undertaken for the European Space Agency. The potential advantages of this technique include increased spacecraft autonomy and lower mission operating costs. Estimations of navigation uncertainties have been obtained using simulations of different pulsar combinations and navigation strategies. We find that the pulsar PSR B1937 + 21 has potential to allow spacecraft positioning uncertainties of ~2 and ~5 km in the direction of the pulsar after observation times of 10 and 1 h respectively, for ranges up to 30 AU. This could be achieved autonomously on the spacecraft using a focussing X-ray instrument of effective area ~50 cm together with a high performance atomic clock. The Mercury Imaging X-ray Spectrometer (MIXS) instrument, due to be launched on the ESA/JAXA BepiColombo mission to Mercury in 2018, is an example of an instrument that may be further developed as a practical telescope for XNAV. For a manned mission to Mars, where an XNAV system could provide valuable redundancy, observations of the three pulsars PSR B1937 + 21, B1821-24 and J0437-4715 would enable a three-dimensional positioning uncertainty of ~30 km for up to 3 months without the need to contact Earth-based systems. A lower uncertainty may be achieved, for example, by use of extended observations or, if feasible, by use of a larger instrument. X-ray instrumentation suitable for use in an operational XNAV subsystem must be designed to require only modest resources, especially in terms of size, mass and power. A system with a focussing optic is required in order to reduce the sky and particle background against which the source must be measured. We examine possible options for future developments in terms of simpler, lower-cost Kirkpatrick-Baez optics. We also discuss the principal design and development challenges that must be addressed in order to realise an operational XNAV system. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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168. A possible 55-d X-ray period of the ultraluminous accreting pulsar M82 X-2.
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Kong, Albert K. H., Chin-Ping Hu, Lupin Chun-Che Lin, Li, K. L., Ruolan Jin, Liu, C. Y., and David Chien-Chang Yen
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X-ray astronomy , *GALACTIC X-ray sources , *ELECTROMAGNETIC waves , *SPACE astronomy ,PULSAR detection - Abstract
We report on the possible detection of a 55-d X-ray modulation for the ultraluminous accreting pulsar M82 X-2 from archival Chandra observations. Because M82 X-2 is known to have a 2.5-d orbital period, if the 55-d period is real, then it will be the superorbital period of the system. We also investigated variabilities of three other nearby ultraluminous X-ray sources in the central region of M82 with the Chandra data, and we did not find any evidence of periodicities. Furthermore, we re-examined the previously reported 62-d periodicity near the central region of M82 by performing a systematic timing study with all the archival Rossi X-Ray Timing Explorer and Swift data. Using various dynamic timing analysis methods, we have confirmed that the 62-d period is not stable, suggesting that it is not the orbital period of M82 X-1; this is in agreement with previous work. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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169. Extending DEAP with Active Sampling for Evolutionary Supervised Learning
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Sana Ben Hamida, Ghita Benjelloun, Laboratoire d'analyse et modélisation de systèmes pour l'aide à la décision (LAMSADE), Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), and Ben Hamida, Sana
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business.industry ,Computer science ,Supervised learning ,random sampling ,Genetic Programming ,Sampling (statistics) ,DEAP ,[INFO.INFO-LG] Computer Science [cs]/Machine Learning [cs.LG] ,Machine learning ,computer.software_genre ,pulsar detection ,[INFO.INFO-LG]Computer Science [cs]/Machine Learning [cs.LG] ,active learning ,occupancy detection ,weighted sampling ,Artificial intelligence ,business ,computer - Abstract
International audience; Complexity, variety and large sizes of data bases make the Knowledge extraction a difficult task for supervised machine learning techniques. It is important to provide these techniques additional tools to improve their efficiency when dealing with such data. A promising strategy is to reduce the size of the training sample seen by the learner and to change it regularly along the learning process. Such strategy known as active learning, is suitable for iterative learning algorithms such as Evolutionary Algorithms. This paper presents some sampling techniques for active learning and how they can be applied in a hierarchical way. Then, it details how these techniques could be implemented into DEAP, a Python framework for Evolutionary Algorithms. A comparative study demonstrates how active learning improve the evolutionary learning on two data bases for detecting pulsars and occupancy in buildings.
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- 2021
170. A glitch in the millisecond pulsar J0613-0200.
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McKee, J. W., Janssen, G. H., Stappers, B. W., Lyne, A. G., Caballero, R. N., Lentati, L., Desvignes, G., Jessner, A., Jordan, C. A., Karuppusamy, R., Kramer, M., Cognard, I., Champion, D. J., Graikou, E., Lazarus, P., Osłowski, S., Perrodin, D., Shaifullah, G., Tiburzi, C., and Verbiest, J. P. W.
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VERY large array telescopes , *ANTENNA arrays , *RADIO telescopes ,PULSAR detection - Abstract
We present evidence for a small glitch in the spin evolution of the millisecond pulsar J0613-0200, using the EPTA Data Release 1.0, combined with Jodrell Bank analogue filterbank times of arrival (TOAs) recorded with the Lovell telescope and Effelsberg Pulsar Observing System TOAs. A spin frequency step of 0.82(3) nHz and frequency derivative step of -1.6(39) × 10-19 Hz s-1 are measured at the epoch of MJD 50888(30). After PSR B1821-24A, this is only the second glitch ever observed in a millisecond pulsar, with a fractional size in frequency of Δv/v = 2.5(1) × 10-12, which is several times smaller than the previous smallest glitch. PSR J0613-0200 is used in gravitational wave searches with pulsar timing arrays, and is to date only the second such pulsar to have experienced a glitch in a combined 886 pulsar-years of observations. We find that accurately modelling the glitch does not impact the timing precision for pulsar timing array applications. We estimate that for the current set of millisecond pulsars included in the International Pulsar Timing Array, there is a probability of ~50 per cent that another glitch will be observed in a timing array pulsar within 10 years. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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171. A millisecond pulsar in an extremely wide binary system.
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Bassa, C. G., Janssen, G. H., Stappers, B. W., Tauris, T. M., Wevers, T., Jonker, P. G., Lentati, L., Verbiest, J. P. W., Desvignes, G., Graikou, E., Guillemot, L., Freire, P. C. C., Lazarus, P., Caballero, R. N., Champion, D. J., Cognard, I., Jessner, A., Jordan, C., Karuppusamy, R., and Kramer, M.
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BINARY systems (Astronomy) , *PULSATING stars , *ASTRONOMICAL photometry , *RADIAL velocity of stars ,PULSAR detection - Abstract
We report on 22 yr of radio timing observations of the millisecond pulsar J1024-0719 by the telescopes participating in the European Pulsar Timing Array (EPTA). These observations reveal a significant second derivative of the pulsar spin frequency and confirm the discrepancy between the parallax and Shklovskii distances that has been reported earlier. We also present optical astrometry, photometry and spectroscopy of 2MASS J10243869-0719190. We find that it is a low-metallicity main-sequence star (K7V spectral type, [M/H] = -1.0, Teff = 4050 ± 50 K) and that its position, proper motion and distance are consistent with those of PSR J1024-0719. We conclude that PSR J1024-0719 and 2MASS J10243869-0719190 form a common proper motion pair and are gravitationally bound. The gravitational interaction between the main-sequence star and the pulsar accounts for the spin frequency derivatives, which in turn resolves the distance discrepancy. Our observations suggest that the pulsar and main-sequence star are in an extremely wide (Pb >200 yr) orbit. Combining the radial velocity of the companion and proper motion of the pulsar, we find that the binary system has a high spatial velocity of 384 ± 45 km s-1 with respect to the local standard of rest and has a Galactic orbit consistent with halo objects. Since the observed main-sequence companion star cannot have recycled the pulsar to millisecond spin periods, an exotic formation scenario is required. We demonstrate that this extremely wide-orbit binary could have evolved from a triple system that underwent an asymmetric supernova explosion, though find that significant fine-tuning during the explosion is required. Finally, we discuss the implications of the long period orbit on the timing stability of PSR J1024-0719 in light of its inclusion in pulsar timing arrays. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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172. ON THE GALACTIC DISTRIBUTIONS OF RADIO PULSARS AND PLASMA DENSITY.
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Ankay, A., Yazgan, E., and Kutukcu, P.
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PLASMA density , *GALACTIC dynamics , *DISPERSION (Atmospheric chemistry) , *ASTRONOMICAL observations ,PULSAR detection - Abstract
A brief review of distance measurement methods for some astronomical sources is presented. Galactic plasma density distribution as related to the distribution of radio pulsars is discussed and a method for constructing relations between dispersion measure and distance for Galactic radio pulsars in small solid angle intervals is described. Dispersion measure - distance relations for radio pulsars based on this approach in the Galactic longitude and latitude intervals of ▵ l = 0° 2° and ▵ b = 0° 2° are displayed and comparisons are made with the predictions of the two commonly used models. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
173. Detection of dispersed radio pulses: a machine learning approach to candidate identification and classification.
- Author
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Devine, Thomas Ryan, Goseva-Popstojanova, Katerina, and McLaughlin, Maura
- Subjects
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RADIO pulse time modulation , *MACHINE learning , *ASTRONOMICAL observations , *SIGNAL-to-noise ratio ,PULSAR detection - Abstract
Searching for extraterrestrial, transient signals in astronomical data sets is an active area of current research. However, machine learning techniques are lacking in the literature concerning single-pulse detection. This paper presents a new, two-stage approach for identifying and classifying dispersed pulse groups (DPGs) in single-pulse search output. The first stage identified DPGs and extracted features to characterize them using a new peak identification algorithm which tracks sloping tendencies around local maxima in plots of signal-to-noise ratio versus dispersion measure. The second stage used supervised machine learning to classify DPGs. We created four benchmark data sets: one unbalanced and three balanced versions using three different imbalance treatments. We empirically evaluated 48 classifiers by training and testing binary and multiclass versions of six machine learning algorithms on each of the four benchmark versions. While each classifier had advantages and disadvantages, all classifiers with imbalance treatments had higher recall values than those with unbalanced data, regardless of the machine learning algorithm used. Based on the benchmarking results, we selected a subset of classifiers to classify the full, unlabelled data set of over 1.5 million DPGs identified in 42 405 observations made by the Green Bank Telescope. Overall, the classifiers using a multiclass ensemble tree learner in combination with two oversampling imbalance treatments were the most efficient; they identified additional known pulsars not in the benchmark data set and provided six potential discoveries, with significantly less false positives than the other classifiers. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
174. Fast radio bursts - A brief review: Some questions, fewer answers.
- Author
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Katz, J. I.
- Subjects
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SOLAR radio bursts , *SOLAR radio emission , *ASTRONOMICAL observations , *PLASMA density ,PULSAR detection - Abstract
Fast radio bursts (FRBs) are millisecond bursts of radio radiation at frequencies of about 1 GHz, recently discovered in pulsar surveys. They have not yet been definitively identified with any other astronomical object or phenomenon. The bursts are strongly dispersed, indicating passage through a high column density of low density plasma. The most economical interpretation is that this is the intergalactic medium, indicating that FRB are at 'cosmological' distances with redshifts in the range 0.3-1.3. Their inferred brightness temperatures are as high as 10 K, implying coherent emission by 'bunched' charges, as in radio pulsars. I review the astronomical sites, objects and emission processes that have been proposed as the origin of FRB, with particular attention to soft gamma repeaters (SGRs) and giant pulsar pulses. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
175. Mathematical Model for Measuring Pulsar Parameters by Pulsar Timing Observations and Precision Estimation.
- Author
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Ting-gao, Yang, Yu-ping, Gao, Ming-lei, Tong, Cheng-shi, Zhao, and Feng, Gao
- Subjects
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MATHEMATICAL models , *MATHEMATICS , *PRECISION (Information retrieval) , *ECLIPTIC ,PULSAR detection - Abstract
Pulsar rotational and astrometric parameters can be measured with a very high precision by pulsar timing observations. The pulsar timing model, the methods to measure the pulsar parameters by least squares fitting and to estimate their covariances are briefly described. The mathematical relations between the timing residuals of a pulsar and the errors of its different parameters are derived in the ecliptic coordinate system. The relationships of the measuring precisions of pulsar's ecliptic longitude, latitude, and annual parallax with the absolute value of pulsar's ecliptic latitude are shown by curves. And the relations of the measuring precisions of pulsar's astrometric parameters with the pulsar's latitudinal parameter itself are discussed as well. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
176. Spin-down of Pulsars, and Their Electromagnetic and Gravitational Wave Radiations.
- Author
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Yue-zhu, Zhang, Yan-yan, Fu, Yi-huan, Wei, Cheng-min, Zhang, Shao-hua, Yu, Yuan-yue, Pan, Yuan-qi, Guo, and De-hua, Wang
- Subjects
- *
GRAVITATIONAL wave astronomy , *ELECTROMAGNETIC pulses , *SPIN-down time , *FLUID dynamics ,PULSAR detection - Abstract
Pulsars posses extremely strong magnetic fields, and their magnetic axis does not coincide with their rotation axis, this causes the pulsars to emit electromagnetic radiations. Pulsars rely on their rotational energy to compensate for the energy loss caused by the electromagnetic radiation, which leads to the gradually decelerated spin of pulsars. According to the theoretical deduction, we have calculated the initial period of the Crab Nebula pulsar, and derived the period evolution of the pulsar at any time in the future under the effect of the electromagnetic radiation. Considered the possible existence of quadrupole moment in the mass distribution of a pulsar, the gravitational wave radiation will also make the pulsar spin down, hence the variation of spin period of the Crab pulsar under the effect of gravitational wave radiation is further analyzed. Finally, combining the two kinds of radiation mechanisms, the evolution of spin period of the Crab pulsar under the joint action of these two kinds of radiation mechanisms is analyzed. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
177. Luminosity-dependent change of the emission diagram in the X-ray pulsar 4U 1626-67.
- Author
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Koliopanos, Filippos and Gilfanov, Marat
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X-ray absorption , *EMISSION spectroscopy , *LUMINOSITY ,PULSAR detection - Abstract
We detect variability of the Fe Ka emission line in the spectrum of X-ray pulsar 4U 1626-67, correlated with changes in its luminosity and in the shape of its pulse profile. Analysis of archival Chandra and RXTE observations revealed the presence of an intrinsically narrow Fe Ka emission line in the spectrum obtained during the source's current high-luminosity period. However, the line was not present during an XMM-Newton observation seven years earlier, when the source was ~three times fainter. The line is resolved by the high-energy grating of Chandra at the 98 per cent confidence level, and its small intrinsic width, s = 36.4+15.3 -11.3 eV, suggests reflection off an accretion disc at the radius R (7.5+8.2 -3.8) 108 cm assuming a Keplerian disk, viewed at an inclination angle of 20?. This value is consistent with the radius of the magnetosphere of the pulsar, suggesting that the line originates near the inner edge of a disc that is truncated by the magnetic field of the neutron star. Timing analysis of the XMM-Newton and RXTE data revealed a major change in the pulse profile of the source from a distinct double-peaked shape during the high-luminosity state when the line was present, to a much more complex multipeak structure during the low-luminosity state. We argue that the appearance of the line and the change in the shape of the pulse profile are correlated and are the result of a major change in the emission diagram of the accretion column, from a pencil-beam pattern at low luminosity, to a fan-beam pattern at high luminosity. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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178. A search for rotating radio transients and fast radio bursts in the Parkes high-latitude pulsar survey.
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Rane, A., Lorimer, D. R., Bates, S. D., McMann, N., McLaughlin, M. A., and Rajwade, K.
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RADIO transmitter-receivers , *SOLAR radio bursts , *UNCERTAINTY (Information theory) , *ASTRONOMICAL surveys ,PULSAR detection - Abstract
Discoveries of rotating radio transients and fast radio bursts (FRBs) in pulsar surveys suggest that more of such transient sources await discovery in archival data sets. Here we report on a single-pulse search for dispersed radio bursts over a wide range of Galactic latitudes (|b| < 60°) in data previously searched for periodic sources by Burgay et al. We re-detected 20 of the 42 pulsars reported by Burgay et al. and one rotating radio transient reported by Burke-Spolaor. No FRBs were discovered in this survey. Taking into account this result, and other recent surveys at Parkes, we corrected for detection sensitivities based on the search software used in the analyses and the different back-ends used in these surveys and find that the all-sky FRB event rate for sources with a fluence above 4.0 Jy ms at 1.4 GHz to be R = 4.4+5.2 -3.1 × 10³ FRBs d-1 sky-1, where the uncertainties represent a 99 per cent confidence interval. While this rate is lower than inferred from previous studies, as we demonstrate, this combined event rate is consistent with the results of all systematic FRB searches at Parkes to date and does not require the need to postulate a dearth of FRBs at intermediate latitudes. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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- View/download PDF
179. An extremely bright gamma-ray pulsar in the Large Magellanic Cloud.
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GAMMA rays , *LARGE magellanic cloud , *MAGNETOSPHERE , *NEUTRON stars ,PULSAR detection - Abstract
Pulsars are rapidly spinning, highly magnetized neutron stars, created in the gravitational collapse of massive stars. We report the detection of pulsed giga--electron volt gamma rays from the young pulsar PSR J0540--6919 in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. This is the first gamma-ray pulsar detected in another galaxy. It has the most luminous pulsed gamma-ray emission yet observed, exceeding the Crab pulsar's by a factor of 20. PSR J0540--6919 presents an extreme test case for understanding the structure and evolution of neutron star magnetospheres. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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180. Low-frequency spectral turn-overs in millisecond pulsars studied from imaging observations.
- Author
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Kuniyoshi, M., Verbiest, J. P. W., Lee, K. J., Adebahr, B., Kramer, M., and Noutsos, A.
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FLUX (Energy) , *INTERSTELLAR medium , *SENSITIVITY analysis , *LIGHT scattering ,PULSAR detection - Abstract
Measurements of pulsar flux densities are of great importance for understanding the pulsar emission mechanism and for predictions of pulsar survey yields and the pulsar population at large. Typically these flux densities are determined from phase-averaged 'pulse profiles', but this method has limited applicability at low frequencies because the observed pulses can easily be spread out by interstellar effects like scattering or dispersion, leading to a non-pulsed continuum component that is necessarily ignored in this type of analysis. In particular for the class of the millisecond pulsars (MSPs) at frequencies below 200 MHz, such interstellar effects can seriously compromise detectability and measured flux densities. In this paper, we investigate MSP spectra based on a complementary approach, namely through investigation of archival continuum imaging data. Even though these images lose sensitivity to pulsars since the on-pulse emission is averaged with off-pulse noise, they are insensitive to effects from scattering and provide a reliable way to determine the flux density and spectral indices of MSPs based on both pulsed and unpulsed components. Using the 74 MHz VLSSr as well as the 325 MHz WENSS and 1.4 GHz NVSS catalogues, we investigate the imaging flux densities of MSPs and evaluate the likelihood of spectral turn-overs in this population. We determine three new MSP spectral indices and identify six new MSPs with likely spectral turn-overs. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
181. Taking the Pulse of Pulsars.
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PULSAR detection ,SIGNALS & signaling ,ASTRONOMERS - Abstract
The article focuses on the development of pulsars, a new signal from space discovered by astronomer Anthony Hewish of Cambridge University in England. Hewish reveals that one of the pulsars blips every 1.27 seconds, another at 1.19-second intervals, and pulsar four pulses every quarter of a second. Meanwhile, astronomers suggest that pulsar theories continued to grow beyond the pulsating neutron-star and white-dwarf-star theories.
- Published
- 1968
182. Trends of Evolutionary Machine Learning to Address Big Data Mining
- Author
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Ghita Benjelloun, Sana Ben Hamida, Hmida Hmida, Laboratoire d'analyse et modélisation de systèmes pour l'aide à la décision (LAMSADE), Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Université Paris sciences et lettres (PSL), Université de Tunis El Manar (UTM), Inès Saad, Camille Rosenthal-Sabroux, Faiez Gargouri, and Pierre-Emmanuel Arduin
- Subjects
Active learning (machine learning) ,Computer science ,Big data ,Genetic Programming ,Active Learning ,Genetic programming ,02 engineering and technology ,Machine learning ,computer.software_genre ,01 natural sciences ,Data Sampling ,Machine Learning ,[INFO.INFO-LG]Computer Science [cs]/Machine Learning [cs.LG] ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,Information system ,010303 astronomy & astrophysics ,Big data mining ,business.industry ,Pulsar Detection ,Evolutionary data mining ,Sampling (statistics) ,Big Data Mining ,Active data ,Horizontal Parallelization ,Higgs Boson Classification ,020201 artificial intelligence & image processing ,Artificial intelligence ,business ,computer - Abstract
International audience; Improving decisions by better mining the available data in an Information System is a common goal in many decision making environments. However, the complexity and the large size of the collected data in modern systems make this goal a challenge for mining methods. Evolutionary Data Mining Algorithms (EDMA), such as Genetic Programming (GP), are powerful meta-heuristics with an empirically proven efficiency on complex machine learning problems. They are expected to be applied to real-world big data tasks and applications in our daily life. Thus, they need, as all machine learning techniques, to be scaled to Big Data bases. This paper review some solutions that could be applied to help EDMA to deal with Big Data challenges. Two solutions are then selected and explained. The first one is based on the algorithmic manipulation involving the introduction of the active learning paradigm thanks to the active data sampling. The second is based on the processing manipulation involving horizontal scaling thanks to the processing distribution over networked nodes. This work explains how each solution is introduced to GP. As preliminary experiences, the extended GP is applied to solve two complex machine learning problem: the Higgs Boson classification problem and the Pulsar detection problem. Experimental results are then discussed and compared to value the efficiency of each solution.
- Published
- 2021
183. Tryton Supercomputer Capabilities for Analysis of Massive Data Streams.
- Author
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Krawczyk, Henryk, Nykiel, Michał, and Proficz, Jerzy
- Subjects
- *
SUPERCOMPUTERS , *DATA analysis , *RADIO telescopes , *COMPUTER software , *THREE-dimensional imaging , *OIL spills , *SIMULATION methods & models ,PULSAR detection - Abstract
The recently deployed supercomputer Tryton, located in the Academic Computer Center of Gdansk University of Technology, provides great means for massive parallel processing. Moreover, the status of the Center as one of the main network nodes in the PIONIER network enables the fast and reliable transfer of data produced by miscellaneous devices scattered in the area of the whole country. The typical examples of such data are streams containing radio-telescope and satellite observations. Their analysis, especially with real-time constraints, can be challenging and requires the usage of dedicated software components. We propose a solution for such parallel analysis using the supercomputer, supervised by the KASKADA platform, which with the conjunction with immerse 3D visualization techniques can be used to solve problems such as pulsar detection and chronometric or oil-spill simulation on the sea surface. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
184. Localising fast radio bursts and other transients using interferometric arrays.
- Author
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Obrocka, M., Stappers, B., and Wilkinson, P.
- Subjects
- *
SOLAR radio bursts , *INTERSTELLAR medium , *ASTRONOMICAL spectroscopy , *ASTRONOMICAL observations ,PULSAR detection - Abstract
A new population of sources emitting fast and bright transient radio bursts (FRBs) has recently been identified. Their observed high dispersion measures suggests an extragalactic origin, and accurately determining their positions and distances will provide an opportunity to study the magneto-ionic properties of the intergalactic medium. So far, FRBs have all been found using large dishes equipped with multi-pixel arrays. While these dishes are well-suited to discovering transient sources, they are poor at providing accurate localisations. A 2D snapshot image of the sky, made with a correlation interferometer array, can accurately localise many compact radio sources simultaneously. However, the required time resolution and the need to detect them in real time makes this currently impractical. In a beam-forming approach many narrow tied-array beams (TABs) are produced and the advantages of single dishes and interferometers can be combined. We present a proof-of-concept analysis of a new non-imaging method that utilises the additional spectral and comparative spatial information obtained from multiply overlapping TABs to estimate a transient source location with up to arcsecond accuracy in almost real time. We demonstrate this for a variety of interferometric configurations, that is LOFAR and MeerKAT, and show that the estimated angular position may be sufficient for identifying a host galaxy or other related object, without reference to other simultaneous or follow-up observations. In cases where the position is less accurately determined, we can still significantly reduce the area that needs to be searched for associated emission at other wavelengths and from potential host galaxies. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
185. The High Time Resolution Universe Pulsar Survey - XII. Galactic plane acceleration search and the discovery of 60 pulsars.
- Author
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Ng, C., Champion, D. J., Bailes, M., Barr, E. D., Bates, S. D., Bhat, N. D. R., Burgay, M., Burke-Spolaor, S., Flynn, C. M. L., Jameson, A., Johnston, S., Keith, M. J., Kramer, M., Levin, L., Petroff, E., Possenti, A., Stappers, B. W., van Straten, W., Tiburzi, C., and Eatough, R. P.
- Subjects
- *
ACCELERATION (Mechanics) , *GALAXIES , *RADIO telescopes , *RADIO interference , *SEARCH algorithms ,PULSAR detection - Abstract
We present initial results from the low-latitude Galactic plane region of the High Time Resolution Universe pulsar survey conducted at the Parkes 64-m radio telescope. We discuss the computational challenges arising from the processing of the terabyte-sized survey data. Two new radio interference mitigation techniques are introduced, as well as a partially coherent segmented acceleration search algorithm which aims to increase our chances of discovering highly relativistic short-orbit binary systems, covering a parameter space including potential pulsar-black hole binaries. We show that under a constant acceleration approximation, a ratio of data length over orbital period of ≈0.1 results in the highest effectiveness for this search algorithm. From the 50 per cent of data processed thus far, we have redetected 435 previously known pulsars and discovered a further 60 pulsars, two of which are fast-spinning pulsars with periods less than 30 ms. PSR J1101-6424 is a millisecond pulsar whose heavy white dwarf (WD) companion and short spin period of 5.1 ms indicate a rare example of full-recycling via Case A Roche lobe overflow. PSR J1757-27 appears to be an isolated recycled pulsar with a relatively long spin period of 17 ms. In addition, PSR J1244-6359 is a mildly recycled binary system with a heavy WD companion, PSR J1755-25 has a significant orbital eccentricity of 0.09 and PSR J1759-24 is likely to be a long-orbit eclipsing binary with orbital period of the order of tens of years. Comparison of our newly discovered pulsar sample to the known population suggests that they belong to an older population. Furthermore, we demonstrate that our current pulsar detection yield is as expected from population synthesis. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
186. The Parkes multibeam pulsar survey - VII. Timing of four millisecond pulsars and the underlying spin-period distribution of the Galactic millisecond pulsar population.
- Author
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Lorimer, D. R., Esposito, P., Manchester, R. N., Possenti, A., Lyne, A. G., McLaughlin, M. A., Kramer, M., Hobbs, G., Stairs, I. H., Burgay, M., Eatough, R. P., Keith, M. J., Faulkner, A. J., D'Amico, N., Camilo, F., Corongiu, A., and Crawford, F.
- Subjects
- *
ASTRONOMICAL observations , *STELLAR populations , *GAMMA distributions , *LOGNORMAL distribution ,PULSAR detection - Abstract
We present timing observations of 4-ms pulsars discovered in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. PSRs J1552-4937 and J1843-1448 are isolated objects with spin periods of 6.28 and 5.47 ms, respectively. PSR J1727-2946 is in a 40-d binary orbit and has a spin period of 27 ms. The 4.43-ms pulsar J1813-2621 is in a circular 8.16-d binary orbit around a low-mass companion star with a minimum companion mass of 0.2 M⊙. Combining these results with detections from five other Parkes multibeam surveys, gives a well-defined sample of 56 pulsars with spin periods below 20 ms. We develop a likelihood analysis to constrain the functional form which best describes the underlying distribution of spin periods for millisecond pulsars. The best results were obtained with a lognormal distribution. A gamma distribution is less favoured, but still compatible with the observations. Uniform, power-law and Gaussian distributions are found to be inconsistent with the data. Galactic millisecond pulsars being found by current surveys appear to be in agreement with a lognormal distribution which allows for the existence of pulsars with periods below 1.5 ms. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
187. Properties and observability of glitches and anti-glitches in accreting pulsars.
- Author
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Ducci, L., Pizzochero, P. M., Doroshenko, V., Santangelo, A., Mereghetti, S., and Ferrigno, C.
- Subjects
- *
STAR observations , *ACCRETION disks , *X-ray astronomy , *NEUTRON stars , *X-ray binaries , *STARQUAKES ,PULSAR detection - Abstract
Several glitches have been observed in young, isolated radio pulsars, while a clear detection in accretion-powered X-ray pulsars is still lacking. We use the Pizzochero snowplow model for pulsar glitches as well as starquake models to determine for the first time the expected properties of glitches in accreting pulsars and their observability. Since some accreting pulsars show accretion-induced long-term spin-up, we also investigate the possibility that anti-glitches occur in these stars. We find that glitches caused by quakes in a slow accreting neutron star are very rare and their detection extremely unlikely. On the contrary, glitches and anti-glitches caused by a transfer of angular momentum between the superfluid neutron vortices and the non-superfluid component may take place in accreting pulsars more often. We calculate the maximum jump in angular velocity of an anti-glitch and we find that it is expected to be ∆Ωa-gl ≈ 10-5-10-4 rad s-1.We also note that since accreting pulsars usually have rotational angular velocities lower than those of isolated glitching pulsars, both glitches and anti-glitches are expected to have long rise and recovery timescales compared to isolated glitching pulsars, with glitches and anti-glitches appearing as a simple step in angular velocity. Among accreting pulsars, we find that GX 1+4 is the best candidate for the detection of glitches with currently operating X-ray instruments and future missions such as the proposed Large Observatory for X-ray Timing (LOFT). [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
188. Pulsar timing noise and the minimum observation time to detect gravitational waves with pulsar timing arrays.
- Author
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Lasky, Paul D., Melatos, Andrew, Ravi, Vikram, and Hobbs, George
- Subjects
- *
ASTRONOMICAL observations , *GRAVITATIONAL waves , *GALACTIC redshift , *SUPERFLUIDITY ,PULSAR detection - Abstract
The sensitivity of pulsar timing arrays to gravitational waves is, at some level, limited by timing noise. Red timing noise - the stochastic wandering of pulse arrival times with a red spectrum - is prevalent in slow-spinning pulsars and has been identified in many millisecond pulsars. Phenomenological models of timing noise, such as from superfluid turbulence, suggest that the timing noise spectrum plateaus below some critical frequency, fc, potentially aiding the hunt for gravitational waves. We examine this effect for individual pulsars by calculating minimum observation times, Tmin(fc), over which the gravitational wave signal becomes larger than the timing noise plateau. We do this in two ways: (1) in a model-independent manner, and (2) by using the superfluid turbulence model for timing noise as an example to illustrate how neutron star parameters can be constrained. We show that the superfluid turbulence model can reproduce the data qualitatively from a number of pulsars observed as part of the Parkes Pulsar Timing Array. We further show how a value of fc, derived either through observations or theory, can be related to Tmin. This provides a diagnostic whereby the usefulness of timing array pulsars for gravitational-wave detection can be quantified. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
189. The Short Bursts in SGR 1806-20, 1E 1048-5937, and SGR 0501+4516.
- Author
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ZHIJIE QU, ZHAOSHENG LI, YUPENG CHEN, SHI DAI, LONG JI, RENXIN XU, and SHU ZHANG
- Subjects
- *
X-ray diffraction , *BREMSSTRAHLUNG , *LUMINOSITY , *EMISSIONS (Air pollution) ,PULSAR detection - Abstract
We analyzed temporal and spectral properties, focusing on the short bursts, for three anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs), including SGR 1806-20, 1E 1048-5937, and SGR 0501+4516. Using the data from XMM-Newton, we located the short bursts by the Bayesian blocks algorithm. The short bursts' duration distributions for three sources were fitted by two lognormal functions. The spectra of shorter bursts (<0:2 s) and longer bursts (=0:2 s) can be well fitted in a two blackbody components model or optically thin thermal bremsstrahlung model for SGR 0501+4516. We also found that there is a positive correlation between the burst luminosity and the persistent luminosity with a power law index ¼ 1:23 ± 0:18. The energy ratio of this persistent emission to the time averaged short bursts is in the range of 10-10³, being comparable to the case in Type I X-ray burst. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
190. Simulated low-intensity optical pulsar observation with single-photon detector.
- Author
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Leeb, W. R., Alves, J., Meingast, S., and Brunner, M.
- Subjects
- *
PHOTON detectors , *SINGLE photon generation , *NEUTRON stars , *VERY large telescopes , *SIGNAL-to-noise ratio , *OPTICAL radiometry ,PULSAR detection - Abstract
Context. Optical radiation of pulsars offers valuable clues to the physics of neutron stars, which are our only probes of the most extreme states of matter in the present-day universe. Still, only about 1% of all cataloged pulsars have known optical counterparts. Aims. The goal of this work is to develop an observational method optimized for discovering faint optical pulsars. Methods. A single-photon detector transforms the signal received by the telescope into a pulse sequence. The events obtained are time tagged and transformed into a histogram of event time differences. The histogram envelope presents the autocorrelation of the recorded optical signal and thus displays any periodicity of the input signal. Results. Simulations show that faint pulsars radiating in the optical regime can be detected in a straightforward way. As an example, a fictitious pulsar with a V-magnitude of 24.6 mag and a signature like the Crab pulsar can be discovered within one minute using an 8-m class telescope. At the detector's peak sensitivity the average optical flux density would then amount to Fv = 0:63 μJy. With a 40-m class telescope, such as the forthcoming European ELT, the detection of optical pulsars with magnitudes V < 30 mag is within reach for a measurement time of one minute. A two-hour "blind search" with the ELT could reach V ~ 31:3 mag. Conclusions. This method allows detecting faint periodic optical radiation with simple equipment and easy signal processing. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
191. Detecting Dark Matter with Imploding Pulsars in the Galactic Center.
- Author
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Bramante, Joseph and Linden, Tim
- Subjects
- *
DARK matter , *INTERSTELLAR medium , *GALACTIC center , *MILKY Way ,PULSAR detection - Abstract
The paucity of old millisecond pulsars observed at the galactic center of the Milky Way could be the result of dark matter accumulating in and destroying neutron stars. In regions of high dark matter density, dark matter clumped in a pulsar can exceed the Schwarzschild limit and collapse into a natal black hole which destroys the pulsar. We examine what dark matter models are consistent with this hypothesis and find regions of parameter space where dark matter accumulation can significantly degrade the neutron star population within the galactic center while remaining consistent with observations of old millisecond pulsars in globular clusters and near the solar position. We identify what dark matter couplings and masses might cause a young pulsar at the galactic center to unexpectedly extinguish. Finally, we find that pulsar collapse age scales inversely with the dark matter density and linearly with the dark matter velocity dispersion. This implies that maximum pulsar age is spatially dependent on position within the dark matter halo of the Milky Way. In turn, this pulsar age spatial dependence will be dark matter model dependent. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
192. Fermi-LAT detection of gamma-ray pulsars above 10 GeV.
- Author
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Saz Parkinson, P. M. and Fermi-LAT Collaboration
- Subjects
- *
GAMMA rays , *NATURAL satellites , *POWER law (Mathematics) , *FERMI surfaces , *MATHEMATICAL models , *PARTICLES (Nuclear physics) ,PULSAR detection - Abstract
The Large Area Telescope (LAT) on board the Fermi satellite has detected ∼120 pulsars above 100 MeV. While most γ-ray pulsars have spectra that are well modeled by a power law with an exponential cut-off at around a few GeV, some show significant pulsed high-energy (HE, >10 GeV) emission. I present a study of HE emission from LAT γ-ray pulsars and discuss prospects for the detection of pulsations at very high energies (VHE, >100 GeV) with ground-based instruments. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
193. Multi-wavelength studies of the gamma-ray pulsar PSR J1907+0602.
- Author
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Pandel, Dirk and Scott, Robert
- Subjects
- *
WAVELENGTHS , *GAMMA rays , *NEBULAE , *IMAGE analysis ,PULSAR detection - Abstract
PSR J1907+0602 is a radio-faint, 107-ms GeV gamma-ray pulsar that was discovered with the Fermi LAT in a blind pulsar search. PSR J1907+0602 is located near the bright, extended TeV gamma-ray source MGRO J1908+06 which may be an associated pulsar wind nebula. We present an analysis of XMM-Newton X-ray data and EVLA radio data of the pulsar. We detect a faint X-ray source coincident with the gamma-ray pulsar and investigate its spectral and timing properties. We also find marginal evidence for a bow shock in the X-ray images. The pulsar was not detected with the EVLA, and we derive upper limits on the time-averaged radio flux in multiple frequency bands. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
194. DETECTION OF GRAVITATIONAL WAVES USING PULSAR TIMING.
- Author
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MANCHESTER, R. N.
- Subjects
- *
GRAVITATIONAL waves , *NEUTRON stars , *SUPERNOVAE , *ASTROPHYSICS , *QUARK stars ,PULSAR detection - Published
- 2012
195. RELATIVISTIC SPIN-PRECESSION IN BINARY PULSARS.
- Author
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KRAMER, MICHAEL
- Subjects
- *
GRAVITATIONAL waves , *GENERAL relativity (Physics) , *PARTICLE physics , *GRAVITATIONAL fields , *PARTICLES (Nuclear physics) , *SPECIAL relativity (Physics) ,PULSAR detection - Published
- 2012
196. Radio Searches for Pulsars and Short-Duration Transients.
- Author
-
McLaughlin, Maura
- Subjects
- *
GRAVITATIONAL waves , *TRANSIENTS (Dynamics) , *TELESCOPES , *ASTROPHYSICS ,PULSAR detection - Abstract
I discuss methods and current software packages for radio searches for pulsars and short-duration transients. I then describe the properties of the current pulsar population and the status of and predictions for ongoing and future surveys. The presently observed pulsar population numbers around 2000 and is expected to roughly double over the next five years, with the number of millisecond pulsars expected to more than triple. Finally, I discuss individual objects discovered in the Green Bank Telescope 350-MHz Drift-Scan Survey and the Arecibo Pulsar ALFA Survey. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
197. High Magnetic Field Rotation-powered Pulsars.
- Author
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Ng, C.-Y. and Kaspi, V. M.
- Subjects
- *
X-rays , *STELLAR oscillations , *STELLAR magnetic fields , *MAGNETARS ,PULSAR detection - Abstract
Anomalous X-ray pulsars and soft gamma repeaters have recently emerged as a unified class of neutron stars, identified by dramatic X-ray and gamma-ray outbursts and via luminous Xray pulsations, both thought to be powered by the decay of an enormous internal magnetic field. This "magnetar" hypothesis has raised the question of these objects' physical relationship with conventional rotation-powered pulsars (RPPs). The highest magnetic-field RPPs might therefore be expected to be transition objects between the two populations. The recently reported magnetar-like outburst of PSR J1846-0258, previously thought to be purely rotation-powered, clearly supports this suggestion. Here we review the observational properties of the highest magnetic-field RPPs known, and show some common characteristics that are notable among RPPs, which are plausibly related to their high fields. Using these objects, we consider the evidence for proposed "magnetothermal evolution" in neutron stars, and argue that while some exists, it is not yet conclusive. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
198. Pulsar Timing with the Fermi LAT.
- Author
-
Ray, Paul S., Kerr, Matthew, and Parent, Damien
- Subjects
- *
TELESCOPES , *MAXIMUM likelihood statistics , *WAVELENGTHS , *NEUTRON stars , *PHOTONS ,PULSAR detection - Abstract
We present an overview of precise pulsar timing using data from the Large Area Telescope (LAT) on Fermi. We describe the analysis techniques including a maximum likelihood method for determining pulse times of arrival from unbinned photon data. In addition to determining the spindown behavior of the pulsars and detecting glitches and timing noise, such timing analyses allow the precise determination of the pulsar position, thus enabling detailed multiwavelength follow up. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
199. The luminosity function of cluster pulsars.
- Author
-
Bagchi, Manjari and Lorimer, Duncan R.
- Subjects
- *
STELLAR luminosity function , *SIMULATION methods & models , *RADIO astronomy , *ASTRONOMICAL observations , *RADIATION sources , *PLASMA diffusion ,PULSAR detection - Abstract
We study luminosities of millisecond pulsars in globular clusters by fitting the observed luminosity distribution with single and double power laws. We use simulations to model the observed distribution as the brighter part of some parent distribution for Terzan 5 and try to find a model which simultaneously agrees with the observed diffuse radio flux, total predicted number of pulsars and observed luminosity distribution. We find that wide ranges of parameters for log-normal and power-law distributions give such good models. No clear difference between the luminosity distributions of millisecond pulsars in globular clusters and normal disk pulsars was seen. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
200. The Radio-loud Magnetar PSR J1622-4950.
- Author
-
Levin, L., Bailes, M., Bates, S. D., Bhat, N. D. R., Burgay, M., Burke-Spolaor, S., D'Amico, N., Johnston, S., Keith, M., Kramer, M., Milia, S., Possenti, A., Rea, N., Stappers, B., and van Straten, W.
- Subjects
- *
NEUTRON stars , *RADIO sources (Astronomy) , *COSMIC magnetic fields , *RADIO waves , *ASTRONOMICAL observations , *PLASMA diffusion ,PULSAR detection - Abstract
The High Time Resolution Universe survey for pulsars and fast transients has yielded the discovery of a slow radio pulsar, PSR J1622-4950, that despite its high dispersion measure exhibited a highly variable flux density and integrated pulse profile. The pulsar shares many properties with the two previously known magnetars that emit radio pulsations, including a similarly high inferred magnetic field strength. In contrast to other magnetars, PSR J1622-4950 shows no observed variations in X-ray emission. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
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