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1
Bailes, M. « Geodetic Precession in Binary Pulsars ». Symposium - International Astronomical Union 125 (1987) : 410. http://dx.doi.org/10.1017/s0074180900161054.
Texte intégralRésumé :
We have calculated the probability of observing geodetic precession in the binary pulsar PSR1913+16 for several different progenitor systems. Such an observation would support the asymmetric kick hypothesis for the origin of pular velocities. The results are shown to be dependent on the assumed progenitor but not to a strong degree. It is concluded that the probability of an observation to date is less than 20 percent in contrast to past predictions. In 15 years we expect this figure to be near 60 percent. We conclude that the null result to date cannot be taken as evidence against the asymmetric kick hypothesis for the origin of pulsar velocities. We develop our model and apply it to binary pulsars in general. We conclude that the likelihood of observing geodetic precession in the near future is low.A complete version of this paper is soon to be submitted to a scientific journal.
2
Yin, Qian, Yefan Li, Jiajie Li, Xin Zheng et Ping Guo. « Pulsar-candidate Selection Using a Generative Adversarial Network and ResNeXt ». Astrophysical Journal Supplement Series 264, no 1 (13 décembre 2022) : 2. http://dx.doi.org/10.3847/1538-4365/ac9e54.
Texte intégralRésumé :
Abstract Pulsar research has been a hot topic in the area of astronomy since they were first discovered. Pulsar discovery is fundamental for pulsar research. While pulsars are now visible across the electromagnetic spectrum, pulsar searches with modern radio telescopes are most promising. As the performance of astronomical instruments improves, the number of pulsar candidates detected by modern radio telescopes grows at an exponential rate. The application of artificial intelligence to the field of pulsar-candidate identification can automatically and efficiently address the identification problem with enormous amounts of data. However, there are still significant challenges in enhancing the accuracy of deep-learning-based pulsar-candidate identification. These problems result primarily from the fact that real pulsar data is scarce: the number of candidates that can be successfully identified as real pulsars (positive samples) is much smaller than those candidates that turn out to not be pulsars but instead radio-frequency interference or noise (negative samples). This makes it difficult to train a machine-learning model that can accurately select those candidates that are real pulsars. Therefore a novel pulsar-candidate identification framework is proposed that combines a deep convolutional generative adversarial neural network (DCGAN) and a deep aggregation residual network (ResNeXt). To overcome sample imbalance, the DCGAN is utilized to generate images that approximate real pulsars, while observed and generated candidates are employed together to train the pulsar-candidate identification model ResNeXt. Experiments on the HTRU Medlat data set back up the framework’s performance. The precision, recall, and F1-score of the framework are 100%.
3
MANCHESTER, R. N. « PULSAR SEARCHING AND TIMING ». International Journal of Modern Physics D 22, no 01 (janvier 2013) : 1341007. http://dx.doi.org/10.1142/s0218271813410071.
Texte intégralRésumé :
More than 2000 pulsars are now known. These pulsars may be divided into a number of different classes according to their period, period derivative, binary properties, emission characteristics and so on. Some important classes have relatively few members, e.g. double-neutron-star binary systems, and so continued searches for currently unknown pulsars are important. Such searches are being undertaken at various observatories around the world. Somewhat unexpectedly, the Fermi Gamma-ray Observatory, has proved to be an efficient pulsar detector, especially for millisecond pulsars (MSPs). The great stability of pulsar periods, especially for MSPs, leads to a number of important applications of pulsar timing. The detection and study of relativistic orbit perturbations in double-neutron-star systems has proved to be a powerful tool with measurements of the original binary pulsar, PSR B1913+16, and more recently the double pulsar, PSR J0737-3039A/B, showing that Einstein's general theory of relativity accurately describes these gravitational interactions. Direct detection of gravitational waves using pulsar timing is close to being achieved with the development of pulsar timing arrays (PTAs) in Europe, North America and Australia. Combining data from these PTAs to form the International Pulsar Timing Array (IPTA) will lead to improved significance of such a detection. Ultimately, detailed study of gravitational-wave sources will be possible using future large radio telescopes such as FAST and the SKA.
4
Stairs, I. H. « Binary pulsars and tests of general relativity ». Proceedings of the International Astronomical Union 5, S261 (avril 2009) : 218–27. http://dx.doi.org/10.1017/s1743921309990433.
Texte intégralRésumé :
AbstractBinary pulsars are a valuable laboratory for gravitational experiments. Double-neutron-star systems such as the double pulsar provide the most stringent tests of strong-field gravity available to date, while pulsars with white-dwarf companions constrain departures from general relativity based on the difference in gravitational binding energies in the two stars. Future observations may open up entirely new tests of the predictions of general relativity.
5
Desvignes, Gregory, Michael Kramer, Kejia Lee, Joeri van Leeuwen, Ingrid Stairs, Axel Jessner, Ismaël Cognard, Laura Kasian, Andrew Lyne et Ben W. Stappers. « Radio emission from a pulsar’s magnetic pole revealed by general relativity ». Science 365, no 6457 (5 septembre 2019) : 1013–17. http://dx.doi.org/10.1126/science.aav7272.
Texte intégralRésumé :
Binary pulsars are affected by general relativity (GR), causing the spin axis of each pulsar to precess. We present polarimetric radio observations of the pulsar PSR J1906+0746 that demonstrate the validity of the geometrical model of pulsar polarization. We reconstruct the (sky-projected) polarization emission map over the pulsar’s magnetic pole and predict the disappearance of the detectable emission by 2028. Two tests of GR are performed using this system, including the spin precession for strongly self-gravitating bodies. We constrain the relativistic treatment of the pulsar polarization model and measure the pulsar beaming fraction, with implications for the population of neutron stars and the expected rate of neutron star mergers.
6
Wielebinski, Richard. « Pulsar Studies at High Radio Frequencies ». International Astronomical Union Colloquium 177 (2000) : 205–10. http://dx.doi.org/10.1017/s0252921100059480.
Texte intégralRésumé :
AbstractPulsars were discovered at 81.5 MHz and a lot of the studies of these exciting objects have been made up to the present time at radio frequencies below 1.6 GHz. The reasons for this concentration on the low radio frequency characteristics of pulsars is the fact that the spectra are very steep and that very few radio telescopes exist that are capable of efficient operations at high radio frequencies. The Effelsberg 100-m radio telescope of the Max-Planck-Institut fur Radioastronomie operates regularly up to the frequency of 50 GHz and was used to study pulsars at cm/mm-wavelengths. In the southern skies the Parkes 64-m telescope has been used to study pulsars up to 8.4 GHz. One pulsar has been detected at 87 GHz with the 30-m Pico Veleta telescope of IRAM.The studies of pulsars over the whole frequency range are of great importance because this is necessary for the elucidation of the mechanism that is responsible for the pulsar emission. The high polarization of pulsar radio emission at lower radio frequencies has supported the hypothesis of a coherent emission mechanism, which is required to generate the high luminosity. It has been known for some time that pulsars, unlike other radio sources, have a lower polarization at high radio frequencies. Recently a change of pulsar spectrum, a flattening or possibly an inversion has been observed at the highest radio frequencies. The inversion of the pulsar spectrum seems to coincide with a complete depolarization of some pulsars.Millisecond pulsars are less luminous than normal pulsars. This makes them even more difficult to detect at higher radio frequencies. Recent observations have extended the spectra of ten millisecond pulsars up to 4.85 GHz. The results imply that millisecond pulsars have properties very similar to normal (slow) pulsars, which suggests similar emission mechanisms.
7
Lorimer, Duncan R., et Maura A. McLaughlin. « Probing fundamental physics with pulsars ». Proceedings of the International Astronomical Union 5, H15 (novembre 2009) : 131–36. http://dx.doi.org/10.1017/s1743921310008513.
Texte intégralRésumé :
AbstractPulsars provide a wealth of information about General Relativity, the equation of state of superdense matter, relativistic particle acceleration in high magnetic fields, the Galaxy's interstellar medium and magnetic field, stellar and binary evolution, celestial mechanics, planetary physics and even cosmology. The wide variety of physical applications currently being investigated through studies of radio pulsars rely on: (i) finding interesting objects to study via large-scale and targeted surveys; (ii) high-precision timing measurements which exploit their remarkable clock-like stability. We review current surveys and the principles of pulsar timing and highlight progress made in the rotating radio transients, intermittent pulsars, tests of relativity, understanding pulsar evolution, measuring neutron star masses and the pulsar timing array
8
Liu, Xiao-Jin, Benjamin Stappers et Cees Bassa. « Kinematic effects on high order spin frequency derivatives ». Proceedings of the International Astronomical Union 13, S337 (septembre 2017) : 362–63. http://dx.doi.org/10.1017/s1743921317009061.
Texte intégralRésumé :
AbstractThe radial velocity of a pulsar induces the Doppler effect on its intrinsic spin properties. In particular, it can generate a contribution to the frequency second derivative. We estimated this effect for each of the International Pulsar Timing Array pulsars. We also assessed the possibility of measuring the frequency second derivative in the observational data.
9
Izvekova, V. A., A. D. Kuz'min, V. M. Malofeev, W. Sieber, A. Jessner et R. Wielebinski. « New Observations of the Time Alignment of Pulse Profiles at High and Low Frequencies ». International Astronomical Union Colloquium 128 (1992) : 7–8. http://dx.doi.org/10.1017/s0002731600154630.
Texte intégralRésumé :
Exact timing measurements allow a determination of the phase shift between observations of a pulsar at different frequencies. It has become clear from these observations that a simple dipole magnetic field configuration can not explain the time lag observed for many pulsars between profiles at high frequencies (Kuz'min et al. 1986).There are cases which might better be explained by a combination of dipole and quadrupole field components (Davies et al. 1984). We report in this paper on new pulsar time alignment observations of a number of pulsars at high and low frequencies which support the general picture outlined above.
10
Ronchi, M., N. Rea, V. Graber et N. Hurley-Walker. « Long-period Pulsars as Possible Outcomes of Supernova Fallback Accretion ». Astrophysical Journal 934, no 2 (1 août 2022) : 184. http://dx.doi.org/10.3847/1538-4357/ac7cec.
Texte intégralRésumé :
Abstract For about half a century, the radio pulsar population was observed to spin in the ∼0.002–12 s range, with different pulsar classes having a spin-period evolution that differs substantially depending on their magnetic fields or past accretion history. The recent detection of several slowly rotating pulsars has reopened the long-standing question of the exact physics, and observational biases, driving the upper bound of the period range of the pulsar population. In this work, we perform a parameter study of the spin-period evolution of pulsars interacting with supernova fallback matter and specifically look at the fallback accretion disk scenario. Depending on the initial conditions at formation, this evolution can differ substantially from the typical dipolar spin-down, resulting in pulsars that show spin periods longer than their coeval peers. By using general assumptions for the pulsar spin period and magnetic field at birth, initial fallback accretion rates, and including magnetic field decay, we find that very long spin periods (≳100 s) can be reached in the presence of strong, magnetar-like magnetic fields (≳1014 G) and moderate initial fallback accretion rates (∼1022−1027 g s−1). In addition, we study the cases of two recently discovered periodic radio sources, the pulsar PSR J0901–4046 (P = 75.9 s) and the radio transient GLEAM-X J162759.5–523504.3 (P = 1091 s), in light of our model. We conclude that the supernova fallback scenario could represent a viable channel to produce a population of long-period isolated pulsars that only recent observation campaigns are starting to unveil.
11
Bower, Geoffrey C. « The Galactic center pulsar SGR J1745–29 ». Proceedings of the International Astronomical Union 9, S303 (octobre 2013) : 444–48. http://dx.doi.org/10.1017/s1743921314001100.
Texte intégralRésumé :
AbstractThe discovery of the Galactic center pulsar SGR J1745–29 has provided an important new window into plasma processes in the Galactic center (GC) interstellar medium, the population of compact objects in the GC, and the prospects for probing general relativistic effects through timing of a Sgr A* pulsar companion. We discuss here radio observations of the pulsar and how they are providing fresh insights. In particular, our results show that recent pulsar surveys had the sensitivity to detect many pulsars in the GC region without significant losses due to interstellar scattering. This raise the question of why only this pulsar close to Sgr A* has been detected.
12
Chen, Qiang, Yong Zhao et Lixia Yan. « X-ray Pulsar Signal Denoising Based on Variational Mode Decomposition ». Entropy 23, no 9 (8 septembre 2021) : 1181. http://dx.doi.org/10.3390/e23091181.
Texte intégralRésumé :
Pulsars, especially X-ray pulsars detectable for small-size detectors, are highly accurate natural clocks suggesting potential applications such as interplanetary navigation control. Due to various complex cosmic background noise, the original pulsar signals, namely photon sequences, observed by detectors have low signal-to-noise ratios (SNRs) that obstruct the practical uses. This paper presents the pulsar denoising strategy developed based on the variational mode decomposition (VMD) approach. It is actually the initial work of our interplanetary navigation control research. The original pulsar signals are decomposed into intrinsic mode functions (IMFs) via VMD, by which the Gaussian noise contaminating the pulsar signals can be attenuated because of the filtering effect during signal decomposition and reconstruction. Comparison experiments based on both simulation and HEASARC-archived X-ray pulsar signals are carried out to validate the effectiveness of the proposed pulsar denoising strategy.
13
Wex, Norbert, et Michael Kramer. « Gravity Tests with Radio Pulsars ». Universe 6, no 9 (22 septembre 2020) : 156. http://dx.doi.org/10.3390/universe6090156.
Texte intégralRésumé :
The discovery of the first binary pulsar in 1974 has opened up a completely new field of experimental gravity. In numerous important ways, pulsars have taken precision gravity tests quantitatively and qualitatively beyond the weak-field slow-motion regime of the Solar System. Apart from the first verification of the existence of gravitational waves, binary pulsars for the first time gave us the possibility to study the dynamics of strongly self-gravitating bodies with high precision. To date there are several radio pulsars known which can be utilized for precision tests of gravity. Depending on their orbital properties and the nature of their companion, these pulsars probe various different predictions of general relativity and its alternatives in the mildly relativistic strong-field regime. In many aspects, pulsar tests are complementary to other present and upcoming gravity experiments, like gravitational-wave observatories or the Event Horizon Telescope. This review gives an introduction to gravity tests with radio pulsars and its theoretical foundations, highlights some of the most important results, and gives a brief outlook into the future of this important field of experimental gravity.
14
McCulloch, P. M. « Closing Comments : Observations ». International Astronomical Union Colloquium 128 (1992) : 410–11. http://dx.doi.org/10.1017/s0002731600155659.
Texte intégralRésumé :
During the course of this colloquium many papers have been presented on observational aspects of pulsar astronomy. In the following discussion I have not attempted to be comprehensive but have selected a number of areas of interest to me.The basic pulsar properties appear to be consistent over the full range of pulsar periods from 1 ms to 4s, implying that the emission mechanism is the same for all pulsars. There was a general consensus among the observers that the radio emission occurs low down in the pulsar's magnetosphere above the magnetic polar region.
15
Kopeikin, Sergei. « Stability of pulsar rotational and orbital periods ». Proceedings of the International Astronomical Union 5, H15 (novembre 2009) : 226–27. http://dx.doi.org/10.1017/s1743921310008938.
Texte intégralRésumé :
AbstractMillisecond and binary pulsars are the most stable astronomical standards of frequency. They can be applied to solving a number of problems in astronomy and time-keeping metrology including the search for a stochastic gravitational wave background in the early universe, testing general relativity, and establishing a new time-scale. The full exploration of pulsar properties requires that proper unbiased estimates of spin and orbital parameters of the pulsar be obtained. These estimates depend essentially on the random noise components present in pulsar timing residuals. The instrumental white noise has predictable statistical properties and makes no harm for interpretation of timing observations, while the astrophysical/geophyeical low-frequency noise corrupts them, thus, reducing the quality of tests of general relativity and decreasing the stability of the pulsar time scale.
16
Zhou, Linyong, Shanping You, Bimo Ren, Xuhong Yu et Xiaoyao Xie. « A novel image classification model based on adversarial training for pulsar candidate identification ». Journal of Intelligent & ; Fuzzy Systems 39, no 5 (19 novembre 2020) : 7657–69. http://dx.doi.org/10.3233/jifs-200925.
Texte intégralRésumé :
Pulsars are highly magnetized, rotating neutron stars with small volume and high density. The discovery of pulsars is of great significance in the fields of physics and astronomy. With the development of artificial intelligent, image recognition models based on deep learning are increasingly utilized for pulsar candidate identification. However, pulsar candidate datasets are characterized by unbalance and lack of positive samples, which has contributed the traditional methods to fall into poor performance and model bias. To this end, a general image recognition model based on adversarial training is proposed. A generator, a classifier, and two discriminators are included in the model. Theoretical analysis demonstrates that the model has a unique optimal solution, and the classifier happens to be the inference network of the generator. Therefore, the samples produced by the generator significantly augment the diversity of training data. When the model reaches equilibrium, it can not only predict labels for unseen data, but also generate controllable samples. In experiments, we split part of data from MNIST for training. The results reveal that the model not only behaves better classification performance than CNN, but also has better controllability than CGAN and ACGAN. Then, the model is applied to pulsar candidate dataset HTRU and FAST. The results exhibit that, compared with CNN model, the F-score has increased by 1.99% and 3.67%, and the Recall has also increased by 6.28% and 8.59% respectively.
17
Liang, Ruixing. « Contribution of Pulsars to the AMS-02 Positron Excess ». Journal of Physics : Conference Series 2346, no 1 (1 septembre 2022) : 012008. http://dx.doi.org/10.1088/1742-6596/2346/1/012008.
Texte intégralRésumé :
Abstract In this paper we tested the pulsar interpretation of positron excess, measured by the Alpha Magnetic Spectrometer-02 (AMS-02), by using the list of objects from the Australian National Telescope Facility pulsar catalog (ATNF catalog). We take into account in the calculation the energy losses that cosmic rays encounter when propagating through the Galaxy and we included the secondary positrons which are produced through the collision of cosmic rays against the atoms of the interstellar space. We firstly hypothesized the possibility of a single pulsar contributing to the positron flux. We consider for this case Geminga since it is near and very powerful. Geminga alone can fit very well the data with a spectral index of 1.8 and an efficiency of 70%. It is however unrealistic that only one pulsar contributes to the AMS-02 positron data. Therefore, we decide to find among all pulsars in the ATNF catalog the top 20 pulsars that contributed to the flux on Earth. We then calculated the total positron flux of these pulsars and found it to fit the AMS-02 data very well at efficiencies between 30~70%. We came to a conclusion that the pulsars are viable interpretations of the positron excess that the AMS-02 detected.
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Martsen, Ashley R., Scott M. Ransom, Megan E. DeCesar, Paulo C. C. Freire, Jason W. T. Hessels, Anna Y. Q. Ho, Ryan S. Lynch, Ingrid H. Stairs et Yuankun Wang. « Radio Pulse Profiles and Polarization of the Terzan 5 Pulsars ». Astrophysical Journal 941, no 1 (1 décembre 2022) : 22. http://dx.doi.org/10.3847/1538-4357/aca156.
Texte intégralRésumé :
Abstract Terzan 5 is a rich globular cluster within the galactic bulge containing 39 known millisecond pulsars, the largest known population of any globular cluster. These faint pulsars do not have sufficient signal-to-noise ratio (S/N) to measure reliable flux density or polarization information from individual observations in general. We combined over 5.2 days of archival data, at 1500 and 2000 MHz, taken with the Green Bank Telescope over the past 12 years. We created high-S/N profiles for 32 of the pulsars and determined precise rotation measures (RMs) for 28. We used the RMs, pulsar positions, and dispersion measures to map the projected parallel component of the Galactic magnetic field toward the cluster. The 〈B ∣∣〉 shows a rough gradient of ∼6 nG arcsec−1 (∼160 nG pc−1) or, fractionally, a change of ∼20% in the R.A. direction across the cluster, implying Galactic magnetic field variability at sub-parsec scales. We also measured average flux densities S ν for the pulsars, ranging from ∼10 μJy to ∼2 mJy, and an average spectral index α = −1.35, where S ν ∝ ν α . This spectral index is flatter than most known pulsars, likely a selection effect due to the high frequencies used in pulsar searches to mitigate dispersion and scattering. We used flux densities from each observation to constrain the scintillation properties toward the cluster, finding strong refractive modulation on timescales of months. The inferred pulsar luminosity function is roughly power law, with slope ( d log N ) / ( d log L ) = − 1 at the high-luminosity end. At the low-luminosity end, there are incompleteness effects, implying that Terzan 5 contains many more pulsars.
19
Roy, Tridib. « Some glimpses of the plasma processes involved in power spectra of radio pulsars ». Monthly Notices of the Royal Astronomical Society 504, no 4 (21 avril 2021) : 5001–20. http://dx.doi.org/10.1093/mnras/stab1110.
Texte intégralRésumé :
ABSTRACT Although more than a half-century since pulsar discovery, the field of pulsar astronomy has attained an unprecedented level of success and has opened several windows in astronomy, very few theories have been put forwarded to investigate the nature of power spectra and emission properties of radio pulsars. There has been a copious amount of observation dedicated to investigating the nature and shape of radio pulsar’s power spectra. In this paper, I have suggested some alternative plasma processes in the frame of general parametric instability, such as Stimulated Raman Scattering (SRS) and Stimulated Compton Scattering (SCS) as a potential probe to generate power spectra theoretically. There are basically three prominent processes in which electromagnetic waves can undergo scattering in an ambient plasma medium. First, one is very well-known Compton scattering; it is when the scattering of radiation occurs by a single electron. The second and third ones are SRS and SCS, which are the relatively less known plasma phenomena. By definition, SRS is a process where the scattering of radiation occurs by longitudinal electron plasma mode, whereas SCS occurs by highly damped electron plasma mode. I have explored the possibility of explaining the radio power spectra of pulsar under different circumstances of plasma. I have computed the growth rates of SRS and SCS instabilities numerically. Thereafter, I have produced full radio power spectra of the pulsars PSRB 2111+46, PSRB 0329+54 theoretically by assuming typical pulsar parameters, dispersion relation associated with the plasma of three-wave interacting parametric instability process and the spatial variation associated with different plasma parameters like plasma density, Lorentz factor of electrons, frequency, and input flux of the pump wave.
20
Johnson, Aaron D., Sarah J. Vigeland, Xavier Siemens et Stephen R. Taylor. « Gravitational-wave Statistics for Pulsar Timing Arrays : Examining Bias from Using a Finite Number of Pulsars ». Astrophysical Journal 932, no 2 (1 juin 2022) : 105. http://dx.doi.org/10.3847/1538-4357/ac6f5e.
Texte intégralRésumé :
Abstract Recently, many different pulsar timing array (PTA) collaborations have reported strong evidence for a common stochastic process in their data sets. The reported amplitudes are in tension with previously computed upper limits. In this paper, we investigate how using a subset of a set of pulsars biases Bayesian upper limit recovery. We generate 500 simulated PTA data sets, based on the NANOGrav 11 yr data set with an injected stochastic gravitational-wave background (GWB). We then compute the upper limits by sampling the individual pulsar likelihoods, and combine them through a factorized version of the PTA likelihood to obtain upper limits on the GWB amplitude, using different numbers of pulsars. We find that it is possible to recover an upper limit (95% credible interval) below the injected value, and that it is significantly more likely for this to occur when using a subset of pulsars to compute the upper limit. When picking pulsars to induce the maximum possible bias, we find that the 95% Bayesian upper limit recovered is below the injected value in 10.6% of the realizations (53 of 500). Further, we find that if we choose a subset of pulsars in order to obtain a lower upper limit than when using the full set of pulsars, the distribution of the upper limits obtained from these 500 realizations is shifted to lower-amplitude values.
21
Manchester, R. N. « Pulsars and gravity ». International Journal of Modern Physics D 24, no 06 (27 avril 2015) : 1530018. http://dx.doi.org/10.1142/s0218271815300189.
Texte intégralRésumé :
Pulsars are wonderful gravitational probes. Their tiny size and stellar mass give their rotation periods a stability comparable to that of atomic frequency standards. This is especially true of the rapidly rotating "millisecond pulsars" (MSPs). Many of these rapidly rotating pulsars are in orbit with another star, allowing pulsar timing to probe relativistic perturbations to the orbital motion. Pulsars have provided the most stringent tests of theories of relativistic gravitation, especially in the strong-field regime, and have shown that Einstein's general theory of relativity is an accurate description of the observed motions. Many other gravitational theories are effectively ruled out or at least severely constrained by these results. MSPs can also be used to form a "Pulsar Timing Array" (PTA). PTAs are Galactic-scale interferometers that have the potential to directly detect nanohertz gravitational waves from astrophysical sources. Orbiting super-massive black holes in the cores of distant galaxies are the sources most likely to be detectable. Although no evidence for gravitational waves has yet been found in PTA data sets, the latest limits are seriously constraining current ideas on galaxy and black-hole evolution in the early universe.
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Hobbs, G., R. Manchester, A. Teoh et M. Hobbs. « The ATNF Pulsar Catalog ». Symposium - International Astronomical Union 218 (2004) : 139–40. http://dx.doi.org/10.1017/s0074180900180829.
Texte intégralRésumé :
The number of known pulsars has significantly increased over the past few years. We have searched the literature to find papers announcing the discovery of pulsars or giving improved parameters for them. Data from the papers have been entered into a new pulsar catalog that can be accessed via a web interface or from the command line (on Solaris or Linux machines). The user may request over 120 different parameters, select pulsars of interest, generate custom variables and choose between different ways of displaying or tabulating the datA. Full bibliographic references are available for all observed parameters.
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LORIMER, D. R. « THE DOUBLE PULSAR SYSTEM J0737–3039 ». International Journal of Modern Physics A 20, no 29 (20 novembre 2005) : 7035–44. http://dx.doi.org/10.1142/s0217751x05030788.
Texte intégralRésumé :
The double pulsar system J0737 – 3039 – a 22.7 ms pulsar in a compact 2.4 hr orbit about a 2.7 s pulsar was one of the long-awaited "holy grails" of pulsar astronomy. After only two years of timing, the system is close to surpassing the original Hulse-Taylor binary as a test of general relativity. On-going timing should soon reveal second-order effects in the post-Newtonian parameters. In addition, the observed interactions of the radio beams of the two pulsars provide a unique laboratory for probing neutron star magnetospheres and relativistic winds. Finally, a revised estimate of the cosmic rate of double neutron star mergers including J0737 – 3039 boosts previous estimates by an order of magnitude and suggests a high detection rate for the advanced LIGO gravitational wave detector.
24
Malov, IF. « Two Types of Pulsar ». Australian Journal of Physics 40, no 6 (1987) : 731. http://dx.doi.org/10.1071/ph870731.
Texte intégralRésumé :
Some arguments for the subdivision of pulsars into two classes are considered: (i) short-period pulsars described by Smith's (1973) model and (ii) long-period pulsars for which the hollow-cone model is valid. The data for PSR 1937 + 21 (P = 1�56 ms) are in good agreement with this conception, this pulsar being a typical representative of the first group of pulsars.
25
Kramer, Michael. « Pulsars as probes of gravity and fundamental physics ». International Journal of Modern Physics D 25, no 14 (décembre 2016) : 1630029. http://dx.doi.org/10.1142/s0218271816300299.
Texte intégralRésumé :
Radio-loud neutron stars known as pulsars allow a wide range of experimental tests for fundamental physics, ranging from the study of super-dense matter to tests of General Relativity (GR) and its alternatives. As a result, pulsars provide strong-field tests of gravity, they allow for the direct detection of gravitational waves in a “pulsar timing array” (PTA), and they promise the future study of black hole properties. This contribution gives an overview of the on-going experiments and recent results.
26
GUSEINOV, OKTAY H., AŞKIN ANKAY, SEVINÇ O. TAGIEVA et M. ÖZGÜR TAŞKIN. « DEPENDENCE OF THE X-RAY LUMINOSITY AND PULSAR WIND NEBULA ON DIFFERENT PARAMETERS OF PULSARS AND THE EVOLUTIONARY EFFECTS ». International Journal of Modern Physics D 13, no 02 (février 2004) : 197–213. http://dx.doi.org/10.1142/s0218271804004505.
Texte intégralRésumé :
Dependences of the X-ray luminosity (Lx) of young single pulsars, due to ejection of relativistic particles, on electric field intensity, rate of rotational energy loss (Ė), magnetic field, period, and some other parameters of neutron stars are discussed. Influence of the magnetic field and effects of some other parameters of neutron stars on the Lx-Ė and the Lx-τ (characteristic time) dependences are considered. Evolutionary factors also play an important role in our considerations. Only the pulsars with L2–10 keV >1033 erg/s have pulsar wind nebula around them. The pulsars from which γ-ray radiation has been observed have low X-ray luminosity in general.
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Krishnan, V. Venkatraman, M. Bailes, W. van Straten, N. Wex, P. C. C. Freire, E. F. Keane, T. M. Tauris et al. « Lense–Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system ». Science 367, no 6477 (30 janvier 2020) : 577–80. http://dx.doi.org/10.1126/science.aax7007.
Texte intégralRésumé :
Radio pulsars in short-period eccentric binary orbits can be used to study both gravitational dynamics and binary evolution. The binary system containing PSR J1141–6545 includes a massive white dwarf (WD) companion that formed before the gravitationally bound young radio pulsar. We observed a temporal evolution of the orbital inclination of this pulsar that we infer is caused by a combination of a Newtonian quadrupole moment and Lense–Thirring (LT) precession of the orbit resulting from rapid rotation of the WD. LT precession, an effect of relativistic frame dragging, is a prediction of general relativity. This detection is consistent with an evolutionary scenario in which the WD accreted matter from the pulsar progenitor, spinning up the WD to a period of <200 seconds.
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Venkatesh, T. S. Sachin, et Gaurav Pundir. « PERISTOLE : Package That Generates Time Delay Plots Caused by Gravitational Lensing ». Research Notes of the AAS 6, no 12 (6 décembre 2022) : 255. http://dx.doi.org/10.3847/2515-5172/aca6ec.
Texte intégralRésumé :
Abstract We present PERISTOLE to study the various time delays associated with the pulsar rotation and other general relativistic aspects of binary pulsars. It is made available as an open-source python package which takes some parameters of the double pulsar system as input and outputs the rotational and latitudinal lensing delays along with the geometric and Shapiro delays that arise due to gravitational lensing. This package was intended to provide a way to quickly analyze, evaluate and study the differences between variations of the same systems and also to quantify the consequences that different parameters have over the system. Through this research note, we briefly describe the motivation behind PERISTOLE and showcase its capabilities using the only double pulsar system ever found, J0737–3039.
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Biggs, James D. « Meridional Compression of Radio Pulsar Beams ». International Astronomical Union Colloquium 128 (1992) : 22–25. http://dx.doi.org/10.1017/s0002731600154691.
Texte intégralRésumé :
AbstractWe have studied the radio pulsar emission beam assuming a) a magnetic dipole field geometry and b) that the beam geometry is defined by the field lines that are not contained within the light cylinder. In general, the beam is compressed in the meridional direction. When the magnetic and rotation axes are aligned the beam is circular and as, the angle between these axes increases, the ratio of meridional to longitudinal dimension decreases monotonically to the minimum value 0.62 when the axes are orthogonal. This beam shape is thus consistent with that inferred from the study of circular polarization in average pulse profiles by Radhakrishnan and Rankin. Evidence for meridional compression is also found in the extensive observational study of Lyne and Manchester (1988).The beam evolution was determined using this data set, the beamwidth being found proportional to P–1/2, where P is the pulsar period. This relation implies that the more rapidly rotating pulsars should have larger beams, and this should aid in their detection. The more numerous, slower pulsars should have somewhat smaller beams than previously determined. This implies that the pulsar birthrate is probably close to the highest current estimates (1 in 25yr).
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Ulyanov, O. M. « HISTORY OF LOW-FREQUENCY RESEARCH OF PULSARS ». Radio physics and radio astronomy 26, no 2 (23 juin 2021) : 130–47. http://dx.doi.org/10.15407/rpra26.02.130.
Texte intégralRésumé :
Purpose: The main most pronounced events, which occurred in the initial period of the pulsars’ study at the decameter wavelength range, are presented. The example of the main scientific problems, which were formulated at the very beginning of pulsar research, shows how the emphasis and priorities of these studies have been changing over time, which tasks have finally been solved, and which are still waiting to be solved. It is shown how the ongoing modernization of the UTR-2 radio telescope have allowed to acquire new qualities in astrophysical research being made with this radio telescope and to identify new scientific directions. The example of the cited references shows how the pulsar research efforts in Ukraine have been developed and how they were integrated into the world astrophysical research of these unique objects. The purpose of this work is to show the relationship between the past and the present on the example of pulsars for longer than a semi-centennial period and to show how the scientific problems that were formulated in the past, and which could not be solved under the then-existing technical conditions, were solved by the subsequent generations of researchers. Design/methodology/approach: The methods of comparison and historical parallels show how the low-frequency studies of pulsars have been developed and evolved almost from their discovery until now. Findings: It is shown how quantitative transformations and technical development, as well as non-standard scientific approaches, unhackneyed thought and international cooperation allow to solve complex radio astronomical problems related to the low-frequency studies of pulsars. Conclusions: The paper provides a historical overview of more than half a century-long radio astronomical studies of pulsars, having been and still being made at the decameter band using the UTR-2 radio telescope. The “old” and current priorities in pulsar research are given, and it is shown how qualitatively the technical parameters of back end facility and computer performance have been changed in studying the coherent pulsar radio emission nature. Key words: aberration; frequency band; pulse; interpulse; dispersion measure; rotation measure; plasma; pulsar; radio telescope
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Zhou, Shiqi, Erbil Gügercinoğlu, Jianping Yuan, Mingyu Ge et Cong Yu. « Pulsar Glitches : A Review ». Universe 8, no 12 (1 décembre 2022) : 641. http://dx.doi.org/10.3390/universe8120641.
Texte intégralRésumé :
∼6% of all known pulsars have been observed to exhibit sudden spin-up events, known as glitches. For more than fifty years, these phenomena have played an important role in helping to understand pulsar (astro)physics. Based on the review of pulsar glitches search method, the progress made in observations in recent years is summarized, including the achievements obtained by Chinese telescopes. Glitching pulsars demonstrate great diversity of behaviours, which can be broadly classified into four categories: normal glitches, slow glitches, glitches with delayed spin-ups, and anti-glitches. The main models of glitches that have been proposed are reviewed and their implications for neutron star structure are critically examined regarding our current understanding. Furthermore, the correlations between glitches and emission changes, which suggest that magnetospheric state-change is linked to the pulsar-intrinsic processes, are also described and discussed in some detail.
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Larchenkova, T. I., et O. V. Doroshenko. « A Possible Manifestation Of Microlensing In Pulsar Timing ». Symposium - International Astronomical Union 173 (1996) : 239–40. http://dx.doi.org/10.1017/s0074180900231409.
Texte intégralRésumé :
Gravitational lensing and the time delay of a pulsar signal in the gravitational field of a mass are General Relativistic effects that may be used as a tool to detect the observational parameters of dark matter in our Galaxy. We propose to use observations of the time delay of pulses from pulsars to detect lensing objects located close to the line of the sight, to study the distribution of dark matter in our Galaxy. We discuss the possibility of finding such an event by measuring the delay of pulses from a pulsar, and apply it to data for PSR B0525+21.
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Slee, OB, SK Alurkar et AD Bobra. « Flux Densities, Spectra and Variability of Pulsars at Metre Wavelengths ». Australian Journal of Physics 39, no 1 (1986) : 103. http://dx.doi.org/10.1071/ph860103.
Texte intégralRésumé :
We present the results of two-frequency flux density measurements of 74 pulsars with the Culgoora circular array. We show that the spectral index of a typical pulsar steepens markedly from 80 to 1400 MHz, but we found no significant relationship between the metre-wave spectral index and the published pulsar parameters
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Ma, Zhi, Zi-Yi You, Ying Liu, Shi-Jun Dang, Dan-Dan Zhang, Ru-Shuang Zhao, Pei Wang, Si-Yao Li et Ai-Jun Dong. « A Preliminary Study of Large Scale Pulsar Candidate Sifting Based on Parallel Hybrid Clustering ». Universe 8, no 9 (5 septembre 2022) : 461. http://dx.doi.org/10.3390/universe8090461.
Texte intégralRésumé :
Pulsar candidate sifting is an essential part of pulsar analysis pipelines for discovering new pulsars. To solve the problem of data mining of a large number of pulsar data using a Five-hundred-meter Aperture Spherical radio Telescope (FAST), a parallel pulsar candidate sifting algorithm based on semi-supervised clustering is proposed, which adopts a hybrid clustering scheme based on density hierarchy and the partition method, combined with a Spark-based parallel model and a sliding window-based partition strategy. Experiments on the two datasets, HTRU (The High Time-Resolution Universe Survey) 2 and AOD-FAST (Actual Observation Data from FAST), show that the algorithm can excellently identify the pulsars with high performance: On HTRU2, the Precision and Recall rates are 0.946 and 0.905, and those on AOD-FAST are 0.787 and 0.994, respectively; the running time on both datasets is also significantly reduced compared with its serial execution mode. It can be concluded that the proposed algorithm provides a feasible idea for astronomical data mining of FAST observation.
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Potapov, Vladimir A., et Sergei M. Kopeikin. « Timing of binary pulsars and the search for the low-frequency gravitational waves ». Proceedings of the International Astronomical Union 5, H15 (novembre 2009) : 234. http://dx.doi.org/10.1017/s1743921310008999.
Texte intégralRésumé :
AbstractMillisecond and binary pulsars are the most stable natural standards of astronomical time giving us a unique opportunity to search for gravitational waves (GW) and to test General Relativity. GWs from violent events in early Universe and from the ensemble of galactic and extragalactic objects perturb propagation of radio pulses from a pulsar to observer bringing about stochastic fluctuations in the times of arrival of the pulses (TOA). If one observes the pulsar over a sufficiently long time span, the fluctuations will be registered as a low-frequency, correlated noise affecting the timing residuals in the frequency range 10−12 ÷ 10−7 Hz. This work demonstrates how the standard procedure of processing of the pulsar timing data can bias the estimate of the upper limit on the density of the GW background (GWB).
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Ransom, Scott M. « Pulsars are cool. Seriously. » Proceedings of the International Astronomical Union 8, S291 (août 2012) : 3–10. http://dx.doi.org/10.1017/s1743921312023046.
Texte intégralRésumé :
AbstractEver since the first pulsar was discovered by Bell and Hewish over 40 years ago, we've known that not only are pulsars fascinating and truly exotic objects, but that we can use them as powerful tools for basic physics and astrophysics as well. Taylor and Hulse hammered these views home with their discovery and timing of the spectacular “binary pulsar” in the 1970s and 1980s. In the last two decades a host of surprises and a promise of phenomenal scientific riches in the future has come from the millisecond pulsars. As our instrumentation has become more sensitive and better suited to measuring the pulses from these objects, they've given us new tests of general relativity, fantastic probes of the interstellar medium, constraints on the physics of ultra-dense matter, new windows into binary and stellar evolution, and the promise of a direct detection of gravitational waves. These things really are cool, and there is much more we will do with them in the future.
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Bak Nielsen, Ann-Sofie, Gemma H. Janssen, Golam Shaifullah, Joris P. W. Verbiest, David J. Champion, Grégory Desvignes, Lucas Guillemot et al. « Timing stability of three black widow pulsars ». Monthly Notices of the Royal Astronomical Society 494, no 2 (7 avril 2020) : 2591–99. http://dx.doi.org/10.1093/mnras/staa874.
Texte intégralRésumé :
ABSTRACT We study the timing stability of three black widow pulsars (BWPs), both in terms of their long-term spin evolution and their shorter term orbital stability. The erratic timing behaviour and radio eclipses of the first two BWP systems discovered (PSRs B1957+20 and J2051−0827) were assumed to be representative for this class of pulsars. With several new black widow systems added to this population in the last decade, there are now several systems known that do not show these typical orbital variations or radio eclipses. We present timing solutions using 7–8 yr of observations from four of the European Pulsar Timing Array telescopes for PSRs J0023+0923, J2214+3000, and J2234+0944, and confirm that two of these systems do not show any significant orbital variability over our observing time span, both in terms of secular or orbital parameters. The third pulsar PSR J0023+0923 shows orbital variability and we discuss the implications for the timing solution. Our results from the long-term timing of these pulsars provide several new or improved parameters compared to earlier works. We discuss our results regarding the stability of these pulsars, and the stability of the class of BWPs in general, in the context of the binary parameters, and discuss the potential of the Roche lobe filling factor of the companion star being an indicator for stability of these systems.
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Kramer, M., A. Jessner, P. Müller et R. Wielebinski. « A high frequency search for highly dispersed pulsars ». International Astronomical Union Colloquium 160 (1996) : 13–14. http://dx.doi.org/10.1017/s0252921100040884.
Texte intégralRésumé :
The majority of known pulsars have been discovered by pulsar searches at low radio frequencies (v< 1 GHz). However, such searches are subject to various deleterious effects, viz the Galactic background radiation (∝v−2.8), dispersion smearing (∝v−3) and also scatter broadening (∝v−4.4). Dispersion smearing and, in particular, scatter broadening prohibit the detection of pulsars with high dispersion measures at low frequencies (cf. Fig. 1a). This is highlighted by the fact that all 11 known pulsars with DM>600 cm−3pc have been discovered during the only two surveys performed to date above 1 GHz, i.e. at 1.4 GHz by Clifton et al. (1992) and at 1.5 GHz by Johnston et al. (1992). However, scattering is still a limiting factor at even 1.4/1.5 GHz. For example B1750—24 is observed with a double component profile at 4.85 GHz (Kijak et al. 1996), whereas at 1.4 GHz the components are completely smeared out due to scatter broadening (cf. Clifton et al. 1992). Therefore, the galactic population of highly dispersed pulsars is still not known. In order to reveal this hidden sample, we have recently started a search in Effelsberg at 4.85 GHz where limitations due to scattering are essentially not existent (see Fig. 1a). The use of this extraordinary high frequency for pulsar searches enables us to observe with a large bandwidth but a small number of filterbank channels, so that the necessary computer power is radically reduced. However, the general steepness of pulsar spectra demands a highly sensitive observing system, otherwise, only the most luminous sources can be detected. A serious disadvantage of a high frequency search is the small telescope beam requiring a lot of observing time to search even a small area of the sky. A restriction of the search area is therefore highly recommended.
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Jaodand, Amruta, Jason W. T. Hessels et Anne Archibald. « A decade of transitional millisecond pulsars ». Proceedings of the International Astronomical Union 13, S337 (septembre 2017) : 47–51. http://dx.doi.org/10.1017/s1743921317010407.
Texte intégralRésumé :
AbstractTransitional millisecond pulsars (tMSPs), which are systems that harbor a pulsar in the throes of the recycling process, have emerged as a new source class since the discovery of the first such system a decade ago. These systems switch between accretion-powered low-mass X-ray binary (LMXB) and rotation-powered radio millisecond pulsar (RMSP) states, and provide exciting avenues to understand the physical processes that spin-up neutron stars to millisecond periods. During the last decade, three tMSPs, as well as a candidate source, have been extensively probed using systematic, multi-wavelength campaigns. Here we review the observational highlights from these campaigns and our general understanding of tMSPs.
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Doroshenko, Oleg V., et Sergei M. Kopeikin. « Relativistic effect of gravitational deflection of light in binary pulsars ». International Astronomical Union Colloquium 160 (1996) : 131. http://dx.doi.org/10.1017/s0252921100041269.
Texte intégralRésumé :
Timing formula for data processing of observations of binary pulsars that accounts for the relativistic deflection of light in the gravitational field of the pulsar’s companion is presented, and the measurability of this effect along with its variance estimates is discussed. The deflection of the pulsar’s pulse trajectory in the gravitational field of its companion leads to variation in the pulsar’s rotational phase. This variation appears as a narrow sharp growth of the magnitude of the post-fit residuals in the vicinity of the moment of the superior conjunction of the pulsar with its companion. In contrast to the relativistic Shapiro effect, the amplitude of the effect of gravitational deflection of the pulsar radio beam has two peaks with opposite signs, which become sharper as the inclinationiof the pulsar’s orbit approaches to the right angle. The effect under consideration influences the estimation of parameters of the relativistic Shapiro effect in the binary pulsars with nearly edgewise orbits. Its inclusion in the fitting procedure provides a more careful measurement of the sine of the orbital inclinationi, as well as the masses of the pulsar and its companion. This permits an improved testing of alternative theories of gravity in the strong field regime. The effect of the gravitational deflection of light has been numerically investigated for binary pulsars with nearly edgewise orbits. It is shown that the effect is observed in general only when cosi is less than 0.003. This estimate becomes less restrictive as the pulsar’s spin axis approaches the line of sight.
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Rammala, Isabella, Aris Karastergiou et Griffin Foster. « Broadband observations of pulsar profiles and frequency dependent DMs ». Proceedings of the International Astronomical Union 13, S337 (septembre 2017) : 400–401. http://dx.doi.org/10.1017/s1743921317010353.
Texte intégralRésumé :
AbstractThe aim of our project is to search for ways to best extract information on pulsar profiles and the interstellar medium (ISM), using the wide frequency bands that are typical of radio telescopes today. Pulsar profiles typically show a strong dependence on frequency. This depends both on the intrinsic radio emission mechanism, and the interaction of the radio waves with the ISM that lies between the pulsars and our detectors on Earth, due mostly to the effects of dispersion and scattering. In this work, we make use of radio pulsar beam models from the existing literature, to generate simulated pulse profiles, observed across various bands (centre frequencies and bandwidths), for each beam model. For all the chosen geometric parameters of the pulsar beam, observed in any frequency band, the simulated profiles manifest a relative shift in phase in their observed components, as a result of the intrinsic profile evolution. This relative shift in phase could be interpreted as an additional component to the ISM induced dispersion measure (DM). This additional DM component due to profile evolution is frequency dependent. We discuss the systematics introduced to pulsar data due to this effect.
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Zhao, Hongyang, Jing Jin, Longqi Wang, Bingjie Shan, Yi Shen et Yu Jiang. « A Pulsar Search Method Combining a New Feature Representation and Convolutional Neural Network* ». Astrophysical Journal 929, no 1 (1 avril 2022) : 18. http://dx.doi.org/10.3847/1538-4357/ac52ef.
Texte intégralRésumé :
Abstract The radiation energy of X-ray pulsars is mainly concentrated in the high-energy ray bands, so processing high-energy photon signals is helpful for discovering some young and active pulsars. To quickly and accurately detect effective pulsar signals from a large number of samples within a finite observation time, an automatic identification algorithm for pulsar candidates based on X-ray observations is developed in this paper. First, the autocorrelation operation is used to improve the signal-to-noise ratio of the profile and solve the initial phase misalignment problem. Then, the candidate frequency range is expanded, and the output signal is folded according to these frequencies to obtain a series of profiles. The six statistical features of these profiles are extracted to generate frequency-feature curves. Compared with the traditional epoch folding method, the frequency-feature curves show more consistent characteristics. To improve the classification accuracy, the frequency-feature curves are converted into two-dimensional images, and ConvNets are used for deep feature extraction and classification. A simulation method based on the nonhomogeneous Poisson process is utilized to create the training set, and generative adversarial networks are used for data augmentation to solve the class imbalance problem caused by limited pulsar samples. Finally, the RXTE observation data of PSR B0531+21, PSR B0540-69, and PSR B1509-58 are selected for testing. The experimental results show that the highest recall and precision reached 0.996 and 0.983, respectively. Demonstrating the considerable potential of this method for identifying pulsar candidates based on X-ray observations.
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Doroshenko, O. V., Yu P. Ilyasov et V. V. Oreshko. « Pulsar timing at Kalyazin (Russia) ». International Astronomical Union Colloquium 177 (2000) : 57–60. http://dx.doi.org/10.1017/s0252921100059017.
Texte intégralRésumé :
AbstractRegular timing observations of millisecond and binary pulsars are made with the 64-m radio telescope at Kalyazin (Russia). Filterbank 160-channel receiver is used for observations at 0.6 GHz in two circular orthogonal polarization. Precise local time service (based upon a rubidium standards and hydrogen maser) is used for measurements of Times-of-Arrival (TOA) from radio pulsars. A local time scale is compared by GPS and TV-systems with the basic AT-scales (UTC(USNO) and UTC(SU)) within an accuracy about 50nsper day. Recently the second 1.4 GHz receiver (250 kHz × 64 channels) was constructed and installed at Kalyazin radio telescope. There is a possibility to combine a part of the 1.4 GHz back-end with the 2.2 GHz front-end to produce timing observations at three frequencies simultaneously. We present a results of precise timing observations conducted by the Kalyazin pulsar system. Most of data were obtained at 0.6 GHz in 1997–1999. The data will be used for valuable applications in fundamental metrology, interstellar medium, general relativity and pulsar physics itself.
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Doroshenko, V., A. Santangelo, V. F. Suleimanov et S. S. Tsygankov. « An observational argument against accretion in magnetars ». Astronomy & ; Astrophysics 643 (novembre 2020) : A173. http://dx.doi.org/10.1051/0004-6361/202038948.
Texte intégralRésumé :
The phenomenology of anomalous X-ray pulsars is usually interpreted within the paradigm of very highly magnetized neutron stars, also known as magnetars. According to this paradigm, the persistent emission of anomalous X-ray pulsars (AXPs) is powered by the decay of the magnetic field. However, an alternative scenario in which the persistent emission is explained through accretion is also discussed in literature. In particular, AXP 4U 0142+61 has been suggested to be either an accreting neutron star or a white dwarf. Here, we rule out this scenario based on the observed X-ray variability properties of the source. We directly compare the observed power spectra of 4U 0142+61 and of two other magnetars, 1RXS J170849.0−400910 and 1E 1841−045 with that of the X-ray pulsar 1A 0535+262, and of the intermediate polar GK Persei. In addition, we include a bright young radio pulsar PSR B1509-58 for comparison. We show that, unlike accreting sources, no aperiodic variability within the expected frequency range is observed in the power density spectrum of the magnetars and the radio pulsar. Considering that strong variability is an established feature of all accreting systems from young stellar objects to super-massive black holes and the absence of the variability reports from other magnetars, we conclude that our results also indicate that magnetars, in general, are not powered by accretion.
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Sobey, C., S. Johnston, S. Dai, M. Kerr, R. N. Manchester, L. S. Oswald, A. Parthasarathy, R. M. Shannon et P. Weltevrede. « A polarization census of bright pulsars using the ultrawideband receiver on the Parkes radio telescope ». Monthly Notices of the Royal Astronomical Society 504, no 1 (26 mars 2021) : 228–47. http://dx.doi.org/10.1093/mnras/stab861.
Texte intégralRésumé :
ABSTRACT We present high signal-to-noise ratio, full polarization pulse profiles for 40 bright, ‘slowly’ rotating (non-recycled) pulsars using the new ultrawideband low-frequency (UWL; 704–4032 MHz) receiver on the Parkes radio telescope. We obtain updated and accurate interstellar medium parameters towards these pulsars (dispersion measures and Faraday rotation measures), and reveal Faraday dispersion towards PSR J1721–3532 caused by interstellar scattering. We find general trends in the pulse profiles including decreasing fractional linear polarization and increasing degree of circular polarization with increasing frequency, consistent with previous studies, while also revealing new features and frequency evolution. This demonstrates results that can be obtained using UWL monitoring observations of slow pulsars, which are valuable for improving our understanding of pulsar emission and the intervening interstellar medium. The calibrated data products are publicly available.
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Kondratiev, V. I., M. V. Popov, V. A. Soglasnov et S. V. Kostyuk. « Frequency Structure of Radio Scintillations for Several Pulsars ». International Astronomical Union Colloquium 182 (2001) : 43–46. http://dx.doi.org/10.1017/s025292110000066x.
Texte intégralRésumé :
AbstractScintillation times and decorrelation bandwidths for the pulsars B0329+54, B1641-15, B1508+55 and B1919+21 are determined. The results are based on observations made with different instruments and at different radio frequencies. All objects but the pulsar B1508+55 were detected to have more than one frequency scale. The obtained values of scattering parameters are not contrary in general to the Kkolmogorov form of density fluctuation spectrum.
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Butsaracom, Kritaporn, Brandon Khan Cantlay et Maneenate Wechakama. « Fitting electron spectrum from AMS-02 by pulsar electrons ». Journal of Physics : Conference Series 2145, no 1 (1 décembre 2021) : 012003. http://dx.doi.org/10.1088/1742-6596/2145/1/012003.
Texte intégralRésumé :
Abstract In this work, we aim to explain the latest data of cosmic-ray electrons from AMS-02 by an electron background model and pulsar electrons. We consider an electron background model which includes primary and secondary electrons. We assume that pulsars are major sources of the electron excess. Since electrons easily lose their energy through the interstellar radiation field and the magnetic field via inverse Compton scattering and synchrotron radiation, respectively, they propagate in a short length. We adopt nearby pulsar data in the distance of 1 kpc from the Australia Telescope National Facility (ATNF) pulsar catalogue. By using a Green’s function of an electron propagation model, we then fit pulsar parameters (i.e. the spectral index, the fraction of the total spin-down energy and the cutoff energy) for several cases of a single pulsar. With a combination of the electron background model, several cases of pulsar spectrum are able to explain the electron excess.
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Anderson, S. B., F. A. Jenet, V. M. Kaspi, T. A. Prince, J. S. Sandhu, S. C. Unwin et José Navarro. « Giant Micropulses from PSR J0437–4715 ». International Astronomical Union Colloquium 160 (1996) : 211–12. http://dx.doi.org/10.1017/s025292110004149x.
Texte intégralRésumé :
Although individual radio pulses from pulsars vary in amplitude from pulse to pulse, their height distribution in general does not extend to amplitudes more than 10 times the mean. Two notable exceptions are the Crab pulsar and PSR B1937+21 (Lundgren 1995, Cognard et al. 1996 and references therein) which occasionally emit single radio pulses that have amplitudes more than 100 times the mean. Here we report on the detection of short time-scale, extremely large amplitude radio pulses from the nearby millisecond pulsar PSR J0437–4715. The events we have observed are distinguished by having peak flux densities in excess of 10 times the average pulse amplitude, and occur only within a very narrow (80 µs) window centered on the main pulse.
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Lazarov, Andon D. « ISAR Imaging of a Rotating Asteroid Irradiated by Pulsar’s Electromagnetic Emission ». Cybernetics and Information Technologies 19, no 2 (1 juin 2019) : 38–50. http://dx.doi.org/10.2478/cait-2019-0014.
Texte intégralRésumé :
Abstract The aim of the present study is imaging of moving objects, asteroids illuminated by continuous coherent wideband pulsar’s signals. As pulsars are located on more than thousands of light years from Earth, objects crossing pulsars’ emission beams are considered as second sources of electromagnetic waves, carrying object’s shape and velocity information that can be extracted by application pulsar emission-based inverse aperture synthesis. Inverse Synthetic Aperture Radar (ISAR) scenario, geometry and kinematics are analytically described. Models of pulsar signals and ISAR signals secondary emitted by asteroids are developed. White Gaussian noise of high level is added to the deterministic reemitted signal in order to approach the real signal scenario. Two-Dimensional (2D) Fourier transform for image extraction is applied. Special iterative noise removing procedure is suggested for asteroid’s image enhancement. To verify mathematical model and imaging algorithms numerical experiments are carried out.
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Hessels, J. W. T. « Charting the Transient Radio Sky on Sub-Second Time-Scales with LOFAR ». Proceedings of the International Astronomical Union 7, S285 (septembre 2011) : 104. http://dx.doi.org/10.1017/s174392131200035x.
Texte intégralRésumé :
SummaryThe LOw Frequency ARray (LOFAR) is a radio interferometric telescope that promises to open a largely unexplored window on transient sources in the “radio sky”, from time-scales of nanoseconds to years. An important aspect of this will be the study of radio-emitting neutron stars in their various incarnations: slow pulsars, young pulsars, millisecond pulsars, magnetars, rotating radio transients, intermittent pulsars, et cetera. Pulsars and their brethren are the prototype of the more general “fast transients”: sub-second, dispersed radio bursts which point the way to extreme, and potentially still unknown, phenomena. For instance, prompt radio bursts from supernovæ and other extra-galactic bursts have been hypothesized; these could prove to be powerful cosmological probes.This talk discussed LOFAR's impressive ability to observe pulsars and to enlarge greatly the discovery space for (even rarer) fast transients. It also presented the latest pulsar observations made during LOFAR's commissioning period. These are demonstrating powerful observing techniques that will be crucial for the next generation of radio telescopes as well as the effort to increase our understanding of the dynamic nature of the Universe.An expanded version of the talk can be found at http://adsabs.harvard.edu/abs/2011A