Journal articles: 'Pulsars: individual'

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Fierro, J. M., Z. Arzoumanian, M. Bailes, J. F. Bell, D. L. Bertsch, K. T. S. Brazier, J. Chiang, et al. "EGRET High-Energy gamma -Ray Pulsar Studies. II. Individual Millisecond Pulsars." Astrophysical Journal 447 (July 1995): 807. http://dx.doi.org/10.1086/175919.

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Manchester, R. N. "Finding Pulsars at Parkes." Publications of the Astronomical Society of Australia 18, no. 1 (2001): 1–11. http://dx.doi.org/10.1071/as01002.

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AbstractThere are many reasons why it is important to increase the number of known pulsars. Not only do pulsar searches continue to improve statistical estimates of, for example, pulsar birthrates, lifetimes and the Galactic distribution, but they continue to turn up interesting and, in some cases, unique individual pulsars. In the early days of pulsar astronomy, the Molonglo radio telescope led the world as a pulsar detection instrument. However, the Parkes radio telescope, with its frequency versatility and greater tracking ablility, combined with sensitive receivers and powerful computer detection algorithms, is now the world’s most successful telescope at finding pulsars. The Parkes multibeam survey, begun in 1997, by itself will come close to doubling the number of known pulsars. Parkes has also been very successful at finding millisecond pulsars (MSPs), especially in globular clusters. One third of the known MSPs have been found in just one cluster, 47 Tucanae.

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Lynch, Ryan S. "The hunt for new pulsars with the Green Bank Telescope." Proceedings of the International Astronomical Union 8, S291 (August 2012): 41–46. http://dx.doi.org/10.1017/s1743921312023113.

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AbstractThe Green Bank Telescope (GBT) is the largest fully steerable radio telescope in the world and is one of our greatest tools for discovering and studying radio pulsars. Over the last decade, the GBT has successfully found over 100 new pulsars through large-area surveys. Here I discuss the two most recent—the GBT 350 MHz Drift-scan survey and the Green Bank North Celestial Cap survey. The primary science goal of both surveys is to find interesting individual pulsars, including young pulsars, rotating radio transients, exotic binary systems, and especially bright millisecond pulsars (MSPs) suitable for inclusion in Pulsar Timing Arrays, which are trying to directly detect gravitational waves. These two surveys have combined to discover 85 pulsars to date, among which are 14 MSPs and many unique and fascinating systems. I present highlights from these surveys and discuss future plans. I also discuss recent results from targeted GBT pulsar searches of globular clusters and Fermi sources.

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Wu, Xinji, and Wen Xu. "A Determination of Pulsar Emission Geometry from Polarization Observations." International Astronomical Union Colloquium 128 (1992): 400–403. http://dx.doi.org/10.1017/s0002731600155623.

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AbstractOne of the important problems in pulsar studies is to determine the magnetic inclination angle α, the intrinsic width of the radiation beam (2ρ) and the angle (α + β) between the observer's direction and the rotation axis. In this paper we solve this problem for individual pulses by using the observed pulse width (2Δ𝜙), the swing of polarization angle (2Δψ), and its central gradient (dψ/d𝜙)max.From the polar cap model we establish three basic geometrical relations, a complete set of equations from which explicit solutions can be obtained using the observed data. This is the first time that the orientation of pulsar emission is solved analytically solely on the basis of a geometrical model. However, the results are shown to be sensitively connected to the polarization-angle swing (2Δψ), which is not well measured for most pulsars. So the number of pulsars to which our method can be applied is limited. The importance of the measurement of Δψ is seen from our method. To ensure the credibility of our results, we have discussed the conditions to be satisfied by all reliable pulsar measurements. Our method is shown to be more favorable for pulsars with large pulse width 2Δ𝜙, large central gradient (dψ/d𝜙)max and large magnetic inclination angle α. Out of 120 pulsars (from Lyne and Manchester 1988), 40 are solvable, and 7 are believed to be reliable. We discuss our method for the determination of pulsar geometry in comparison with other methods.

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Suleymanova, S. A., V. A. Izvekova, and V. D. Pugachev. "Individual Pulse Polarization of Pulsars at Low Frequencies." International Astronomical Union Colloquium 160 (1996): 257–60. http://dx.doi.org/10.1017/s0252921100041646.

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AbstractThis paper presents the results of the measurements of linear polarization characteristics of individual pulses at frequencies 40, 60 and 103 MHz for 10 strong pulsars. We have measured total intensity, linear polarization percentage and angle along the pulse window and obtained distribution displays for these data.Two orthogonal polarization modes are common features in the radiation of pulsars at low frequency. The energy ratio of these two modes can change significantly between different frequencies. The linear polarisation percentage has a general tendency to increase at low frequencies, but by very different factors for different components of the integrated intensity profile. The relationship between the polarization properties of PSR 0943+10 and its mode changing behaviour was studied. It is shown that the energy ratio and the frequency of occurence of two polarization modes change simultaneously with changes in the integrated intensity profile.

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Joshi, B. C., M. Kramer, A. G. Lyne, M. A. McLaughlin, and I. H. Stairs. "Giant Pulses in Millisecond Pulsars." Symposium - International Astronomical Union 218 (2004): 319–20. http://dx.doi.org/10.1017/s0074180900181252.

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Giant pulses (GPs), occasional individual pulses with an intensity 100 times the average intensity, have been detected in four pulsars to date. Their origin is not well understood, but studies suggest a connection between the strength of magnetic field at the light cylinder Blc and the existence of GPs. Here, we report on detection of significant Large Amplitude Pulses (LAPs) in two more pulsars with high values of Blc, PSRs J0218+4232 and B1957+20, observed using Giant Meterwave Radio Telescope (GMRT).

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Nowakowski, Leszek A. "Finding Pulsar Emission Heights from Dual–Frequency Observations." International Astronomical Union Colloquium 177 (2000): 219–20. http://dx.doi.org/10.1017/s0252921100059510.

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AbstractWe present a method that allows to find the radial separation of regions emitting individual components of pulsar average profiles at two radio frequencies. It may also be used for single–frequency observations in pulsars that have intensity–dependent average profiles and/or mode–switching. Preliminary results for three radio pulsars are presented, obtained using average profiles from non-simultaneous observations.

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Basu, A., B. Shaw, D. Antonopoulou, M. J. Keith, A. G. Lyne, M. B. Mickaliger, B. W. Stappers, P. Weltevrede, and C. A. Jordan. "The Jodrell bank glitch catalogue: 106 new rotational glitches in 70 pulsars." Monthly Notices of the Royal Astronomical Society 510, no. 3 (November 25, 2021): 4049–62. http://dx.doi.org/10.1093/mnras/stab3336.

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ABSTRACT Pulsar glitches are rapid spin-up events that occur in the rotation of neutron stars, providing a valuable probe into the physics of the interiors of these objects. Long-term monitoring of a large number of pulsars facilitates the detection of glitches and the robust measurements of their parameters. The Jodrell Bank pulsar timing programme regularly monitors more than 800 radio pulsars and has accrued, in some cases, over 50 yr of timing history on individual objects. In this paper, we present 106 new glitches in 70 radio pulsars as observed up to the end of 2018. For 70 per cent of these pulsars, the event we report is its only known glitch. For each new glitch, we provide measurements of its epoch, amplitude, and any detected changes to the spin-down rate of the star. Combining these new glitches with those listed in the Jodrell Bank glitch catalogue, we analyse a total sample of 543 glitches in 178 pulsars. We model the distribution of glitch amplitudes and spin-down rate changes using a mixture of two Gaussian components. We corroborate the known dependence of glitch rate and activity on pulsar spin-down rates and characteristic ages, and show that younger pulsars tend to exhibit larger glitches. Pulsars with spin-down rates between 10−14 and 10−10.5 Hz s−1 show a mean reversal of 1.8 per cent of their spin-down as a consequence of glitches. Our results are qualitatively consistent with the superfluid vortex unpinning models of pulsar glitches.

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Lu, T., P. C. Zhu, and J. S. Kui. "Does the Radio Luminosity of Pulsar Grow up in its Later Stage?" Symposium - International Astronomical Union 125 (1987): 50. http://dx.doi.org/10.1017/s007418090016036x.

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In usual statistical analyses, because of diversities of proper parameters of pulsars, some interesting features might be smeared. In order to remove these diversities, we use the mean values for all quantities of pulsars, instead of values of individual pulsar, to do statistical analyses. logP/P3 - log τ and logL - logτ have been plotted, here τ P/2P and L denote the characteristic time scale and the radio luminosity of pulsars respectively. The most striking feature is that after its initial dropping to a dip at about τ∼106 yrs, the radio luminosity of pulsar appears to grow up evidently and then redrop again. This feature is difficult to be understood in usual models. However, two tentative interpretations have been given in this paper.

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Hobbs, George. "Pulsars and Gravitational Wave Detection." Publications of the Astronomical Society of Australia 22, no. 3 (2005): 179–83. http://dx.doi.org/10.1071/as04063.

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AbstractThe number of known millisecond pulsars has dramatically increased in the last few years. Regular observations of these pulsars may allow gravitational waves with frequencies ∼10−9 Hz to be detected. A ‘pulsar timing array’ is therefore complimentary to other searches for gravitational waves using ground-based or space-based interferometers that are sensitive to much higher frequencies. In this review we describe (1) the basic methods for using an array of pulsars as a gravitational wave detector, (2) the sources of the potentially detectable waves, (3) current limits on individual sources and a stochastic background, and (4) the new project recently started using the Parkes radio telescope.

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Anderson, S. B., F. A. Jenet, V. M. Kaspi, T. A. Prince, J. S. Sandhu, S. C. Unwin, and José Navarro. "Giant Micropulses from PSR J0437–4715." International Astronomical Union Colloquium 160 (1996): 211–12. http://dx.doi.org/10.1017/s025292110004149x.

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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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Kondratiev, Vladislav. "New results from LOFAR." Proceedings of the International Astronomical Union 8, S291 (August 2012): 47–52. http://dx.doi.org/10.1017/s1743921312023125.

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AbstractThe LOw Frequency Array, LOFAR, is a next generation radio telescope with its core in the Netherlands and elements distributed throughout Europe. It has exceptional collecting area and wide bandwidths at frequencies from 10 MHz up to 250 MHz. It is in exactly this frequency range where pulsars are brightest and also where they exhibit rapid changes in their emission profiles. Although LOFAR is still in the commissioning phase it is already collecting data of high quality. I will present highlights from our commissioning observations which will include: unique constraints on the site of pulsar emission, individual pulse studies, observations of millisecond pulsars, using pulsars to constrain the properties of the magneto-ionic medium and pilot pulsars surveys. I will also discuss future science projects and advances in the observing capabilities.

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Rankin, Joanna M. "Single Pulses and the Plasma-physical Processes of Pulsar Radio Emission." Proceedings of the International Astronomical Union 13, S337 (September 2017): 73–78. http://dx.doi.org/10.1017/s1743921317010341.

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AbstractPulsars were discovered on the basis of their individual pulses, first by Jocelyn Bell and then by many others. This was chart-recorder science as computers were not yet in routine use. Single pulses carry direct information about the emission process as revealed in the detailed properties of their polarization characteristics. Early analyses of single pulses proved so dizzyingly complex that attention shifted to study of average profiles. This is turn led to models of pulsar emission beams—in particular the core/double-cone model—which now provides a foundation for understanding single-pulse sequences. We mention some of the 21stC single-pulse surveys and conclude with a brief discussion of our own recent analyses leading to the identification of the pulsar radio-emission mechanism of both slow and millsecond pulsars.

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Johnson, Aaron D., Sarah J. Vigeland, Xavier Siemens, and Stephen R. Taylor. "Gravitational-wave Statistics for Pulsar Timing Arrays: Examining Bias from Using a Finite Number of Pulsars." Astrophysical Journal 932, no. 2 (June 1, 2022): 105. http://dx.doi.org/10.3847/1538-4357/ac6f5e.

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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.

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Singal, Ashok K. "Giant Radio Pulses from Pulsars." International Astronomical Union Colloquium 182 (2001): 61–64. http://dx.doi.org/10.1017/s0252921100000701.

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AbstractWe present some results from our observations of giant pulses from PSR B0950+08 at 103 MHz. These observations, now extending over a year, have shown the highest rate of occurrence of giant pulses seen from any known pulsar. Large fluctuations in the intensity levels of individual giant pulses and in their occurrence rate per unit interval of time are seen during a single day’s observations, as well as from one day to the next. We conclude that these intensity variations are likely to be intrinsic to the pulsar.

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McKee, James W. "Pulsar science with data from the Large European Array for Pulsars." Proceedings of the International Astronomical Union 13, S337 (September 2017): 374–75. http://dx.doi.org/10.1017/s1743921317009462.

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AbstractThe Large European Array for Pulsars (LEAP) is a European Pulsar Timing Array project that combines the Lovell, Effelsberg, Nançay, Sardinia, and Westerbork radio telescopes into a single tied-array, and makes monthly observations of a set of millisecond pulsars (MSPs). The overview of our experiment is presented in Bassa et al. (2016). Baseband data are recorded at a central frequency of 1396 MHz and a bandwidth of 128 MHz at each telescope, and are correlated offline on a cluster at Jodrell Bank Observatory using a purpose-built correlator, detailed in Smits et al. (2017). LEAP offers a substantial increase in sensitivity over that of the individual telescopes, and can operate in timing and imaging modes (notably in observations of the galactic centre radio magnetar; Wucknitz 2015). To date, 4 years of observations have been reduced. Here, we report on the scientific projects which have made use of LEAP data.

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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, and Yuankun Wang. "Radio Pulse Profiles and Polarization of the Terzan 5 Pulsars." Astrophysical Journal 941, no. 1 (December 1, 2022): 22. http://dx.doi.org/10.3847/1538-4357/aca156.

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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.

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Xie, Yi, and Shuangnan Zhang. "Modeling pulsar time noise with long term decay modulated by short term oscillations of the magnetic fields of neutron stars." Proceedings of the International Astronomical Union 8, S291 (August 2012): 561. http://dx.doi.org/10.1017/s1743921312024878.

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AbstractWe model the evolution of the magnetic fields of neutron stars as consisting of a long term power-law decay modulated by short term small amplitude oscillations. Our model predictions on the timing noise of neutron stars agree well with the observed statistical properties and correlations of normal radio pulsars. For individual pulsars our model can effectively reduce their timing residuals, thus offering the potential of more sensitive detections of gravitational waves with pulsar timing arrays. Finally our model can also re-produce their observed correlation and oscillations of second derivative of frenquency, as well as the “slow glitch” phenomenon.

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Miles, M. T., R. M. Shannon, M. Bailes, D. J. Reardon, S. Buchner, H. Middleton, and R. Spiewak. "Mode changing in J1909 − 3744: the most precisely timed pulsar." Monthly Notices of the Royal Astronomical Society 510, no. 4 (December 8, 2021): 5908–15. http://dx.doi.org/10.1093/mnras/stab3549.

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ABSTRACT We present baseband radio observations of the millisecond pulsar J1909 − 3744, the most precisely timed pulsar, using the MeerKAT telescope as part of the MeerTime pulsar timing array campaign. During a particularly bright scintillation event the pulsar showed strong evidence of pulse mode changing, among the first millisecond pulsars and the shortest duty cycle millisecond pulsar to do so. Two modes appear to be present, with the weak (lower signal-to-noise ratio) mode arriving 9.26 ± 3.94 μs earlier than the strong counterpart. Further, we present a new value of the jitter noise for this pulsar of 8.20 ± 0.14 ns in one hour, finding it to be consistent with previous measurements taken with the MeerKAT (9 ± 3 ns) and Parkes (8.6 ± 0.8 ns) telescopes, but inconsistent with the previously most precise measurement taken with the Green Bank telescope (14 ± 0.5 ns). Timing analysis on the individual modes is carried out for this pulsar, and we find an approximate $10\, \mathrm{per\,cent}$ improvement in the timing precision is achievable through timing the strong mode only as opposed to the full sample of pulses. By forming a model of the average pulse from templates of the two modes, we time them simultaneously and demonstrate that this timing improvement can also be achieved in regular timing observations. We discuss the impact an improvement of this degree on this pulsar would have on searches for the stochastic gravitational wave background, as well as the impact of a similar improvement on all MeerTime PTA pulsars.

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Posselt, B., A. Karastergiou, S. Johnston, A. Parthasarathy, L. S. Oswald, R. A. Main, A. Basu, et al. "The Thousand Pulsar Array program on MeerKAT – IX. The time-averaged properties of the observed pulsar population." Monthly Notices of the Royal Astronomical Society 520, no. 3 (February 15, 2023): 4582–600. http://dx.doi.org/10.1093/mnras/stac3383.

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ABSTRACT We present the largest single survey to date of average profiles of radio pulsars, observed and processed using the same telescope and data reduction software. Specifically, we present measurements for 1170 pulsars, observed by the Thousand Pulsar Array programme at the 64-dish SARAO MeerKAT radio telescope, in a frequency band from 856 to 1712 MHz. We provide rotation measures (RM), dispersion measures, flux densities, and polarization properties. The catalogue includes 254 new RMs that substantially increase the total number of known pulsar RMs. Our integration times typically span over 1000 individual rotations per source. We show that the radio (pseudo-) luminosity has a strong, shallow dependence on the spin-down energy, proportional to $\dot{E}^{0.15\pm 0.04}$, that contradicts some previous proposals of population synthesis studies. In addition, we find a significant correlation between the steepness of the observed flux density spectra and $\dot{E}$, and correlations of the fractional linear polarization with $\dot{E}$, the spectral index, and the pulse width, which we discuss in the context of what is known about pulsar radio emission and how pulsars evolve with time. On the whole, we do not see significant correlations with the estimated surface magnetic field strength, and the correlations with $\dot{E}$ are much stronger than those with the characteristic age. This finding lends support to the suggestion that magnetic dipole braking may not be the dominant factor for the evolution of pulsar rotation over the lifetimes of pulsars. A public data release of the high-fidelity time-averaged pulse profiles in full polarization accompanies our catalogue.

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Hobbs, G., D. Miller, R. N. Manchester, J. Dempsey, J. M. Chapman, J. Khoo, J. Applegate, et al. "The Parkes Observatory Pulsar Data Archive." Publications of the Astronomical Society of Australia 28, no. 3 (2011): 202–14. http://dx.doi.org/10.1071/as11016.

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AbstractThe Parkes pulsar data archive currently provides access to 144044 data files obtained from observations carried out at the Parkes observatory since the year 1991. Around 105 files are from surveys of the sky, the remainder are observations of 775 individual pulsars and their corresponding calibration signals. Survey observations are included from the Parkes 70 cm and the Swinburne Intermediate Latitude surveys. Individual pulsar observations are included from young pulsar timing projects, the Parkes Pulsar Timing Array and from the PULSE@Parkes outreach program. The data files and access methods are compatible with Virtual Observatory protocols. This paper describes the data currently stored in the archive and presents ways in which these data can be searched and downloaded.

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Pugachev, V. D., Yu P. Shitov, and A. G. Soin. "The Phase Stability of Micropulses from PSR 1133+16." International Astronomical Union Colloquium 128 (1992): 340–42. http://dx.doi.org/10.1017/s0002731600155477.

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As is very well known, there are two different kinds of time structure of the individual pulses of pulsars. There are microstructures with time scales less than 1 ms and subpulse structures, the usual scale of which is of the order of 10 ms. Subpulses are a result of the radiation beam rotation and in many cases demonstrate some regularity of arrival phases. In contrast, microstructure looks rather like a short pulse of noise with random phases of micropulse appearance in the radio emission window of the pulsar. Because the appearance phases of micropulses are random in the pulsar period, it is very difficult to establish what the fundamental character of these micropulses is: are they a temporal variation of radio emission intensity or the result of narrow beam rotation?

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Chatterjee, Shami. "Science with radio pulsar astrometry." Proceedings of the International Astronomical Union 8, S291 (August 2012): 269. http://dx.doi.org/10.1017/s1743921312023824.

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AbstractHigh precision astrometry on radio pulsars can provide model-independent estimates of their distances and velocities. Such estimates serve to calibrate models of the Galactic electron density distribution, thereby improving distance estimates for the entire pulsar population. They can provide independent astrometric information for precision pulse timing, reducing the number of fit parameters and thus potentially improving the sensitivity of pulsar timing arrays to the gravitational wave background. Individual neutron stars also serve as laboratories for astrophysics. For example, distances to highly luminous recycled pulsars identified by the Fermi gamma ray space telescope will constrain their energetics and may serve to probe the equation of state for nuclear matter at extremes of density and pressure. Here we provide an update on ongoing astrometry programs with the Very Long Baseline Array and the scientific results from these efforts.

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Tauris, T. M., and E. P. J. van den Heuvel. "New Direct Observational Evidence for Kicks in SNe." International Astronomical Union Colloquium 177 (2000): 595–96. http://dx.doi.org/10.1017/s0252921100060693.

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We present an updated list of direct strong evidence in favour of kicks being imparted to newborn neutron stars. In particular we discuss the new cases of evidence resulting from recent observations of the X-ray binary Circinus X-1 and the newly discovered binary radio pulsar PSR J1141–6545. We conclude that the assumption that neutron stars receive a kick velocity at their formation is unavoidable (van den Heuvel & van Paradijs 1997).This assumption explains a large variety of observations, ranging from direct observed properties of individual binary pulsars and Be/X-ray binaries to the observed birth rates and dynamical properties of the populations of LMXBs, binary recycled pulsars as well as the motion and distribution of single pulsars. Below we give an updated list in favour of kicks based on the compilation given by van den Heuvel & van Paradijs (1997) – see references therein for details.

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Eya, I. O., J. O. Urama, and A. E. Chukwude. "ENTRAINMENT FACTOR OF INDIVIDUAL GLITCH FRACTIONAL MOMENT OF INERTIA." Revista Mexicana de Astronomía y Astrofísica 55, no. 1 (May 31, 2019): 3–9. http://dx.doi.org/10.22201/ia.01851101p.2019.55.01.01.

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The superfluid in the inner crust of a neutron star is assumed to be the reservoir of momentum released in a pulsar glitch. Recently, due to crustal entrainment, it appears debatable whether the magnitude of the inner crust is sufficient to contain the superfluid responsible for large glitches. This paper calculates the fractional moment of inertia (FMI)(i.e. the ratio of the inner crust superfluid moment of inertia to that of the coupled components) associated with individual glitches. It is shown that the effective moment of inertia associated with the transferred momentum is that of the entrained neutrons. The FMI for glitches in three pulsars, which exhibit the signature of exhausting their momentum reservoir, were calculated and scaled with the entrainment factor. Some of the glitches require an inner crust superfluid with moment of inertia larger than the current suggested values of 7-10% of the stellar moment of inertia.

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Celora, T., V. Khomenko, M. Antonelli, and B. Haskell. "The effect of non-linear mutual friction on pulsar glitch sizes and rise times." Monthly Notices of the Royal Astronomical Society 496, no. 4 (July 6, 2020): 5564–74. http://dx.doi.org/10.1093/mnras/staa1930.

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ABSTRACT Observations of pulsar glitches have the potential to provide constraints on the dynamics of the high density interior of neutron stars. However, to do so, realistic glitch models must be constructed and compared to the data. We take a step towards this goal by testing non-linear models for the mutual friction force, which is responsible for the exchange of angular momentum between the neutron superfluid and the observable normal component in a glitch. In particular, we consider a non-linear dependence of the drag force on the relative velocity between superfluid vortices and the normal component, in which the contributions of both kelvin and phonon excitations are included. This non-linear model produces qualitatively new features, and is able to reproduce the observed bimodal distribution of glitch sizes in the pulsar population. The model also suggests that the differences in size distributions in individual pulsars may be due to the glitches being triggered in regions with different pinning strengths, as stronger pinning leads to higher vortex velocities and a qualitatively different mutual friction coupling with respect to the weak pinning case. Glitches in pulsars that appear to glitch quasi-periodically with similar sizes may thus be due to the same mechanisms as smaller events in pulsars that have no preferred glitch size, but simply originate in stronger pinning regions, possibly in the core of the star.

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Chennamangalam, Jayanth, D. R. Lorimer, Ilya Mandel, and Manjari Bagchi. "Constraining the luminosity function parameters and population size of radio pulsars in globular clusters." Proceedings of the International Astronomical Union 8, S291 (August 2012): 257–60. http://dx.doi.org/10.1017/s1743921312023794.

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AbstractThe luminosity distribution of Galactic radio pulsars is believed to be log-normal in form. Applying this functional form to populations of pulsars in globular clusters, we employ Bayesian methods to explore constraints on the mean and standard deviation of the function, as well as the total number of pulsars in the cluster. Our analysis is based on an observed number of pulsars down to some limiting flux density, measurements of flux densities of individual pulsars, as well as diffuse emission from the direction of the cluster. We apply our analysis to Terzan 5 and demonstrate, under reasonable assumptions, that the number of potentially observable pulsars is in a 95.45% credible interval of 133+101−58. Beaming considerations would increase the true population size by approximately a factor of two.

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Kazbegi, A. Z., G. Z. Machabeli, and G. I. Melikidze. "A Model for the Drifting-Subpulse Phenomenon." International Astronomical Union Colloquium 128 (1992): 296–98. http://dx.doi.org/10.1017/s0002731600155374.

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The subpulse drift phenomena—that is, periodic subpulse phase variations in the individual-pulse sequences—was discovered by Drake and Craft (1968) in the beginning of the pulsar era. Many observational programs have been carried out since then, and it has been shown a) that only a minority of pulsars exhibit the phenomenon, and b) that only some of these can be characterized by a definite drift rate (Huguenin, Taylor, and Troland 1970, Backer 1970, Taylor and Huguenin 1971).

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Brook, Paul, and Aris Karastergiou. "Finding Pulsar Variability in 50 Years of Data." Proceedings of the International Astronomical Union 13, S337 (September 2017): 317–18. http://dx.doi.org/10.1017/s1743921317008766.

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AbstractFifty years of pulsar data has led to the discovery of emission and rotation variability on timescales of months and years; we have developed techniques to identify this long timescale variability. Individual observations may be too noisy to identify subtle changes in a pulse profile; we use Gaussian process regression to model noisy observations and produce a continuous map of pulse profile variability. Generally, multiple observing epochs are required to obtain the pulsar spin frequency derivative. Gaussian process regression is, therefore, also used to monitor this rate of spindown. We have applied variability detection techniques to both millisecond and long period pulsar datasets. I will discuss the techniques used and present the most interesting results from the pulsars analysed.

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Foster, R. S., L. Fairhead, and D. C. Backer. "Spectral Analysis of Four Recycled Pulsars." International Astronomical Union Colloquium 128 (1992): 150–53. http://dx.doi.org/10.1017/s0002731600154976.

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AbstractFlux density measurements of four recycled pulsars, PSR 1620-26, PSR 1821-24, PSR 1855+09, and PSR 1937+21, have been made to determine their spectral indices in the range between 425 MHz to 3 GHz. The four objects are shown to have indices that range from –1.3 to –2.6. The luminosities of these four pulsars are spread over nearly three orders of magnitude. An analytic pulse component model is developed for each object. Individual components are allowed to have different spectral indices and hence different component ratios as a function of frequency. Component separations are evaluated as a function of frequency. The analytic models are used to determine dispersion measures with a precision better than 0.01 pc cm–3 for each object. The intrinsic pulse widths of each of these objects is less than ~4 percent of their respective pulse periods.

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Karastergiou, Aris, Paul Brook, Steve Roberts, Sarah Buchner, and Simon Johnston. "Long timescale radio emission variability and spin-down changes in PSR J0738-4042." Proceedings of the International Astronomical Union 8, S291 (August 2012): 161. http://dx.doi.org/10.1017/s1743921312023496.

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AbstractRecently, PSR J0738-4042 has grown a bright new emission component in its average pulse profile. Using data from Parkes and HartRAO, spanning back to the early 1980s, and applying statistical techniques to model the pulse profile shape with time, we have uncovered unexpected long-term variability, which is very well correlated with changes in the spin-down rate. We present these findings in the context of a growing population of radio-variable pulsars with correlated timing irregularities, including the intermittent pulsars, state-changing pulsars and other individual examples.

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ZHANG, SHUANG-NAN, and YI XIE. "MODELING PULSAR TIME NOISE WITH LONG TERM POWER LAW DECAY MODULATED BY SHORT TERM OSCILLATIONS OF THE MAGNETIC FIELDS OF NEUTRON STARS." International Journal of Modern Physics D 22, no. 11 (September 2013): 1360012. http://dx.doi.org/10.1142/s0218271813600122.

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We model the evolution of the magnetic fields of neutron stars as consisting of a long term power-law decay modulated by short term small amplitude oscillations. Our model predictions on the timing noise [Formula: see text] of neutron stars agree well with the observed statistical properties and correlations of normal radio pulsars. Fitting the model predictions to the observed data, we found that their initial parameter implies their initial surface magnetic dipole magnetic field strength B0 ~ 5 × 1014 G when t0 = 0.4 yr and that the oscillations have amplitude K ~ 10-8 to 10-5 and period T on the order of years. For individual pulsars our model can effectively reduce their timing residuals, thus offering the potential of more sensitive detections of gravitational waves with pulsar timing arrays. Finally our model can also re-produce their observed correlation and oscillations of [Formula: see text], as well as the "slow glitch" phenomenon.

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Main, R. A., S. A. Sanidas, J. Antoniadis, C. Bassa, S. Chen, I. Cognard, M. Gaikwad, et al. "Measuring interstellar delays of PSR J0613−0200 over 7 yr, using the Large European Array for Pulsars." Monthly Notices of the Royal Astronomical Society 499, no. 1 (September 28, 2020): 1468–79. http://dx.doi.org/10.1093/mnras/staa2955.

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ABSTRACT Using data from the Large European Array for Pulsars, and the Effelsberg telescope, we study the scintillation parameters of the millisecond pulsar PSR J0613−0200 over a 7 yr timespan. The ‘secondary spectrum’ – the 2D power spectrum of scintillation – presents the scattered power as a function of time delay, and contains the relative velocities of the pulsar, observer, and scattering material. We detect a persistent parabolic scintillation arc, suggesting scattering is dominated by a thin, anisotropic region. The scattering is poorly described by a simple exponential tail, with excess power at high delays; we measure significant, detectable scattered power at times out to ${\sim}5 \, \mu {\rm s}$, and measure the bulk scattering delay to be between 50 to 200 ns with particularly strong scattering throughout 2013. These delays are too small to detect a change of the pulse profile shape, yet they would change the times of arrival as measured through pulsar timing. The arc curvature varies annually, and is well fitted by a one-dimensional scattering screen ${\sim}40{{\ \rm per\ cent}}$ of the way towards the pulsar, with a changing orientation during the increased scattering in 2013. Effects of uncorrected scattering will introduce time delays correlated over time in individual pulsars, and may need to be considered in gravitational wave analyses. Pulsar timing programmes would benefit from simultaneously recording in a way that scintillation can be resolved, in order to monitor the variable time delays caused by multipath propagation.

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RAY, ALAK, and AJIT KEMBHAVI. "FORMATION OF MILLISECOND PULSARS IN GLOBULAR CLUSTERS." Modern Physics Letters A 03, no. 03 (February 1988): 229–35. http://dx.doi.org/10.1142/s0217732388000271.

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The low upper limit to the period derivative of the millisecond pulsar PSR 1821–24 occurring in the globular cluster M28 implies that it is not a part of any binary system. Various formation scenarios of such a pulsar, involving tidal capture of two stars into a gravitationally bound system, spin-up of the neutron star and disruption or unbinding of the companion star are considered in this letter. Of particular interest to these scenarios is the effect of tidal dissipation of orbital energy on the evolution of the individual stars and the binary system. We consider a scenario in which a massive white dwarf is captured tidally by a low mass star that has evolved off the main sequence, and later collapses to form a neutron star and eventually disrupts the degenerate helium core of the erstwhile companion due to unstable Roche-lobe overflow.

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McKinnon, Mark M., and Daniel R. Stinebring. "The Mode-Separated Pulse Profiles of Pulsar Radio Emission." International Astronomical Union Colloquium 177 (2000): 261–64. http://dx.doi.org/10.1017/s0252921100059650.

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AbstractTwo modes of orthogonal polarization are generally observed in the radio emission from pulsars. Essentially all attempts to calculate the average profiles of the individual modes have assumed that the modes occur separately. We have presented evidence, however, that the modes occur simultaneously. Therefore, we believe that “mode-separated” pulse profiles which have been published to date reveal little about the polarization properties of the individual modes.Calculating mode-separated pulse profiles for superposed orthogonal modes is complicated by the unknown polarization properties of the individual modes. However, the simplest model of pulsar radio emission which can explain the wide variety in the emission’s polarization is one in which the individual modes are completely polarized. We use our simple model to compute the average profiles of the orthogonal modes in PSR B0525+21. The total intensity of the two mode profiles resembles the overall pulse profile, and each profile is highly linearly polarized.

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Cheung, W. M., and K. S. Cheng. "Unpulsed High-Energy Radiation from the Crab Pulsar and Nebula." International Astronomical Union Colloquium 142 (1994): 827–31. http://dx.doi.org/10.1017/s0252921100078167.

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AbstractGenerally, people believe that the unpulsed high-energy gamma rays from the direction of Crab Nebula and pulsar comes from the nebula. But it is entirely possible that the unpulsed high-energy gamma rays from the direction of the Crab Nebula and pulsar are actually emitted from a region extending to a couple of light cylinder radii from the pulsar instead of from the extensive nebula. In this conference paper, we study the possibility that the unpulsed high-energy gamma rays from 100 MeV to 10 GeV are emitted from the extensive nebula. In our model, two pulsed photon beams from two different outer gaps cross each other beyond the light cylinder and result in pair production. Since the pitch angles of these pairs do not correlate with the local magnetic field, and the typical mean free path for pair production is comparable to the local radius of curvature, the subsequent synchrotron radiation and inverse-Compton scattering produce unpulsed X-rays and gamma-rays respectively.Subject headings: acceleration of particles — gamma rays: theory — ISM: individual (Crab Nebula) — pulsars: individual (Crab) — radiation mechanisms: nonthermal

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Zhang, C., C. Wang, G. Hobbs, C. J. Russell, D. Li, S. B. Zhang, S. Dai, et al. "Applying saliency-map analysis in searches for pulsars and fast radio bursts." Astronomy & Astrophysics 642 (September 30, 2020): A26. http://dx.doi.org/10.1051/0004-6361/201937234.

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Context. We investigate the use of saliency-map analysis to aid in searches for transient signals, such as fast radio bursts and individual pulses from radio pulsars. Aims. Our aim is to demonstrate that saliency maps provide the means to understand predictions from machine learning algorithms and can be implemented in pipelines used to search for transient events. Methods. We implemented a new deep learning methodology to predict whether any segment of the data contains a transient event. The algorithm was trained using real and simulated data sets. We demonstrate that the algorithm is able to identify such events. The output results are visually analysed via the use of saliency maps. Results. We find that saliency maps can produce an enhanced image of any transient feature without the need for de-dispersion or removal of radio frequency interference. The maps can be used to understand which features in the image were used in making the machine learning decision and to visualise the transient event. Even though the algorithm reported here was developed to demonstrate saliency-map analysis, we have detected a single burst event, in archival data, with dispersion measure of 41 cm−3 pc that is not associated with any currently known pulsar.

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Lassus, A., R. van Haasteren, C. M. F. Mingarelli, K. J. Lee, and A. Vecchio. "A data analysis library for gravitational wave detection." Proceedings of the International Astronomical Union 8, S291 (August 2012): 438–40. http://dx.doi.org/10.1017/s1743921312024428.

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AbstractOne of the main goals of Pulsar Timing Arrays (PTAs) is the direct detection of gravitational waves (GWs). A first detection will be a major leap for astronomy and substantial effort is currently going into timing as many pulsars as possible, with the highest possible accuracy. As part of the individual PTA projects, several groups are developing data analysis methods for the final stage of a gravitational-waves search pipeline: the analysis of the timing residuals. Here we report the progress of on-going work to develop, within a Bayesian framework, a comprehensive and user friendly analysis library to search for gravitational waves in PTA data.

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Millhouse, M., A. Melatos, G. Howitt, J. B. Carlin, L. Dunn, and G. Ashton. "An updated glitch rate law inferred from radio pulsars." Monthly Notices of the Royal Astronomical Society 511, no. 3 (January 29, 2022): 3304–19. http://dx.doi.org/10.1093/mnras/stac194.

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ABSTRACT Radio pulsar glitches probe far-from-equilibrium processes involving stress accumulation and relaxation in neutron star interiors. Previous studies of glitch rates have focused on individual pulsars with as many recorded glitches as possible. In this work, we analyse glitch rates using all available data including objects that have glitched never or once. We assume the glitch rate follows a homogeneous Poisson process, and therefore exclude pulsars that exhibit quasiperiodic glitching behaviour. Calculating relevant Bayes factors shows that a model in which the glitch rate λ scales as a power of the characteristic age τ is preferred over models that depend arbitrarily on powers of the spin frequency ν and/or its time derivative $\dot{\nu }$. For λ = A(τ/τref)−γ, where τref = 1 yr is a reference time, the posterior distributions are unimodal with $A=0.0066_{-0.002}^{+0.003}\ \rm {yr}^{-1}$ and $\gamma =0.27_{-0.03}^{+0.03}$. Importantly, the data exclude with 99 per cent confidence the possibility γ = 1 canvassed in the literature. When objects with zero-recorded glitches are included, the age-based rate law is still preferred and the posteriors change to give $A=0.0099_{-0.003}^{+0.004}\ \rm {yr}^{-1}$ and $\gamma =0.31_{-0.03}^{+0.03}$. The updated estimates still support increased glitch activity for younger pulsars, while demonstrating that the large number of objects with zero glitches contain important statistical information about the rate, provided that they are part of the same population as opposed to a disjoint population which never glitches for some unknown physical reason.

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Schmidtke, P. C., A. P. Cowley, and A. Udalski. "An analysis of optical periods in individual Small Magellanic Cloud Be/X-ray pulsars." Monthly Notices of the Royal Astronomical Society 431, no. 1 (February 27, 2013): 252–78. http://dx.doi.org/10.1093/mnras/stt159.

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Songsheng, Yu-Yang, Yi-Qian Qian, Yan-Rong Li, Pu Du, Jie-Wen Chen, Yan Wang, Soumya D. Mohanty, and Jian-Min Wang. "Search for Continuous Gravitational-wave Signals in Pulsar Timing Residuals: A New Scalable Approach with Diffusive Nested Sampling." Astrophysical Journal 922, no. 2 (December 1, 2021): 228. http://dx.doi.org/10.3847/1538-4357/ac25fc.

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Abstract Detecting continuous nanohertz gravitational waves (GWs) generated by individual close binaries of supermassive black holes (CB-SMBHs) is one of the primary objectives of pulsar timing arrays (PTAs). The detection sensitivity is slated to increase significantly as the number of well-timed millisecond pulsars will increase by more than an order of magnitude with the advent of next-generation radio telescopes. Currently, the Bayesian analysis pipeline using parallel tempering Markov Chain Monte Carlo has been applied in multiple studies for CB-SMBH searches, but it may be challenged by the high dimensionality of the parameter space for future large-scale PTAs. One solution is to reduce the dimensionality by maximizing or marginalizing over uninformative parameters semianalytically, but it is not clear whether this approach can be extended to more complex signal models without making overly simplified assumptions. Recently, the method of diffusive nested (DNest) sampling has shown capability in coping with high dimensionality and multimodality effectively in Bayesian analysis. In this paper, we apply DNest to search for continuous GWs in simulated pulsar timing residuals and find that it performs well in terms of accuracy, robustness, and efficiency for a PTA including  ( 10 2 ) pulsars. DNest also allows a simultaneous search of multiple sources elegantly, which demonstrates its scalability and general applicability. Our results show that it is convenient and also highly beneficial to include DNest in current toolboxes of PTA analysis.

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Ray, Alak, Bence Kocsis, and Simon Portegies Zwart. "Detecting gravitational waves from the Galactic center with pulsar timing." Proceedings of the International Astronomical Union 9, S303 (October 2013): 419–23. http://dx.doi.org/10.1017/s1743921314001045.

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AbstractBlack holes orbiting the supermassive black hole (SMBH) Sgr A* in the Galactic center (GC) of the Milky Way generate gravitational waves (GW). The resulting spectrum, due to stars and black holes (BHs), is continuous below 40 nHz while individual BHs within about 200 AU of the central SMBH stick out in the spectrum at higher frequencies. The GWs can be detected by timing radio pulsars within a few parsecs of this region. Future observations with the Square Kilometer Array of such pulsars with sufficient timing accuracy may be sensitive to signals from intermediate mass BHs (IMBH) in a 3 year observation baseline. The recent detection of radio pulsations from the magnetar SGR J1745–29 very near the GC opens up the possibilities of detecting millisecond pulsars (which can be used as probes of the GWs) through lines of sight with only moderate pulse and angular broadening due to scattering.

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Carlin, J. B., and A. Melatos. "Long-term statistics of pulsar glitches triggered by a Brownian stress accumulation process." Monthly Notices of the Royal Astronomical Society 494, no. 3 (April 8, 2020): 3383–91. http://dx.doi.org/10.1093/mnras/staa935.

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ABSTRACT A microphysics-agnostic meta-model of rotational glitches in rotation-powered pulsars is developed, wherein the globally averaged internal stress accumulates as a Brownian process between glitches, and a glitch is triggered once a critical threshold is surmounted. Precise, falsifiable predictions are made regarding long-term event statistics in individual pulsars. For example, the Spearman cross-correlation coefficient between the size of a glitch and the waiting time until the next glitch should exceed 0.25 in all pulsars. Among the six pulsars with the most recorded glitches, PSR J0537−6910 and PSR J0835−4510 are consistent with the predictions of the meta-model, while PSR J1740−3015 and PSR J0631+1036 are not. PSR J0534+2200 and PSR J1341−6220 are only consistent with the meta-model, if there exists an undetected population of small glitches with small waiting times, which we do not resolve. The results are compared with a state-dependent Poisson process, another microphysics-agnostic meta-model in the literature. The results are also applied briefly to recent pulse-to-pulse observations of PSRJ0835−4510, which appear to reveal evidence for a negative fluctuation in rotation frequency just prior to the 2016 glitch.

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Weisberg, Joel M. "The Galactic Electron Density Distribution." International Astronomical Union Colloquium 160 (1996): 447–54. http://dx.doi.org/10.1017/s025292110004207x.

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AbstractPulsars are excellent probes of the galactic free electron layer. Interstellar dispersion and scattering measurably affect the observed pulsar signals, thereby providing information on the distribution and density of the free electrons causing these phenomena.Primary calibration of galactic electron density models is achieved through adjusting their parameters to fit the observed dispersion of pulsars having independently measured distances. The distances are determined via kinematic analyses of HI absorption spectra, through angular or timing parallax measurements, and from associations with other objects of known distances.The models have become steadily more refined as the body of data upon which they are based has grown. Independent distance measurements continue to accrue. The discovery of pulsars in globular clusters provided high latitude lines of sight for probing the z-distribution (Reynolds 1989). Additional calibration has been provided through incorporation of interstellar scattering measurements into the modelling process (Cordeset al. 1991). Individual spiral arms are now explicitly modelled (Taylor & Cordes 1993).While great progress has been achieved with these models, there are still uncertainties in modelling the electron density of the local region and the inner Galaxy, and in the z–distribution of the electron layer. Currently anticipated observations will help to resolve some of these issues.

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Bednarek, W., J. Sitarek, and T. Sobczak. "TeV gamma-ray emission initiated by the population or individual millisecond pulsars within globular clusters." Monthly Notices of the Royal Astronomical Society 458, no. 1 (February 17, 2016): 1083–95. http://dx.doi.org/10.1093/mnras/stw367.

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Sourie, Aurélien, and Nicolas Chamel. "Vortex pinning in the superfluid core of neutron stars and the rise of pulsar glitches." Monthly Notices of the Royal Astronomical Society: Letters 493, no. 1 (January 28, 2020): L98—L102. http://dx.doi.org/10.1093/mnrasl/slaa015.

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ABSTRACT Timing of the Crab and Vela pulsars has recently revealed very peculiar evolutions of their spin frequency during the early stage of a glitch. We show that these differences can be interpreted from the interactions between neutron superfluid vortices and proton fluxoids in the core of these neutron stars. In particular, pinning of individual vortices to fluxoids is found to have a dramatic impact on the mutual friction between the neutron superfluid and the rest of the star. The number of fluxoids attached to vortices turns out to be a key parameter governing the global dynamics of the star. These results may have implications for the interpretation of other astrophysical phenomena such as pulsar-free precession or the r-mode instability.

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Kramer, Michael. "Separation of integrated pulse shapes into unique sub-components." International Astronomical Union Colloquium 160 (1996): 215–16. http://dx.doi.org/10.1017/s0252921100041518.

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Average pulse profiles are generally separable into several components whereas individual components can be described by a Gaussian shape. One generally distinguishes betweencoreandconalcomponents, although it is yet unclear whether core and conal components originate from the same (Lyne & Manchester 1988) or a different emission mechanism (Rankin 1983). Investigating this problem, we studied the behaviour of individual components observed in about 200 profiles of 18 pulsars measured at three different frequencies, i.e. at 1.4 GHz, 4.75 GHz and 10.55 GHz. We unambiguously determined the number, location, width, flux density and spectral index of individual components using a special technique (Kramer et al. 1994). The applied method ensures that only intrinsic features of the pulse profiles are fitted by comparing off-pulse noise statistics and post-fit residuals as a goodness-of-fit estimator. As a first result, we note that all high S/N pulsar profiles can be accurately described by using only a small number (usually ≤ 5) of gaussian components, although we also find an example of a seven component pulse shape (B0740–28). Fitted components determined for different observations of the same pulsar were averaged, producing a grand mean profile which is completely noise-free and thus suitable for a reliable flux density measurement of individual components, for an accurate determination of the pulse width to calculate opening angles, ρ, of the emission cone, or for use as a template for obtaining pulse arrival times.

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Wu, Xinji, Wen Xu, and Joanna M. Rankin. "On the Separation of the Components in the Mean Pulse Profile of PSR 1451-68 and their Spectral Behavior." International Astronomical Union Colloquium 128 (1992): 172–75. http://dx.doi.org/10.1017/s0002731600155027.

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AbstractWe have developed a method to understand the detailed structure of the mean pulse profile of pulsars, namely, the Gaussian fit separation of the average profile (GFSAP) method, in which we assume the total profile is the superposition of several individual Gaussian-distributed components. Linear polarization data is used to simplify the fitting. The components of PSR 1451–68 are separated and their spectral indices calculated. We find that the profile of PSR 1451–68 is actually quintuple instead of triple, which is in agreement with the idea that quintuple is the prototype shape of pulsar profiles. The core component is shown to have the steepest spectrum, while the inner cone has the flattest. Another conclusion from PSR 1451–68 is that the core width does not change with frequency.

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Török, Gabriel, Kateřina Goluchová, Eva Šrámková, Martin Urbanec, and Odele Straub. "Time-scale of twin-peak quasi-periodic oscillations and mass of accreting neutron stars." Monthly Notices of the Royal Astronomical Society 488, no. 3 (July 12, 2019): 3896–903. http://dx.doi.org/10.1093/mnras/stz1929.

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ABSTRACT Einstein’s general relativity predicts that orbital motion of accreted gas approaching a neutron star (NS) in a NS low-mass X-ray binary (LMXB) system occurs on a time-scale proportional to the NS mass. Radiation of the gas accounts for most of the observed LMXBs variability. In more than a dozen of sources twin-peak quasi-periodic oscillations (QPOs) have been observed. Inspired by the expected proportionality between periods of orbital motion and NS mass we present a straightforward comparison among these sources. We investigate relations between QPO periods and their ratios and identify characteristic time-scales of QPOs associated with individual sources. These time-scales are likely determined by the relative mass of each NS. We show that the characteristic time-scale of the millisecond pulsar XTE J1807.4−294 is longer than for most other NS LMXBs. Consequently, models of QPOs that consider geodesic orbital frequencies imply that the X-ray pulsars’ mass has to be about $50{{\ \rm per\ cent}}$ higher than the average mass of other sources. Consideration of other X-ray pulsars indicates that the exceptionality of XTE J1807.4−294 cannot be related to NS magnetic field in any simple manner. We suggest that QPOs observed in this source can help to discriminate between the proposed versions of the NS equation of state.

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Suleimanova, S. A., and V. D. Pugachev. "Polarization of individual pulses of radio pulsars at the low frequencies 40, 60, and 103 MHz." Astronomy Reports 46, no. 4 (April 2002): 309–26. http://dx.doi.org/10.1134/1.1471396.

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Journal articles on the topic 'Pulsars: individual'

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