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  • 1
    Electronic Resource
    Electronic Resource
    Evolution of magnetohydrodynamic waves in a homogeneous isothermal medium (1981)
    Springer
    Astrophysics 17 (1981), S. 183-193 
    Details
    ISSN: 1573-8191
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01005201
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    Paper (German National Licenses)
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  • 2
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    Fast radio bursts counterparts in the scenario of supergiant pulses (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-03
    Description: We discuss identification of possible counterparts and persistent sources related to fast radio bursts (FRBs) in the framework of the model of supergiant pulses from young neutron stars with large spin-down luminosities. In particular, we demonstrate that at least some of the sources of FRBs can be observed as ultraluminous X-ray sources (ULXs). At the moment no ULXs are known to be coincident with localization areas of FRBs. We searched for a correlation of FRB positions with galaxies in the 2MASS Redshift survey catalogue. Our analysis produced statistically insignificant overabundance ( p -value  4 per cent) of galaxies in error boxes of FRBs. In the very near future with even modestly increased statistics of FRBs and with the help of dedicated X-ray observations and all-sky X-ray surveys it will be possible to decisively prove or falsify the supergiant pulses model.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Settling accretion on to isolated neutron stars from interstellar medium (2015)
    Oxford University Press
    Details
    Publication Date: 2015-01-14
    Description: We apply the model of subsonic settling accretion on to isolated neutron stars accreting from the interstellar medium (AINS). We show that in this regime the expected mean X-ray luminosity from AINS turns out to be two to three orders of magnitude as small as the maximum possible Bondi value, i.e. 10 27 –10 28  erg s –1 . The intrinsically unstable character of settling accretion due to long plasma cooling time leads to regular appearance of X-ray flares with a duration of about 1 h and a maximum luminosity of about the Bondi value, ~10 31  erg s –1 . This feature can be used to distinguish AINS from other dim X-ray sources. With the sensitivity of the forthcoming all-sky X-ray surveys the expected number of the potentially detectable AINS can be from a few to 10.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Modified pulsar current analysis: probing magnetic field evolution (2014)
    Oxford University Press
    Details
    Publication Date: 2014-08-29
    Description: We use a modified pulsar current analysis to study magnetic field decay in radio pulsars. In our approach, we analyse the flow not along the spin period axis as has been performed in previous studies, but study the flow along the direction of growing characteristic age, $\tau =P/(2\dot{P})$ . We perform extensive tests of the method and find that in most of the cases it is able to uncover non-negligible magnetic field decay (more than a few tens of per cent during the studied range of ages) in normal radio pulsars for realistic initial properties of neutron stars. However, precise determination of the magnetic field decay time-scale is not possible at present. The estimated time-scale may differ by a factor of few for different sets of initial distributions of neutron star parameters. In addition, some combinations of initial distributions and/or selection effects can also mimic enhanced field decay. We apply our method to the observed sample of radio pulsars at distances 〈10 kpc in the range of characteristic ages 8 10 4  〈  〈 10 6 yr where, according to our study, selection effects are minimized. By analysing pulsars in the Parkes Multibeam and Swinburne surveys, we find that, in this range, the field decays roughly by a factor of 2. With an exponential fit, this corresponds to the decay time-scale ~4 10 5 yr. With larger statistics and better knowledge of the initial distribution of spin periods and magnetic field strength, this method can be a powerful tool to probe magnetic field decay in neutron stars.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Neutron star's initial spin period distribution (2013)
    Oxford University Press
    Details
    Publication Date: 2013-05-26
    Description: We analyse different possibilities to explain the wide initial spin period distribution of radio pulsars presented by Noutsos et al. With a population synthesis modelling, we demonstrate that magnetic field decay can be used to interpret the difference between the recent results by Noutsos et al and those by Popov and Turolla, where a much younger population of neutron stars associated with supernova remnants with known ages has been studied. In particular, an exponential field decay with mag  = 5 Myr can produce a ‘tail’ in the reconstructed initial spin period distribution up to P 0  〉 1 s starting with a standard Gaussian with 〈 P 0 〉 = 0.3 s and P  = 0.15 s. Another option to explain the difference between initial spin period distributions from Noutsos et al. and Popov and Turolla – the emerging magnetic field – is also briefly discussed.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Post-fall-back evolution of multipolar magnetic fields and radio pulsar activation (2016)
    Oxford University Press
    Details
    Publication Date: 2016-09-03
    Description: It has long been unclear if the small-scale magnetic structures on the neutron star (NS) surface could survive the fall-back episode. The study of the Hall cascade by Cumming, Arras & Zweibel hinted that energy in small-scales structures should dissipate on short time-scales. Our new 2D magneto-thermal simulations suggest the opposite. For the first ~10 kyr after the fall-back episode with accreted mass 10 –3 M , the observed NS magnetic field appears dipolar, which is insensitive to the initial magnetic topology. In framework of the Ruderman & Sutherland, vacuum gap model during this interval, non-thermal radiation is strongly suppressed. After this time, the initial (i.e. multipolar) structure begins to re-emerge through the NS crust. We distinguish three evolutionary epochs for the re-emergence process: the growth of internal toroidal field, the advection of buried poloidal field, and slow Ohmic diffusion. The efficiency of the first two stages can be enhanced when small-scale magnetic structure is present. The efficient re-emergence of high-order harmonics might significantly affect the curvature of the magnetospheric field lines in the emission zone. So, only after few 10 4 yr would be the NS starts shining as a pulsar again, which is in correspondence with radio silence of central compact objects. In addition, these results can explain the absence of good candidates for thermally emitting NSs with freshly re-emerged field among radio pulsars (), as NSs have time to cool down, and supernova remnants can already dissipate.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Probing the surface magnetic field structure in RX J1856.5-3754 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-11-19
    Description: The evolution of magnetic field in isolated neutron stars is one of the most important ingredients in the attempt to build a unified description of these objects. A prediction of field evolution models is the existence of an equilibrium configuration, in which the Hall cascade vanishes. Recent calculations have explored the field structure in this stage, called the Hall attractor. We use X-ray data of near-by, cooling neutron stars to probe this prediction, as these sources are surmised to be close to or at Hall attractor phase. We show that the source RX J1856.5–3754 might be closer to the attractor than other sources of its class. Our modelling indicates that the properties of surface thermal emission, assuming that the star is in the Hall attractor, are in contradiction to the spectral data of RX J1856.5–3754.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Rapidly rotating neutron star progenitors (2016)
    Oxford University Press
    Details
    Publication Date: 2016-09-20
    Description: Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In this paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the bse (Binary Star Evolution) population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core–envelope coupling, characterized by the coupling time, c . The validity of this approach is checked by direct mesa calculations of the evolution of a rotating 15 M star. From comparison of the calculated spin distribution of young neutron stars with the observed one, reported by Popov and Turolla, we infer the value c ~= 5  x  10 5 yr. We show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being ~0.1–1 per cent of the total core collapses, depending on the common envelope efficiency.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Fast radio bursts as giant pulses from young rapidly rotating pulsars (2016)
    Oxford University Press
    Details
    Publication Date: 2016-08-08
    Description: We discuss possible association of fast radio bursts (FRBs) with supergiant pulses emitted by young pulsars (ages ~ tens to hundreds of years) born with regular magnetic field but very short – few milliseconds – spin periods. We assume that FRBs are extra-Galactic events coming from distances d 100 Mpc and that most of the dispersion measure (DM) comes from the material in the freshly ejected SNR shell. We then predict that for a given burst the DM should decrease with time and that FRBs are not expected to be seen below ~300 MHz due to free–free absorption in the expanding ejecta. A supernova might have been detected years before the burst; FRBs are mostly associated with star-forming galaxies. The model requires that some pulsars are born with very fast spins, of the order of few milliseconds. The observed distribution of spin-down powers $\dot{E}$ in young energetic pulsars is consistent with equal birth rate per decade of $\dot{E}$ . Accepting this injection distribution and scaling the intrinsic brightness of FRBs with $\dot{E}$ , we predict the following properties of a large sample of FRBs: (i) the brightest observed events come from a broad distribution in distances; (ii) for repeating bursts brightness either remains nearly constant (if the spin-down time is longer than the age of the pulsar) or decreases with time otherwise; in the latter case DM $\propto \dot{E}$ .
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Gaussian mixture models and the population synthesis of radio pulsars (2013)
    Oxford University Press
    Details
    Publication Date: 2013-08-22
    Description: Recently, Lee et al. used Gaussian mixture models (GMM) to study the radio pulsar population. P – Ṗ plane, they found four clusters. We develop this approach further and apply it to different synthetic pulsar populations in order to determine whether the method can effectively select groups of sources that are physically different. We check several combinations of initial conditions as well as the models of pulsar evolution and the selection effects. We find that in the case of rapidly evolving objects, the GMM is oversensitive to parameter variations and does not produce stable results. We conclude that the method does not help much to identify the subpopulations with different initial parameters or/and evolutionary paths. For the same reason, the GMM does not discriminate effectively between theoretical population synthesis models of normal radio pulsars.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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