How Common Are Magnetars? The Consequences of Magnetic-Field Decay

Ultramagnetized neutron stars or magnetars have been invoked to explain several astrophysical phenomena. We examine how the magnetic field of a magnetar will decay over time and how this decay affects the cooling of the object. We find that for sufficiently strong nascent fields, field decay alters the cooling evolution significantly relative to similarly magnetized neutron stars with constant fields. As a result, old magnetars can be expected to be bright in the soft X-ray band. The soft X-ray source RXJ~0720.4$-$3125 may well be the nearest such old magnetar.Comment: 7 pages, 1 figure, accepted for publication in Ap. J. Letter

Neutron star cooling after deep crustal heating in the X-ray transient KS 1731-260

We simulate the cooling of the neutron star in the X-ray transient KS 1731-260 after the source returned to quiescence in 2001 from a long (>~ 12.5 yr) outburst state. We show that the cooling can be explained assuming that the crust underwent deep heating during the outburst stage. In our best theoretical scenario the neutron star has no enhanced neutrino emission in the core, and its crust is thin, superfluid, and has the normal thermal conductivity. The thermal afterburst crust-core relaxation in the star may be not over.Comment: 5 pages, 2 figures, accepted by MNRAS. In v.2, two references added and typos correcte

Updated Electron-Conduction Opacities: The Impact on Low-Mass Stellar Models

We review the theory of electron-conduction opacity, a fundamental ingredient in the computation of low-mass stellar models; shortcomings and limitations of the existing calculations used in stellar evolution are discussed. We then present new determinations of the electron-conduction opacity in stellar conditions for an arbitrary chemical composition, that improve over previous works and, most importantly, cover the whole parameter space relevant to stellar evolution models (i.e., both the regime of partial and high electron degeneracy). A detailed comparison with the currently used tabulations is also performed. The impact of our new opacities on the evolution of low-mass stars is assessed by computing stellar models along both the H- and He-burning evolutionary phases, as well as Main Sequence models of very low-mass stars and white dwarf cooling tracks.Comment: 11 pages, 6 figures, ApJ in pres

Variability in the Thermal Emission from Accreting Neutron Star Transients

The composition of the outer 100 m of a neutron star sets the heat flux that flows outwards from the core. For an accreting neutron star in an X-ray transient, the thermal quiescent flux depends sensitively on the amount of hydrogen and helium remaining on the surface after an accretion outburst and on the composition of the underlying ashes of previous H/He burning. Because H/He has a higher thermal conductivity, a larger mass of H/He implies a shallower thermal gradient through the low density envelope and hence a higher effective temperature for a given core temperature. The mass of residual H and He varies from outburst to outburst, so the thermal quiescent flux is variable even though the core temperature is constant for timescales < 10 000 yr. Heavy elements settle from a H/He envelope in a few hours; we therefore model the quiescent envelope as two distinct layers, H/He over heavier elements, and treat the mass of H/He as a free parameter. We find that the emergent thermal quiescent flux can vary by a factor of 2 to 3 between different quiescent epochs. The variation is more pronounced at lower interior temperatures, making systems with low quiescent luminosities and frequent outbursts, such as SAX J1808.4-3658, ideal candidates from which to observe this effect. We compute, for different ash compositions, the interior temperatures of Cen X-4, Aql X-1, and SAX J1808.4-3658. In the case of Aql X-1, the inferred high interior temperature suggests that neutrino cooling contributes to the neutron star's thermal balance.Comment: 14 pages, 5 figures, uses emulateapj5 and psnfss fonts. To be published in The Astrophysical Journa

Ab initio based equation of state of dense water for planetary and exoplanetary modeling

This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.As a first step toward a multi-phase equation of state for dense water, we develop a temperature-dependent equation of state for dense water covering the liquid and plasma regimes and extending to the super-ionic and gas regimes. This equation of state covers the complete range of conditions encountered in planetary modeling. We use first principles quantum molecular dynamics simulations and its Thomas-Fermi extension to reach the highest pressures encountered in giant planets several times the size of Jupiter. Using these results, as well as the data available at lower pressures, we obtain a parametrization of the Helmholtz free energy adjusted over this extended temperature and pressure domain. The parametrization ignores the entropy and density jumps at phase boundaries but we show that it is sufficiently accurate to model interior properties of most planets and exoplanets. We produce an equation of state given in analytical form that is readily usable in planetary modeling codes and dynamical simulations {\bf (a fortran implementation can be found at http://www.ioffe.ru/astro/H2O/)}. The EOS produced is valid for the entire density range relevant to planetary modeling, {\bf for densities where quantum effects for the ions can be neglected, and for temperatures below 50,000K. We use this equation of state to calculate the mass-radius relationship of exoplanets up to 5,000M_Earth, explore temperature effects in ocean and wet Earth-like planets, and quantify the influence of the water EOS for the core on the gravitational moments of Jupiter.s. Part of this work was supported by the SNR grant PLANETLAB 12-BS04-0015 and the Programme National de Planetologie (PNP) of CNRS-INSU co-funded by CNES. Funding and support from Paris Sciences et Lettres (PSL) university through the project origins and conditions for the emergence of life is also acknowledged. This work was performed using HPC resources from GENCI- TGCC (Grant 2017- A0030406113

Magnetars as cooling neutron stars with internal heating

We study thermal structure and evolution of magnetars as cooling neutron stars with a phenomenological heat source in a spherical internal layer. We explore the location of this layer as well as the heating rate that could explain high observable thermal luminosities of magnetars and would be consistent with the energy budget of neutron stars. We conclude that the heat source should be located in an outer magnetar's crust, at densities rho < 5e11 g/cm^3, and should have the heat intensity of the order of 1e20 erg/s/cm^3. Otherwise the heat energy is mainly emitted by neutrinos and cannot warm up the surface.Comment: 8 pages, 5 figures, submitted to MNRA

Shear viscosity of degenerate electron matter

We calculate the partial electron shear viscosity $\eta_{ee}$ limited by electron-electron collisions in a strongly degenerate electron gas taking into account the Landau damping of transverse plasmons. The Landau damping strongly suppresses $\eta_{ee}$ in the domain of ultrarelativistic degenerate electrons and modifies its %asymptotic temperature behavior. The efficiency of the electron shear viscosity in the cores of white dwarfs and envelopes of neutron stars is analyzed.Comment: 16 pages, 4 figures, accepted to Journal of Physics

The method of diffusion bonding in a vacuum without the application of external pressure.

Developed and experimentally confirmed a new technology of diffusion bonding in a vacuum without the application of external pressure for "bronzing" Surface axial piston pumps. Thus the pressure necessary for diffusion bonding is generated by the difference of thermal expansion of bronze and steel during heating and soaking at 750 ° C for 30 minutes. Thus, in cases where bronzing molding, welding, diffusion deposition difficult and the use of classical methods of diffusion bonding is not possible (can not attach an external mechanical pressure), the proposed method of diffusion bonding is effective.Разработана и экспериментально подтверждена новая технология диффузионной сварки в вакууме без приложения внешнего давления для «бронзирования» рабочих поверхностей аксиально-поршневых гидронасосов. При этом давление, необходимое для обеспечения диффузионной сварки, формируется за счет разности термического расширения бронзы и стали в процессе нагрева и выдержки при 750 °С, 30 минут. Таким образом для случаев, когда бронзирование методами литья, наплавки, диффузионного напыления затруднительно, а использование классических способов диффузионной сварки не представляется возможным (не удается приложить внешнее механическое давление), предложенный способ диффузионной сварки эффективен.Хозяйственный договор № 37/2005 от 24.01.2005 г., «Создание производственной технологии бронзирования цилиндрических отверстий блока цилиндров типа 310.4.56.260 СБ» заключенный между ОАО «ПСМ» - заказчик и УГЛТУ – исполнитель

Powering Anomalous X-ray Pulsars by Neutron Star Cooling

Using recently calculated analytic models for the thermal structure of ultramagnetized neutron stars, we estimate the thermal fluxes from young ($t\sim 1000$ yr) ultramagnetized ($B \sim 10^{15}$ G) cooling neutron stars. We find that the pulsed X-ray emission from objects such as 1E 1841-045 and 1E 2259+586 as well as many soft-gamma repeaters can be explained by photon cooling if the neutron star possesses a thin insulating envelope of matter of low atomic weight at densities $\rho < 10^{7}-10^{8}$ g/cm$^3$. The total mass of this insulating layer is $M \sim 10^{-11}-10^{-8} M_\odot$.Comment: 8 pages, 1 figure, to appear in Ap.J. Letters (one reference entry corrected, no other changes