Hydrogen and helium abundances in neutron-star atmospheres.
Hydrogen and helium burning and diffusion in neutron star atmosphere
Rosen, L. C.↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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The instability of stellar structures intermediate between white dwarfs and neutron stars
Instability of stellar structures intermediate between dwarfs and neutron stars
Cameron, A. G. W.↗
Neutron star models based on an improved equation of state
Neutron star models based on equation of state for cold degenerate matter, taking into account nuclear forces and clustering
Cameron, A. G. W.↗
The effects of nuclear forces on the maximum mass limit of neutron stars
Nuclear forces effects on maximum mass limit of neutron stars models using V gamma type potentials
Tsuruta, S.↗
Neutron star binaries, pulsars and burst sources
Unresolved issues involving neutron star binaries, pulsars, and burst sources are described. Attention is drawn to the types of observations most likely to resolve them. Many of these observations are likely to be carried out during the next decade by one or more missions that have been approved or proposed. Flux measurements with an imaging detector and broad-band spectroscopic studies in the energy range 30-150 keV are discussed. The need for soft X-ray and X-ray observations with an instrument which has arcminute angular resolution and an effective area substantially greater than of ROSAT or EXOSAT is also discussed.
Lamb, F. K.↗
Low-luminosity accretion onto magnetized neutron stars
The behavior of matter accreting at low rates (M is less than 10 to the 16th g/s) onto the polar caps of a highly magnetized (B = 10 to the 12th G) neutron star is investigated. Flow solutions are found for the case in which the matter undergoes a stationary collisionless shock. It is found that the cyclotron emission is the dominant energy loss mechanism and can yield continuum spectra resembling those observed from X-ray pulsars. A number of relations among the accretion rate, the surface magnetic field, the shock height, and the characteristic electron and ion temperatures are obtained. For magnetic fields greater than 10 to the 12th G, typical values of KTe are several times the cyclotron energy at the surface of the neutron star. When the field drops below 10 to the 12th G, the electrons become very hot and emit gamma-rays.
Langer, S. H.↗
Spectral signatures of the MeV-PeV radiation from accreting neutron stars
The formation of the high-energy gamma-ray and neutrino spectrum produced by the injection of a power-law proton distribution extending up to Ep = 10 exp 16 eV in the magnetosphere of accreting neutron stars is discussed. The resulting proton spectrum is calculated in the presence of advection and cooling by interactions with the X-ray spectrum of the neutron star, leading to several components of a secondary photon spectrum extending from the MeV to the PeV range, and neutrino spectrum extending from about 0.1 TeV to 0.1 PeV. The shapes of the resulting high-energy secondary spectra depend sensitively on the accreting source's X-ray spectrum and energy density as well as the magnetic field strength involved. Detailed spectra are calculated for the specific examples of Her X-1 and Cyg X-3.
Rudak, B.↗
Aspects of Neutron Star and Black Hole Transients in RXTE Observations
Scans of the the galactic center with the Proportional Counter Array on the Rossi X-ray Timing Explorer have discovered the outbursts of many neutron star and black hole binary transients early in the outbursts. We have had observations during the rise of the transients which allow us to study the spectral and timing characteristics. Some of the transients are also identified as radio sources, with compact cores and jet ejections. A recent example is H 1743-322, a recurrent black hole candidate, in which the ejection of radio emitting plasma is correlated with changes in the spectral characteristics. I will review the properties of black hole transients compare the characteristics of neutron star transients.
Swank, J.↗
Gamma rays, X-rays, and optical light from the cobalt and the neutron star in SN 1987A
Recent developments in modeling the X-ray and gamma-ray emission from SN 1987A are discussed by taking into account both the decaying cobalt and the buried neutron star. The light curve and the spectra evolution of X-rays and gamma-rays are well modeled up to day of about 300 if mixing of Co-56 into hydrogen-rich envelope is assumed. However, the 16-28 keV flux observed by Ginga declines very slowly, whereas the spherical mixing model predicts that the flux should have decreased by a large factor at t greater than 300d. It is shown that this problem can be solved if the photoelectric absorption of X-rays is effectively reduced as a result of the formation of chemically inhomogeneous clumps. Based on the adopted hydrodynamical model and the abundance distribution, predictions are offered for future optical, X-ray, and gamma-ray light curves by taking into account other radioactive sources and various types of the central source, e.g., a buried neutron star accreting the reinfalling material or an isolated pulsar.
Kumagai, Shiomi↗
Soft X-ray spectral fits of Geminga with model neutron star atmospheres
The spectrum of the soft X-ray pulsar Geminga consists of two components, a softer one which can be interpreted as thermal-like radiation from the surface of the neutron star, and a harder one interpreted as radiation from a polar cap heated by relativistic particles. We have fitted the soft spectrum using a detailed magnetized hydrogen atmosphere model. The fitting parameters are the hydrogen column density, the effective temperature T(sub eff), the gravitational redshift z, and the distance to radius ratio, for different values of the magnetic field B. The best fits for this model are obtained when B less than or approximately 1 x 10(exp 12) G and z lies on the upper boundary of the explored range (z = 0.45). The values of T(sub eff) approximately = (2-3) x 10(exp 5) K are a factor of 2-3 times lower than the value of T(sub eff) obtained for blackbody fits with the same z. The lower T(sub eff) increases the compatibility with some proposed schemes for fast neutrino cooling of neutron stars (NSs) by the direct Urca process or by exotic matter, but conventional cooling cannot be excluded. The hydrogen atmosphere fits also imply a smaller distance to Geminga than that inferred from a blackbody fit. An accurate evaluation of the distance would require a better knowledge of the ROSAT Position Sensitive Proportional Counter (PSPC) response to the low-energy region of the incident spectrum. Our modeling of the soft component with a cooler magnetized atmosphere also implies that the hard-component fit requires a characteristic temperature which is higher (by a factor of approximately 2-3) and a surface area which is smaller (by a factor of 10(exp 3), compared to previous blackbody fits.
Meyer, R. D.↗
Do gamma-ray bursts originate from an extended Galactic Halo of high-velocity neutron stars?
The gamma-ray burst brightness distribution is inhomogeneous and the distribution on the sky is nearly isotropic. These features argue against an association of gamma-ray bursts with those Galactic objects that are known to exhibit a strong concentration toward the Galactic center or plane. The observed statistical properties indicate a cosmological origin. Circumstantial evidence suggests that neutron stars are involved in the burst phenomenon. Here we consider Population II neutron stars in an extended Galactic Halo (EGH) as an alternative to cosmological scenarios. The Burst and Transient Source Experiment (BATSE) data indicate a small deviation from isotropy near the 2 sigma level of statistical significance. If confirmed for an increasing number of bursts, these anisotropies could rule out cosmological scenarios. On the other hand, EGH models require small anisotropies like those observed by BATSE. We consider simple distribution models to determine the generic properties such halos must have to be consistent with the observations and discuss the implications of the corresponding distance scale on burst models.
Hartmann, Dieter H.↗
GROWTH on S190510g: DECam Observation Planning and Follow-up of a Distant Binary Neutron Star Merger Candidate
The first two months of the third Advanced LIGO and Virgo observing run (2019 April–May) showed that distant gravitational-wave (GW) events can now be readily detected. Three candidate mergers containing neutron stars (NS) were reported in a span of 15 days, all likely located more than 100 Mpc away. However, distant events such as the three new NS mergers are likely to be coarsely localized, which highlights the importance of facilities and scheduling systems that enable deep observations over hundreds to thousands of square degrees to detect the electromagnetic counterparts. On 2019 May 10 02:59:39.292 UT the GW candidate S190510g was discovered and initially classified as a binary neutron star (BNS) merger with 98% probability. The GW event was localized within an area of 3462 deg2, later refined to 1166 deg2 (90%) at a distance of 227 ± 92 Mpc. We triggered Target-of-Opportunity observations with the Dark Energy Camera (DECam), a wide-field optical imager mounted at the prime focus of the 4 m Blanco Telescope at Cerro Tololo Inter-American Observatory in Chile. This Letter describes our DECam observations and our real-time analysis results, focusing in particular on the design and implementation of the observing strategy. Within 24 hr of the merger time, we observed 65% of the total enclosed probability of the final skymap with an observing efficiency of 94%. We identified and publicly announced 13 candidate counterparts. S190510g was reclassified 1.7 days after the merger, after our observations were completed, with a "BNS merger" probability reduced from 98% to 42% in favor of a "terrestrial classification.
Igor Andreoni↗
X-ray bursts - The maximum mass of a neutron star
A review of the great variety of observed properties of X-ray burst sources is presented, including the MXB 1730-355, called the rapid burster. Hypotheses regarding the sources of bursts are discussed, and two models for the rapid burster are described. The first postulates that they are caused by a collapsed object with a mass of approximately 10 solar masses surrounded by a disk of gas spiralling inward. The second posits a neutron star with a strong magnetic field. Theoretical questions regarding the mass of neutron stars are discussed, and prerequisites for such research are identified. Various research projects investigating these questions are described.
Morrison, N. D.↗
Sensitivity of model calculations to uncertain inputs, with an application to neutron star envelopes
A method is given for determining the sensitivity of certain types of calculations to the uncertainties in the input physics or model parameters; this method is applicable to problems that involve solutions to coupled, ordinary differential equations. In particular the sensitivity of calculations of the thermal structure of neutron star envelopes to uncertainties in the opacity and equation of state is examined. It is found that the uncertainties in the relationship between the surface and interior temperatures of a neutron star are due almost entirely to the imprecision in the values of the conductive opacity in the region where the ions form a liquid; here the conductive opacity is, for the most part, due to the scattering of electrons from ions.
Epstein, R. I.↗
Why galactic gamma-ray bursts might depend on environment: Blast waves around neutron stars
Although galactic models for gamma-ray bursts are hard to reconcile with the isotropy data, the issue is still sufficiently open that both options should be explored. The most likely 'triggers' for bursts in our Galaxy would be violent disturbances in the magnetospheres of neutron stars. Any event of this kind is likely to expel magnetic flux and plasma at relativistic speed. Such ejecta would be braked by the interstellar medium (ISM), and a gamma-ray flash may result from this interaction. The radiative efficiency, of this mechanism would depend on the density of the circumstellar ISM. Therefore, even if neutron stars were uniformly distributed in space (at least within 1-2 kpc of the Sun), the observed locations of bursts would correlate with regions of above-average ISM density.
Rees, Martin J.↗
The Nature of the Unidentified EUV Sources: Accreting Isolated Neutron Stars?
The aims of this project were: (1) to investigate the nature of the EUVE (Extreme Ultraviolet Explorer Satellite) 'NOID' sources, objects detected in the EUV bandpass but with no previous identification at optical or other energies; (2) to study the possible association of NOID sources with nearby, isolated neutron stars among the 1e9 predicted to exist in the Galaxy. These dead radio pulsars have not been detected so far in large numbers, but accretion from the interstellar medium can make them bright at EUV wavelengths; and (3) to use the EUVE data to set constraints on neutron star evolution, accretion physics and population properties. The original objectives of our program remain relevant. Indeed, the level of research in this area has increased substantially since our proposal was submitted as a result of new data from the ROSAT (Roentgen Satellite).
Madau, Piero↗
Constraints on the mass-radius relation for the neutron star in the X-ray burst source 4U/MXB 1820-30 located in the globular cluster NGC 6624
From the spectral evolution of seven X-ray bursts observed from 4U/MXB 1820-30 (Haberl et al., 1986) during the phases of photospheric expansion and cooling, constraints are derived on the mass-radius relation of the neutron star in this system. Taking into account the uncertainty in the source distance and the possible anisotropy of the burst emission. If during bursts with radius expansion the outer layers of the neutron star are of a hydrogen-poor composition, none of the current equations of state of high-density matter is excluded. For a hydrogen-rich composition, only very soft equations of state are allowed.
Van Paradijs, J.↗
Gravitational radiation from neutron stars.
Calculation of gravitational radiation from pulsating and rotating objects according to weak field limit formula of general relativity and applied to neutron star data
GRAVITATIONAL RADIATION↗