SEARCH · Engineering Papers

Results for “NEUTRON STARS”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,117 records · Page 62

All sources NASA NTRS DOE OSTI

NASA NTRS1978

Potential drops above pulsar polar caps - Ultrarelativistic particle acceleration along the curved magnetic field

The paper calculates the acceleration of a nonneutral stream of charged particles from the surface of an isolated rotating magnetized neutron star in the case where the particle stream flows along the open field lines of a curved poloidal magnetic field. It is shown that very large electrostatic potential drops can occur in steady unidirectional space-charge-limited flow along the curved open field lines. The explicit incorporation of magnetic field line curvature is the essential element leading to this new result, assuming that all the charges are supplied by emission from the surface. It is emphasized that the current flow and charge density are unique if all of the assumptions are met, with the result that the accelerating electric field near the stellar surface is quite small compared to the vacuum field.

Scharlemann, E. T.↗

NASA NTRS1978

Consequences of narrow cyclotron emission from Hercules X-1

Explanations of the line feature in the hard X-ray (58 keV) spectrum of the compact X-ray source Hercules X-1 are presented. The most important characteristic of the emission (interpreted as a cyclotron emission from a strong magnetic field, i.e., B greater than one trillion Gauss) is that the FWHM is less than 12 keV, with a total observed luminosity in the line of approximately 1% of the total X-ray luminosity. If the source region is only at the magnetic poles of a neutron star, the electrons are confined to a path nearly parallel to the B-field lines, and the angle of emission will be narrow. Photon emission under such circumstances is also discussed; and it is suggested that photons can leave either through holes in the shell formed by the hard X-rays, or can escape through the shell itself. Attention is given to the accretion flow structure near the magnetopause, as a critical parameter of narrow line emission.

Weaver, R. P.↗

NASA NTRS1978

Period variations in pulsating X-ray sources. II - Torque variations and stellar response

A statistical description of variations in the torque acting on a rotating neutron star is developed in terms of stationary random processes and is used to calculate the torque power spectrum, stellar response power spectrum, and the total mean square variation in the crustal angular velocity of the star. The response of a star with a finite frequency internal mode is calculated with the aid of phenomenological equations which correspond to a generalized two-component model of the star. The form of the stellar response functions is examined in a number of limiting cases of physical interest, and the dependence of the response power on both the period of observation and the time over which fluctuating torques have been acting is discussed.

Lamb, F. K.↗

NASA NTRS1979

X-ray spectra of X Persei

The GSFC cosmic X-ray spectroscopy experiment on OSO 8 observed X Per for 20 days during two observations in 1976 February and 1977 February. The spectrum of X Per varies in phase with its 13.9 minute period, hardening significantly at X-ray minimum. Unlike other X-ray binary pulsar spectra, those of X Per do not exhibit iron line emission or strong absorption features. Our data show no evidence for a 22 hour periodicity in the X-ray intensity of X Per. These results indicate that the X-ray emission from X Per may be originating from a neutron star in a low-density region far from the optically identified Be star.

Becker, R. H.↗

NASA NTRS1979

Highly compact binary X-ray sources

It is proposed that many of the X-ray sources associated with the galactic bulge are accreting neutron stars or black holes with masses of at least about 1 solar mass in ultrashort-period binary systems with very low-mass (no more than about 0.5 solar mass) stellar companions. It is demonstrated that this hypothesis may provide a coherent picture of the evolutionary history and observational properties of these sources, including the apparent lack of conspicuous optical counterparts and the apparent absence of X-ray eclipses.

Joss, P. C.↗

NASA NTRS1979

Further analysis of SAS 3 observations of the rapid burster /MXB 1730-335/

SAS 3 observations of the rapid burster MXB 1730-335 are analyzed with specific reference to the rapidly repetitive type II bursts and also the type I bursts. It is found that: (1) there are two stable patterns in the recurrence of the rapidly repetitive type II bursts, designated modes I and II; (2) the range of type II burst energies is a factor of about 100 for mode I and a factor of about 10 for mode II; (3) type II burst spectra are best fitted by a blackbody of constant temperature (of the order of 18 million K), constant column density, and decreasing intensity; and (4) type I bursts are best fitted by a blackbody spectrum with decreasing temperature (approximately 24 million K during the first few seconds and 16 million K about 10 sec later). The spectral fits for both types of burst are shown to yield sizes for the emission region comparable to the radius of a neutron star. A model for the rapid burster is suggested.

Marshall, H. L.↗

NASA NTRS1979

Photoneutrino reactions in a superstrong magnetoactive plasma

The neutrino luminosity due to the photoneutrino process in the presence of a superstrong magnetoactive electron plasma appropriate for neutron stars is computed. The results indicate that for relatively low temperatures, between 100 million and 500 million K, the energy loss rate is significantly reduced both in the low-density regime below about 10 million g/cu cm (by the magnetic field) and in the high-density regime above that value (by plasmon excitations). These effects are temperature dependent, and they are less pronounced when the temperature is in the range from 500 million to 1 billion K.

Chou, C. K.↗

NASA NTRS1979

Gamma-ray line astronomy

Gamma-ray astronomy is a valuable source of information on solar activity, supernovae, and nucleosynthesis. Cosmic gamma-ray lines were first observed from solar flares and more recently from the galactic center and a transient event. The latter may give an important insight into nuclear reactions taking place near neutron stars and black holes and a measure of the gravitational redshifts of such objects.

Ramaty, R.↗

NASA NTRS1979

A search for X-ray pulsations from the Galactic Centre

A search has been conducted for periodic X-ray behavior in the Galactic Center, a region known to contain several point sources. No pulsations are detected in the range from about 2 sec to 2000 sec. The assumption that part of the steady flux from the Galactic Center is due to the steady contribution of bursters is discussed. It is also noted that the absence of pulsations does not necessarily undermine the proposed binary-neutron star models for the burst sources.

Cordova, F. A.↗

NASA NTRS1979

Soft X-ray emission from the Lupus Loop and Sn 1006 supernova remnants

X-ray maps of the Lupus region have been obtained in a raster scan observation from SAS 3. These show the Lupus Loop to be a faint extended source of soft X-rays with a temperature about 2.5 million K. The most prominent feature of the region is the A.D. 1006 supernova remnant, which is unexpectedly bright at 0.2-1.0 keV. One speculative interpretation of the low-energy flux from SN 1006 is as blackbody radiation from a hot neutron star.

Winkler, P. F., Jr.↗

NASA NTRS1979

X-ray observations of AM Herculis from OSO 8

X-ray observations of the white dwarf binary system AM Herculis in the range 2 to 250 keV, taken by OSO 8, are presented and compared with balloon and Ariel 5 measurements. The composite spectrum of the 2 to 40 and 20 to 250 keV fluxes determined by the proportional counter and the high energy scintillation spectrometer, respectively, on board the satellite is shown averaged over the entire binary cycle. Variations in spectral shape and intensity between the OSO 8 results and balloon measurements taken 10 to 20 days apart are observed. Results indicate the presence of a spectral break at about 15 keV on some occasions, similar to that seen in Her X-1, however presumably caused by a different mechanism than in the neutron star. It is also considered unlikely that the gamma-ray tail observed by Ariel 5 existed during OSO 8 observations.

Coe, M. J.↗

NASA NTRS1979

Observations of pulsating X-ray binaries 4U0900-40 and 4U1223-62

A sounding-rocket observation of the pulsating X-ray binaries 4U 0900-40 (Vela X-1) and 4U 1223-62 (GX301-2, Wray 977) over the energy range from 0.5 to 27 keV is reported. No short-time-scale periodicities in the range from 2 msec to 20 sec are found for either source, although both exhibit some minor flaring activity on time scales of a few seconds. The data for Vela X-1 suggest that the time-averaged spectra are complex and that the pulse-resolved spectra are also complex and variable, with significant fluctuations above 10 keV. When compared with other observations at different epochs, the spectral data for 4U 1223-62 confirm large variability in both intensity and spectral characteristics. It is concluded that the intrapulse changes observed in the spectral behavior of Vela X-1 must reflect changes in the surface magnetic fields and the plasma flows near the neutron star.

Ku, W. H.-M.↗

NASA NTRS1979

Possible radio emission mechanism for pulsars

A mathematical model is presented and discussed as a possible mechanism to describe radio emission from pulsars. The model determines that the magnetic field in the neutron proton electron (npe) layer of a neutron star results from a quasistationary eddy current of superconducting and normal protons relative to normal electrons, which generates radio emission by the Josephson effect. The radiation propagates in the magnetically active medium, from the optically thick npe layer to the magnetosphere through breaks in the crust. As a result, hot radio spots form on the surface of the star, and a radiation pattern forms near the magnetic poles, the cross section of which gives the observed pulse structure. Due to the specific properties of the mechanism, variations of the quasistationary current are converted to amplitude frequency variations of the radiation spectrum. Variations of the fine structure of the spectrum pulse amplitude and spectral index, as well as their correlation are discussed.

Kovalev, Y. A.↗

NASA NTRS1980

The 1979 X-ray outburst of Cen X-4

X-ray observations of the first major outburst (since its initial discovery in 1969) of the "classical" transient X-ray source Cen X-4 were obtained with the Ariel 5 All-Sky Monitor. The flare light curve exhibits a double-peaked maximum at a level of approximately 4 times the Crab nebula, and its duration and characteristic decay time scale are the shortest yet observed from the class of "soft" X-ray transients. A total X-ray output of approximately 3 x 10 to the 43rd power ergs, a factor of approximately 20 less than that of the 1969 outburst is estimated. In addition, evidence is found for a regular modulation of the flux during the decline phase at a period of 8.2 plus or minus 0.2 hours. The existing data are consistent with a source model involving episodic mass exchange from a late-type dwarf onto a neutron star comparison in a relatively close binary system.

Kaluzienski, L. J.↗

NASA NTRS1979

An absorption feature in the spectrum of the pulsed hard X-ray flux from 4U0115 + 63

A spectral feature, apparently an absorption line, has been observed at an energy of 20.1 + or - 0.5 keV in the pulsed flux of the 3.61-s X-ray pulsar 4U 0115+63 by using the UCSD/MIT instrument on HEAO 1. The line strength, expressed as equivalent width, is 3.1 + or - 0.5 keV. Although essentially unresolved, the feature has a depth more than 60% of the continuum flux. If the feature arises by cyclotron resonance absorption near the magnetic poles of the neutron star, it implies a magnetic field of between approximately 1.8 and 2.5 x 10 to the 12th G, depending on the gravitational redshift (no more than about 5-40%).

Wheaton, W. A.↗

NASA NTRS1979

Iron lines from X-ray binaries

A summary of the observational evidence of iron lines from satellite X-ray detectors and binary X-ray pulsars is presented. The current theories consider that the continua X-rays from X-ray pulsars originate at or near the surface of neutron stars, and they can then heat or fluoresce iron ions in surrounding physical regions to create the observed emission. Measurements of the line energy, intensity, and width, and the phase dependence of these quantities can help determine the relative importance of contributions of relative sources. The evidence is presented that the iron emission from some sources contains more than one component, and the spectra of other X-ray binaries including transients and cataclysmic variables also contain iron lines. Some implications of the observed line emission are discussed.

Pravdo, S. H.↗

NASA NTRS1979

A search for low energy gamma rays from CG 195+4

A 13-deg-wide region of sky containing the high-energy gamma-ray source CG 195+4 was searched for X-ray and gamma-ray emission in the energy interval from 0.035 to 8.737 MeV. The balloon-altitude measurements were undertaken on October 4, 1977, at Palestine, Texas, and used an actively collimated scintillation counter. As a result of the measurements, low upper limits have been found for the spectrum from the source. Combined with the positive detections made with satellites at high energies, the measurements show that the photon number spectrum must have a spectral index harder than 2.0. The data appear inconsistent with models of the source in which the presumed neutron star is surrounded by a cloud thick to X-rays. Negative results of the search for periodicity are discussed.

Haymes, R. C.↗

NASA NTRS1979

Theories of magnetospheres around accreting compact objects

The paper reviews theoretical models of magnetospheres formed around neutron stars and other strongly magnetized compact objects in the presence of mass accretion from a companion star. Emphasis is placed on the interaction of the accretion process with the magnetic field of the compact object and the formation of a magnetosphere. The following models are discussed: magnetospheres with polar funnels; closed magnetospheres and their instabilities; models of internal flow; and disk accretion magnetospheres.

Vasyliunas, V. M.↗