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At least 1,747 records · Page 97
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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

Interstellar scattering, the North Polar Spur, and a possible new class of compact galactic radio sources

Claims for a galactic-latitude dependence of interstellar angular broadening based on interplanetary-scintillation (IPS) observations are investigated. Analysis of the statistics of the angular sizes in an IPS survey shows that there is no evidence for increased angular broadening in the galactic plane. A region of sky about 500 sq deg of arc in area is considered in which significant angular broadening is thought to exist. An association between this region and the nearby North Polar Spur is proposed on the basis of the former's extension off the galactic plane to high latitudes. An evaluation of two-frequency angular-broadening measurements suggests that the data used to support the conclusion about a galactic-latitude dependence are not statistically significant. A study of pulsar data and implications for the angular broadening expected in the interstellar medium for sources at galactic latitudes below + or - 10 deg indicates the possible existence of a previously unsuspected class of compact galactic nonthermal radio sources, designated 'scintars'.

Rickard, J. J.↗
NASA NTRS1979

Helios 2-Vela-Ariel 5 gamma-ray burst source position

The gamma-ray burst of January 28, 1976, one of 18 events thus far detected in interplanetary space with Helios 2, was also observed with the Vela 5A and 6A and the Ariel 5 satellites. A small source field is obtained from the intersection of the region derived from the observed time delays between Helios 2 and Vela 5A and 6A, with the source region independently found with the Ariel 5 X-ray detector. This area contains neither any steady X-ray source as scanned by HEAO 1 nor any previously cataloged X-ray, radio, or infrared sources, X-ray transients, quasars, Seyferts, globular clusters, flare stars, pulsars, white dwarfs, or high enery gamma-ray sources. The region is, however, within the source field of a gamma-ray transient observed in 1974 by Jacobson et al. (1978) which exhibited nuclear gamma-ray line structure.

Cline, T. L.↗
NASA NTRS1979

Thermonuclear flashes on accreting neutron stars

Observations of X-ray bursts from binary pulsars and globular clusters are reviewed. The previously proposed hypothesis is considered that such X-ray bursts result from thermonuclear flashes on accreting neutron stars. A general scenario for this mechanism is outlined, and numerical computations of the evolution of the surface layers of an accreting neutron star are discussed. The relation of these calculations to X-ray bursts and other phenomena is examined. Possible improvements in the numerical calculations are suggested.

Joss, P. C.↗
NASA NTRS1979

Double core evolution and X-ray binaries

The evolution of a 16-solar mass star and a 1-solar mass neutron star is followed through the common-envelope binary phase. It is found that the encounter of the neutron star with a yellow giant leads to coalescence of the two cores, while encounter with a red giant leads to hydrodynamic expansion and probable ejection of the common envelope. Within the context of the two rotation laws (1) uniform rotation (investigated in the present study), and (2) uniform specific angular momentum (considered in an earlier study), the results are independent of the choice for the angular-momentum distribution in the common envelope. Implications of the results for the binary pulsar phase are discussed.

Taam, R. E.↗
NASA NTRS1979

Pulse-phase spectroscopy of Hercules X-1

The 6-18 keV and the 40-60 keV X-ray spectrum of Hercules X-1 were simultaneously observed with the A-2 experiment on HEAO-1. By combining these measurements with the results of an earlier observation of this X-ray pulsar, evidence was found for a component of emission above 40 keV which is above an extrapolation from lower energies, by a factor which depends on the phase of the pulse. These data were compared to previous hard X-ray observations and possible models were discussed.

Pravdo, S. H.↗
NASA NTRS1979

Observations of the transient X-ray source 4U 0115+63

Results are presented for HEAO A-2 pointed observations and Ariel 5 A11-Sky Monitor observations of the X-ray transient 4U 0115 + 63. The transient source pulses with a period of 3.6136 s + or - 0.0004 s, has a hard spectrum typical of an X-ray binary pulsar, and has a broad iron line emission feature. A discussion of the transient behavior is given, and inferences are made concerning the nature of the X-ray source based on the pointed data.

Rose, L. A.↗
NASA NTRS1979

Ultrahigh energy neutrinos from galactic neutron stars

An attempt is made to estimate the production rate of ultrahigh energy (UHE) neutrinos from galactic neutron stars. The statistics of various stellar populations are reviewed as well as an evolutionary scheme linking several neutron star environments. An observational test for predicting stellar evolution is made using two mass ratio intervals of less than 0.3 and greater than or approximately equal to 0.3, which is supported by kinematical evidence. Attention is given to the problem of the target material that is required by UHE protons accelerated from the pulsar's surface to their rotational kinetic energy, and to the detectability of neutron stars in the UHE neutrinos by employing the deep underwater muon and neutrino detector (DUMAND) array.

Helfand, D. J.↗
NASA NTRS1979

Jupiter's magnetosphere and radiation belts

Radioastronomy and Pioneer data reveal the Jovian magnetosphere as a rotating magnetized source of relativistic particles and radio emission, comparable to astrophysical cosmic ray and radio sources, such as pulsars. According to Pioneer data, the magnetic field in the outer magnetosphere is radially extended into a highly time variable disk-shaped configuration which differs fundamentally from the earth's magnetosphere. The outer disk region, and the energetic particles confined in it, are modulated by Jupiter's 10 hr rotation period. The entire outer magnetosphere appears to change drastically on time scales of a few days to a week. In addition to its known modulation of the Jovian decametric radio bursts, Io was found to absorb some radiation belt particles and to accelerate others, and most importantly, to be a source of neutral atoms, and by inference, a heavy ion plasma which may significantly affect the hydrodynamic flow in the magnetosphere. Another important Pioneer finding is that the Jovian outer magnetosphere generates, or permits to escape, fluxes of relativistic electrons of such intensities that Jupiter may be regarded as the dominant source of 1 to 30 MeV cosmic ray electrons in the heliosphere.

Kennel, C. F.↗
NASA NTRS1979

Implications of cyclotron features in the X-ray spectrum of Her X-1

The X-ray spectra from binary pulsars is investigated through the modification of physical processes due to an intense magnetic field. An effective scattering cross section for line photons and the Coulomb cross section for electron-ion collisions, treating the electrons relativistically, are calculated. The quantization of electron orbits in strong fields are discussed. The absorption cross sections and emission rates for cyclotron photons are calculated. An application of the results to the data from Hercules X-1 is examined.

Bussard, R.↗
NASA NTRS1979

GSFC Contributions to the NATO X-ray Astronomy Institute, Erice, July 1979

An overview of X-ray astronomical spectroscopy in general is presented and results obtained by HEAO 1 and 2 as well as earlier spacecraft are examined. Particular emphasis is given to the spectra of supernova remnants; galactic binary X-ray sources, cataclysmic variables, bulges, pulsars, and stars; the active nuclei of Seyfert 1 galaxy, BL Lac, and quasars; the diffuse X-ray background; and galactic clusters.

Holt, S. S.↗
NASA NTRS1980

The evolution of supernova remnants in different galactic environments, and its effects on supernova statistics

Examination of the interaction between supernova (SN) ejecta and the various environments in which the explosive event might occur shows that only a small fraction of the many SNs produce observable supernova remnants (SNRs). This fraction, which is found to depend weakly upon the lower mass limit of the SN progenitors, and more strongly on the specfic characteristics of the associated interstellar medium, decreases from approximately 15 percent near the galctic center to 10 percent at Rgal approximately 10 kpc and drops nearly to zero for Rgal 15 kpc. Generally, whether a SNR is detectable is determined by the density of the ambient interstellar medium in which it is embeeede. The presence of large, low density cavities arpund stellar associations due to the combined effects of stellar winds and supernova shells strongly suggests that a large portion of the detectable SNRs have runway stars as their progenitors. These results explain the differences between the substantially larger SN rates in the galaxy derived both from pulsar statistics and from observations of SN events in external galaxies, when compared to the substantially smaller SN rates derived form galactic SNR statistics.

Kafatos, M.↗
NASA NTRS1980

Differential radio astronomy of galactic objects

A differential astrometry technique is discussed. An improved proper motion and a parallax limit for pulsar 1929 + 10 is presented as well as a limit on the space velocity of the enigmatic object in SgrA.

Backer, D. C.↗
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

Workshop on the Physics of Planetary and Astrophysical Magnetospheres, Snowmass, Colo., July 30-August 4, 1978, Proceedings

The paper presents theoretical and observational works in the field of planetary and astrophysical magnetospheres. The magnetospheres of earth and Jupiter are analyzed along with pulsar magnetospheres and X-ray source magnetospheres. Consideration is given to coherent radio emissions in space and astrophysics and collective radio emissions from plasmas. Theories of magnetospheres around accreting compact objects are also presented.

Kennel, C. F.↗
NASA NTRS1979

DUMAND Summer Workshop, University of California, La Jolla, Calif., July 24-September 2, 1978, Proceedings. Volume 2 - UHE interactions, neutrino astronomy

The volume covers categories on inelastic neutrino scattering and the W-boson, and other ultra-high-energy processes, on pulsars, quasars and galactic nuclei, as well as other point sources and constants from gamma ray astronomy. Individual subjects include weak intermediate vector bosons and DUMAND, the Monte Carlo simulation of inelastic neutrino scattering in DUMAND, and Higgs boson production by very high-energy neutrinos. The observability of the neutrino flux from the inner region of the galactic disk, the diffuse fluxes of high-energy neutrinos, as well as the significance of gamma ray observations for neutrino astronomy are also among the topics covered.

Roberts, A.↗
NASA NTRS1979

X-ray evidence for electron-ion equilibrium and ionization nonequilibrium in Young supernova remnants

X-ray emission up to 25 keV from the supernova remnants Cas A and Tycho has been detected with the A-2 spectroscopy experiment on HEAO 1. The spectra must include continuum components with effective temperature of about 10 to the 8th K which could arise from optically thin plasmas in the collisionless shock fronts. This is the first indication of electron-ion temperature equilibrium in the expanding shell of young remnants. The equivalent widths of the K-alpha and K-beta iron line blends in Cas A have also been measured and it is found that their ratio is not compatible with the measured X-ray temperature in the collisional ionization equilibrium model. Finally, an unsuccessful search has been conducted for hard X-ray pulsars in both remnants.

Pravdo, S. H.↗
NASA NTRS1980

Thermal X-ray emission from neutron stars

In the present paper, the status of theories concerning the thermal properties of neutron stars are reviewed, and means by which observational astronomy may contribute to future studies are examined. Particular attention is given to program of the Einstein Observatory (HEAO 2) which calls for observations of over 50 SNR and 35 radio pulsars. The present paper includes a survey of all objects within 350 pc of the earth.

Helfand, D. J.↗