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At least 469 records · Page 26
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NASA NTRS1972

On the nature of the Monoceros supernova remnant.

A dynamical expansion time of 300,000 years and an envelope of 100 km/sec are derived for the filamentary Monoceros Loop supernova remnant. Through arguments connecting three O stars with the supernova remnant, a lower limit of 25-30 solar masses is derived for the progenitor star. A thermal soft X-ray point source is predicted based on the hypothesis of a cooling neutron star. By analogy, we interpret the Cygnus Loop X-ray source as a neutron star.

Gebel, W. L.↗
NASA NTRS1972

Upper limits to the X-ray luminosities of five supernovae.

Examination of data from the OSO-III X-ray telescope for evidence of X-ray emission from five optically detected extragalactic supernovae during the period from March 1967 to June 1968. Upper limits to the X-ray emission in the range from 7.7 to 113 keV near optical maximum (within 30 days) fall in the range from 10 to the minus 8th to 10 to the minus 10th ergs/sq cm-sec. Reasonable estimates of the distances to these supernovae lead to upper limits on the total energies of from 10 to the 50th to 10 to the 51st ergs.

Ulmer, M.↗
NASA NTRS1973

The attenuation of X-rays emitted by supernovae

The attenuation of X-rays in Arnett's C-12 detonation supernova model is computed. The attenuation of X-rays in the filaments of the Crab Nebula is computed using a model for the filaments by Woltjer and a model by Davidson and Tucker. An empirical expression by Gorenstein, Kellogg, and Gursky for the optical thickness of the interstellar medium for three supernova remnants is analyzed.

Schocken, K.↗
NASA NTRS1974

Spectrophotometry of supernovae

Studies were made of a type II supernova (SN 1970g in M 101) and a type I supernova (SN 1972e in NGC 5253) covering the wavelength range from 3200 to 10,000 A. The absolute spectral energy distributions show that both types have a continuum that varies slowly and uniformly with time and carries the bulk of the radiated flux at early epochs. Some lines in both types have P Cygni profiles: broad emissions with broad absorptions at their violet edges. Some lines are common to both types and persist throughout the evolution of the spectrum.

Kirshner, R. P.↗
NASA NTRS1975

Electromagnetic pulse from supernovae

Upper and lower limits to the radiated electromagnetic pulse from a supernova are calculated assuming that the mass fraction of the matter expanding inside the dipole magnetic field shares energy and maintains the pressure balance in the process. A supernova model is described in which the explosion occurs in old low-mass stars containing less than 10% hydrogen in their ejecta and a remnant neutron star is produced. The analysis indicates that although the surface layer of a star of 1 g/cu thickness may be shock-accelerated to an energy factor of about 100 and may expand into the vacuum with an energy factor approaching 10,000, the equatorial magnetic field will retard this expansion so that the inner, more massive ejecta layers will effectively accelerate the presumed canonical dipole magnetic field to greater velocities than would the surface layer alone. A pulse of 10 to the 46th power ergs in a width of about 150 cm will result which will not be affected by circumstellar matter or electron self-radiation effects. It is shown that interstellar matter will attenuate the pulse, but that charge separation may reduce the attenuation and allow a larger pulse to escape.

Colgate, S. A.↗
NASA NTRS1976

X-ray emission from the supernova remnant G287.8-0.5

The GSFC Cosmic X-ray spectroscopy experiment on OSO-8 observed a weak galactic X-ray source near theta 2 at 288 deg, b2 at -1 deg. The spectrum for this source between 2-20 keV is well represented by a thermal spectrum of kT = 7.34(+3.6), sub -2.6 keV with an intense iron emission line centered at 6.5 + or - .2 keV. The error box of the Uhuru source 4U1043-59, the only known X-ray source in our field of view, contains the radio supernova remnant G287.8-0.5. The possible association of the X-ray source with this supernova remnant is discussed.

Becker, R. H.↗
NASA NTRS1975

The radio spectrum of Vela supernova and its implication on the propagation of cosmic rays from sources

A detailed analysis of the radio spectrum of the Vela supernova remnant has been carried out to show that the positive spectral shape below 80 MHz can be understood on the basis of Razin effect. This result requires most of the gas in the remnant to be stratified into high density clumps with intense magnetic fields and large cosmic ray densities. The free-free emission is found to be partly responsible for the observed flat radio spectrum. In order to account for both the gamma ray flux above 100 MeV and the radio spectrum, the equipartition between the cosmic ray density and magnetic field seems to break down. The total cosmic ray energy residing in the supernova is found to be about ten to the forty-ninth ergs, which is much smaller than the value obtained without taking into account the stratification of gas.

Stephens, S. A.↗
NASA NTRS1976

Detection of X-ray emission from the remnant of the supernova 1006 A.D.

Results are reported for OSO-7 observations which positively identify the supernova remnant SN 1006 as a weak source of X-ray emission. Acceptable fits to the spectrum are obtained for both a power law with an energy index of about -2.3 and for thermal bremsstrahlung at a temperature corresponding to about 4 keV. The X-ray intensity over the range from 1 to 10 keV is found to be about 9 by 10 to the -11th power erg/sq cm per sec, and it is assumed that the X-rays originate in a plasma shell 4.4 pc in radius and heated by an expanding blast wave. The distance of SN 1006 is estimated as 1.2 kpc, its X-ray luminosity (1-10 keV) as about 1.6 by 10 to the 34th power erg/sec, and its initial kinetic energy as of the order of 10 to the 50th power ergs. It is noted that the reverse-shock model of X-ray production is also consistent with the data and that SN 1006 is the only supernova remnant for which both X-ray and radio emission have been detected, but no optical filaments have been observed.

Winkler, P. F., Jr.↗
NASA NTRS1976

X-ray evidence for the supernova origin of the North Polar spur

Soft X-ray observations during four scans across the North Polar radio continuum spur have provided additional evidence that the spur encircles an old supernova remnant. From the measured intensity of the X-ray emission, and the known diameter of the remnant, it is estimated that its age is several hundred thousand years and that the supernova was of Type II, with an energy between 10 to the 51st and 10 to the 53rd ergs.

Cruddace, R. G.↗
NASA NTRS1976

Effect of nearby supernova explosions on atmospheric ozone

An investigation has been conducted of the probable effects of a nearby supernova event on the ozone layer of the earth. It is found that the ozone depletion, although smaller than that estimated by Ruderman (1974), is still significant, and could, as a result of cosmic rays, extend over periods of time from 1000 to 10,000 years. However, the probability of the occurrence of such an event within the past 100 million years appears to be low. The calculated ozone depletion seems to be the major effect of a supernova on a earth-like planet at a distance in the range from 5 to 10 pc.

Whitten, R. C.↗
NASA NTRS1977

Gamma rays and supernova explosions

Thermal radiation associated with the explosion of supernovae is investigated. High temperature is required to produce copious gamma radiation of this sort. It appears that type 11 supernovae do not release much of their energy as gamma ray continuum radiation.

Arnett, W. D.↗
NASA NTRS1977

Soft X-ray sources and supernova remnants in Cygnus - Rocket and Apollo-Soyuz results

Soft X-ray observations of the Cygnus region obtained from proportional counters aboard a rocket and also on the Apollo-Soyuz mission are reported. It is found that Cyg X-6, a source whose flux in confined to the 0.5-2.0-keV band, is a long narrow filament oriented nearly perpendicular to the galactic plane. This feature has a linear dimension greater than or of the order of 150 parsecs, and its spectrum is adequately described by an exponential. Another intense soft source whose flux is also confined to the 0.5-2.0-keV band has been discovered near Gamma Cygni. This source, designed Cyg X-7, has a spectrum characterized by a temperature of 1.5 to 5 million K and a hydrogen column density of at least 10 to the 21st power per sq cm. The possible association of Cyg X-7 with the supernova remnant DR 4 is discussed. An interpretation of this object in terms of the standard adiabatic spherical-shock-wave model yields plausible values for the free paramenters. HB 21, another old supernova remnant, has not been detected as a soft X-ray source.

Davidsen, A. F.↗
NASA NTRS1977

Supernovae, grains and the formation of the solar system

An investigation is conducted concerning the possibility that observed Mg-26 anomalies in meteorites may be related to a nucleosynthetic event which preceded the formation of the solar system by at most a few million years. The Al-26, which decayed to form the observed excess Mg-26, could have been produced in either explosive carbon burning or in a high temperature carbon burning shell source immediately preceding the explosion. The results of supernova grain condensation calculations are presented and related to the hypothesis that a 'last event' supernova was indeed related to the formation of the solar system and thus might have created the observed isotopic anomalies in magnesium, oxygen, neon, and xenon.

Lattimer, J. M.↗
NASA NTRS1978

Gamma line radiation from supernovae

Recent calculations of core collapse or massive stars result in explosive ejection of the mantle by a reflected shock. These hydrodynamic results are important for predictions of explosive nucleosynthesis and gamma-ray line emission from supernovae. Previous estimates, based on simple parameterized models or the nucleosynthesis in an average supernova, are compared with these latest results.

Arnett, W. D.↗
NASA NTRS1978

Ionization of interstellar H2 clouds by supernovae

Two destruction mechanisms for molecular hydrogen in the H I regions of the interstellar medium were given by Stecher and Williams (1967). The first is dominant in weak radiation fields and involves photon excitation (at about 1000 A) to the first excited electronic state with a subsequent decay into the vibrational continuum of the ground state. The second destruction mechanism is dominant in the strong photon fields that exist when a supernova explosion occurs. It involves photoionization (at about 1000 A) from metastable high vibrational levels produced by photon excitation (in the same wavelength range) to an excited electronic state and subsequent decay to bound vibrational levels. It is shown that ionization of molecular hydrogen can occur at considerable distances from such supernova events while the atomic hydrogen remains neutral. The effect should be observable in the dispersion measures of new pulsars.

Stecher, T. P.↗
NASA NTRS1978

The generation of gravitational radiation by escaping supernova neutrinos

Formulae for the gravitational radiation due to the anisotropic axisymmetric emission of neutrinos from a small source are derived. We find that a burst of neutrinos released anisotropically from a supernova will generate a burst of gravitational radiation that may be comparable in amplitude and energy to the gravitational radiation generated by the fluid motion in the collapse of the supernova core.

Epstein, R.↗
NASA NTRS1978

Optical emission from a fast shock wave - The remnants of Tycho's supernova and SN 1006

The faint optical filaments in Tycho's supernova remnant appear to be emission from a shock front moving at 5600 km/s. The intensity of the hydrogen lines, the absence of forbidden lines of heavy elements in the spectrum, and the width of the filaments are explained by a model in which a collisionless shock wave is moving into partially neutral gas. The presence of the neutral gas can be used to set an upper limit of approximately 5 x 10 to the 47th power ergs to the energy in ionizing radiation emitted by a Type I supernova. The patchy neutral gas is probably part of the warm neutral component of the interstellar medium. The existing information on the remnant of SN 1006 indicates that its emission is similar in nature to that from Tycho's remnant.

Chevalier, R. A.↗
NASA NTRS1978

Detection of star formation regions near supernova remnant W44

Observations of two infrared objects embedded in molecular clouds near the supernova remnant W44 are presented. W44-IRS1 offers compelling evidence that it is a star whose formation was recently induced by expansion of the supernova remnant. W44-IRS2 lies beyond the remnant, possibly apart from the region of its influence.

Wootten, A.↗