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Seward, F. D.

Publications and source records attributed to Seward, F. D..

47 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

An X-ray map of SN 1006 from the Einstein Observatory

An X-ray map of the SN 1006 supernova remnant acquired by the imaging proportional counter of the Einstein Observatory in the energy range 0.1-4 keV is presented. The image obtained from the imaging proportional counter shows a limb-brightened nebula, almost circular in outline with enhanced emission in two quadrants. The hardness ratio map reveals a large range of temperatures over the object, with the highest values near the limbs of the enhanced emission regions. Consideration of a three-dimensional model of the object indicates the presence of a shell of electron temperature varying between 10 to the 6th and 10 to the 7th K and density varying between 0.3 and 6/cu cm surrounding a fairly uniform interior, of electron temperature 1.5 x 10 to the 6th K and density 1.0/cu cm. The optical filaments are observed to lie parallel with the faintest edge of the X-ray shell, about 1 arcmin from the peak of X-ray emission. Mass visible in the X-ray image of 5-15 solar masses suggests that the supernova may have been of type II. No evidence is obtained for a hot stellar remnant.

Pye, J. P.↗
NASA NTRS1981

X-ray survey of the Small Magellanic Cloud

A region of over 40 square degrees centered on the Small Magellanic Cloud (SMC) has been surveyed with the imaging instruments of the Einstein Observatory. The survey is approximately complete to a luminosity of 10 to the 36th ergs/sec, and the faintest source detected, if in the SMC, has a luminosity of approximately 3 x 10 to the 35th ergs/sec. Twenty-six sources were clearly seen. Five are identified with objects not associated with the SMC. The only previously known source detected was SMC X-1 which, when in a high state, is the brightest source in the SMC. The second brightest source observed, a previously unknown supernova remnant (SNR), is located in the central part of the SMC. Four other weaker sources are probably also SNRs in the SMC. The remaining 15 sources are not yet identified and, since some are far from the center of the cloud, are probably not all members of the SMC.

Seward, F. D.↗
NASA NTRS1980

Einstein X-ray observations of Proxima Centauri and the surrounding region

The first detection of both quiescent and flaring soft X-ray emission from a dMe flare star, Proxima Centauri (dM5e) is reported. The data are analyzed for temporal variability and spectral characteristics. The quiescent state is characterized by a mean X-ray luminosity of 1.5 x 10 to the 27th erg s/s, corresponding to a mean surface flux of 700,000 erg s/sq cm-s, and an inferred temperature of 4-million K. The flare that is detected has a peak flux of 7.4 x 10 to the 27th erg s/s and a peak temperature of 17-million K. The implications of these data for models of the quiescent and flare coronae of dMe stars are discussed.

Haisch, B. M.↗
NASA NTRS1979

X-rays from Eta Carinae and the surrounding nebula

Two X-ray pictures have been obtained of the Eta Car nebula using the imaging detectors of the Einstein Observatory. One covers a field 1-deg square with a resolution of 1 arcmin; the second covers a field 25 arcmin in diameter with resolution of a few arcsec. These show a region of diffuse X-ray emission with luminosity 10 to the 35th ergs/s. The sources have been positively identified as the peculiar object Eta Car, a Wolf-Rayet star, a cluster of O stars, and five individual O stars. The Eta Car X-ray source is extended and coincides with the outer shell of the diffuse object Eta Car itself. One X-ray bright spot may be emission from a central object within Eta Car.

Seward, F. D.↗
NASA NTRS1979

Einstein observations of extended galactic X-ray sources

Features of the X-ray pictures taken aboard the space observatory are presented. Imaging proportional counter pictures in three broad X-ray energy ranges were obtained. The X-ray spectrum of supernova remnants is described.

Seward, F. D.↗
NASA NTRS1974

Electrons at low altitudes: A difficult background problem for soft X-ray astronomy

Quasi-trapped and precipitating electrons have been observed with rocket-borne X-ray astronomy detectors in the altitude range 150 to 500 km. Because the flights occured at low magnetic latitudes the electrons were unexpected. Data from many flights are combined to derive altitude dependence, an average electron spectrum, and variation with solar activity. Development of electron-rejecting collimators is discussed, and laboratory and flight data on these collimators are presented.

Seward, F. D.↗
NASA NTRS1974

The geographical distribution of difference 100-keV electrons above the earth's atmosphere

Modern soft X-ray astronomical observations are made with large-area proportional counters that have very thin plastic windows. The counters are consequently very sensitive to low energy electrons. An electron with only a few keV of energy can penetrate a typical window, and a flux of approximately 100 electrons per square centimeter sec-ster can double the background counting rate during a typical observation. These electrons produce an undersiable effect which, is impossible to distinguish from X ray data. Consequently, an electron-free region is needed for accurate astronomical observations. Geographical regions of weak electron flux from low altitude satellite data are derived. These regions can be compared with the locations of rocket launching sites. The best sites should be those farthest from electron regions.

Seward, F. D.↗
NASA NTRS1972

Observation of several X-ray sources in 1970 September.

Position and intensity measurements made with proportional counters in the 2 to 12 keV band are described. The instruments were launched from Johnson Atoll, and four scans were carried out during the 525 sec spent above 200 km. In comparing the results with the Uhuru survey, only a few differences are noted. One variable source, 2U 1908+0, was weaker. The case of the Magellanic Cloud sources is discussed.

Price, R. E.↗